Micropython Esp8266

MicroPython Documentation
Release 1.9
Damien P. George, Paul Sokolovsky, and contributors
May 26, 2017

CONTENTS
1 Quick reference for the ESP8266 1

1.1 Installing MicroPython . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 General board control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.3 Networking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.4 Delay and timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.5 Timers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.6 Pins and GPIO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.7 PWM (pulse width modulation) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.8 ADC (analog to digital conversion) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.9 Software SPI bus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.10 Hardware SPI bus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.11 I2C bus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.12 Deep-sleep mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.13 OneWire driver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.14 NeoPixel driver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.15 APA102 driver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.16 DHT driver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.17 WebREPL (web browser interactive prompt) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2 MicroPython libraries 9
2.1 Python standard libraries and micro-libraries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2 MicroPython-specific libraries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
2.3 Libraries specific to the ESP8266 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
3 MicroPython Differences from CPython 57

3.1 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
3.2 Core Language . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
3.3 Builtin Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
3.4 Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
4 MicroPython license information 71
5 MicroPython documentation contents 73

5.1 General information about the ESP8266 port . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
5.2 MicroPython tutorial for ESP8266 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
5.3 The MicroPython language . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
6 Indices and tables 113
Python Module Index 115
i
Index 117
ii
CHAPTER
ONE
QUICK REFERENCE FOR THE ESP8266
The Adafruit Feather HUZZAH board (image attribution: Adafruit).
1.1 Installing MicroPython
See the corresponding section of tutorial: Getting started with MicroPython on the ESP8266. It also includes a
troubleshooting subsection.
1.2 General board control
The MicroPython REPL is on UART0 (GPIO1=TX, GPIO3=RX) at baudrate 115200. Tab-completion is useful to
find out what methods an object has. Paste mode (ctrl-E) is useful to paste a large slab of Python code into the REPL.
The machine module:
import machine
machine.freq() # get the current frequency of the CPU

machine.freq(160000000) # set the CPU frequency to 160 MHz
1
MicroPython Documentation, Release 1.9
The esp module:

import esp
esp.osdebug(None) # turn off vendor O/S debugging messages

esp.osdebug(0) # redirect vendor O/S debugging messages to UART(0)
1.3 Networking
The network module:

import network
wlan = network.WLAN(network.STA_IF) # create station interface

wlan.active(True) # activate the interface
wlan.scan() # scan for access points
wlan.isconnected() # check if the station is connected to an AP
wlan.connect('essid', 'password') # connect to an AP
wlan.config('mac') # get the interface's MAC adddress
wlan.ifconfig() # get the interface's IP/netmask/gw/DNS addresses
ap = network.WLAN(network.AP_IF) # create access-point interface

ap.active(True) # activate the interface
ap.config(essid='ESP-AP') # set the ESSID of the access point
A useful function for connecting to your local WiFi network is:

def do_connect():
import network
wlan = network.WLAN(network.STA_IF)
wlan.active(True)
if not wlan.isconnected():
print('connecting to network...')
wlan.connect('essid', 'password')
while not wlan.isconnected():
pass
print('network config:', wlan.ifconfig())
Once the network is established the socket module can be used to create and use TCP/UDP sockets as usual.
1.4 Delay and timing
Use the time module:

import time
time.sleep(1) # sleep for 1 second

time.sleep_ms(500) # sleep for 500 milliseconds
time.sleep_us(10) # sleep for 10 microseconds
start = time.ticks_ms() # get millisecond counter
delta = time.ticks_diff(time.ticks_ms(), start) # compute time difference
2 Chapter 1. Quick reference for the ESP8266

1.5 Timers
Virtual (RTOS-based) timers are supported. Use the machine.Timer class with timer ID of -1:
from machine import Timer
tim = Timer(-1)
tim.init(period=5000, mode=Timer.ONE_SHOT, callback=lambda t:print(1))
tim.init(period=2000, mode=Timer.PERIODIC, callback=lambda t:print(2))
The period is in milliseconds.
1.6 Pins and GPIO
Use the machine.Pin class:

from machine import Pin
p0 = Pin(0, Pin.OUT) # create output pin on GPIO0

p0.high() # set pin to high
p0.low() # set pin to low
p0.value(1) # set pin to high
p2 = Pin(2, Pin.IN) # create input pin on GPIO2

print(p2.value()) # get value, 0 or 1
p4 = Pin(4, Pin.IN, Pin.PULL_UP) # enable internal pull-up resistor

p5 = Pin(5, Pin.OUT, value=1) # set pin high on creation
Available pins are: 0, 1, 2, 3, 4, 5, 12, 13, 14, 15, 16, which correspond to the actual GPIO pin numbers of ESP8266
chip. Note that many end-user boards use their own adhoc pin numbering (marked e.g. D0, D1, ...). As MicroPython
supports different boards and modules, physical pin numbering was chosen as the lowest common denominator. For
mapping between board logical pins and physical chip pins, consult your board documentation.
Note that Pin(1) and Pin(3) are REPL UART TX and RX respectively. Also note that Pin(16) is a special pin (used for
wakeup from deepsleep mode) and may be not available for use with higher-level classes like Neopixel.
1.7 PWM (pulse width modulation)
PWM can be enabled on all pins except Pin(16). There is a single frequency for all channels, with range between 1
and 1000 (measured in Hz). The duty cycle is between 0 and 1023 inclusive.
Use the machine.PWM class:
from machine import Pin, PWM
pwm0 = PWM(Pin(0)) # create PWM object from a pin

pwm0.freq() # get current frequency
pwm0.freq(1000) # set frequency
pwm0.duty() # get current duty cycle
pwm0.duty(200) # set duty cycle
pwm0.deinit() # turn off PWM on the pin
pwm2 = PWM(Pin(2), freq=500, duty=512) # create and configure in one go
1.5. Timers 3
1.8 ADC (analog to digital conversion)
ADC is available on a dedicated pin. Note that input voltages on the ADC pin must be between 0v and 1.0v.
Use the machine.ADC class:
from machine import ADC
adc = ADC(0) # create ADC object on ADC pin

adc.read() # read value, 0-1024
1.9 Software SPI bus
There are two SPI drivers. One is implemented in software (bit-banging) and works on all pins, and is accessed via
the machine.SPI class:
from machine import Pin, SPI
# construct an SPI bus on the given pins

# polarity is the idle state of SCK
# phase=0 means sample on the first edge of SCK, phase=1 means the second
spi = SPI(-1, baudrate=100000, polarity=1, phase=0, sck=Pin(0), mosi=Pin(2), miso=Pin(4))
spi.init(baudrate=200000) # set the baudrate
spi.read(10) # read 10 bytes on MISO

spi.read(10, 0xff) # read 10 bytes while outputing 0xff on MOSI
buf = bytearray(50) # create a buffer

spi.readinto(buf) # read into the given buffer (reads 50 bytes in this case)
spi.readinto(buf, 0xff) # read into the given buffer and output 0xff on MOSI
spi.write(b'12345') # write 5 bytes on MOSI
buf = bytearray(4) # create a buffer

spi.write_readinto(b'1234', buf) # write to MOSI and read from MISO into the buffer
spi.write_readinto(buf, buf) # write buf to MOSI and read MISO back into buf
1.10 Hardware SPI bus
The hardware SPI is faster (up to 80Mhz), but only works on following pins: MISO is GPIO12, MOSI is GPIO13,
and SCK is GPIO14. It has the same methods as the bitbanging SPI class above, except for the pin parameters for the
constructor and init (as those are fixed):
from machine import Pin, SPI
hspi = SPI(1, baudrate=80000000, polarity=0, phase=0)
(SPI(0) is used for FlashROM and not available to users.)

1.11 I2C bus
The I2C driver is implemented in software and works on all pins, and is accessed via the machine.I2C class:
from machine import Pin, I2C
# construct an I2C bus

i2c = I2C(scl=Pin(5), sda=Pin(4), freq=100000)
i2c.readfrom(0x3a, 4) # read 4 bytes from slave device with address 0x3a

i2c.writeto(0x3a, '12') # write '12' to slave device with address 0x3a
buf = bytearray(10) # create a buffer with 10 bytes

i2c.writeto(0x3a, buf) # write the given buffer to the slave
1.12 Deep-sleep mode
Connect GPIO16 to the reset pin (RST on HUZZAH). Then the following code can be used to sleep, wake and check
the reset cause:
import machine
# configure RTC.ALARM0 to be able to wake the device

rtc = machine.RTC()
rtc.irq(trigger=rtc.ALARM0, wake=machine.DEEPSLEEP)
# check if the device woke from a deep sleep

if machine.reset_cause() == machine.DEEPSLEEP_RESET:
print('woke from a deep sleep')
# set RTC.ALARM0 to fire after 10 seconds (waking the device)

rtc.alarm(rtc.ALARM0, 10000)
# put the device to sleep

machine.deepsleep()
1.13 OneWire driver
The OneWire driver is implemented in software and works on all pins:

import onewire
ow = onewire.OneWire(Pin(12)) # create a OneWire bus on GPIO12

ow.scan() # return a list of devices on the bus
ow.reset() # reset the bus
ow.readbyte() # read a byte
ow.writebyte(0x12) # write a byte on the bus
ow.write('123') # write bytes on the bus
ow.select_rom(b'12345678') # select a specific device by its ROM code
There is a specific driver for DS18S20 and DS18B20 devices:
1.11. I2C bus 5

import time, ds18x20

ds = ds18x20.DS18X20(ow)
roms = ds.scan()
ds.convert_temp()
time.sleep_ms(750)
for rom in roms:
print(ds.read_temp(rom))
Be sure to put a 4.7k pull-up resistor on the data line. Note that the convert_temp() method must be called each
time you want to sample the temperature.
1.14 NeoPixel driver
Use the neopixel module:

from neopixel import NeoPixel
pin = Pin(0, Pin.OUT) # set GPIO0 to output to drive NeoPixels

np = NeoPixel(pin, 8) # create NeoPixel driver on GPIO0 for 8 pixels
np[0] = (255, 255, 255) # set the first pixel to white
np.write() # write data to all pixels
r, g, b = np[0] # get first pixel colour
For low-level driving of a NeoPixel:

import esp
esp.neopixel_write(pin, grb_buf, is800khz)
1.15 APA102 driver
Use the apa102 module:

from apa102 import APA102
clock = Pin(14, Pin.OUT) # set GPIO14 to output to drive the clock

data = Pin(13, Pin.OUT) # set GPIO13 to output to drive the data
apa = APA102(clock, data, 8) # create APA102 driver on the clock and the data pin for 8 pixels
apa[0] = (255, 255, 255, 31) # set the first pixel to white with a maximum brightness of 31
apa.write() # write data to all pixels
r, g, b, brightness = apa[0] # get first pixel colour
For low-level driving of an APA102:

import esp
esp.apa102_write(clock_pin, data_pin, rgbi_buf)
1.16 DHT driver
The DHT driver is implemented in software and works on all pins:

import dht
import machine
d = dht.DHT11(machine.Pin(4))
d.measure()
d.temperature() # eg. 23 (°C)
d.humidity() # eg. 41 (% RH)
d = dht.DHT22(machine.Pin(4))
d.measure()
d.temperature() # eg. 23.6 (°C)
d.humidity() # eg. 41.3 (% RH)
1.17 WebREPL (web browser interactive prompt)
WebREPL (REPL over WebSockets, accessible via a web browser) is an experimental feature available in
ESP8266 port. Download web client from https://github.com/micropython/webrepl (hosted version available at
http://micropython.org/webrepl), and configure it by executing:
import webrepl_setup
and following on-screen instructions. After reboot, it will be available for connection. If you disabled automatic
start-up on boot, you may run configured daemon on demand using:
import webrepl
webrepl.start()
The supported way to use WebREPL is by connecting to ESP8266 access point, but the daemon is also started on STA
interface if it is active, so if your router is set up and works correctly, you may also use WebREPL while connected to
your normal Internet access point (use the ESP8266 AP connection method if you face any issues).
Besides terminal/command prompt access, WebREPL also has provision for file transfer (both upload and download).
Web client has buttons for the corresponding functions, or you can use command-line client webrepl_cli.py from
the repository above.
See the MicroPython forum for other community-supported alternatives to transfer files to ESP8266.
1.17. WebREPL (web browser interactive prompt) 7


CHAPTER
TWO
MICROPYTHON LIBRARIES
Warning: Important summary of this section

• MicroPython implements a subset of Python functionality for each module.
• To ease extensibility, MicroPython versions of standard Python modules usually have u (micro) prefix.
• Any particular MicroPython variant or port may miss any feature/function described in this general docu-
mentation, due to resource constraints.
This chapter describes modules (function and class libraries) which are built into MicroPython. There are a few
categories of modules:
• Modules which implement a subset of standard Python functionality and are not intended to be extended by the
user.
• Modules which implement a subset of Python functionality, with a provision for extension by the user (via
Python code).
• Modules which implement MicroPython extensions to the Python standard libraries.
• Modules specific to a particular port and thus not portable.
Note about the availability of modules and their contents: This documentation in general aspires to describe all mod-
ules and functions/classes which are implemented in MicroPython. However, MicroPython is highly configurable,
and each port to a particular board/embedded system makes available only a subset of MicroPython libraries. For
officially supported ports, there is an effort to either filter out non-applicable items, or mark individual descriptions
with “Availability:” clauses describing which ports provide a given feature. With that in mind, please still be warned
that some functions/classes in a module (or even the entire module) described in this documentation may be unavail-
able in a particular build of MicroPython on a particular board. The best place to find general information of the
availability/non-availability of a particular feature is the “General Information” section which contains information
pertaining to a specific port.
Beyond the built-in libraries described in this documentation, many more modules from the Python standard library,
as well as further MicroPython extensions to it, can be found in the micropython-lib repository.
2.1 Python standard libraries and micro-libraries
The following standard Python libraries have been “micro-ified” to fit in with the philosophy of MicroPython. They
provide the core functionality of that module and are intended to be a drop-in replacement for the standard Python
library. Some modules below use a standard Python name, but prefixed with “u”, e.g. ujson instead of json. This
is to signify that such a module is micro-library, i.e. implements only a subset of CPython module functionality.
By naming them differently, a user has a choice to write a Python-level module to extend functionality for better
compatibility with CPython (indeed, this is what done by micropython-lib project mentioned above).
9
On some embedded platforms, where it may be cumbersome to add Python-level wrapper modules to achieve naming
compatibility with CPython, micro-modules are available both by their u-name, and also by their non-u-name. The
non-u-name can be overridden by a file of that name in your package path. For example, import json will first
search for a file json.py or directory json and load that package if it is found. If nothing is found, it will fallback
to loading the built-in ujson module.
2.1.1 Builtin Functions
All builtin functions are described here. They are also available via builtins module.
abs()
all()
any()
bin()
class bool
class bytearray
class bytes
callable()
chr()
classmethod()
compile()
class complex
delattr(obj, name)
The argument name should be a string, and this function deletes the named attribute from the object given by
obj.
class dict
dir()
divmod()
enumerate()
eval()
exec()
filter()
class float
class frozenset
getattr()
globals()
hasattr()
hash()
hex()
id()
10 Chapter 2. MicroPython libraries

input()
class int
classmethod from_bytes(bytes, byteorder)

In MicroPython, byteorder parameter must be positional (this is compatible with CPython).
to_bytes(size, byteorder)
In MicroPython, byteorder parameter must be positional (this is compatible with CPython).
isinstance()
issubclass()
iter()
len()
class list
locals()
map()
max()
class memoryview
min()
next()
class object
oct()
open()
ord()
pow()
print()
property()
range()
repr()
reversed()
round()
class set
setattr()
class slice
The slice builtin is the type that slice objects have.
sorted()
staticmethod()
class str
sum()
2.1. Python standard libraries and micro-libraries 11

super()
class tuple
type()
zip()
2.1.2 array – arrays of numeric data
See Python array for more information.

Supported format codes: b, B, h, H, i, I, l, L, q, Q, f, d (the latter 2 depending on the floating-point support).
Classes
class array.array(typecode[, iterable ])

Create array with elements of given type. Initial contents of the array are given by an iterable. If it is not
provided, an empty array is created.
append(val)
Append new element to the end of array, growing it.
extend(iterable)
Append new elements as contained in an iterable to the end of array, growing it.
2.1.3 gc – control the garbage collector
Functions
gc.enable()
Enable automatic garbage collection.
gc.disable()
Disable automatic garbage collection. Heap memory can still be allocated, and garbage collection can still be
initiated manually using gc.collect().
gc.collect()
Run a garbage collection.
gc.mem_alloc()
Return the number of bytes of heap RAM that are allocated.
gc.mem_free()
Return the number of bytes of available heap RAM.
2.1.4 math – mathematical functions
The math module provides some basic mathematical functions for working with floating-point numbers.
Note: On the pyboard, floating-point numbers have 32-bit precision.
Availability: not available on WiPy. Floating point support required for this module.

Functions
math.acos(x)
Return the inverse cosine of x.
math.acosh(x)
Return the inverse hyperbolic cosine of x.
math.asin(x)
Return the inverse sine of x.
math.asinh(x)
Return the inverse hyperbolic sine of x.
math.atan(x)
Return the inverse tangent of x.
math.atan2(y, x)
Return the principal value of the inverse tangent of y/x.
math.atanh(x)
Return the inverse hyperbolic tangent of x.
math.ceil(x)
Return an integer, being x rounded towards positive infinity.
math.copysign(x, y)
Return x with the sign of y.
math.cos(x)
Return the cosine of x.
math.cosh(x)
Return the hyperbolic cosine of x.
math.degrees(x)
Return radians x converted to degrees.
math.erf(x)
Return the error function of x.
math.erfc(x)
Return the complementary error function of x.
math.exp(x)
Return the exponential of x.
math.expm1(x)
Return exp(x) - 1.
math.fabs(x)
Return the absolute value of x.
math.floor(x)
Return an integer, being x rounded towards negative infinity.
math.fmod(x, y)
Return the remainder of x/y.
math.frexp(x)
Decomposes a floating-point number into its mantissa and exponent. The returned value is the tuple (m, e)
such that x == m * 2**e exactly. If x == 0 then the function returns (0.0, 0), otherwise the relation
0.5 <= abs(m) < 1 holds.

math.gamma(x)
Return the gamma function of x.
math.isfinite(x)
Return True if x is finite.
math.isinf(x)
Return True if x is infinite.
math.isnan(x)
Return True if x is not-a-number
math.ldexp(x, exp)
Return x * (2**exp).
math.lgamma(x)
Return the natural logarithm of the gamma function of x.
math.log(x)
Return the natural logarithm of x.
math.log10(x)
Return the base-10 logarithm of x.
math.log2(x)
Return the base-2 logarithm of x.
math.modf(x)
Return a tuple of two floats, being the fractional and integral parts of x. Both return values have the same sign
as x.
math.pow(x, y)
Returns x to the power of y.
math.radians(x)
Return degrees x converted to radians.
math.sin(x)
Return the sine of x.
math.sinh(x)
Return the hyperbolic sine of x.
math.sqrt(x)
Return the square root of x.
math.tan(x)
Return the tangent of x.
math.tanh(x)
Return the hyperbolic tangent of x.
math.trunc(x)
Return an integer, being x rounded towards 0.
Constants
math.e
base of the natural logarithm
math.pi
the ratio of a circle’s circumference to its diameter

2.1.5 sys – system specific functions
Functions
sys.exit(retval=0)
Terminate current program with a given exit code. Underlyingly, this function raise as SystemExit exception.
If an argument is given, its value given as an argument to SystemExit.
sys.print_exception(exc, file=sys.stdout)
Print exception with a traceback to a file-like object file (or sys.stdout by default).
Difference to CPython
This is simplified version of a function which appears in the traceback module in CPython. Unlike
traceback.print_exception(), this function takes just exception value instead of exception type, ex-
ception value, and traceback object; file argument should be positional; further arguments are not supported.
CPython-compatible traceback module can be found in micropython-lib.
Constants
sys.argv
A mutable list of arguments the current program was started with.
sys.byteorder
The byte order of the system (“little” or “big”).
sys.implementation
Object with information about the current Python implementation. For MicroPython, it has following attributes:
•name - string “micropython”
•version - tuple (major, minor, micro), e.g. (1, 7, 0)
This object is the recommended way to distinguish MicroPython from other Python implementations (note that
it still may not exist in the very minimal ports).
CPython mandates more attributes for this object, but the actual useful bare minimum is implemented in Mi-
croPython.
sys.maxsize
Maximum value which a native integer type can hold on the current platform, or maximum value representable
by MicroPython integer type, if it’s smaller than platform max value (that is the case for MicroPython ports
without long int support).
This attribute is useful for detecting “bitness” of a platform (32-bit vs 64-bit, etc.). It’s recommended to not
compare this attribute to some value directly, but instead count number of bits in it:
bits = 0
v = sys.maxsize
while v:
bits += 1
v >>= 1
if bits > 32:
# 64-bit (or more) platform

...
else:
# 32-bit (or less) platform
# Note that on 32-bit platform, value of bits may be less than 32
# (e.g. 31) due to peculiarities described above, so use "> 16",
# "> 32", "> 64" style of comparisons.
sys.modules
Dictionary of loaded modules. On some ports, it may not include builtin modules.
sys.path
A mutable list of directories to search for imported modules.
sys.platform
The platform that MicroPython is running on. For OS/RTOS ports, this is usually an identifier of the OS, e.g.
"linux". For baremetal ports it is an identifier of a board, e.g. “pyboard” for the original MicroPython
reference board. It thus can be used to distinguish one board from another. If you need to check whether your
program runs on MicroPython (vs other Python implementation), use sys.implementation instead.
sys.stderr
Standard error stream.
sys.stdin
Standard input stream.
sys.stdout
Standard output stream.
sys.version
Python language version that this implementation conforms to, as a string.
sys.version_info
Python language version that this implementation conforms to, as a tuple of ints.
2.1.6 ubinascii – binary/ASCII conversions
This module implements conversions between binary data and various encodings of it in ASCII form (in both direc-
tions).
Functions
ubinascii.hexlify(data[, sep ])
Convert binary data to hexadecimal representation. Returns bytes string.
If additional argument, sep is supplied, it is used as a separator between hexadecimal values.
ubinascii.unhexlify(data)
Convert hexadecimal data to binary representation. Returns bytes string. (i.e. inverse of hexlify)
ubinascii.a2b_base64(data)
Convert Base64-encoded data to binary representation. Returns bytes string.
ubinascii.b2a_base64(data)
Encode binary data in Base64 format. Returns string.

2.1.7 ucollections – collection and container types
This module implements advanced collection and container types to hold/accumulate various objects.
Classes
ucollections.namedtuple(name, fields)
This is factory function to create a new namedtuple type with a specific name and set of fields. A namedtuple is
a subclass of tuple which allows to access its fields not just by numeric index, but also with an attribute access
syntax using symbolic field names. Fields is a sequence of strings specifying field names. For compatibility
with CPython it can also be a a string with space-separated field named (but this is less efficient). Example of
use:
from ucollections import namedtuple
MyTuple = namedtuple("MyTuple", ("id", "name"))

t1 = MyTuple(1, "foo")
t2 = MyTuple(2, "bar")
print(t1.name)
assert t2.name == t2[1]
ucollections.OrderedDict(...)
dict type subclass which remembers and preserves the order of keys added. When ordered dict is iterated over,
keys/items are returned in the order they were added:
from ucollections import OrderedDict
# To make benefit of ordered keys, OrderedDict should be initialized

# from sequence of (key, value) pairs.
d = OrderedDict([("z", 1), ("a", 2)])
# More items can be added as usual
d["w"] = 5
d["b"] = 3
for k, v in d.items():
print(k, v)
Output:
z 1
a 2
w 5
b 3
2.1.8 uhashlib – hashing algorithms
This module implements binary data hashing algorithms. The exact inventory of available algorithms depends on a
board. Among the algorithms which may be implemented:
• SHA256 - The current generation, modern hashing algorithm (of SHA2 series). It is suitable for
cryptographically-secure purposes. Included in the MicroPython core and any board is recommended to provide
this, unless it has particular code size constraints.
• SHA1 - A previous generation algorithm. Not recommended for new usages, but SHA1 is a part of number
of Internet standards and existing applications, so boards targetting network connectivity and interoperatiability
will try to provide this.

• MD5 - A legacy algorithm, not considered cryptographically secure. Only selected boards, targetting interoper-
atibility with legacy applications, will offer this.
Constructors
class uhashlib.sha256([data ])
Create an SHA256 hasher object and optionally feed data into it.
class uhashlib.sha1([data ])
Create an SHA1 hasher object and optionally feed data into it.
class uhashlib.md5([data ])
Create an MD5 hasher object and optionally feed data into it.
Methods
hash.update(data)
Feed more binary data into hash.
hash.digest()
Return hash for all data passed through hash, as a bytes object. After this method is called, more data cannot be
fed into the hash any longer.
hash.hexdigest()
This method is NOT implemented. Use ubinascii.hexlify(hash.digest()) to achieve a similar
effect.
2.1.9 uheapq – heap queue algorithm
This module implements the heap queue algorithm.

A heap queue is simply a list that has its elements stored in a certain way.
Functions
uheapq.heappush(heap, item)
Push the item onto the heap.
uheapq.heappop(heap)
Pop the first item from the heap, and return it. Raises IndexError if heap is empty.
uheapq.heapify(x)
Convert the list x into a heap. This is an in-place operation.
2.1.10 uio – input/output streams
This module contains additional types of stream (file-like) objects and helper functions.

Conceptual hierarchy
Conceptual hierarchy of stream base classes is simplified in MicroPython, as described in this section.
(Abstract) base stream classes, which serve as a foundation for behavior of all the concrete classes, adhere to few
dichotomies (pair-wise classifications) in CPython. In MicroPython, they are somewhat simplified and made implicit
to achieve higher efficiencies and save resources.
An important dichotomy in CPython is unbuffered vs buffered streams. In MicroPython, all streams are currently
unbuffered. This is because all modern OSes, and even many RTOSes and filesystem drivers already perform buffering
on their side. Adding another layer of buffering is counter- productive (an issue known as “bufferbloat”) and takes
precious memory. Note that there still cases where buffering may be useful, so we may introduce optional buffering
support at a later time.
But in CPython, another important dichotomy is tied with “bufferedness” - it’s whether a stream may incur short
read/writes or not. A short read is when a user asks e.g. 10 bytes from a stream, but gets less, similarly for writes. In
CPython, unbuffered streams are automatically short operation susceptible, while buffered are guarantee against them.
The no short read/writes is an important trait, as it allows to develop more concise and efficient programs - something
which is highly desirable for MicroPython. So, while MicroPython doesn’t support buffered streams, it still provides
for no-short-operations streams. Whether there will be short operations or not depends on each particular class’ needs,
but developers are strongly advised to favor no-short-operations behavior for the reasons stated above. For example,
MicroPython sockets are guaranteed to avoid short read/writes. Actually, at this time, there is no example of a short-
operations stream class in the core, and one would be a port-specific class, where such a need is governed by hardware
peculiarities.
The no-short-operations behavior gets tricky in case of non-blocking streams, blocking vs non-blocking behavior
being another CPython dichotomy, fully supported by MicroPython. Non-blocking streams never wait for data either
to arrive or be written - they read/write whatever possible, or signal lack of data (or ability to write data). Clearly,
this conflicts with “no-short-operations” policy, and indeed, a case of non-blocking buffered (and this no-short-ops)
streams is convoluted in CPython - in some places, such combination is prohibited, in some it’s undefined or just not
documented, in some cases it raises verbose exceptions. The matter is much simpler in MicroPython: non-blocking
stream are important for efficient asynchronous operations, so this property prevails on the “no-short-ops” one. So,
while blocking streams will avoid short reads/writes whenever possible (the only case to get a short read is if end of
file is reached, or in case of error (but errors don’t return short data, but raise exceptions)), non-blocking streams may
produce short data to avoid blocking the operation.
The final dichotomy is binary vs text streams. MicroPython of course supports these, but while in CPython text
streams are inherently buffered, they aren’t in MicroPython. (Indeed, that’s one of the cases for which we may
introduce buffering support.)
Note that for efficiency, MicroPython doesn’t provide abstract base classes corresponding to the hierarchy above, and
it’s not possible to implement, or subclass, a stream class in pure Python.
Functions
uio.open(name, mode=’r’, **kwargs)

Open a file. Builtin open() function is aliased to this function. All ports (which provide access to file system)
are required to support mode parameter, but support for other arguments vary by port.

Classes
class uio.FileIO(...)
This is type of a file open in binary mode, e.g. using open(name, "rb"). You should not instantiate this
class directly.
class uio.TextIOWrapper(...)
This is type of a file open in text mode, e.g. using open(name, "rt"). You should not instantiate this class
directly.
class uio.StringIO([string ])
class uio.BytesIO([string ])
In-memory file-like objects for input/output. StringIO is used for text-mode I/O (similar to a normal file opened
with “t” modifier). BytesIO is used for binary-mode I/O (similar to a normal file opened with “b” modifier).
Initial contents of file-like objects can be specified with string parameter (should be normal string for StringIO or
bytes object for BytesIO). All the usual file methods like read(), write(), seek(), flush(), close()
are available on these objects, and additionally, a following method:
getvalue()
Get the current contents of the underlying buffer which holds data.
2.1.11 ujson – JSON encoding and decoding
This modules allows to convert between Python objects and the JSON data format.
Functions
ujson.dumps(obj)
Return obj represented as a JSON string.
ujson.loads(str)
Parse the JSON str and return an object. Raises ValueError if the string is not correctly formed.
2.1.12 uos – basic “operating system” services
The os module contains functions for filesystem access and urandom function.
Port specifics
The filesystem has / as the root directory and the available physical drives are accessible from here. They are currently:
/flash – the internal flash filesystem
/sd – the SD card (if it exists)
Functions
uos.chdir(path)
Change current directory.
uos.getcwd()
Get the current directory.

uos.ilistdir([dir ])
This function returns an iterator which then yields 3-tuples corresponding to the entries in the directory that it is
listing. With no argument it lists the current directory, otherwise it lists the directory given by dir.
The 3-tuples have the form (name, type, inode):
•name is a string (or bytes if dir is a bytes object) and is the name of the entry;
•type is an integer that specifies the type of the entry, with 0x4000 for directories and 0x8000 for regular
files;
•inode is an integer corresponding to the inode of the file, and may be 0 for filesystems that don’t have such
a notion.
uos.listdir([dir ])
With no argument, list the current directory. Otherwise list the given directory.
uos.mkdir(path)
Create a new directory.
uos.remove(path)
Remove a file.
uos.rmdir(path)
Remove a directory.
uos.rename(old_path, new_path)
Rename a file.
uos.stat(path)
Get the status of a file or directory.
uos.statvfs(path)
Get the status of a fileystem.
Returns a tuple with the filesystem information in the following order:
•f_bsize – file system block size
•f_frsize – fragment size
•f_blocks – size of fs in f_frsize units
•f_bfree – number of free blocks
•f_bavail – number of free blocks for unpriviliged users
•f_files – number of inodes
•f_ffree – number of free inodes
•f_favail – number of free inodes for unpriviliged users
•f_flag – mount flags
•f_namemax – maximum filename length
Parameters related to inodes: f_files, f_ffree, f_avail and the f_flags parameter may return 0 as
they can be unavailable in a port-specific implementation.
uos.sync()
Sync all filesystems.
uos.urandom(n)
Return a bytes object with n random bytes. Whenever possible, it is generated by the hardware random number
generator.

2.1.13 ure – regular expressions
This module implements regular expression operations. Regular expression syntax supported is a subset of CPython
re module (and actually is a subset of POSIX extended regular expressions).
Supported operators are:
’.’ Match any character.
’[]’ Match set of characters. Individual characters and ranges are supported.
’^’
’$’
’?’
’*’
’+’
’??’
’*?’
’+?’
Counted repetitions ({m,n}), more advanced assertions, named groups, etc. are not supported.
Functions
ure.compile(regex)
Compile regular expression, return regex object.
ure.match(regex, string)
Match regex against string. Match always happens from starting position in a string.
ure.search(regex, string)
Search regex in a string. Unlike match, this will search string for first position which matches regex
(which still may be 0 if regex is anchored).
ure.DEBUG
Flag value, display debug information about compiled expression.
Regex objects
Compiled regular expression. Instances of this class are created using ure.compile().
regex.match(string)
regex.search(string)
regex.split(string, max_split=-1)
Match objects
Match objects as returned by match() and search() methods.

match.group([index ])
Only numeric groups are supported.

2.1.14 usocket – socket module
This module provides access to the BSD socket interface.

See the corresponding CPython module for comparison.
CPython used to have a socket.error exception which is now deprecated, and is an alias of OSError. In MicroPy-
thon, use OSError directly.
For efficiency and consistency, socket objects in MicroPython implement a stream (file-like) interface directly. In
CPython, you need to convert a socket to a file-like object using makefile() method. This method is still supported
by MicroPython (but is a no-op), so where compatibility with CPython matters, be sure to use it.
Socket address format(s)
The functions below which expect a network address, accept it in the format of (ipv4_address, port), where
ipv4_address is a string with dot-notation numeric IPv4 address, e.g. "8.8.8.8", and port is integer port num-
ber in the range 1-65535. Note the domain names are not accepted as ipv4_address, they should be resolved first using
socket.getaddrinfo().
Functions
socket.socket(socket.AF_INET, socket.SOCK_STREAM, socket.IPPROTO_TCP)

Create a new socket using the given address family, socket type and protocol number.
socket.getaddrinfo(host, port)
Translate the host/port argument into a sequence of 5-tuples that contain all the necessary arguments for creating
a socket connected to that service. The list of 5-tuples has following structure:
(family, type, proto, canonname, sockaddr)
The following example shows how to connect to a given url:

s = socket.socket()
s.connect(socket.getaddrinfo('www.micropython.org', 80)[0][-1])
CPython raises a socket.gaierror exception (OSError subclass) in case of error in this function. Mi-
croPython doesn’t have socket.gaierror and raises OSError directly. Note that error numbers of
getaddrinfo() form a separate namespace and may not match error numbers from uerrno module. To
distinguish getaddrinfo() errors, they are represented by negative numbers, whereas standard system er-
rors are positive numbers (error numbers are accessible using e.args[0] property from an exception object).
The use of negative values is a provisional detail which may change in the future.

Constants
socket.AF_INET
socket.AF_INET6
Address family types. Availability depends on a particular board.
socket.SOCK_STREAM
socket.SOCK_DGRAM
Socket types.
socket.IPPROTO_UDP
socket.IPPROTO_TCP
IP protocol numbers.
socket.SOL_*
Socket option levels (an argument to setsockopt()). The exact inventory depends on a board.
socket.SO_*
Socket options (an argument to setsockopt()). The exact inventory depends on a board.
Constants specific to WiPy:
socket.IPPROTO_SEC
Special protocol value to create SSL-compatible socket.
class socket
Methods
socket.close()
Mark the socket closed. Once that happens, all future operations on the socket object will fail. The remote end
will receive no more data (after queued data is flushed).
Sockets are automatically closed when they are garbage-collected, but it is recommended to close() them ex-
plicitly, or to use a with statement around them.
socket.bind(address)
Bind the socket to address. The socket must not already be bound.
socket.listen([backlog ])
Enable a server to accept connections. If backlog is specified, it must be at least 0 (if it’s lower, it will be
set to 0); and specifies the number of unaccepted connections that the system will allow before refusing new
connections. If not specified, a default reasonable value is chosen.
socket.accept()
Accept a connection. The socket must be bound to an address and listening for connections. The return value is
a pair (conn, address) where conn is a new socket object usable to send and receive data on the connection, and
address is the address bound to the socket on the other end of the connection.
socket.connect(address)
Connect to a remote socket at address.
socket.send(bytes)
Send data to the socket. The socket must be connected to a remote socket. Returns number of bytes sent, which
may be smaller than the length of data (“short write”).
socket.sendall(bytes)
Send all data to the socket. The socket must be connected to a remote socket. Unlike send(), this method will
try to send all of data, by sending data chunk by chunk consecutively.

The behavior of this method on non-blocking sockets is undefined. Due to this, on MicroPython, it’s recom-
mended to use write() method instead, which has the same “no short writes” policy for blocking sockets, and
will return number of bytes sent on non-blocking sockets.
socket.recv(bufsize)
Receive data from the socket. The return value is a bytes object representing the data received. The maximum
amount of data to be received at once is specified by bufsize.
socket.sendto(bytes, address)
Send data to the socket. The socket should not be connected to a remote socket, since the destination socket is
specified by address.
socket.recvfrom(bufsize)
Receive data from the socket. The return value is a pair (bytes, address) where bytes is a bytes object representing
the data received and address is the address of the socket sending the data.
socket.setsockopt(level, optname, value)
Set the value of the given socket option. The needed symbolic constants are defined in the socket module (SO_*
etc.). The value can be an integer or a bytes-like object representing a buffer.
socket.settimeout(value)
Set a timeout on blocking socket operations. The value argument can be a nonnegative floating point number
expressing seconds, or None. If a non-zero value is given, subsequent socket operations will raise an OSError
exception if the timeout period value has elapsed before the operation has completed. If zero is given, the socket
is put in non-blocking mode. If None is given, the socket is put in blocking mode.
CPython raises a socket.timeout exception in case of timeout, which is an OSError subclass. MicroPy-
thon raises an OSError directly instead. If you use except OSError: to catch the exception, your code will
work both in MicroPython and CPython.
socket.setblocking(flag)
Set blocking or non-blocking mode of the socket: if flag is false, the socket is set to non-blocking, else to
blocking mode.
This method is a shorthand for certain settimeout() calls:
•sock.setblocking(True) is equivalent to sock.settimeout(None)
•sock.setblocking(False) is equivalent to sock.settimeout(0)
socket.makefile(mode=’rb’, buffering=0)
Return a file object associated with the socket. The exact returned type depends on the arguments given to make-
file(). The support is limited to binary modes only (‘rb’, ‘wb’, and ‘rwb’). CPython’s arguments: encoding,
errors and newline are not supported.
As MicroPython doesn’t support buffered streams, values of buffering parameter is ignored and treated as
if it was 0 (unbuffered).
Closing the file object returned by makefile() WILL close the original socket as well.

socket.read([size ])
Read up to size bytes from the socket. Return a bytes object. If size is not given, it reads all data available
from the socket until EOF; as such the method will not return until the socket is closed. This function tries to
read as much data as requested (no “short reads”). This may be not possible with non-blocking socket though,
and then less data will be returned.
socket.readinto(buf [, nbytes ])
Read bytes into the buf. If nbytes is specified then read at most that many bytes. Otherwise, read at most
len(buf) bytes. Just as read(), this method follows “no short reads” policy.
Return value: number of bytes read and stored into buf.
socket.readline()
Read a line, ending in a newline character.
Return value: the line read.
socket.write(buf )
Write the buffer of bytes to the socket. This function will try to write all data to a socket (no “short writes”).
This may be not possible with a non-blocking socket though, and returned value will be less than the length of
buf.
Return value: number of bytes written.
2.1.15 ussl – SSL/TLS module
This module provides access to Transport Layer Security (previously and widely known as “Secure Sockets Layer”)
encryption and peer authentication facilities for network sockets, both client-side and server-side.
Functions
ssl.wrap_socket(sock, server_side=False, keyfile=None, certfile=None, cert_reqs=CERT_NONE,

ca_certs=None)
Takes a stream sock (usually usocket.socket instance of SOCK_STREAM type), and returns an instance of
ssl.SSLSocket, which wraps the underlying stream in an SSL context. Returned object has the usual stream
interface methods like read(), write(), etc. In MicroPython, the returned object does not expose socket interface
and methods like recv(), send(). In particular, a server-side SSL socket should be created from a normal socket
returned from accept() on a non-SSL listening server socket.
Depending on the underlying module implementation for a particular board, some or all keyword arguments
above may be not supported.
Warning: Some implementations of ssl module do NOT validate server certificates, which makes an SSL
connection established prone to man-in-the-middle attacks.
Exceptions
ssl.SSLError
This exception does NOT exist. Instead its base class, OSError, is used.
Constants
ssl.CERT_NONE
ssl.CERT_OPTIONAL

ssl.CERT_REQUIRED
Supported values for cert_reqs parameter.
2.1.16 ustruct – pack and unpack primitive data types
See Python struct for more information.

Supported size/byte order prefixes: @, <, >, !.
Supported format codes: b, B, h, H, i, I, l, L, q, Q, s, P, f, d (the latter 2 depending on the floating-point support).
Functions
ustruct.calcsize(fmt)
Return the number of bytes needed to store the given fmt.
ustruct.pack(fmt, v1, v2, ...)
Pack the values v1, v2, ... according to the format string fmt. The return value is a bytes object encoding the
values.
ustruct.pack_into(fmt, buffer, offset, v1, v2, ...)
Pack the values v1, v2, ... according to the format string fmt into a buffer starting at offset. offset may be negative
to count from the end of buffer.
ustruct.unpack(fmt, data)
Unpack from the data according to the format string fmt. The return value is a tuple of the unpacked values.
ustruct.unpack_from(fmt, data, offset=0)
Unpack from the data starting at offset according to the format string fmt. offset may be negative to count from
the end of buffer. The return value is a tuple of the unpacked values.
2.1.17 utime – time related functions
The utime module provides functions for getting the current time and date, measuring time intervals, and for delays.
Time Epoch: Unix port uses standard for POSIX systems epoch of 1970-01-01 00:00:00 UTC. However, embedded
ports use epoch of 2000-01-01 00:00:00 UTC.
Maintaining actual calendar date/time: This requires a Real Time Clock (RTC). On systems with underlying
OS (including some RTOS), an RTC may be implicit. Setting and maintaining actual calendar time is responsi-
bility of OS/RTOS and is done outside of MicroPython, it just uses OS API to query date/time. On baremetal
ports however system time depends on machine.RTC() object. The current calendar time may be set using
machine.RTC().datetime(tuple) function, and maintained by following means:
• By a backup battery (which may be an additional, optional component for a particular board).
• Using networked time protocol (requires setup by a port/user).
• Set manually by a user on each power-up (many boards then maintain RTC time across hard resets, though some
may require setting it again in such case).
If actual calendar time is not maintained with a system/MicroPython RTC, functions below which require reference to
current absolute time may behave not as expected.

Functions
utime.localtime([secs ])
Convert a time expressed in seconds since the Epoch (see above) into an 8-tuple which contains: (year, month,
mday, hour, minute, second, weekday, yearday) If secs is not provided or None, then the current time from the
RTC is used.
•year includes the century (for example 2014).
•month is 1-12
•mday is 1-31
•hour is 0-23
•minute is 0-59
•second is 0-59
•weekday is 0-6 for Mon-Sun
•yearday is 1-366
utime.mktime()
This is inverse function of localtime. It’s argument is a full 8-tuple which expresses a time as per localtime. It
returns an integer which is the number of seconds since Jan 1, 2000.
utime.sleep(seconds)
Sleep for the given number of seconds. Some boards may accept seconds as a floating-point number to sleep for a
fractional number of seconds. Note that other boards may not accept a floating-point argument, for compatibility
with them use sleep_ms() and sleep_us() functions.
utime.sleep_ms(ms)
Delay for given number of milliseconds, should be positive or 0.
utime.sleep_us(us)
Delay for given number of microseconds, should be positive or 0.
utime.ticks_ms()
Returns an increasing millisecond counter with an arbitrary reference point, that wraps around after some value.
This value is not explicitly exposed, but we will refer to it as TICKS_MAX to simplify discussion. Period
of the values is TICKS_PERIOD = TICKS_MAX + 1. TICKS_PERIOD is guaranteed to be a power of
two, but otherwise may differ from port to port. The same period value is used for all of ticks_ms(),
ticks_us(), ticks_cpu() functions (for simplicity). Thus, these functions will return a value in range [0
.. TICKS_MAX], inclusive, total TICKS_PERIOD values. Note that only non-negative values are used. For the
most part, you should treat values returned by these functions as opaque. The only operations available for them
are ticks_diff() and ticks_add() functions described below.
Note: Performing standard mathematical operations (+, -) or relational operators (<, <=, >, >=) directly on these
value will lead to invalid result. Performing mathematical operations and then passing their results as arguments
to ticks_diff() or ticks_add() will also lead to invalid results from the latter functions.
utime.ticks_us()
Just like ticks_ms() above, but in microseconds.
utime.ticks_cpu()
Similar to ticks_ms() and ticks_us(), but with the highest possible resolution in the system. This is
usually CPU clocks, and that’s why the function is named that way. But it doesn’t have to be a CPU clock, some
other timing source available in a system (e.g. high-resolution timer) can be used instead. The exact timing unit
(resolution) of this function is not specified on utime module level, but documentation for a specific port may
provide more specific information. This function is intended for very fine benchmarking or very tight real-time
loops. Avoid using it in portable code.

Availability: Not every port implements this function.

utime.ticks_add(ticks, delta)
Offset ticks value by a given number, which can be either positive or negative. Given a ticks value, this
function allows to calculate ticks value delta ticks before or after it, following modular-arithmetic definition
of tick values (see ticks_ms() above). ticks parameter must be a direct result of call to ticks_ms(),
ticks_us(), or ticks_cpu() functions (or from previous call to ticks_add()). However, delta can
be an arbitrary integer number or numeric expression. ticks_add() is useful for calculating deadlines for
events/tasks. (Note: you must use ticks_diff() function to work with deadlines.)
Examples:
# Find out what ticks value there was 100ms ago
print(ticks_add(time.ticks_ms(), -100))
# Calculate deadline for operation and test for it

deadline = ticks_add(time.ticks_ms(), 200)
while ticks_diff(deadline, time.ticks_ms()) > 0:
do_a_little_of_something()
# Find out TICKS_MAX used by this port

print(ticks_add(0, -1))
utime.ticks_diff(ticks1, ticks2)
Measure ticks difference between values returned from ticks_ms(), ticks_us(), or ticks_cpu()
functions. The argument order is the same as for subtraction operator, ticks_diff(ticks1, ticks2)
has the same meaning as ticks1 - ticks2. However, values returned by ticks_ms(), etc. func-
tions may wrap around, so directly using subtraction on them will produce incorrect result. That is why
ticks_diff() is needed, it implements modular (or more specifically, ring) arithmetics to produce correct
result even for wrap-around values (as long as they not too distant inbetween, see below). The function returns
signed value in the range [-TICKS_PERIOD/2 .. TICKS_PERIOD/2-1] (that’s a typical range definition
for two’s-complement signed binary integers). If the result is negative, it means that ticks1 occured earlier
in time than ticks2. Otherwise, it means that ticks1 occured after ticks2. This holds only if ticks1
and ticks2 are apart from each other for no more than TICKS_PERIOD/2-1 ticks. If that does not hold,
incorrect result will be returned. Specifically, if two tick values are apart for TICKS_PERIOD/2-1 ticks, that
value will be returned by the function. However, if TICKS_PERIOD/2 of real-time ticks has passed between
them, the function will return -TICKS_PERIOD/2 instead, i.e. result value will wrap around to the negative
range of possible values.
Informal rationale of the constraints above: Suppose you are locked in a room with no means to monitor passing
of time except a standard 12-notch clock. Then if you look at dial-plate now, and don’t look again for another
13 hours (e.g., if you fall for a long sleep), then once you finally look again, it may seem to you that only 1 hour
has passed. To avoid this mistake, just look at the clock regularly. Your application should do the same. “Too
long sleep” metaphor also maps directly to application behavior: don’t let your application run any single task
for too long. Run tasks in steps, and do time-keeping inbetween.
ticks_diff() is designed to accommodate various usage patterns, among them:
Polling with timeout. In this case, the order of events is known, and you will deal only with positive results of
ticks_diff():
# Wait for GPIO pin to be asserted, but at most 500us
start = time.ticks_us()
while pin.value() == 0:
if time.ticks_diff(time.ticks_us(), start) > 500:
raise TimeoutError
Scheduling events. In this case, ticks_diff() result may be negative if an event is overdue:

# This code snippet is not optimized

now = time.ticks_ms()
scheduled_time = task.scheduled_time()
if ticks_diff(now, scheduled_time) > 0:
print("Too early, let's nap")
sleep_ms(ticks_diff(now, scheduled_time))
task.run()
elif ticks_diff(now, scheduled_time) == 0:
print("Right at time!")
task.run()
elif ticks_diff(now, scheduled_time) < 0:
print("Oops, running late, tell task to run faster!")
task.run(run_faster=true)
Note: Do not pass time() values to ticks_diff(), you should use normal mathematical op-
erations on them. But note that time() may (and will) also overflow. This is known as
https://en.wikipedia.org/wiki/Year_2038_problem .
utime.time()
Returns the number of seconds, as an integer, since the Epoch, assuming that underlying RTC is set and main-
tained as described above. If an RTC is not set, this function returns number of seconds since a port-specific
reference point in time (for embedded boards without a battery-backed RTC, usually since power up or reset).
If you want to develop portable MicroPython application, you should not rely on this function to provide higher
than second precision. If you need higher precision, use ticks_ms() and ticks_us() functions, if you
need calendar time, localtime() without an argument is a better choice.
In CPython, this function returns number of seconds since Unix epoch, 1970-01-01 00:00 UTC, as a floating-
point, usually having microsecond precision. With MicroPython, only Unix port uses the same Epoch, and if
floating-point precision allows, returns sub-second precision. Embedded hardware usually doesn’t have floating-
point precision to represent both long time ranges and subsecond precision, so they use integer value with second
precision. Some embedded hardware also lacks battery-powered RTC, so returns number of seconds since last
power-up or from other relative, hardware-specific point (e.g. reset).
2.1.18 uzlib – zlib decompression
This modules allows to decompress binary data compressed with DEFLATE algorithm (commonly used in zlib library
and gzip archiver). Compression is not yet implemented.
Functions
uzlib.decompress(data)
Return decompressed data as bytes.
2.2 MicroPython-specific libraries
Functionality specific to the MicroPython implementation is available in the following libraries.

2.2.1 btree – simple BTree database
The btree module implements a simple key-value database using external storage (disk files, or in general case, a
random-access stream). Keys are stored sorted in the database, and besides efficient retrieval by a key value, a database
also supports efficient ordered range scans (retrieval of values with the keys in a given range). On the application
interface side, BTree database work as close a possible to a way standard dict type works, one notable difference is
that both keys and values must be bytes objects (so, if you want to store objects of other types, you need to serialize
them to bytes first).
The module is based on the well-known BerkelyDB library, version 1.xx.
Example:
import btree
# First, we need to open a stream which holds a database

# This is usually a file, but can be in-memory database
# using uio.BytesIO, a raw flash section, etc.
f = open("mydb", "w+b")
# Now open a database itself

db = btree.open(f)
# The keys you add will be sorted internally in the database

db[b"3"] = b"three"
db[b"1"] = b"one"
db[b"2"] = b"two"
# Prints b'two'
print(db[b"2"])
# Iterate over sorted keys in the database, starting from b"2"

# until the end of the database, returning only values.
# Mind that arguments passed to values() method are *key* values.
# Prints:
# b'two'
# b'three'
for word in db.values(b"2"):
print(word)
del db[b"2"]
# No longer true, prints False

print(b"2" in db)
# Prints:
# b"1"
# b"3"
for key in db:
print(key)
db.close()
# Don't forget to close the underlying stream!

f.close()
2.2. MicroPython-specific libraries 31

Functions
btree.open(stream, *, flags=0, cachesize=0, pagesize=0, minkeypage=0)

Open a database from a random-access stream (like an open file). All other parameters are optional and keyword-
only, and allow to tweak advanced paramters of the database operation (most users will not need them):
•flags - Currently unused.
•cachesize - Suggested maximum memory cache size in bytes. For a board with enough memory using
larger values may improve performance. The value is only a recommendation, the module may use more
memory if values set too low.
•pagesize - Page size used for the nodes in BTree. Acceptable range is 512-65536. If 0, underlying I/O
block size will be used (the best compromise between memory usage and performance).
•minkeypage - Minimum number of keys to store per page. Default value of 0 equivalent to 2.
Returns a BTree object, which implements a dictionary protocol (set of methods), and some additional methods
described below.
Methods
btree.close()
Close the database. It’s mandatory to close the database at the end of processing, as some unwritten data may
be still in the cache. Note that this does not close underlying streamw with which the database was opened, it
should be closed separately (which is also mandatory to make sure that data flushed from buffer to the underlying
storage).
btree.flush()
Flush any data in cache to the underlying stream.
btree.__getitem__(key)
btree.get(key, default=None)
btree.__setitem__(key, val)
btree.__detitem__(key)
btree.__contains__(key)
Standard dictionary methods.
btree.__iter__()
A BTree object can be iterated over directly (similar to a dictionary) to get access to all keys in order.
btree.keys([start_key[, end_key[, flags ]]])
btree.values([start_key[, end_key[, flags ]]])
btree.items([start_key[, end_key[, flags ]]])
These methods are similar to standard dictionary methods, but also can take optional parameters to iterate over
a key sub-range, instead of the entire database. Note that for all 3 methods, start_key and end_key arguments
represent key values. For example, values() method will iterate over values corresponding to they key range
given. None values for start_key means “from the first key”, no end_key or its value of None means “until
the end of database”. By default, range is inclusive of start_key and exclusive of end_key, you can include
end_key in iteration by passing flags of btree.INCL. You can iterate in descending key direction by passing flags
of btree.DESC. The flags values can be ORed together.

Constants
btree.INCL
A flag for keys(), values(), items() methods to specify that scanning should be inclusive of the end key.
btree.DESC
A flag for keys(), values(), items() methods to specify that scanning should be in descending direction of keys.
2.2.2 framebuf — Frame buffer manipulation
This module provides a general frame buffer which can be used to create bitmap images, which can then be sent to a
display.
class FrameBuffer
The FrameBuffer class provides a pixel buffer which can be drawn upon with pixels, lines, rectangles, text and even
other FrameBuffer’s. It is useful when generating output for displays.
For example:
import framebuf
# FrameBuffer needs 2 bytes for every RGB565 pixel

fbuf = FrameBuffer(bytearray(10 * 100 * 2), 10, 100, framebuf.RGB565)
fbuf.fill(0)
fbuf.text('MicroPython!', 0, 0, 0xffff)
fbuf.hline(0, 10, 96, 0xffff)
Constructors
class framebuf.FrameBuffer(buffer, width, height, format, stride=width)

Construct a FrameBuffer object. The parameters are:
•buffer is an object with a buffer protocol which must be large enough to contain every pixel defined by the
width, height and format of the FrameBuffer.
•width is the width of the FrameBuffer in pixels
•height is the height of the FrameBuffer in pixels
•format specifies the type of pixel used in the FrameBuffer; valid values are framebuf.MVLSB,
framebuf.RGB565 and framebuf.GS4_HMSB. MVLSB is monochrome 1-bit color, RGB565 is
RGB 16-bit color, and GS4_HMSB is grayscale 4-bit color. Where a color value c is passed to a method,
c is a small integer with an encoding that is dependent on the format of the FrameBuffer.
•stride is the number of pixels between each horizontal line of pixels in the FrameBuffer. This defaults to
width but may need adjustments when implementing a FrameBuffer within another larger FrameBuffer or
screen. The buffer size must accommodate an increased step size.
One must specify valid buffer, width, height, format and optionally stride. Invalid buffer size or dimensions may
lead to unexpected errors.

Drawing primitive shapes
The following methods draw shapes onto the FrameBuffer.

FrameBuffer.fill(c)
Fill the entire FrameBuffer with the specified color.
FrameBuffer.pixel(x, y[, c ])
If c is not given, get the color value of the specified pixel. If c is given, set the specified pixel to the given color.
FrameBuffer.hline(x, y, w, c)
FrameBuffer.vline(x, y, h, c)
FrameBuffer.line(x1, y1, x2, y2, c)
Draw a line from a set of coordinates using the given color and a thickness of 1 pixel. The line method draws
the line up to a second set of coordinates whereas the hline and vline methods draw horizontal and vertical lines
respectively up to a given length.
FrameBuffer.rect(x, y, w, h, c)
FrameBuffer.fill_rect(x, y, w, h, c)
Draw a rectangle at the given location, size and color. The rect method draws only a 1 pixel outline whereas the
fill_rect method draws both the outline and interior.
Drawing text
FrameBuffer.text(s, x, y[, c ])
Write text to the FrameBuffer using the the coordinates as the upper-left corner of the text. The color of the text
can be defined by the optional argument but is otherwise a default value of 1. All characters have dimensions of
8x8 pixels and there is currently no way to change the font.
Other methods
FrameBuffer.scroll(xstep, ystep)
Shift the contents of the FrameBuffer by the given vector. This may leave a footprint of the previous colors in
the FrameBuffer.
FrameBuffer.blit(fbuf, x, y[, key ])
Draw another FrameBuffer on top of the current one at the given coordinates. If key is specified then it should
be a color integer and the corresponding color will be considered transparent: all pixels with that color value
will not be drawn.
This method works between FrameBuffer’s utilising different formats, but the resulting colors may be unex-
pected due to the mismatch in color formats.
Constants
framebuf.MONO_VLSB
Monochrome (1-bit) color format This defines a mapping where the bits in a byte are vertically mapped with
bit 0 being nearest the top of the screen. Consequently each byte occupies 8 vertical pixels. Subsequent bytes
appear at successive horizontal locations until the rightmost edge is reached. Further bytes are rendered at
locations starting at the leftmost edge, 8 pixels lower.
framebuf.MONO_HLSB
Monochrome (1-bit) color format This defines a mapping where the bits in a byte are horizontally mapped. Each

byte occupies 8 horizontal pixels with bit 0 being the leftmost. Subsequent bytes appear at successive horizontal
locations until the rightmost edge is reached. Further bytes are rendered on the next row, one pixel lower.
framebuf.MONO_HMSB
Monochrome (1-bit) color format This defines a mapping where the bits in a byte are horizontally mapped. Each
byte occupies 8 horizontal pixels with bit 7 being the leftmost. Subsequent bytes appear at successive horizontal
locations until the rightmost edge is reached. Further bytes are rendered on the next row, one pixel lower.
framebuf.RGB565
Red Green Blue (16-bit, 5+6+5) color format
framebuf.GS4_HMSB
Grayscale (4-bit) color format
2.2.3 machine — functions related to the hardware
The machine module contains specific functions related to the hardware on a particular board. Most functions in
this module allow to achieve direct and unrestricted access to and control of hardware blocks on a system (like CPU,
timers, buses, etc.). Used incorrectly, this can lead to malfunction, lockups, crashes of your board, and in extreme
cases, hardware damage. A note of callbacks used by functions and class methods of machine module: all these
callbacks should be considered as executing in an interrupt context. This is true for both physical devices with IDs >=
0 and “virtual” devices with negative IDs like -1 (these “virtual” devices are still thin shims on top of real hardware
and real hardware interrupts). See Writing interrupt handlers.
Reset related functions
machine.reset()
Resets the device in a manner similar to pushing the external RESET button.
machine.reset_cause()
Get the reset cause. See constants for the possible return values.
Interrupt related functions
machine.disable_irq()
Disable interrupt requests. Returns the previous IRQ state which should be considered an opaque value. This
return value should be passed to the enable_irq function to restore interrupts to their original state, before
disable_irq was called.
machine.enable_irq(state)
Re-enable interrupt requests. The state parameter should be the value that was returned from the most recent
call to the disable_irq function.
Power related functions
machine.freq()
Returns CPU frequency in hertz.
machine.idle()
Gates the clock to the CPU, useful to reduce power consumption at any time during short or long periods.
Peripherals continue working and execution resumes as soon as any interrupt is triggered (on many ports this
includes system timer interrupt occurring at regular intervals on the order of millisecond).

machine.sleep()
Stops the CPU and disables all peripherals except for WLAN. Execution is resumed from the point where the
sleep was requested. For wake up to actually happen, wake sources should be configured first.
machine.deepsleep()
Stops the CPU and all peripherals (including networking interfaces, if any). Execution is resumed from
the main script, just as with a reset. The reset cause can be checked to know that we are coming from
machine.DEEPSLEEP. For wake up to actually happen, wake sources should be configured first, like Pin
change or RTC timeout.
Miscellaneous functions
machine.unique_id()
Returns a byte string with a unique identifier of a board/SoC. It will vary from a board/SoC instance to another,
if underlying hardware allows. Length varies by hardware (so use substring of a full value if you expect a short
ID). In some MicroPython ports, ID corresponds to the network MAC address.
machine.time_pulse_us(pin, pulse_level, timeout_us=1000000)
Time a pulse on the given pin, and return the duration of the pulse in microseconds. The pulse_level argument
should be 0 to time a low pulse or 1 to time a high pulse.
If the current input value of the pin is different to pulse_level, the function first (*) waits until the pin input
becomes equal to pulse_level, then (**) times the duration that the pin is equal to pulse_level. If the pin is
already equal to pulse_level then timing starts straight away.
The function will return -2 if there was timeout waiting for condition marked (*) above, and -1 if there was
timeout during the main measurement, marked (**) above. The timeout is the same for both cases and given by
timeout_us (which is in microseconds).
Constants
machine.IDLE
machine.SLEEP
machine.DEEPSLEEP
IRQ wake values.
machine.PWRON_RESET
machine.HARD_RESET
machine.WDT_RESET
machine.DEEPSLEEP_RESET
machine.SOFT_RESET
Reset causes.
machine.WLAN_WAKE
machine.PIN_WAKE
machine.RTC_WAKE
Wake-up reasons.
Classes
class I2C – a two-wire serial protocol
I2C is a two-wire protocol for communicating between devices. At the physical level it consists of 2 wires: SCL and
SDA, the clock and data lines respectively.

I2C objects are created attached to a specific bus. They can be initialised when created, or initialised later on.
Printing the I2C object gives you information about its configuration.
Example usage:
from machine import I2C
i2c = I2C(freq=400000) # create I2C peripheral at frequency of 400kHz

# depending on the port, extra parameters may be required
# to select the peripheral and/or pins to use
i2c.scan() # scan for slaves, returning a list of 7-bit addresses
i2c.writeto(42, b'123') # write 3 bytes to slave with 7-bit address 42

i2c.readfrom(42, 4) # read 4 bytes from slave with 7-bit address 42
i2c.readfrom_mem(42, 8, 3) # read 3 bytes from memory of slave 42,

# starting at memory-address 8 in the slave
i2c.writeto_mem(42, 2, b'\x10') # write 1 byte to memory of slave 42
# starting at address 2 in the slave
Constructors
class machine.I2C(id=-1, *, scl, sda, freq=400000)
Construct and return a new I2C object using the following parameters:
•id identifies the particular I2C peripheral. The default value of -1 selects a software implementation of I2C
which can work (in most cases) with arbitrary pins for SCL and SDA. If id is -1 then scl and sda must be
specified. Other allowed values for id depend on the particular port/board, and specifying scl and sda may
or may not be required or allowed in this case.
•scl should be a pin object specifying the pin to use for SCL.
•sda should be a pin object specifying the pin to use for SDA.
•freq should be an integer which sets the maximum frequency for SCL.
General Methods
I2C.init(scl, sda, *, freq=400000)
Initialise the I2C bus with the given arguments:
•scl is a pin object for the SCL line
•sda is a pin object for the SDA line
•freq is the SCL clock rate
I2C.deinit()
Turn off the I2C bus.
Availability: WiPy.
I2C.scan()
Scan all I2C addresses between 0x08 and 0x77 inclusive and return a list of those that respond. A device
responds if it pulls the SDA line low after its address (including a write bit) is sent on the bus.
Primitive I2C operations The following methods implement the primitive I2C master bus operations and can be
combined to make any I2C transaction. They are provided if you need more control over the bus, otherwise the
standard methods (see below) can be used.

I2C.start()
Generate a START condition on the bus (SDA transitions to low while SCL is high).
Availability: ESP8266.
I2C.stop()
Generate a STOP condition on the bus (SDA transitions to high while SCL is high).
I2C.readinto(buf, nack=True)
Reads bytes from the bus and stores them into buf. The number of bytes read is the length of buf. An ACK will
be sent on the bus after receiving all but the last byte. After the last byte is received, if nack is true then a NACK
will be sent, otherwise an ACK will be sent (and in this case the slave assumes more bytes are going to be read
in a later call).
I2C.write(buf )
Write the bytes from buf to the bus. Checks that an ACK is received after each byte and stops transmitting the
remaining bytes if a NACK is received. The function returns the number of ACKs that were received.
Standard bus operations The following methods implement the standard I2C master read and write operations that
target a given slave device.
I2C.readfrom(addr, nbytes, stop=True)
Read nbytes from the slave specified by addr. If stop is true then a STOP condition is generated at the end of
the transfer. Returns a bytes object with the data read.
I2C.readfrom_into(addr, buf, stop=True)
Read into buf from the slave specified by addr. The number of bytes read will be the length of buf. If stop is
true then a STOP condition is generated at the end of the transfer.
The method returns None.
I2C.writeto(addr, buf, stop=True)
Write the bytes from buf to the slave specified by addr. If a NACK is received following the write of a byte
from buf then the remaining bytes are not sent. If stop is true then a STOP condition is generated at the end of
the transfer, even if a NACK is received. The function returns the number of ACKs that were received.
Memory operations Some I2C devices act as a memory device (or set of registers) that can be read from and written
to. In this case there are two addresses associated with an I2C transaction: the slave address and the memory address.
The following methods are convenience functions to communicate with such devices.
I2C.readfrom_mem(addr, memaddr, nbytes, *, addrsize=8)
Read nbytes from the slave specified by addr starting from the memory address specified by memaddr. The
argument addrsize specifies the address size in bits. Returns a bytes object with the data read.
I2C.readfrom_mem_into(addr, memaddr, buf, *, addrsize=8)
Read into buf from the slave specified by addr starting from the memory address specified by memaddr. The
number of bytes read is the length of buf. The argument addrsize specifies the address size in bits (on ESP8266
this argument is not recognised and the address size is always 8 bits).
I2C.writeto_mem(addr, memaddr, buf, *, addrsize=8)
Write buf to the slave specified by addr starting from the memory address specified by memaddr. The argument

addrsize specifies the address size in bits (on ESP8266 this argument is not recognised and the address size is
always 8 bits).
class Pin – control I/O pins
A pin object is used to control I/O pins (also known as GPIO - general-purpose input/output). Pin objects are com-
monly associated with a physical pin that can drive an output voltage and read input voltages. The pin class has
methods to set the mode of the pin (IN, OUT, etc) and methods to get and set the digital logic level. For analog control
of a pin, see the ADC class.
A pin object is constructed by using an identifier which unambiguously specifies a certain I/O pin. The allowed forms
of the identifier and the physical pin that the identifier maps to are port-specific. Possibilities for the identifier are an
integer, a string or a tuple with port and pin number.
Usage Model:
# create an output pin on pin #0

p0 = Pin(0, Pin.OUT)
# set the value low then high

p0.value(0)
p0.value(1)
# create an input pin on pin #2, with a pull up resistor

p2 = Pin(2, Pin.IN, Pin.PULL_UP)
# read and print the pin value

print(p2.value())
# reconfigure pin #0 in input mode

p0.mode(p0.IN)
# configure an irq callback

p0.irq(lambda p:print(p))
Constructors
class machine.Pin(id, mode=-1, pull=-1, *, value, drive, alt)
Access the pin peripheral (GPIO pin) associated with the given id. If additional arguments are given in the
constructor then they are used to initialise the pin. Any settings that are not specified will remain in their
previous state.
The arguments are:
•id is mandatory and can be an arbitrary object. Among possible value types are: int (an internal Pin
identifier), str (a Pin name), and tuple (pair of [port, pin]).
•mode specifies the pin mode, which can be one of:
–Pin.IN - Pin is configured for input. If viewed as an output the pin is in high-impedance state.
–Pin.OUT - Pin is configured for (normal) output.
–Pin.OPEN_DRAIN - Pin is configured for open-drain output. Open-drain output works in the fol-
lowing way: if the output value is set to 0 the pin is active at a low level; if the output value is 1 the

pin is in a high-impedance state. Not all ports implement this mode, or some might only on certain
pins.
–Pin.ALT - Pin is configured to perform an alternative function, which is port specific. For a pin
configured in such a way any other Pin methods (except Pin.init()) are not applicable (calling
them will lead to undefined, or a hardware-specific, result). Not all ports implement this mode.
–Pin.ALT_OPEN_DRAIN - The Same as Pin.ALT, but the pin is configured as open-drain. Not all
ports implement this mode.
•pull specifies if the pin has a (weak) pull resistor attached, and can be one of:
–None - No pull up or down resistor.
–Pin.PULL_UP - Pull up resistor enabled.
–Pin.PULL_DOWN - Pull down resistor enabled.
•value is valid only for Pin.OUT and Pin.OPEN_DRAIN modes and specifies initial output pin value if
given, otherwise the state of the pin peripheral remains unchanged.
•drive specifies the output power of the pin and can be one of: Pin.LOW_POWER, Pin.MED_POWER or
Pin.HIGH_POWER. The actual current driving capabilities are port dependent. Not all ports implement
this argument.
•alt specifies an alternate function for the pin and the values it can take are port dependent. This argument
is valid only for Pin.ALT and Pin.ALT_OPEN_DRAIN modes. It may be used when a pin supports
more than one alternate function. If only one pin alternate function is supported the this argument is not
required. Not all ports implement this argument.
As specified above, the Pin class allows to set an alternate function for a particular pin, but it does not specify any
further operations on such a pin. Pins configured in alternate-function mode are usually not used as GPIO but
are instead driven by other hardware peripherals. The only operation supported on such a pin is re-initialising,
by calling the constructor or Pin.init() method. If a pin that is configured in alternate-function mode is
re-initialised with Pin.IN, Pin.OUT, or Pin.OPEN_DRAIN, the alternate function will be removed from
the pin.
Methods
Pin.init(mode=-1, pull=-1, *, value, drive, alt)
Re-initialise the pin using the given parameters. Only those arguments that are specified will be set. The rest of
the pin peripheral state will remain unchanged. See the constructor documentation for details of the arguments.
Returns None.
Pin.value([x ])
This method allows to set and get the value of the pin, depending on whether the argument x is supplied or not.
If the argument is omitted then this method gets the digital logic level of the pin, returning 0 or 1 corresponding
to low and high voltage signals respectively. The behaviour of this method depends on the mode of the pin:
•Pin.IN - The method returns the actual input value currently present on the pin.
•Pin.OUT - The behaviour and return value of the method is undefined.
•Pin.OPEN_DRAIN - If the pin is in state ‘0’ then the behaviour and return value of the method is unde-
fined. Otherwise, if the pin is in state ‘1’, the method returns the actual input value currently present on
the pin.
If the argument is supplied then this method sets the digital logic level of the pin. The argument x can be
anything that converts to a boolean. If it converts to True, the pin is set to state ‘1’, otherwise it is set to state
‘0’. The behaviour of this method depends on the mode of the pin:

•Pin.IN - The value is stored in the output buffer for the pin. The pin state does not change, it remains
in the high-impedance state. The stored value will become active on the pin as soon as it is changed to
Pin.OUT or Pin.OPEN_DRAIN mode.
•Pin.OUT - The output buffer is set to the given value immediately.
•Pin.OPEN_DRAIN - If the value is ‘0’ the pin is set to a low voltage state. Otherwise the pin is set to
high-impedance state.
When setting the value this method returns None.
Pin.out_value()
Return the value stored in the output buffer of a pin, regardless of its mode.
Not all ports implement this method.
Pin.__call__([x ])
Pin objects are callable. The call method provides a (fast) shortcut to set and get the value of the pin. It is
equivalent to Pin.value([x]). See Pin.value() for more details.
Pin.mode([mode ])
Get or set the pin mode. See the constructor documentation for details of the mode argument.
Pin.pull([pull ])
Get or set the pin pull state. See the constructor documentation for details of the pull argument.
Pin.drive([drive ])
Get or set the pin drive strength. See the constructor documentation for details of the drive argument.
Not all ports implement this method.
Availability: WiPy.
Pin.irq(handler=None, trigger=(Pin.IRQ_FALLING | Pin.IRQ_RISING), *, priority=1, wake=None)
Configure an interrupt handler to be called when the trigger source of the pin is active. If the pin mode is
Pin.IN then the trigger source is the external value on the pin. If the pin mode is Pin.OUT then the trigger
source is the output buffer of the pin. Otherwise, if the pin mode is Pin.OPEN_DRAIN then the trigger source
is the output buffer for state ‘0’ and the external pin value for state ‘1’.
The arguments are:
•handler is an optional function to be called when the interrupt triggers.
•trigger configures the event which can generate an interrupt. Possible values are:
–Pin.IRQ_FALLING interrupt on falling edge.
–Pin.IRQ_RISING interrupt on rising edge.
–Pin.IRQ_LOW_LEVEL interrupt on low level.
–Pin.IRQ_HIGH_LEVEL interrupt on high level.
These values can be OR’ed together to trigger on multiple events.
•priority sets the priority level of the interrupt. The values it can take are port-specific, but higher values
always represent higher priorities.
•wake selects the power mode in which this interrupt can wake up the system. It can be machine.IDLE,
machine.SLEEP or machine.DEEPSLEEP. These values can also be OR’ed together to make a pin
generate interrupts in more than one power mode.
This method returns a callback object.

Constants The following constants are used to configure the pin objects. Note that not all constants are available on
all ports.
Pin.IN
Pin.OUT
Pin.OPEN_DRAIN
Pin.ALT
Pin.ALT_OPEN_DRAIN
Selects the pin mode.
Pin.PULL_UP
Pin.PULL_DOWN
Selects whether there is a pull up/down resistor. Use the value None for no pull.
Pin.LOW_POWER
Pin.MED_POWER
Pin.HIGH_POWER
Selects the pin drive strength.
Pin.IRQ_FALLING
Pin.IRQ_RISING
Pin.IRQ_LOW_LEVEL
Pin.IRQ_HIGH_LEVEL
Selects the IRQ trigger type.
class Signal – control and sense external I/O devices
The Signal class is a simple extension of Pin class. Unlike Pin, which can be only in “absolute” 0 and 1 states, a
Signal can be in “asserted” (on) or “deasserted” (off) states, while being inverted (active-low) or not. Summing up, it
adds logical inversion support to Pin functionality. While this may seem a simple addition, it is exactly what is needed
to support wide array of simple digital devices in a way portable across different boards, which is one of the major
MicroPython goals. Regardless whether different users have an active-high or active-low LED, a normally open or
normally closed relay - you can develop single, nicely looking application which works with each of them, and capture
hardware configuration differences in few lines on the config file of your app.
Following is the guide when Signal vs Pin should be used:
• Use Signal: If you want to control a simple on/off (including software PWM!) devices like LEDs, multi-segment
indicators, relays, buzzers, or read simple binary sensors, like normally open or normally closed buttons, pulled
high or low, Reed switches, moisture/flame detectors, etc. etc. Summing up, if you have a real physical de-
vice/sensor requiring GPIO access, you likely should use a Signal.
• Use Pin: If you implement a higher-level protocol or bus to communicate with more complex devices.
The split between Pin and Signal come from the usecases above and the architecture of MicroPython: Pin offers the
lowest overhead, which may be important when bit-banging protocols. But Signal adds additional flexibility on top of
Pin, at the cost of minor overhead (much smaller than if you implemented active-high vs active-low device differences
in Python manually!). Also, Pin is low-level object which needs to be implemented for each support board, while
Signal is a high-level object which comes for free once Pin is implemented.
If in doubt, give the Signal a try! Once again, it is developed to save developers from the need to handle unexciting
differences like active-low vs active-high signals, and allow other users to share and enjoy your application, instead of
being frustrated by the fact that it doesn’t work for them simply because their LEDs or relays are wired in a slightly
different way.
Constructors
class machine.Signal(pin_obj, invert=False)

class machine.Signal(pin_arguments..., *, invert=False)

Create a Signal object. There’re two ways to create it:
•By wrapping existing Pin object - universal method which works for any board.
•By passing required Pin parameters directly to Signal constructor, skipping the need to create intermediate
Pin object. Available on many, but not all boards.
The arguments are:
•pin_obj is existing Pin object.
•pin_arguments are the same arguments as can be passed to Pin constructor.
•invert - if True, the signal will be inverted (active low).
Methods
Signal.value([x ])
This method allows to set and get the value of the signal, depending on whether the argument x is supplied or
not.
If the argument is omitted then this method gets the signal level, 1 meaning signal is asserted (active) and 0 -
signal inactive.
If the argument is supplied then this method sets the signal level. The argument x can be anything that converts
to a boolean. If it converts to True, the signal is active, otherwise it is inactive.
Correspondence between signal being active and actual logic level on the underlying pin depends on whether
signal is inverted (active-low) or not. For non-inverted signal, active status corresponds to logical 1, inactive -
to logical 0. For inverted/active-low signal, active status corresponds to logical 0, while inactive - to logical 1.
Signal.on()
Activate signal.
Signal.off()
Deactivate signal.
class RTC – real time clock
The RTC is and independent clock that keeps track of the date and time.
Example usage:
rtc = machine.RTC()
rtc.init((2014, 5, 1, 4, 13, 0, 0, 0))
print(rtc.now())
Constructors
class machine.RTC(id=0, ...)
Create an RTC object. See init for parameters of initialization.
Methods
RTC.init(datetime)
Initialise the RTC. Datetime is a tuple of the form:
(year, month, day[, hour[, minute[, second[, microsecond[,
tzinfo]]]]])

RTC.now()
Get get the current datetime tuple.
RTC.deinit()
Resets the RTC to the time of January 1, 2015 and starts running it again.
RTC.alarm(id, time, /*, repeat=False)
Set the RTC alarm. Time might be either a millisecond value to program the alarm to current time + time_in_ms
in the future, or a datetimetuple. If the time passed is in milliseconds, repeat can be set to True to make the
alarm periodic.
RTC.alarm_left(alarm_id=0)
Get the number of milliseconds left before the alarm expires.
RTC.cancel(alarm_id=0)
Cancel a running alarm.
RTC.irq(*, trigger, handler=None, wake=machine.IDLE)
Create an irq object triggered by a real time clock alarm.
•trigger must be RTC.ALARM0
•handler is the function to be called when the callback is triggered.
•wake specifies the sleep mode from where this interrupt can wake up the system.
Constants
RTC.ALARM0
irq trigger source
class SPI – a Serial Peripheral Interface bus protocol (master side)
SPI is a synchronous serial protocol that is driven by a master. At the physical level, a bus consists of 3 lines: SCK,
MOSI, MISO. Multiple devices can share the same bus. Each device should have a separate, 4th signal, SS (Slave
Select), to select a particular device on a bus with which communication takes place. Management of an SS signal
should happen in user code (via machine.Pin class).
Constructors
class machine.SPI(id, ...)
Construct an SPI object on the given bus, id. Values of id depend on a particular port and its hardware. Values
0, 1, etc. are commonly used to select hardware SPI block #0, #1, etc. Value -1 can be used for bitbanging
(software) implementation of SPI (if supported by a port).
With no additional parameters, the SPI object is created but not initialised (it has the settings from the last
initialisation of the bus, if any). If extra arguments are given, the bus is initialised. See init for parameters of
initialisation.
Methods
SPI.init(baudrate=1000000, *, polarity=0, phase=0, bits=8, firstbit=SPI.MSB, sck=None, mosi=None,
miso=None, pins=(SCK, MOSI, MISO))
Initialise the SPI bus with the given parameters:
•baudrate is the SCK clock rate.
•polarity can be 0 or 1, and is the level the idle clock line sits at.
•phase can be 0 or 1 to sample data on the first or second clock edge respectively.

•bits is the width in bits of each transfer. Only 8 is guaranteed to be supported by all hardware.
•firstbit can be SPI.MSB or SPI.LSB.
•sck, mosi, miso are pins (machine.Pin) objects to use for bus signals. For most hardware SPI blocks
(as selected by id parameter to the constructor), pins are fixed and cannot be changed. In some cases,
hardware blocks allow 2-3 alternative pin sets for a hardware SPI block. Arbitrary pin assignments are
possible only for a bitbanging SPI driver (id = -1).
•pins - WiPy port doesn’t sck, mosi, miso arguments, and instead allows to specify them as a tuple of
pins parameter.
SPI.deinit()
Turn off the SPI bus.
SPI.read(nbytes, write=0x00)
Read a number of bytes specified by nbytes while continuously writing the single byte given by write.
Returns a bytes object with the data that was read.
SPI.readinto(buf, write=0x00)
Read into the buffer specified by buf while continuously writing the single byte given by write. Returns
None.
Note: on WiPy this function returns the number of bytes read.
SPI.write(buf )
Write the bytes contained in buf. Returns None.
Note: on WiPy this function returns the number of bytes written.
SPI.write_readinto(write_buf, read_buf )
Write the bytes from write_buf while reading into read_buf. The buffers can be the same or different, but
both buffers must have the same length. Returns None.
Note: on WiPy this function returns the number of bytes written.
Constants
SPI.MASTER
for initialising the SPI bus to master; this is only used for the WiPy
SPI.MSB
set the first bit to be the most significant bit
SPI.LSB
set the first bit to be the least significant bit
class Timer – control hardware timers
Hardware timers deal with timing of periods and events. Timers are perhaps the most flexible and heterogeneous kind
of hardware in MCUs and SoCs, differently greatly from a model to a model. MicroPython’s Timer class defines a
baseline operation of executing a callback with a given period (or once after some delay), and allow specific boards to
define more non-standard behavior (which thus won’t be portable to other boards).
See discussion of important constraints on Timer callbacks.
Note: Memory can’t be allocated inside irq handlers (an interrupt) and so exceptions raised within a handler don’t
give much information. See micropython.alloc_emergency_exception_buf() for how to get around
this limitation.

Constructors
class machine.Timer(id, ...)
Construct a new timer object of the given id. Id of -1 constructs a virtual timer (if supported by a board).
Methods
Timer.deinit()
Deinitialises the timer. Stops the timer, and disables the timer peripheral.
Constants
Timer.ONE_SHOT
Timer.PERIODIC
Timer operating mode.
class UART – duplex serial communication bus
UART implements the standard UART/USART duplex serial communications protocol. At the physical level it con-
sists of 2 lines: RX and TX. The unit of communication is a character (not to be confused with a string character)
which can be 8 or 9 bits wide.
UART objects can be created and initialised using:
from machine import UART
uart = UART(1, 9600) # init with given baudrate

uart.init(9600, bits=8, parity=None, stop=1) # init with given parameters
Supported paramters differ on a board:

Pyboard: Bits can be 7, 8 or 9. Stop can be 1 or 2. With parity=None, only 8 and 9 bits are supported. With parity
enabled, only 7 and 8 bits are supported.
WiPy/CC3200: Bits can be 5, 6, 7, 8. Stop can be 1 or 2.
A UART object acts like a stream object and reading and writing is done using the standard stream methods:
uart.read(10) # read 10 characters, returns a bytes object
uart.read() # read all available characters
uart.readline() # read a line
uart.readinto(buf) # read and store into the given buffer
uart.write('abc') # write the 3 characters
Constructors
class machine.UART(id, ...)
Construct a UART object of the given id.
Methods
UART.deinit()
Turn off the UART bus.
UART.any()
Returns an integer counting the number of characters that can be read without blocking. It will return 0 if there
are no characters available and a positive number if there are characters. The method may return 1 even if there
is more than one character available for reading.
For more sophisticated querying of available characters use select.poll:

poll = select.poll()
poll.register(uart, select.POLLIN)
poll.poll(timeout)
UART.read([nbytes ])
Read characters. If nbytes is specified then read at most that many bytes, otherwise read as much data as
possible.
Return value: a bytes object containing the bytes read in. Returns None on timeout.
UART.readinto(buf [, nbytes ])
Read bytes into the buf. If nbytes is specified then read at most that many bytes. Otherwise, read at most
len(buf) bytes.
Return value: number of bytes read and stored into buf or None on timeout.
UART.readline()
Read a line, ending in a newline character.
Return value: the line read or None on timeout.
UART.write(buf )
Write the buffer of bytes to the bus.
Return value: number of bytes written or None on timeout.
UART.sendbreak()
Send a break condition on the bus. This drives the bus low for a duration longer than required for a normal
transmission of a character.
class WDT – watchdog timer
The WDT is used to restart the system when the application crashes and ends up into a non recoverable state. Once
started it cannot be stopped or reconfigured in any way. After enabling, the application must “feed” the watchdog
periodically to prevent it from expiring and resetting the system.
Example usage:
from machine import WDT
wdt = WDT(timeout=2000) # enable it with a timeout of 2s
wdt.feed()
Availability of this class: pyboard, WiPy.
Constructors
class machine.WDT(id=0, timeout=5000)
Create a WDT object and start it. The timeout must be given in seconds and the minimum value that is accepted
is 1 second. Once it is running the timeout cannot be changed and the WDT cannot be stopped either.
Methods
wdt.feed()
Feed the WDT to prevent it from resetting the system. The application should place this call in a sensible place
ensuring that the WDT is only fed after verifying that everything is functioning correctly.

2.2.4 micropython – access and control MicroPython internals
Functions
micropython.const(expr)
Used to declare that the expression is a constant so that the compile can optimise it. The use of this function
should be as follows:
from micropython import const
CONST_X = const(123)
CONST_Y = const(2 * CONST_X + 1)
Constants declared this way are still accessible as global variables from outside the module they are declared
in. On the other hand, if a constant begins with an underscore then it is hidden, it is not available as a global
variable, and does not take up any memory during execution.
This const function is recognised directly by the MicroPython parser and is provided as part of the micropython
module mainly so that scripts can be written which run under both CPython and MicroPython, by following the
above pattern.
micropython.opt_level([level ])
If level is given then this function sets the optimisation level for subsequent compilation of scripts, and returns
None. Otherwise it returns the current optimisation level.
micropython.alloc_emergency_exception_buf(size)
Allocate size bytes of RAM for the emergency exception buffer (a good size is around 100 bytes). The buffer
is used to create exceptions in cases when normal RAM allocation would fail (eg within an interrupt handler)
and therefore give useful traceback information in these situations.
A good way to use this function is to put it at the start of your main script (eg boot.py or main.py) and then the
emergency exception buffer will be active for all the code following it.
micropython.mem_info([verbose ])
Print information about currently used memory. If the verbose argument is given then extra information is
printed.
The information that is printed is implementation dependent, but currently includes the amount of stack and
heap used. In verbose mode it prints out the entire heap indicating which blocks are used and which are free.
micropython.qstr_info([verbose ])
Print information about currently interned strings. If the verbose argument is given then extra information is
printed.
The information that is printed is implementation dependent, but currently includes the number of interned
strings and the amount of RAM they use. In verbose mode it prints out the names of all RAM-interned strings.
micropython.stack_use()
Return an integer representing the current amount of stack that is being used. The absolute value of this is not
particularly useful, rather it should be used to compute differences in stack usage at different points.
micropython.heap_lock()
micropython.heap_unlock()
Lock or unlock the heap. When locked no memory allocation can occur and a MemoryError will be raised if
any heap allocation is attempted.
These functions can be nested, ie heap_lock() can be called multiple times in a row and the lock-depth will
increase, and then heap_unlock() must be called the same number of times to make the heap available again.

micropython.kbd_intr(chr)
Set the character that will raise a KeyboardInterrupt exception. By default this is set to 3 during script execution,
corresponding to Ctrl-C. Passing -1 to this function will disable capture of Ctrl-C, and passing 3 will restore it.
This function can be used to prevent the capturing of Ctrl-C on the incoming stream of characters that is usually
used for the REPL, in case that stream is used for other purposes.
micropython.schedule(fun, arg)
Schedule the function fun to be executed “very soon”. The function is passed the value arg as its single argument.
“very soon” means that the MicroPython runtime will do its best to execute the function at the earliest possible
time, given that it is also trying to be efficient, and that the following conditions hold:
•A scheduled function will never preempt another scheduled function.
•Scheduled functions are always executed “between opcodes” which means that all fundamental Python
operations (such as appending to a list) are guaranteed to be atomic.
•A given port may define “critical regions” within which scheduled functions will never be executed. Func-
tions may be scheduled within a critical region but they will not be executed until that region is exited. An
example of a critical region is a preempting interrupt handler (an IRQ).
A use for this function is to schedule a callback from a preempting IRQ. Such an IRQ puts restrictions on the
code that runs in the IRQ (for example the heap may be locked) and scheduling a function to call later will lift
those restrictions.
There is a finite stack to hold the scheduled functions and schedule will raise a RuntimeError if the stack is full.
2.2.5 network — network configuration
This module provides network drivers and routing configuration. To use this module, a MicroPython variant/build
with network capabilities must be installed. Network drivers for specific hardware are available within this module
and are used to configure hardware network interface(s). Network services provided by configured interfaces are then
available for use via the socket module.
For example:
# configure a specific network interface
# see below for examples of specific drivers
import network
nic = network.Driver(...)
print(nic.ifconfig())
# now use socket as usual

import socket
addr = socket.getaddrinfo('micropython.org', 80)[0][-1]
s = socket.socket()
s.connect(addr)
s.send(b'GET / HTTP/1.1\r\nHost: micropython.org\r\n\r\n')
data = s.recv(1000)
s.close()
Functions
network.phy_mode([mode ])
Get or set the PHY mode.
If the mode parameter is provided, sets the mode to its value. If the function is called without parameters,
returns the current mode.

The possible modes are defined as constants:

• MODE_11B – IEEE 802.11b,
• MODE_11G – IEEE 802.11g,
• MODE_11N – IEEE 802.11n.
class WLAN
This class provides a driver for WiFi network processor in the ESP8266. Example usage:
import network
# enable station interface and connect to WiFi access point
nic = network.WLAN(network.STA_IF)
nic.active(True)
nic.connect('your-ssid', 'your-password')
# now use sockets as usual
Constructors
class network.WLAN(interface_id)
Create a WLAN network interface object. Supported interfaces are network.STA_IF (station aka client, connects
to upstream WiFi access points) and network.AP_IF (access point, allows other WiFi clients to connect). Avail-
ability of the methods below depends on interface type. For example, only STA interface may connect() to an
access point.
Methods
wlan.active([is_active ])
Activate (“up”) or deactivate (“down”) network interface, if boolean argument is passed. Otherwise, query
current state if no argument is provided. Most other methods require active interface.
wlan.connect(ssid, password)
Connect to the specified wireless network, using the specified password.
wlan.disconnect()
Disconnect from the currently connected wireless network.
wlan.scan()
Scan for the available wireless networks.
Scanning is only possible on STA interface. Returns list of tuples with the information about WiFi access points:
(ssid, bssid, channel, RSSI, authmode, hidden)
bssid is hardware address of an access point, in binary form, returned as bytes object. You can use
ubinascii.hexlify() to convert it to ASCII form.
There are five values for authmode:
•0 – open
•1 – WEP
•2 – WPA-PSK
•3 – WPA2-PSK

•4 – WPA/WPA2-PSK
and two for hidden:
•0 – visible
•1 – hidden
wlan.status()
Return the current status of the wireless connection.
The possible statuses are defined as constants:
•STAT_IDLE – no connection and no activity,
•STAT_CONNECTING – connecting in progress,
•STAT_WRONG_PASSWORD – failed due to incorrect password,
•STAT_NO_AP_FOUND – failed because no access point replied,
•STAT_CONNECT_FAIL – failed due to other problems,
•STAT_GOT_IP – connection successful.
wlan.isconnected()
In case of STA mode, returns True if connected to a WiFi access point and has a valid IP address. In AP mode
returns True when a station is connected. Returns False otherwise.
wlan.ifconfig([(ip, subnet, gateway, dns) ])
Get/set IP-level network interface parameters: IP address, subnet mask, gateway and DNS server. When called
with no arguments, this method returns a 4-tuple with the above information. To set the above values, pass a
4-tuple with the required information. For example:
nic.ifconfig(('192.168.0.4', '255.255.255.0', '192.168.0.1', '8.8.8.8'))
wlan.config(‘param’)
wlan.config(param=value, ...)
Get or set general network interface parameters. These methods allow to work with additional parameters
beyond standard IP configuration (as dealt with by wlan.ifconfig()). These include network-specific
and hardware-specific parameters. For setting parameters, keyword argument syntax should be used, multiple
parameters can be set at once. For querying, parameters name should be quoted as a string, and only one
parameter can be queries at time:
# Set WiFi access point name (formally known as ESSID) and WiFi channel
ap.config(essid='My AP', channel=11)
# Query params one by one
print(ap.config('essid'))
print(ap.config('channel'))
Following are commonly supported parameters (availability of a specific parameter depends on network tech-
nology type, driver, and MicroPython port).
Parameter Description
mac MAC address (bytes)
essid WiFi access point name (string)
channel WiFi channel (integer)
hidden Whether ESSID is hidden (boolean)
authmode Authentication mode supported (enumeration, see module constants)
password Access password (string)

2.2.6 uctypes – access binary data in a structured way
This module implements “foreign data interface” for MicroPython. The idea behind it is similar to CPython’s ctypes
modules, but the actual API is different, streamlined and optimized for small size. The basic idea of the module is
to define data structure layout with about the same power as the C language allows, and the access it using familiar
dot-syntax to reference sub-fields.
See also:
Module ustruct Standard Python way to access binary data structures (doesn’t scale well to large and complex
structures).
Defining structure layout
Structure layout is defined by a “descriptor” - a Python dictionary which encodes field names as keys and other
properties required to access them as associated values. Currently, uctypes requires explicit specification of offsets for
each field. Offset are given in bytes from a structure start.
Following are encoding examples for various field types:
• Scalar types:
"field_name": uctypes.UINT32 | 0
in other words, value is scalar type identifier ORed with field offset (in bytes) from the start of the structure.
• Recursive structures:
"sub": (2, {
"b0": uctypes.UINT8 | 0,
"b1": uctypes.UINT8 | 1,
})
i.e. value is a 2-tuple, first element of which is offset, and second is a structure descriptor dictionary (note:
offsets in recursive descriptors are relative to a structure it defines).
• Arrays of primitive types:
"arr": (uctypes.ARRAY | 0, uctypes.UINT8 | 2),
i.e. value is a 2-tuple, first element of which is ARRAY flag ORed with offset, and second is scalar element type
ORed number of elements in array.
• Arrays of aggregate types:
"arr2": (uctypes.ARRAY | 0, 2, {"b": uctypes.UINT8 | 0}),
i.e. value is a 3-tuple, first element of which is ARRAY flag ORed with offset, second is a number of elements
in array, and third is descriptor of element type.
• Pointer to a primitive type:
"ptr": (uctypes.PTR | 0, uctypes.UINT8),
i.e. value is a 2-tuple, first element of which is PTR flag ORed with offset, and second is scalar element type.
• Pointer to an aggregate type:
"ptr2": (uctypes.PTR | 0, {"b": uctypes.UINT8 | 0}),

i.e. value is a 2-tuple, first element of which is PTR flag ORed with offset, second is descriptor of type pointed
to.
• Bitfields:
"bitf0": uctypes.BFUINT16 | 0 | 0 << uctypes.BF_POS | 8 << uctypes.BF_LEN,
i.e. value is type of scalar value containing given bitfield (typenames are similar to scalar types, but prefixes with
“BF”), ORed with offset for scalar value containing the bitfield, and further ORed with values for bit offset and
bit length of the bitfield within scalar value, shifted by BF_POS and BF_LEN positions, respectively. Bitfield
position is counted from the least significant bit, and is the number of right-most bit of a field (in other words,
it’s a number of bits a scalar needs to be shifted right to extra the bitfield).
In the example above, first UINT16 value will be extracted at offset 0 (this detail may be important when
accessing hardware registers, where particular access size and alignment are required), and then bitfield whose
rightmost bit is least-significant bit of this UINT16, and length is 8 bits, will be extracted - effectively, this will
access least-significant byte of UINT16.
Note that bitfield operations are independent of target byte endianness, in particular, example above will access
least-significant byte of UINT16 in both little- and big-endian structures. But it depends on the least significant
bit being numbered 0. Some targets may use different numbering in their native ABI, but uctypes always uses
normalized numbering described above.
Module contents
class uctypes.struct(addr, descriptor, layout_type=NATIVE)

Instantiate a “foreign data structure” object based on structure address in memory, descriptor (encoded as a
dictionary), and layout type (see below).
uctypes.LITTLE_ENDIAN
Layout type for a little-endian packed structure. (Packed means that every field occupies exactly as many bytes
as defined in the descriptor, i.e. the alignment is 1).
uctypes.BIG_ENDIAN
Layout type for a big-endian packed structure.
uctypes.NATIVE
Layout type for a native structure - with data endianness and alignment conforming to the ABI of the system on
which MicroPython runs.
uctypes.sizeof(struct)
Return size of data structure in bytes. Argument can be either structure class or specific instantiated structure
object (or its aggregate field).
uctypes.addressof(obj)
Return address of an object. Argument should be bytes, bytearray or other object supporting buffer protocol
(and address of this buffer is what actually returned).
uctypes.bytes_at(addr, size)
Capture memory at the given address and size as bytes object. As bytes object is immutable, memory is actually
duplicated and copied into bytes object, so if memory contents change later, created object retains original value.
uctypes.bytearray_at(addr, size)
Capture memory at the given address and size as bytearray object. Unlike bytes_at() function above, memory
is captured by reference, so it can be both written too, and you will access current value at the given memory
address.

Structure descriptors and instantiating structure objects
Given a structure descriptor dictionary and its layout type, you can instantiate a specific structure instance at a given
memory address using uctypes.struct() constructor. Memory address usually comes from following sources:
• Predefined address, when accessing hardware registers on a baremetal system. Lookup these addresses in
datasheet for a particular MCU/SoC.
• As a return value from a call to some FFI (Foreign Function Interface) function.
• From uctypes.addressof(), when you want to pass arguments to an FFI function, or alternatively, to access some
data for I/O (for example, data read from a file or network socket).
Structure objects
Structure objects allow accessing individual fields using standard dot notation:
my_struct.substruct1.field1. If a field is of scalar type, getting it will produce a primitive value
(Python integer or float) corresponding to the value contained in a field. A scalar field can also be assigned to.
If a field is an array, its individual elements can be accessed with the standard subscript operator [] - both read and
assigned to.
If a field is a pointer, it can be dereferenced using [0] syntax (corresponding to C * operator, though [0] works in C
too). Subscripting a pointer with other integer values but 0 are supported too, with the same semantics as in C.
Summing up, accessing structure fields generally follows C syntax, except for pointer dereference, when you need to
use [0] operator instead of *.
Limitations
Accessing non-scalar fields leads to allocation of intermediate objects to represent them. This means that special care
should be taken to layout a structure which needs to be accessed when memory allocation is disabled (e.g. from an
interrupt). The recommendations are:
• Avoid nested structures. For example, instead of mcu_registers.peripheral_a.register1, define
separate layout descriptors for each peripheral, to be accessed as peripheral_a.register1.
• Avoid other non-scalar data, like array. For example, instead of peripheral_a.register[0] use
peripheral_a.register0.
Note that these recommendations will lead to decreased readability and conciseness of layouts, so they should be used
only if the need to access structure fields without allocation is anticipated (it’s even possible to define 2 parallel layouts
- one for normal usage, and a restricted one to use when memory allocation is prohibited).
2.3 Libraries specific to the ESP8266
The following libraries are specific to the ESP8266.
2.3.1 esp — functions related to the ESP8266
The esp module contains specific functions related to the ESP8266 module.

Functions
esp.sleep_type([sleep_type ])
Get or set the sleep type.
If the sleep_type parameter is provided, sets the sleep type to its value. If the function is called without
parameters, returns the current sleep type.
The possible sleep types are defined as constants:
•SLEEP_NONE – all functions enabled,
•SLEEP_MODEM – modem sleep, shuts down the WiFi Modem circuit.
•SLEEP_LIGHT – light sleep, shuts down the WiFi Modem circuit and suspends the processor periodically.
The system enters the set sleep mode automatically when possible.
esp.deepsleep(time=0)
Enter deep sleep.
The whole module powers down, except for the RTC clock circuit, which can be used to restart the module after
the specified time if the pin 16 is connected to the reset pin. Otherwise the module will sleep until manually
reset.
esp.flash_id()
Read the device ID of the flash memory.
esp.flash_read(byte_offset, length_or_buffer)
esp.flash_write(byte_offset, bytes)
esp.flash_erase(sector_no)
esp.set_native_code_location(start, length)
Set the location that native code will be placed for execution after it is compiled. Native code is emitted when
the @micropython.native, @micropython.viper and @micropython.asm_xtensa decorators
are applied to a function. The ESP8266 must execute code from either iRAM or the lower 1MByte of flash
(which is memory mapped), and this function controls the location.
If start and length are both None then the native code location is set to the unused portion of memory at the
end of the iRAM1 region. The size of this unused portion depends on the firmware and is typically quite small
(around 500 bytes), and is enough to store a few very small functions. The advantage of using this iRAM1
region is that it does not get worn out by writing to it.
If neither start nor length are None then they should be integers. start should specify the byte offset from the
beginning of the flash at which native code should be stored. length specifies how many bytes of flash from start
can be used to store native code. start and length should be multiples of the sector size (being 4096 bytes). The
flash will be automatically erased before writing to it so be sure to use a region of flash that is not otherwise
used, for example by the firmware or the filesystem.
When using the flash to store native code start+length must be less than or equal to 1MByte. Note that the flash
can be worn out if repeated erasures (and writes) are made so use this feature sparingly. In particular, native
code needs to be recompiled and rewritten to flash on each boot (including wake from deepsleep).
In both cases above, using iRAM1 or flash, if there is no more room left in the specified region then the use
of a native decorator on a function will lead to MemoryError exception being raised during compilation of that
function.
2.3. Libraries specific to the ESP8266 55


CHAPTER
THREE
MICROPYTHON DIFFERENCES FROM CPYTHON
The operations listed in this section produce conflicting results in MicroPython when compared to standard Python.
3.1 Syntax
Generated Fri 26 May 2017 09:20:57 UTC
3.1.1 Spaces
uPy requires spaces between literal numbers and keywords, CPy doesn’t
Sample code:
try:
print(eval('1and 0'))
except SyntaxError:
print('Should have worked')
try:
print(eval('1or 0'))
except SyntaxError:
try:
print(eval('1if 1else 0'))
except SyntaxError:
CPy output: uPy output:

0 Should have worked
3.1.2 Unicode
Unicode name escapes are not implemented

Sample code:
print("\N{LATIN SMALL LETTER A}")
57

a NotImplementedError: unicode name escapes
3.2 Core Language

Error messages for methods may display unexpected argument counts
Cause: MicroPython counts “self” as an argument.
Workaround: Interpret error messages with the information above in mind.
Sample code:
try:
[].append()
except Exception as e:
print(e)

append() takes exactly one argument (0 given)
function takes 2 positional arguments but 1 were gi
Method Resolution Order (MRO) is not compliant with CPython

Sample code:
class Foo:
def __str__(self):
return "Foo"
class C(tuple, Foo):

pass
t = C((1, 2, 3))
print(t)

Foo (1, 2, 3)
3.2.1 Classes
Special method __del__ not implemented for user-defined classes

Sample code:
import gc
class Foo():
def __del__(self):
print('__del__')
f = Foo()
del f
58 Chapter 3. MicroPython Differences from CPython

gc.collect()

__del__
When inheriting from multiple classes super() only calls one class
Cause: Depth first non-exhaustive method resolution order
Sample code:
class A:
def __init__(self):
print("A.__init__")
class B(A):
def __init__(self):
print("B.__init__")
super().__init__()
class C(A):
def __init__(self):
print("C.__init__")
super().__init__()
class D(B,C):
def __init__(self):
print("D.__init__")
super().__init__()
D()

D.__init__ D.__init__
B.__init__ B.__init__
C.__init__ A.__init__
A.__init__
Calling super() getter property in subclass will return a property object, not the value
Sample code:
class A:
@property
def p(self):
return {"a":10}
class AA(A):
@property
def p(self):
return super().p
a = AA()
print(a.p)
3.2. Core Language 59


{'a': 10} <property>
3.2.2 Functions
Unpacking function arguments in non-last position isn’t detected as an error

Workaround: The syntax below is invalid, never use it in applications.
Sample code:
print(*(1, 2), 3)

1 2 3 3 1 2
User-defined attributes for functions are not supported

Cause: MicroPython is highly optimized for memory usage.
Workaround: Use external dictionary, e.g. FUNC_X[f] = 0.
Sample code:
def f():
pass
f.x = 0
print(f.x)

0 Traceback (most recent call last):
File "<stdin>", line 10, in <module>
AttributeError: 'function' object has no attribute
3.2.3 Generator
Context manager __exit__() not called in a generator which does not run to completion
Sample code:
class foo(object):
def __enter__(self):
print('Enter')
def __exit__(self, *args):
print('Exit')
def bar(x):
with foo():
while True:
x += 1
yield x
def func():

g = bar(0)
for _ in range(3):
print(next(g))
func()

Enter Enter
1 1
2 2
3 3
Exit
3.2.4 import
__path__ attribute of a package has a different type (single string instead of list of strings) in MicroPython
Cause: MicroPython does’t support namespace packages split across filesystem. Beyond that, MicroPython’s import
system is highly optimized for minimal memory usage.
Workaround: Details of import handling is inherently implementation dependent. Don’t rely on such details in
portable applications.
Sample code:
import modules
print(modules.__path__)

['/home/micropython/micropython-docs/tests/cpydiff/modules']
../tests/cpydiff//modules
Failed to load modules are still registered as loaded

Cause: To make module handling more efficient, it’s not wrapped with exception handling.
Workaround: Test modules before production use; during development, use del sys.modules["name"], or
just soft or hard reset the board.
Sample code:
import sys
try:
from modules import foo
except NameError as e:
print(e)
try:
from modules import foo
print('Should not get here')
except NameError as e:
print(e)
3.2. Core Language 61


foo foo
name 'xxx' is not defined name 'xxx' is not defined
foo Should not get here
name 'xxx' is not defined
MicroPython does’t support namespace packages split across filesystem.

Cause: MicroPython’s import system is highly optimized for simplicity, minimal memory usage, and minimal filesys-
tem search overhead.
Workaround: Don’t install modules belonging to the same namespace package in different directories. For MicroPy-
thon, it’s recommended to have at most 3-component module search paths: for your current application, per-user
(writable), system-wide (non-writable).
Sample code:
import sys
sys.path.append(sys.path[1] + "/modules")
sys.path.append(sys.path[1] + "/modules2")
import subpkg.foo
import subpkg.bar
print("Two modules of a split namespace package imported")

Two modules of a split namespace packageTraceback
imported (most recent call last):
ImportError: no module named 'subpkg.bar'
3.3 Builtin Types
3.3.1 Exception
Exception chaining not implemented

Sample code:
try:
raise TypeError
except TypeError:
raise ValueError


Traceback (most recent call last): Traceback (most recent call last):
File "<stdin>", line 8, in <module> File "<stdin>", line 10, in <module>
TypeError ValueError:
During handling of the above exception, another exception occurred:
Traceback (most recent call last):

ValueError
Assign instance variable to exception

Sample code:
e = Exception()
e.x = 0
print(e.x)

AttributeError: 'Exception' object has no attribute
While loop guards will obscure exception line number reporting due to being optimised onto the end of the code
block
Sample code:
l = ["-foo", "-bar"]
i = 0
while l[i][0] == "-":
print("iter")
i += 1

iter iter
iter iter
Traceback (most recent call last): Traceback (most recent call last):
File "<stdin>", line 10, in <module> File "<stdin>", line 12, in <module>
IndexError: list index out of range IndexError: list index out of range
Exception.__init__ raises TypeError if overridden and called by subclass

Sample code:
class A(Exception):
def __init__(self):
Exception.__init__(self)
a = A()
3.3. Builtin Types 63


File "<stdin>", line 9, in __init__
TypeError: argument should be a 'Exception' not a '
3.3.2 bytearray
Array slice assignment with unsupported RHS

Sample code:
b = bytearray(4)
b[0:1] = [1, 2]
print(b)

bytearray(b'\x01\x02\x00\x00\x00') Traceback (most recent call last):
NotImplementedError: array/bytes required on right
3.3.3 bytes
bytes(...) with keywords not implemented

Workaround: Input the encoding format directly. eg. print(bytes(’abc’, ’utf-8’))
Sample code:
print(bytes('abc', encoding='utf8'))

b'abc' Traceback (most recent call last):
NotImplementedError: keyword argument(s) not yet im
Bytes subscr with step != 1 not implemented

Sample code:
print(b'123'[0:3:2])

b'13' Traceback (most recent call last):
NotImplementedError: only slices with step=1 (aka N
3.3.4 float
uPy and CPython outputs formats differ

Sample code:
print('%.1g' % -9.9)
print('%.1e' % 9.99)
print('%.1e' % 0.999)

-1e+01 -10
1.0e+01 1.00e+01
1.0e+00 1.00e-00
3.3.5 int
No int conversion for int-derived types available

Sample code:
class A(int):
__add__ = lambda self, other: A(int(self) + other)
a = A(42)
print(a+a)

File "<stdin>", line 8, in <lambda>
TypeError: can't convert A to int
Incorrect error message when passing float into to_bytes

Sample code:
try:
int('1').to_bytes(1.0)
except TypeError as e:
print(e)

integer argument expected, got float function missing 1 required positional arguments
3.3.6 list
List delete with step != 1 not implemented

Sample code:
l = [1, 2, 3, 4]
del l[0:4:2]
print(l)


[2, 4] Traceback (most recent call last):
NotImplementedError:
List slice-store with non-iterable on RHS is not implemented

Cause: RHS is restricted to be a tuple or list
Workaround: Use list(<iter>) on RHS to convert the iterable to a list
Sample code:
l = [10, 20]
l[0:1] = range(4)
print(l)

[0, 1, 2, 3, 20] Traceback (most recent call last):
TypeError: object 'range' is not a tuple or list
List store with step != 1 not implemented

Sample code:
l = [1, 2, 3, 4]
l[0:4:2] = [5, 6]
print(l)

[5, 2, 6, 4] Traceback (most recent call last):
3.3.7 str
UnicodeDecodeError not raised when expected

Sample code:
try:
print(repr(str(b"\xa1\x80", 'utf8')))
except UnicodeDecodeError:
print('UnicodeDecodeError')

UnicodeDecodeError '\u0840'
Should not get here
Start/end indices such as str.endswith(s, start) not implemented

Sample code:

print('abc'.endswith('c', 1))

True Traceback (most recent call last):
NotImplementedError: start/end indices
Attributes/subscr not implemented

Sample code:
print('{a[0]}'.format(a=[1, 2]))

NotImplementedError: attributes not supported yet
str(...) with keywords not implemented

Workaround: Input the encoding format directly. eg print(bytes(’abc’, ’utf-8’))
Sample code:
print(str(b'abc', encoding='utf8'))

abc Traceback (most recent call last):
NotImplementedError: keyword argument(s) not yet im
None as first argument for rsplit such as str.rsplit(None, n) not implemented

Sample code:
print('a a a'.rsplit(None, 1))

['a a', 'a'] Traceback (most recent call last):
NotImplementedError: rsplit(None,n)
Instance of a subclass of str cannot be compared for equality with an instance of a str
Sample code:
class S(str):
pass
s = S('hello')
print(s == 'hello')

True False

Subscript with step != 1 is not yet implemented

Sample code:
print('abcdefghi'[0:9:2])

acegi Traceback (most recent call last):
3.3.8 tuple
Tuple load with step != 1 not implemented

Sample code:
print((1, 2, 3, 4)[0:4:2])

(1, 3) Traceback (most recent call last):
3.4 Modules
3.4.1 array
Looking for integer not implemented

Sample code:
import array
print(1 in array.array('B', b'12'))

False Traceback (most recent call last):
Array deletion not implemented

Sample code:
import array
a = array.array('b', (1, 2, 3))
del a[1]
print(a)


array('b', [1, 3]) Traceback (most recent call last):
TypeError: 'array' object does not support item del
Subscript with step != 1 is not yet implemented

Sample code:
import array
a = array.array('b', (1, 2, 3))
print(a[3:2:2])

array('b') Traceback (most recent call last):
3.4.2 deque
Deque not implemented

Workaround: Use regular queues or lists creatively
Sample code:
import collections
D = collections.deque()
print(D)

deque([]) Traceback (most recent call last):
AttributeError: 'module' object has no attribute 'd
3.4.3 json
JSON module does not throw exception when object is not serialisable
Sample code:
import json
a = bytes(x for x in range(256))
try:
z = json.dumps(a)
x = json.loads(z)
except TypeError:
print('TypeError')

TypeError Should not get here
3.4. Modules 69
3.4.4 struct
Struct pack with too few args, not checked by uPy

Sample code:
import struct
try:
print(struct.pack('bb', 1))
except:
print('struct.error')

struct.error b'\x01\x00'
Should not get here
Struct pack with too many args, not checked by uPy

Sample code:
import struct
try:
print(struct.pack('bb', 1, 2, 3))
except:
print('struct.error')

struct.error b'\x01\x02'
Should not get here
3.4.5 sys
Override sys.stdin, sys.stdout and sys.stderr. Impossible as they are stored in read-only memory.
Sample code:
import sys
sys.stdin = None
print(sys.stdin)

None Traceback (most recent call last):
AttributeError: 'module' object has no attribute 's

CHAPTER
FOUR
MICROPYTHON LICENSE INFORMATION
The MIT License (MIT)

Copyright (c) 2013-2015 Damien P. George, and others
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documen-
tation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use,
copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom
the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the
Software.
THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PAR-
TICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFT-
WARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
71
72 Chapter 4. MicroPython license information

CHAPTER
FIVE
MICROPYTHON DOCUMENTATION CONTENTS
5.1 General information about the ESP8266 port
ESP8266 is a popular WiFi-enabled System-on-Chip (SoC) by Espressif Systems.
5.1.1 Multitude of boards
There are a multitude of modules and boards from different sources which carry the ESP8266 chip. MicroPython
tries to provide a generic port which would run on as many boards/modules as possible, but there may be limitations.
Adafruit Feather HUZZAH board is taken as a reference board for the port (for example, testing is performed on it). If
you have another board, please make sure you have datasheet, schematics and other reference materials for your board
handy to look up various aspects of your board functioning.
To make a generic ESP8266 port and support as many boards as possible, following design and implementation
decision were made:
• GPIO pin numbering is based on ESP8266 chip numbering, not some “logical” numbering of a particular board.
Please have the manual/pin diagram of your board at hand to find correspondence between your board pins and
actual ESP8266 pins. We also encourage users of various boards to share this mapping via MicroPython forum,
with the idea to collect community-maintained reference materials eventually.
• All pins which make sense to support, are supported by MicroPython (for example, pins which are used to
connect SPI flash are not exposed, as they’re unlikely useful for anything else, and operating on them will lead
to board lock-up). However, any particular board may expose only subset of pins. Consult your board reference
manual.
• Some boards may lack external pins/internal connectivity to support ESP8266 deepsleep mode.
5.1.2 Technical specifications and SoC datasheets
The datasheets and other reference material for ESP8266 chip are available from the vendor site:
http://bbs.espressif.com/viewtopic.php?f=67&t=225 . They are the primary reference for the chip technical speci-
fications, capabilities, operating modes, internal functioning, etc.
For your convenience, some of technical specifications are provided below:
• Architecture: Xtensa lx106
• CPU frequency: 80MHz overclockable to 160MHz
• Total RAM available: 96KB (part of it reserved for system)
• BootROM: 64KB
73
• Internal FlashROM: None

• External FlashROM: code and data, via SPI Flash. Normal sizes 512KB-4MB.
• GPIO: 16 + 1 (GPIOs are multiplexed with other functions, including external FlashROM, UART, deep sleep
wake-up, etc.)
• UART: One RX/TX UART (no hardware handshaking), one TX-only UART.
• SPI: 2 SPI interfaces (one used for FlashROM).
• I2C: No native external I2C (bitbang implementation available on any pins).
• I2S: 1.
• Programming: using BootROM bootloader from UART. Due to external FlashROM and always-available
BootROM bootloader, ESP8266 is not brickable.
5.1.3 Scarcity of runtime resources
ESP8266 has very modest resources (first of all, RAM memory). So, please avoid allocating too big container objects
(lists, dictionaries) and buffers. There is also no full-fledged OS to keep track of resources and automatically clean
them up, so that’s the task of a user/user application: please be sure to close open files, sockets, etc. as soon as possible
after use.
5.1.4 Boot process
On boot, MicroPython EPS8266 port executes _boot.py script from internal frozen modules. It mounts filesystem
in FlashROM, or if it’s not available, performs first-time setup of the module and creates the filesystem. This part
of the boot process is considered fixed, and not available for customization for end users (even if you build from
source, please refrain from changes to it; customization of early boot process is available only to advanced users and
developers, who can diagnose themselves any issues arising from modifying the standard process).
Once the filesystem is mounted, boot.py is executed from it. The standard version of this file is created during
first-time module set up and has commands to start a WebREPL daemon (disabled by default, configurable with
webrepl_setup module), etc. This file is customizable by end users (for example, you may want to set some
parameters or add other services which should be run on a module start-up). But keep in mind that incorrect modifica-
tions to boot.py may still lead to boot loops or lock ups, requiring to reflash a module from scratch. (In particular, it’s
recommended that you use either webrepl_setup module or manual editing to configure WebREPL, but not both).
As a final step of boot procedure, main.py is executed from filesystem, if exists. This file is a hook to start up a user
application each time on boot (instead of going to REPL). For small test applications, you may name them directly as
main.py, and upload to module, but instead it’s recommended to keep your application(s) in separate files, and have
just the following in main.py:
import my_app
my_app.main()
This will allow to keep the structure of your application clear, as well as allow to install multiple applications on a
board, and switch among them.
5.1.5 Known Issues
Real-time clock
RTC in ESP8266 has very bad accuracy, drift may be seconds per minute. As a workaround, to measure short enough
intervals you can use utime.time(), etc. functions, and for wall clock time, synchronize from the net using
74 Chapter 5. MicroPython documentation contents

included ntpdate.py module.

Due to limitations of the ESP8266 chip the internal real-time clock (RTC) will overflow every 7:45h. If a long-
term working RTC time is required then time() or localtime() must be called at least once within 7 hours.
MicroPython will then handle the overflow.
5.2 MicroPython tutorial for ESP8266
This tutorial is intended to get you started using MicroPython on the ESP8266 system-on-a-chip. If it is your first time
it is recommended to follow the tutorial through in the order below. Otherwise the sections are mostly self contained,
so feel free to skip to those that interest you.
The tutorial does not assume that you know Python, but it also does not attempt to explain any of the details of the
Python language. Instead it provides you with commands that are ready to run, and hopes that you will gain a bit of
Python knowledge along the way. To learn more about Python itself please refer to https://www.python.org.
5.2.1 Getting started with MicroPython on the ESP8266
Using MicroPython is a great way to get the most of your ESP8266 board. And vice versa, the ESP8266 chip is a
great platform for using MicroPython. This tutorial will guide you through setting up MicroPython, getting a prompt,
using WebREPL, connecting to the network and communicating with the Internet, using the hardware peripherals, and
controlling some external components.
Let’s get started!
Requirements
The first thing you need is a board with an ESP8266 chip. The MicroPython software supports the ESP8266 chip
itself and any board should work. The main characteristic of a board is how much flash it has, how the GPIO pins are
connected to the outside world, and whether it includes a built-in USB-serial convertor to make the UART available to
your PC.
The minimum requirement for flash size is 1Mbyte. There is also a special build for boards with 512KB, but it is
highly limited comparing to the normal build: there is no support for filesystem, and thus features which depend on it
won’t work (WebREPL, upip, etc.). As such, 512KB build will be more interesting for users who build from source
and fine-tune parameters for their particular application.
Names of pins will be given in this tutorial using the chip names (eg GPIO0) and it should be straightforward to find
which pin this corresponds to on your particular board.
Powering the board
If your board has a USB connector on it then most likely it is powered through this when connected to your PC.
Otherwise you will need to power it directly. Please refer to the documentation for your board for further details.
Getting the firmware
The first thing you need to do is download the most recent MicroPython firmware .bin file to load onto your ESP8266
device. You can download it from the MicroPython downloads page. From here, you have 3 main choices
• Stable firmware builds for 1024kb modules and above.
• Daily firmware builds for 1024kb modules and above.
5.2. MicroPython tutorial for ESP8266 75

• Daily firmware builds for 512kb modules.

The best bet is nearly always to go for the Stable firmware builds. An exception to this though is if you have an
ESP8266 module with only 512kb of onboard storage. You can easily tell by trying to load a Stable firmware build
and if you get the error below, then you may have to use the Daily firmware builds for 512kb modules.
WARNING: Unlikely to work as data goes beyond end of flash.
Deploying the firmware
Once you have the MicroPython firmware (compiled code), you need to load it onto your ESP8266 device. There are
two main steps to do this: first you need to put your device in boot-loader mode, and second you need to copy across
the firmware. The exact procedure for these steps is highly dependent on the particular board and you will need to
refer to its documentation for details.
If you have a board that has a USB connector, a USB-serial convertor, and has the DTR and RTS pins wired in a
special way then deploying the firmware should be easy as all steps can be done automatically. Boards that have such
features include the Adafruit Feather HUZZAH and NodeMCU boards.
For best results it is recommended to first erase the entire flash of your device before putting on new MicroPython
firmware.
Currently we only support esptool.py to copy across the firmware. You can find this tool here:
https://github.com/espressif/esptool/, or install it using pip:
pip install esptool
Versions starting with 1.3 support both Python 2.7 and Python 3.4 (or newer). An older version (at least 1.2.1 is
needed) works fine but will require Python 2.7.
Any other flashing program should work, so feel free to try them out or refer to the documentation for your board to
see its recommendations.
Using esptool.py you can erase the flash with the command:
esptool.py --port /dev/ttyUSB0 erase_flash
And then deploy the new firmware using:

esptool.py --port /dev/ttyUSB0 --baud 460800 write_flash --flash_size=detect 0 esp8266-20170108-v1.8.
You might need to change the “port” setting to something else relevant for your PC. You may also need to reduce the
baudrate if you get errors when flashing (eg down to 115200). The filename of the firmware should also match the file
that you have.
For some boards with a particular FlashROM configuration (e.g. some variants of a NodeMCU board) you may need
to use the following command to deploy the firmware (note the -fm dio option):
esptool.py --port /dev/ttyUSB0 --baud 460800 write_flash --flash_size=detect -fm dio 0 esp8266-201701
If the above commands run without error then MicroPython should be installed on your board!
Serial prompt
Once you have the firmware on the device you can access the REPL (Python prompt) over UART0 (GPIO1=TX,
GPIO3=RX), which might be connected to a USB-serial convertor, depending on your board. The baudrate is 115200.
The next part of the tutorial will discuss the prompt in more detail.

WiFi
After a fresh install and boot the device configures itself as a WiFi access point (AP) that you can connect to. The
ESSID is of the form MicroPython-xxxxxx where the x’s are replaced with part of the MAC address of your device
(so will be the same everytime, and most likely different for all ESP8266 chips). The password for the WiFi is
micropythoN (note the upper-case N). Its IP address will be 192.168.4.1 once you connect to its network. WiFi
configuration will be discussed in more detail later in the tutorial.
Troubleshooting installation problems
If you experience problems during flashing or with running firmware immediately after it, here are troubleshooting
recommendations:
• Be aware of and try to exclude hardware problems. There are 2 common problems: bad power source quality
and worn-out/defective FlashROM. Speaking of power source, not just raw amperage is important, but also low
ripple and noise/EMI in general. If you experience issues with self-made or wall-wart style power supply, try
USB power from a computer. Unearthed power supplies are also known to cause problems as they source of
increased EMI (electromagnetic interference) - at the very least, and may lead to electrical devices breakdown.
So, you are advised to avoid using unearthed power connections when working with ESP8266 and other boards.
In regard to FlashROM hardware problems, there are independent (not related to MicroPython in any way)
reports (e.g.) that on some ESP8266 modules, FlashROM can be programmed as little as 20 times before
programming errors occur. This is much less than 100,000 programming cycles cited for FlashROM chips of a
type used with ESP8266 by reputable vendors, which points to either production rejects, or second-hand worn-
out flash chips to be used on some (apparently cheap) modules/boards. You may want to use your best judgement
about source, price, documentation, warranty, post-sales support for the modules/boards you purchase.
• The flashing instructions above use flashing speed of 460800 baud, which is good compromise between speed
and stability. However, depending on your module/board, USB-UART convertor, cables, host OS, etc., the
above baud rate may be too high and lead to errors. Try a more common 115200 baud rate instead in such cases.
• If lower baud rate didn’t help, you may want to try older version of esptool.py, which had a different program-
ming algorithm:
pip install esptool==1.0.1
This version doesn’t support --flash_size=detect option, so you will need to specify FlashROM size
explicitly (in megabits). It also requires Python 2.7, so you may need to use pip2 instead of pip in the
command above.
• The --flash_size option in the commands above is mandatory. Omitting it will lead to a corrupted
firmware.
• To catch incorrect flash content (e.g. from a defective sector on a chip), add --verify switch to the commands
above.
• Additionally, you can check the firmware integrity from a MicroPython REPL prompt (assuming you were able
to flash it and --verify option doesn’t report errors):
import esp
esp.check_fw()
If the last output value is True, the firmware is OK. Otherwise, it’s corrupted and need to be reflashed correctly.
• If you experience any issues with another flashing application (not esptool.py), try esptool.py, it is a generally
accepted flashing application in the ESP8266 community.
• If you still experience problems with even flashing the firmware, please refer to esptool.py project page,
https://github.com/espressif/esptool for additional documentation and bug tracker where you can report prob-
lems.

• If you are able to flash firmware, but --verify option or esp.check_fw() return errors even after multiple
retries, you may have a defective FlashROM chip, as explained above.
5.2.2 Getting a MicroPython REPL prompt
REPL stands for Read Evaluate Print Loop, and is the name given to the interactive MicroPython prompt that you can
access on the ESP8266. Using the REPL is by far the easiest way to test out your code and run commands.
There are two ways to access the REPL: either via a wired connection through the UART serial port, or via WiFi.
REPL over the serial port
The REPL is always available on the UART0 serial peripheral, which is connected to the pins GPIO1 for TX and
GPIO3 for RX. The baudrate of the REPL is 115200. If your board has a USB-serial convertor on it then you should
be able to access the REPL directly from your PC. Otherwise you will need to have a way of communicating with the
UART.
To access the prompt over USB-serial you need to use a terminal emulator program. On Windows TeraTerm is a good
choice, on Mac you can use the built-in screen program, and Linux has picocom and minicom. Of course, there are
many other terminal programs that will work, so pick your favourite!
For example, on Linux you can try running:
picocom /dev/ttyUSB0 -b115200
Once you have made the connection over the serial port you can test if it is working by hitting enter a few times. You
should see the Python REPL prompt, indicated by >>>.
WebREPL - a prompt over WiFi
WebREPL allows you to use the Python prompt over WiFi, connecting through a browser. The latest versions of
Firefox and Chrome are supported.
For your convenience, WebREPL client is hosted at http://micropython.org/webrepl . Alternatively, you can install it
locally from the the GitHub repository https://github.com/micropython/webrepl .
Before connecting to WebREPL, you should set a password and enable it via a normal serial connection. Initial
versions of MicroPython for ESP8266 came with WebREPL automatically enabled on the boot and with the ability to
set a password via WiFi on the first connection, but as WebREPL was becoming more widely known and popular, the
initial setup has switched to a wired connection for improved security:
import webrepl_setup
Follow the on-screen instructions and prompts. To make any changes active, you will need to reboot your device.
To use WebREPL connect your computer to the ESP8266’s access point (MicroPython-xxxxxx, see the previous
section about this). If you have already reconfigured your ESP8266 to connect to a router then you can skip this part.
Once you are on the same network as the ESP8266 you click the “Connect” button (if you are connecting via a router
then you may need to change the IP address, by default the IP address is correct when connected to the ESP8266’s
access point). If the connection succeeds then you should see a password prompt.
Once you type the password configured at the setup step above, press Enter once more and you should get a prompt
looking like >>>. You can now start typing Python commands!

Using the REPL
Once you have a prompt you can start experimenting! Anything you type at the prompt will be executed after you
press the Enter key. MicroPython will run the code that you enter and print the result (if there is one). If there is an
error with the text that you enter then an error message is printed.
Try typing the following at the prompt:
>>> print('hello esp8266!')
hello esp8266!
Note that you shouldn’t type the >>> arrows, they are there to indicate that you should type the text after it at the
prompt. And then the line following is what the device should respond with. In the end, once you have entered the
text print("hello esp8266!") and pressed the Enter key, the output on your screen should look exactly like
it does above.
If you already know some python you can now try some basic commands here. For example:
>>> 1 + 2
3
>>> 1 / 2
0.5
>>> 12**34
4922235242952026704037113243122008064
If your board has an LED attached to GPIO2 (the ESP-12 modules do) then you can turn it on and off using the
following code:
>>> import machine
>>> pin = machine.Pin(2, machine.Pin.OUT)
>>> pin.high()
>>> pin.low()
Note that high might turn the LED off and low might turn it on (or vice versa), depending on how the LED is wired
on your board.
Line editing
You can edit the current line that you are entering using the left and right arrow keys to move the cursor, as well as the
delete and backspace keys. Also, pressing Home or ctrl-A moves the cursor to the start of the line, and pressing End
or ctrl-E moves to the end of the line.
Input history
The REPL remembers a certain number of previous lines of text that you entered (up to 8 on the ESP8266). To recall
previous lines use the up and down arrow keys.
Tab completion
Pressing the Tab key will do an auto-completion of the current word that you are entering. This can be very useful to
find out functions and methods that a module or object has. Try it out by typing “ma” and then pressing Tab. It should
complete to “machine” (assuming you imported machine in the above example). Then type ”.” and press Tab again to
see a list of all the functions that the machine module has.

Line continuation and auto-indent
Certain things that you type will need “continuing”, that is, will need more lines of text to make a proper Python
statement. In this case the prompt will change to ... and the cursor will auto-indent the correct amount so you can
start typing the next line straight away. Try this by defining the following function:
>>> def toggle(p):
... p.value(not p.value())
...
...
...
>>>
In the above, you needed to press the Enter key three times in a row to finish the compound statement (that’s the three
lines with just dots on them). The other way to finish a compound statement is to press backspace to get to the start of
the line, then press the Enter key. (If you did something wrong and want to escape the continuation mode then press
ctrl-C; all lines will be ignored.)
The function you just defined allows you to toggle a pin. The pin object you created earlier should still exist (recreate
it if it doesn’t) and you can toggle the LED using:
>>> toggle(pin)
Let’s now toggle the LED in a loop (if you don’t have an LED then you can just print some text instead of calling
toggle, to see the effect):
>>> import time
>>> while True:
... toggle(pin)
... time.sleep_ms(500)
...
...
...
>>>
This will toggle the LED at 1Hz (half a second on, half a second off). To stop the toggling press ctrl-C, which will
raise a KeyboardInterrupt exception and break out of the loop.
The time module provides some useful functions for making delays and doing timing. Use tab completion to find out
what they are and play around with them!
Paste mode
Pressing ctrl-E will enter a special paste mode. This allows you to copy and paste a chunk of text into the REPL. If
you press ctrl-E you will see the paste-mode prompt:
paste mode; Ctrl-C to cancel, Ctrl-D to finish
===
You can then paste (or type) your text in. Note that none of the special keys or commands work in paste mode (eg Tab
or backspace), they are just accepted as-is. Press ctrl-D to finish entering the text and execute it.
Other control commands
There are four other control commands:

• Ctrl-A on a blank line will enter raw REPL mode. This is like a permanent paste mode, except that characters
are not echoed back.
• Ctrl-B on a blank like goes to normal REPL mode.
• Ctrl-C cancels any input, or interrupts the currently running code.
• Ctrl-D on a blank line will do a soft reset.
Note that ctrl-A and ctrl-D do not work with WebREPL.
5.2.3 The internal filesystem
If your devices has 1Mbyte or more of storage then it will be set up (upon first boot) to contain a filesystem. This
filesystem uses the FAT format and is stored in the flash after the MicroPython firmware.
Creating and reading files
MicroPython on the ESP8266 supports the standard way of accessing files in Python, using the built-in open()
function.
To create a file try:
>>> f = open('data.txt', 'w')
>>> f.write('some data')
9
>>> f.close()
The “9” is the number of bytes that were written with the write() method. Then you can read back the contents of
this new file using:
>>> f = open('data.txt')
>>> f.read()
'some data'
>>> f.close()
Note that the default mode when opening a file is to open it in read-only mode, and as a text file. Specify ’wb’ as the
second argument to open() to open for writing in binary mode, and ’rb’ to open for reading in binary mode.
Listing file and more
The os module can be used for further control over the filesystem. First import the module:
>>> import os
Then try listing the contents of the filesystem:

>>> os.listdir()
['boot.py', 'port_config.py', 'data.txt']
You can make directories:

>>> os.mkdir('dir')
And remove entries:

>>> os.remove('data.txt')

Start up scripts
There are two files that are treated specially by the ESP8266 when it starts up: boot.py and main.py. The boot.py
script is executed first (if it exists) and then once it completes the main.py script is executed. You can create these files
yourself and populate them with the code that you want to run when the device starts up.
Accessing the filesystem via WebREPL
You can access the filesystem over WebREPL using the web client in a browser or via the command-line tool. Please
refer to Quick Reference and Tutorial sections for more information about WebREPL.
5.2.4 Network basics
The network module is used to configure the WiFi connection. There are two WiFi interfaces, one for the station
(when the ESP8266 connects to a router) and one for the access point (for other devices to connect to the ESP8266).
Create instances of these objects using:
>>> import network
>>> sta_if = network.WLAN(network.STA_IF)
>>> ap_if = network.WLAN(network.AP_IF)
You can check if the interfaces are active by:

>>> sta_if.active()
False
>>> ap_if.active()
True
You can also check the network settings of the interface by:
>>> ap_if.ifconfig()
('192.168.4.1', '255.255.255.0', '192.168.4.1', '8.8.8.8')
The returned values are: IP address, netmask, gateway, DNS.
Configuration of the WiFi
Upon a fresh install the ESP8266 is configured in access point mode, so the AP_IF interface is active and the STA_IF
interface is inactive. You can configure the module to connect to your own network using the STA_IF interface.
First activate the station interface:
>>> sta_if.active(True)
Then connect to your WiFi network:

>>> sta_if.connect('<your ESSID>', '<your password>')
To check if the connection is established use:

>>> sta_if.isconnected()
Once established you can check the IP address:

>>> sta_if.ifconfig()
('192.168.0.2', '255.255.255.0', '192.168.0.1', '8.8.8.8')

You can then disable the access-point interface if you no longer need it:
>>> ap_if.active(False)
Here is a function you can run (or put in your boot.py file) to automatically connect to your WiFi network:
def do_connect():
import network
sta_if = network.WLAN(network.STA_IF)
if not sta_if.isconnected():
print('connecting to network...')
sta_if.active(True)
sta_if.connect('<essid>', '<password>')
while not sta_if.isconnected():
pass
print('network config:', sta_if.ifconfig())
Sockets
Once the WiFi is set up the way to access the network is by using sockets. A socket represents an endpoint on a
network device, and when two sockets are connected together communication can proceed. Internet protocols are built
on top of sockets, such as email (SMTP), the web (HTTP), telnet, ssh, among many others. Each of these protocols is
assigned a specific port, which is just an integer. Given an IP address and a port number you can connect to a remote
device and start talking with it.
The next part of the tutorial discusses how to use sockets to do some common and useful network tasks.
5.2.5 Network - TCP sockets
The building block of most of the internet is the TCP socket. These sockets provide a reliable stream of bytes between
the connected network devices. This part of the tutorial will show how to use TCP sockets in a few different cases.
Star Wars Asciimation
The simplest thing to do is to download data from the internet. In this case we will use the Star Wars Asciimation
service provided by the blinkenlights.nl website. It uses the telnet protocol on port 23 to stream data to anyone that
connects. It’s very simple to use because it doesn’t require you to authenticate (give a username or password), you can
just start downloading data straight away.
The first thing to do is make sure we have the socket module available:
>>> import socket
Then get the IP address of the server:

>>> addr_info = socket.getaddrinfo("towel.blinkenlights.nl", 23)
The getaddrinfo function actually returns a list of addresses, and each address has more information than we need.
We want to get just the first valid address, and then just the IP address and port of the server. To do this use:
>>> addr = addr_info[0][-1]
If you type addr_info and addr at the prompt you will see exactly what information they hold.
Using the IP address we can make a socket and connect to the server:

>>> s = socket.socket()
>>> s.connect(addr)
Now that we are connected we can download and display the data:
>>> while True:
... data = s.recv(500)
... print(str(data, 'utf8'), end='')
...
When this loop executes it should start showing the animation (use ctrl-C to interrupt it).
You should also be able to run this same code on your PC using normal Python if you want to try it out there.
HTTP GET request
The next example shows how to download a webpage. HTTP uses port 80 and you first need to send a “GET” request
before you can download anything. As part of the request you need to specify the page to retrieve.
Let’s define a function that can download and print a URL:
def http_get(url):
_, _, host, path = url.split('/', 3)
addr = socket.getaddrinfo(host, 80)[0][-1]
s = socket.socket()
s.connect(addr)
s.send(bytes('GET /%s HTTP/1.0\r\nHost: %s\r\n\r\n' % (path, host), 'utf8'))
while True:
data = s.recv(100)
if data:
print(str(data, 'utf8'), end='')
else:
break
s.close()
Make sure that you import the socket module before running this function. Then you can try:
>>> http_get('http://micropython.org/ks/test.html')
This should retrieve the webpage and print the HTML to the console.
Simple HTTP server
The following code creates an simple HTTP server which serves a single webpage that contains a table with the state
of all the GPIO pins:
import machine
pins = [machine.Pin(i, machine.Pin.IN) for i in (0, 2, 4, 5, 12, 13, 14, 15)]
html = """<!DOCTYPE html>

<html>
<head> <title>ESP8266 Pins</title> </head>
<body> <h1>ESP8266 Pins</h1>
<table border="1"> <tr><th>Pin</th><th>Value</th></tr> %s </table>
</body>
</html>
"""

import socket
addr = socket.getaddrinfo('0.0.0.0', 80)[0][-1]
s = socket.socket()
s.bind(addr)
s.listen(1)
print('listening on', addr)
while True:
cl, addr = s.accept()
print('client connected from', addr)
cl_file = cl.makefile('rwb', 0)
while True:
line = cl_file.readline()
if not line or line == b'\r\n':
break
rows = ['<tr><td>%s</td><td>%d</td></tr>' % (str(p), p.value()) for p in pins]
response = html % '\n'.join(rows)
cl.send(response)
cl.close()
5.2.6 GPIO Pins
The way to connect your board to the external world, and control other components, is through the GPIO pins. Not all
pins are available to use, in most cases only pins 0, 2, 4, 5, 12, 13, 14, 15, and 16 can be used.
The pins are available in the machine module, so make sure you import that first. Then you can create a pin using:
>>> pin = machine.Pin(0)
Here, the “0” is the pin that you want to access. Usually you want to configure the pin to be input or output, and you
do this when constructing it. To make an input pin use:
>>> pin = machine.Pin(0, machine.Pin.IN, machine.Pin.PULL_UP)
You can either use PULL_UP or None for the input pull-mode. If it’s not specified then it defaults to None, which is
no pull resistor. You can read the value on the pin using:
>>> pin.value()
0
The pin on your board may return 0 or 1 here, depending on what it’s connected to. To make an output pin use:
>>> pin = machine.Pin(0, machine.Pin.OUT)
Then set its value using:

>>> pin.value(0)
>>> pin.value(1)
Or:
>>> pin.low()
>>> pin.high()

External interrupts
All pins except number 16 can be configured to trigger a hard interrupt if their input changes. You can set code (a
callback function) to be executed on the trigger.
Let’s first define a callback function, which must take a single argument, being the pin that triggered the function. We
will make the function just print the pin:
>>> def callback(p):
... print('pin change', p)
Next we will create two pins and configure them as inputs:

>>> from machine import Pin
>>> p0 = Pin(0, Pin.IN)
>>> p2 = Pin(2, Pin.IN)
An finally we need to tell the pins when to trigger, and the function to call when they detect an event:
>>> p0.irq(trigger=Pin.IRQ_FALLING, handler=callback)
>>> p2.irq(trigger=Pin.IRQ_RISING | Pin.IRQ_FALLING, handler=callback)
We set pin 0 to trigger only on a falling edge of the input (when it goes from high to low), and set pin 2 to trigger on
both a rising and falling edge. After entering this code you can apply high and low voltages to pins 0 and 2 to see the
interrupt being executed.
A hard interrupt will trigger as soon as the event occurs and will interrupt any running code, including Python code. As
such your callback functions are limited in what they can do (they cannot allocate memory, for example) and should
be as short and simple as possible.
5.2.7 Pulse Width Modulation
Pulse width modulation (PWM) is a way to get an artificial analog output on a digital pin. It achieves this by rapidly
toggling the pin from low to high. There are two parameters associated with this: the frequency of the toggling, and
the duty cycle. The duty cycle is defined to be how long the pin is high compared with the length of a single period
(low plus high time). Maximum duty cycle is when the pin is high all of the time, and minimum is when it is low all
of the time.
On the ESP8266 the pins 0, 2, 4, 5, 12, 13, 14 and 15 all support PWM. The limitation is that they must all be at the
same frequency, and the frequency must be between 1Hz and 1kHz.
To use PWM on a pin you must first create the pin object, for example:
>>> import machine
>>> p12 = machine.Pin(12)
Then create the PWM object using:

>>> pwm12 = machine.PWM(p12)
You can set the frequency and duty cycle using:

>>> pwm12.freq(500)
>>> pwm12.duty(512)
Note that the duty cycle is between 0 (all off) and 1023 (all on), with 512 being a 50% duty. If you print the PWM
object then it will tell you its current configuration:

>>> pwm12
PWM(12, freq=500, duty=512)
You can also call the freq() and duty() methods with no arguments to get their current values.
The pin will continue to be in PWM mode until you deinitialise it using:
>>> pwm12.deinit()
Fading an LED
Let’s use the PWM feature to fade an LED. Assuming your board has an LED connected to pin 2 (ESP-12 modules
do) we can create an LED-PWM object using:
>>> led = machine.PWM(machine.Pin(2), freq=1000)
Notice that we can set the frequency in the PWM constructor.

For the next part we will use timing and some math, so import these modules:
>>> import time, math
Then create a function to pulse the LED:

>>> def pulse(l, t):
... for i in range(20):
... l.duty(int(math.sin(i / 10 * math.pi) * 500 + 500))
... time.sleep_ms(t)
You can try this function out using:

>>> pulse(led, 50)
For a nice effect you can pulse many times in a row:

>>> for i in range(10):
... pulse(led, 20)
Remember you can use ctrl-C to interrupt the code.
Control a hobby servo
Hobby servo motors can be controlled using PWM. They require a frequency of 50Hz and then a duty between about
40 and 115, with 77 being the centre value. If you connect a servo to the power and ground pins, and then the signal
line to pin 12 (other pins will work just as well), you can control the motor using:
>>> servo = machine.PWM(machine.Pin(12), freq=50)
>>> servo.duty(40)
>>> servo.duty(115)
>>> servo.duty(77)
5.2.8 Analog to Digital Conversion
The ESP8266 has a single pin (separate to the GPIO pins) which can be used to read analog voltages and convert them
to a digital value. You can construct such an ADC pin object using:

>>> import machine

>>> adc = machine.ADC(0)
Then read its value with:

>>> adc.read()
58
The values returned from the read() function are between 0 (for 0.0 volts) and 1024 (for 1.0 volts). Please note
that this input can only tolerate a maximum of 1.0 volts and you must use a voltage divider circuit to measure larger
voltages.
5.2.9 Power control
The ESP8266 provides the ability to change the CPU frequency on the fly, and enter a deep-sleep state. Both can be
used to manage power consumption.
Changing the CPU frequency
The machine module has a function to get and set the CPU frequency. To get the current frequency use:
>>> import machine
>>> machine.freq()
80000000
By default the CPU runs at 80MHz. It can be change to 160MHz if you need more processing power, at the expense
of current consumption:
>>> machine.freq(160000000)
>>> machine.freq()
160000000
You can change to the higher frequency just while your code does the heavy processing and then change back when
its finished.
Deep-sleep mode
The deep-sleep mode will shut down the ESP8266 and all its peripherals, including the WiFi (but not including the
real-time-clock, which is used to wake the chip). This drastically reduces current consumption and is a good way to
make devices that can run for a while on a battery.
To be able to use the deep-sleep feature you must connect GPIO16 to the reset pin (RST on the Adafruit Feather
HUZZAH board). Then the following code can be used to sleep and wake the device:
import machine
# configure RTC.ALARM0 to be able to wake the device

rtc = machine.RTC()
rtc.irq(trigger=rtc.ALARM0, wake=machine.DEEPSLEEP)
# set RTC.ALARM0 to fire after 10 seconds (waking the device)

rtc.alarm(rtc.ALARM0, 10000)
# put the device to sleep

machine.deepsleep()

Note that when the chip wakes from a deep-sleep it is completely reset, including all of the memory. The boot scripts
will run as usual and you can put code in them to check the reset cause to perhaps do something different if the device
just woke from a deep-sleep. For example, to print the reset cause you can use:
if machine.reset_cause() == machine.DEEPSLEEP_RESET:
print('woke from a deep sleep')
else:
print('power on or hard reset')
5.2.10 Controlling 1-wire devices
The 1-wire bus is a serial bus that uses just a single wire for communication (in addition to wires for ground and
power). The DS18B20 temperature sensor is a very popular 1-wire device, and here we show how to use the onewire
module to read from such a device.
For the following code to work you need to have at least one DS18S20 or DS18B20 temperature sensor with its data
line connected to GPIO12. You must also power the sensors and connect a 4.7k Ohm resistor between the data pin and
the power pin.
import time
import machine
import onewire, ds18x20
# the device is on GPIO12

dat = machine.Pin(12)
# create the onewire object

ds = ds18x20.DS18X20(onewire.OneWire(dat))
# scan for devices on the bus

roms = ds.scan()
print('found devices:', roms)
# loop 10 times and print all temperatures

for i in range(10):
print('temperatures:', end=' ')
ds.convert_temp()
time.sleep_ms(750)
for rom in roms:
print(ds.read_temp(rom), end=' ')
print()
Note that you must execute the convert_temp() function to initiate a temperature reading, then wait at least 750ms
before reading the value.
5.2.11 Controlling NeoPixels
NeoPixels, also known as WS2812 LEDs, are full-colour LEDs that are connected in serial, are individually address-
able, and can have their red, green and blue components set between 0 and 255. They require precise timing to control
them and there is a special neopixel module to do just this.
To create a NeoPixel object do the following:
>>> import machine, neopixel
>>> np = neopixel.NeoPixel(machine.Pin(4), 8)

This configures a NeoPixel strip on GPIO4 with 8 pixels. You can adjust the “4” (pin number) and the “8” (number of
pixel) to suit your set up.
To set the colour of pixels use:
>>> np[0] = (255, 0, 0) # set to red, full brightness
>>> np[1] = (0, 128, 0) # set to green, half brightness
>>> np[2] = (0, 0, 64) # set to blue, quarter brightness
Then use the write() method to output the colours to the LEDs:
>>> np.write()
The following demo function makes a fancy show on the LEDs:

import time
def demo(np):
n = np.n
# cycle
for i in range(4 * n):
for j in range(n):
np[j] = (0, 0, 0)
np[i % n] = (255, 255, 255)
np.write()
time.sleep_ms(25)
# bounce
for i in range(4 * n):
for j in range(n):
np[j] = (0, 0, 128)
if (i // n) % 2 == 0:
np[i % n] = (0, 0, 0)
else:
np[n - 1 - (i % n)] = (0, 0, 0)
np.write()
time.sleep_ms(60)
# fade in/out
for i in range(0, 4 * 256, 8):
for j in range(n):
if (i // 256) % 2 == 0:
val = i & 0xff
else:
val = 255 - (i & 0xff)
np[j] = (val, 0, 0)
np.write()
# clear
for i in range(n):
np[i] = (0, 0, 0)
np.write()
Execute it using:
>>> demo(np)

5.2.12 Temperature and Humidity
DHT (Digital Humidity & Temperature) sensors are low cost digital sensors with capacitive humidity sensors and
thermistors to measure the surrounding air. They feature a chip that handles analog to digital conversion and provide
a 1-wire interface. Newer sensors additionally provide an I2C interface.
The DHT11 (blue) and DHT22 (white) sensors provide the same 1-wire interface, however, the DHT22 requires a
separate object as it has more complex calculation. DHT22 have 1 decimal place resolution for both humidity and
temperature readings. DHT11 have whole number for both.
A custom 1-wire protocol, which is different to Dallas 1-wire, is used to get the measurements from the sensor. The
payload consists of a humidity value, a temperature value and a checksum.
To use the 1-wire interface, construct the objects referring to their data pin:
>>> import dht
>>> import machine
>>> d = dht.DHT11(machine.Pin(4))
>>> import dht

>>> import machine
>>> d = dht.DHT22(machine.Pin(4))
Then measure and read their values with:

>>> d.measure()
>>> d.temperature()
>>> d.humidity()
Values returned from temperature() are in degrees Celsius and values returned from humidity() are a per-
centage of relative humidity.
The DHT11 can be called no more than once per second and the DHT22 once every two seconds for most accurate
results. Sensor accuracy will degrade over time. Each sensor supports a different operating range. Refer to the product
datasheets for specifics.
In 1-wire mode, only three of the four pins are used and in I2C mode, all four pins are used. Older sensors may still
have 4 pins even though they do not support I2C. The 3rd pin is simply not connected.
Pin configurations:
Sensor without I2C in 1-wire mode (eg. DHT11, DHT22, AM2301, AM2302):
1=VDD, 2=Data, 3=NC, 4=GND
Sensor with I2C in 1-wire mode (eg. DHT12, AM2320, AM2321, AM2322):
1=VDD, 2=Data, 3=GND, 4=GND
Sensor with I2C in I2C mode (eg. DHT12, AM2320, AM2321, AM2322):
1=VDD, 2=SDA, 3=GND, 4=SCL
You should use pull-up resistors for the Data, SDA and SCL pins.
To make newer I2C sensors work in backwards compatible 1-wire mode, you must connect both pins 3 and 4 to GND.
This disables the I2C interface.
DHT22 sensors are now sold under the name AM2302 and are otherwise identical.

5.2.13 Next steps
That brings us to the end of the tutorial! Hopefully by now you have a good feel for the capabilities of MicroPython
on the ESP8266 and understand how to control both the WiFi and IO aspects of the chip.
There are many features that were not covered in this tutorial. The best way to learn about them is to read the full
documentation of the modules, and to experiment!
Good luck creating your Internet of Things devices!
5.3 The MicroPython language
MicroPython aims to implement the Python 3.4 standard, and most of the features of MicroPython are identical to
those described by the documentation at docs.python.org.
Differences to standard Python as well as additional features of MicroPython are described in the sections here.
5.3.1 The MicroPython Interactive Interpreter Mode (aka REPL)
This section covers some characteristics of the MicroPython Interactive Interpreter Mode. A commonly used term for
this is REPL (read-eval-print-loop) which will be used to refer to this interactive prompt.
Auto-indent
When typing python statements which end in a colon (for example if, for, while) then the prompt will change to three
dots (...) and the cursor will be indented by 4 spaces. When you press return, the next line will continue at the same
level of indentation for regular statements or an additional level of indentation where appropriate. If you press the
backspace key then it will undo one level of indentation.
If your cursor is all the way back at the beginning, pressing RETURN will then execute the code that you’ve entered.
The following shows what you’d see after entering a for statement (the underscore shows where the cursor winds up):
... _
If you then enter an if statement, an additional level of indentation will be provided:

... if i > 3:
... _
Now enter break followed by RETURN and press BACKSPACE:

... if i > 3:
... break
... _
Finally type print(i), press RETURN, press BACKSPACE and press RETURN again:
... if i > 3:
... break
... print(i)
...
0

1
2
3
>>>
Auto-indent won’t be applied if the previous two lines were all spaces. This means that you can finish entering a
compound statement by pressing RETURN twice, and then a third press will finish and execute.
Auto-completion
While typing a command at the REPL, if the line typed so far corresponds to the beginning of the name of something,
then pressing TAB will show possible things that could be entered. For example type m and press TAB and it should
expand to machine. Enter a dot . and press TAB again. You should see something like:
>>> machine.
__name__ info unique_id reset
bootloader freq rng idle
sleep deepsleep disable_irq enable_irq
Pin
The word will be expanded as much as possible until multiple possibilities exist. For example, type
machine.Pin.AF3 and press TAB and it will expand to machine.Pin.AF3_TIM. Pressing TAB a second time
will show the possible expansions:
>>> machine.Pin.AF3_TIM
AF3_TIM10 AF3_TIM11 AF3_TIM8 AF3_TIM9
>>> machine.Pin.AF3_TIM
Interrupting a running program
You can interrupt a running program by pressing Ctrl-C. This will raise a KeyboardInterrupt which will bring you back
to the REPL, providing your program doesn’t intercept the KeyboardInterrupt exception.
For example:
>>> for i in range(1000000):
... print(i)
...
0
1
2
3
...
6466
6467
6468
KeyboardInterrupt:
>>>
Paste Mode
If you want to paste some code into your terminal window, the auto-indent feature will mess things up. For example,
if you had the following python code:
5.3. The MicroPython language 93

def foo():
print('This is a test to show paste mode')
print('Here is a second line')
foo()
and you try to paste this into the normal REPL, then you will see something like this:
>>> def foo():
... print('This is a test to show paste mode')
... print('Here is a second line')
... foo()
...
File "<stdin>", line 3
IndentationError: unexpected indent
If you press Ctrl-E, then you will enter paste mode, which essentially turns off the auto-indent feature, and changes
the prompt from >>> to ===. For example:
>>>
paste mode; Ctrl-C to cancel, Ctrl-D to finish
=== def foo():
=== print('This is a test to show paste mode')
=== print('Here is a second line')
=== foo()
===
This is a test to show paste mode
Here is a second line
>>>
Paste Mode allows blank lines to be pasted. The pasted text is compiled as if it were a file. Pressing Ctrl-D exits paste
mode and initiates the compilation.
Soft Reset
A soft reset will reset the python interpreter, but tries not to reset the method by which you’re connected to the
MicroPython board (USB-serial, or Wifi).
You can perform a soft reset from the REPL by pressing Ctrl-D, or from your python code by executing:
raise SystemExit
For example, if you reset your MicroPython board, and you execute a dir() command, you’d see something like this:
>>> dir()
['__name__', 'pyb']
Now create some variables and repeat the dir() command:

>>> i = 1
>>> j = 23
>>> x = 'abc'
>>> dir()
['j', 'x', '__name__', 'pyb', 'i']
>>>
Now if you enter Ctrl-D, and repeat the dir() command, you’ll see that your variables no longer exist:
PYB: sync filesystems
PYB: soft reboot

MicroPython v1.5-51-g6f70283-dirty on 2015-10-30; PYBv1.0 with STM32F405RG

Type "help()" for more information.
>>> dir()
['__name__', 'pyb']
>>>
The special variable _ (underscore)
When you use the REPL, you may perform computations and see the results. MicroPython stores the results of the
previous statement in the variable _ (underscore). So you can use the underscore to save the result in a variable. For
example:
>>> 1 + 2 + 3 + 4 + 5
15
>>> x = _
>>> x
15
>>>
Raw Mode
Raw mode is not something that a person would normally use. It is intended for programmatic use. It essentially
behaves like paste mode with echo turned off.
Raw mode is entered using Ctrl-A. You then send your python code, followed by a Ctrl-D. The Ctrl-D will be ac-
knowledged by ‘OK’ and then the python code will be compiled and executed. Any output (or errors) will be sent
back. Entering Ctrl-B will leave raw mode and return the the regular (aka friendly) REPL.
The tools/pyboard.py program uses the raw REPL to execute python files on the MicroPython board.
5.3.2 Writing interrupt handlers
On suitable hardware MicroPython offers the ability to write interrupt handlers in Python. Interrupt handlers - also
known as interrupt service routines (ISR’s) - are defined as callback functions. These are executed in response to
an event such as a timer trigger or a voltage change on a pin. Such events can occur at any point in the execution
of the program code. This carries significant consequences, some specific to the MicroPython language. Others are
common to all systems capable of responding to real time events. This document covers the language specific issues
first, followed by a brief introduction to real time programming for those new to it.
This introduction uses vague terms like “slow” or “as fast as possible”. This is deliberate, as speeds are application
dependent. Acceptable durations for an ISR are dependent on the rate at which interrupts occur, the nature of the main
program, and the presence of other concurrent events.
Tips and recommended practices
This summarises the points detailed below and lists the principal recommendations for interrupt handler code.
• Keep the code as short and simple as possible.
• Avoid memory allocation: no appending to lists or insertion into dictionaries, no floating point.
• Where an ISR returns multiple bytes use a pre-allocated bytearray. If multiple integers are to be shared
between an ISR and the main program consider an array (array.array).

• Where data is shared between the main program and an ISR, consider disabling interrupts prior to accessing the
data in the main program and re-enabling them immediately afterwards (see Critical Sections).
• Allocate an emergency exception buffer (see below).
MicroPython Issues
The emergency exception buffer
If an error occurs in an ISR, MicroPython is unable to produce an error report unless a special buffer is created for the
purpose. Debugging is simplified if the following code is included in any program using interrupts.
import micropython
micropython.alloc_emergency_exception_buf(100)
Simplicity
For a variety of reasons it is important to keep ISR code as short and simple as possible. It should do only what has
to be done immediately after the event which caused it: operations which can be deferred should be delegated to the
main program loop. Typically an ISR will deal with the hardware device which caused the interrupt, making it ready
for the next interrupt to occur. It will communicate with the main loop by updating shared data to indicate that the
interrupt has occurred, and it will return. An ISR should return control to the main loop as quickly as possible. This is
not a specific MicroPython issue so is covered in more detail below.
Communication between an ISR and the main program
Normally an ISR needs to communicate with the main program. The simplest means of doing this is via one or more
shared data objects, either declared as global or shared via a class (see below). There are various restrictions and
hazards around doing this, which are covered in more detail below. Integers, bytes and bytearray objects are
commonly used for this purpose along with arrays (from the array module) which can store various data types.
The use of object methods as callbacks
MicroPython supports this powerful technique which enables an ISR to share instance variables with the underlying
code. It also enables a class implementing a device driver to support multiple device instances. The following example
causes two LED’s to flash at different rates.
import pyb, micropython
class Foo(object):
def __init__(self, timer, led):
self.led = led
timer.callback(self.cb)
def cb(self, tim):
self.led.toggle()
red = Foo(pyb.Timer(4, freq=1), pyb.LED(1))

greeen = Foo(pyb.Timer(2, freq=0.8), pyb.LED(2))
In this example the red instance associates timer 4 with LED 1: when a timer 4 interrupt occurs red.cb() is called
causing LED 1 to change state. The green instance operates similarly: a timer 2 interrupt results in the execution of
green.cb() and toggles LED 2. The use of instance methods confers two benefits. Firstly a single class enables

code to be shared between multiple hardware instances. Secondly, as a bound method the callback function’s first
argument is self. This enables the callback to access instance data and to save state between successive calls. For
example, if the class above had a variable self.count set to zero in the constructor, cb() could increment the
counter. The red and green instances would then maintain independent counts of the number of times each LED
had changed state.
Creation of Python objects
ISR’s cannot create instances of Python objects. This is because MicroPython needs to allocate memory for the object
from a store of free memory block called the heap. This is not permitted in an interrupt handler because heap allocation
is not re-entrant. In other words the interrupt might occur when the main program is part way through performing an
allocation - to maintain the integrity of the heap the interpreter disallows memory allocations in ISR code.
A consequence of this is that ISR’s can’t use floating point arithmetic; this is because floats are Python objects.
Similarly an ISR can’t append an item to a list. In practice it can be hard to determine exactly which code constructs
will attempt to perform memory allocation and provoke an error message: another reason for keeping ISR code short
and simple.
One way to avoid this issue is for the ISR to use pre-allocated buffers. For example a class constructor creates a
bytearray instance and a boolean flag. The ISR method assigns data to locations in the buffer and sets the flag.
The memory allocation occurs in the main program code when the object is instantiated rather than in the ISR.
The MicroPython library I/O methods usually provide an option to use a pre-allocated buffer. For example
pyb.i2c.recv() can accept a mutable buffer as its first argument: this enables its use in an ISR.
A means of creating an object without employing a class or globals is as follows:
def set_volume(t, buf=bytearray(3)):
buf[0] = 0xa5
buf[1] = t >> 4
buf[2] = 0x5a
return buf
The compiler instantiates the default buf argument when the function is loaded for the first time (usually when the
module it’s in is imported).
Use of Python objects
A further restriction on objects arises because of the way Python works. When an import statement is executed
the Python code is compiled to bytecode, with one line of code typically mapping to multiple bytecodes. When the
code runs the interpreter reads each bytecode and executes it as a series of machine code instructions. Given that
an interrupt can occur at any time between machine code instructions, the original line of Python code may be only
partially executed. Consequently a Python object such as a set, list or dictionary modified in the main loop may lack
internal consistency at the moment the interrupt occurs.
A typical outcome is as follows. On rare occasions the ISR will run at the precise moment in time when the object
is partially updated. When the ISR tries to read the object, a crash results. Because such problems typically occur on
rare, random occasions they can be hard to diagnose. There are ways to circumvent this issue, described in Critical
Sections below.
It is important to be clear about what constitutes the modification of an object. An alteration to a built-in type such as
a dictionary is problematic. Altering the contents of an array or bytearray is not. This is because bytes or words are
written as a single machine code instruction which is not interruptible: in the parlance of real time programming the
write is atomic. A user defined object might instantiate an integer, array or bytearray. It is valid for both the main loop
and the ISR to alter the contents of these.

MicroPython supports integers of arbitrary precision. Values between 2**30 -1 and -2**30 will be stored in a single
machine word. Larger values are stored as Python objects. Consequently changes to long integers cannot be considered
atomic. The use of long integers in ISR’s is unsafe because memory allocation may be attempted as the variable’s value
changes.
Overcoming the float limitation
In general it is best to avoid using floats in ISR code: hardware devices normally handle integers and conversion to
floats is normally done in the main loop. However there are a few DSP algorithms which require floating point. On
platforms with hardware floating point (such as the Pyboard) the inline ARM Thumb assembler can be used to work
round this limitation. This is because the processor stores float values in a machine word; values can be shared between
the ISR and main program code via an array of floats.
Exceptions
If an ISR raises an exception it will not propagate to the main loop. The interrupt will be disabled unless the exception
is handled by the ISR code.
General Issues
This is merely a brief introduction to the subject of real time programming. Beginners should note that design errors
in real time programs can lead to faults which are particularly hard to diagnose. This is because they can occur rarely
and at intervals which are essentially random. It is crucial to get the initial design right and to anticipate issues before
they arise. Both interrupt handlers and the main program need to be designed with an appreciation of the following
issues.
Interrupt Handler Design
As mentioned above, ISR’s should be designed to be as simple as possible. They should always return in a short,
predictable period of time. This is important because when the ISR is running, the main loop is not: inevitably the
main loop experiences pauses in its execution at random points in the code. Such pauses can be a source of hard to
diagnose bugs particularly if their duration is long or variable. In order to understand the implications of ISR run time,
a basic grasp of interrupt priorities is required.
Interrupts are organised according to a priority scheme. ISR code may itself be interrupted by a higher priority
interrupt. This has implications if the two interrupts share data (see Critical Sections below). If such an interrupt
occurs it interposes a delay into the ISR code. If a lower priority interrupt occurs while the ISR is running, it will be
delayed until the ISR is complete: if the delay is too long, the lower priority interrupt may fail. A further issue with
slow ISR’s is the case where a second interrupt of the same type occurs during its execution. The second interrupt will
be handled on termination of the first. However if the rate of incoming interrupts consistently exceeds the capacity of
the ISR to service them the outcome will not be a happy one.
Consequently looping constructs should be avoided or minimised. I/O to devices other than to the interrupting device
should normally be avoided: I/O such as disk access, print statements and UART access is relatively slow, and its
duration may vary. A further issue here is that filesystem functions are not reentrant: using filesystem I/O in an ISR
and the main program would be hazardous. Crucially ISR code should not wait on an event. I/O is acceptable if the
code can be guaranteed to return in a predictable period, for example toggling a pin or LED. Accessing the interrupting
device via I2C or SPI may be necessary but the time taken for such accesses should be calculated or measured and its
impact on the application assessed.
There is usually a need to share data between the ISR and the main loop. This may be done either through global
variables or via class or instance variables. Variables are typically integer or boolean types, or integer or byte arrays

(a pre-allocated integer array offers faster access than a list). Where multiple values are modified by the ISR it is
necessary to consider the case where the interrupt occurs at a time when the main program has accessed some, but not
all, of the values. This can lead to inconsistencies.
Consider the following design. An ISR stores incoming data in a bytearray, then adds the number of bytes received to
an integer representing total bytes ready for processing. The main program reads the number of bytes, processes the
bytes, then clears down the number of bytes ready. This will work until an interrupt occurs just after the main program
has read the number of bytes. The ISR puts the added data into the buffer and updates the number received, but the
main program has already read the number, so processes the data originally received. The newly arrived bytes are lost.
There are various ways of avoiding this hazard, the simplest being to use a circular buffer. If it is not possible to use a
structure with inherent thread safety other ways are described below.
Reentrancy
A potential hazard may occur if a function or method is shared between the main program and one or more ISR’s or
between multiple ISR’s. The issue here is that the function may itself be interrupted and a further instance of that
function run. If this is to occur, the function must be designed to be reentrant. How this is done is an advanced topic
beyond the scope of this tutorial.
Critical Sections
An example of a critical section of code is one which accesses more than one variable which can be affected by an ISR.
If the interrupt happens to occur between accesses to the individual variables, their values will be inconsistent. This
is an instance of a hazard known as a race condition: the ISR and the main program loop race to alter the variables.
To avoid inconsistency a means must be employed to ensure that the ISR does not alter the values for the duration of
the critical section. One way to achieve this is to issue pyb.disable_irq() before the start of the section, and
pyb.enable_irq() at the end. Here is an example of this approach:
import pyb, micropython, array
class BoundsException(Exception):
pass
ARRAYSIZE = const(20)
index = 0
data = array.array('i', 0 for x in range(ARRAYSIZE))
def callback1(t):
global data, index
for x in range(5):
data[index] = pyb.rng() # simulate input
index += 1
if index >= ARRAYSIZE:
raise BoundsException('Array bounds exceeded')
tim4 = pyb.Timer(4, freq=100, callback=callback1)
for loop in range(1000):

if index > 0:
irq_state = pyb.disable_irq() # Start of critical section
for x in range(index):
print(data[x])
index = 0

pyb.enable_irq(irq_state) # End of critical section

print('loop {}'.format(loop))
pyb.delay(1)
tim4.callback(None)
A critical section can comprise a single line of code and a single variable. Consider the following code fragment.
count = 0
def cb(): # An interrupt callback
count +=1
def main():
# Code to set up the interrupt callback omitted
while True:
count += 1
This example illustrates a subtle source of bugs. The line count += 1 in the main loop carries a specific race
condition hazard known as a read-modify-write. This is a classic cause of bugs in real time systems. In the main loop
MicroPython reads the value of t.counter, adds 1 to it, and writes it back. On rare occasions the interrupt occurs
after the read and before the write. The interrupt modifies t.counter but its change is overwritten by the main loop
when the ISR returns. In a real system this could lead to rare, unpredictable failures.
As mentioned above, care should be taken if an instance of a Python built in type is modified in the main code and that
instance is accessed in an ISR. The code performing the modification should be regarded as a critical section to ensure
that the instance is in a valid state when the ISR runs.
Particular care needs to be taken if a dataset is shared between different ISR’s. The hazard here is that the higher
priority interrupt may occur when the lower priority one has partially updated the shared data. Dealing with this
situation is an advanced topic beyond the scope of this introduction other than to note that mutex objects described
below can sometimes be used.
Disabling interrupts for the duration of a critical section is the usual and simplest way to proceed, but it disables all
interrupts rather than merely the one with the potential to cause problems. It is generally undesirable to disable an
interrupt for long. In the case of timer interrupts it introduces variability to the time when a callback occurs. In the
case of device interrupts, it can lead to the device being serviced too late with possible loss of data or overrun errors
in the device hardware. Like ISR’s, a critical section in the main code should have a short, predictable duration.
An approach to dealing with critical sections which radically reduces the time for which interrupts are disabled is to
use an object termed a mutex (name derived from the notion of mutual exclusion). The main program locks the mutex
before running the critical section and unlocks it at the end. The ISR tests whether the mutex is locked. If it is, it avoids
the critical section and returns. The design challenge is defining what the ISR should do in the event that access to the
critical variables is denied. A simple example of a mutex may be found here. Note that the mutex code does disable
interrupts, but only for the duration of eight machine instructions: the benefit of this approach is that other interrupts
are virtually unaffected.
Interrupts and the REPL
Interrupt handlers, such as those associated with timers, can continue to run after a program terminates. This may
produce unexpected results where you might have expected the object raising the callback to have gone out of scope.
For example on the Pyboard:
def bar():
foo = pyb.Timer(2, freq=4, callback=lambda t: print('.', end=''))
bar()
This continues to run until the timer is explicitly disabled or the board is reset with ctrl D.

5.3.3 Maximising Python Speed
This tutorial describes ways of improving the performance of MicroPython code. Optimisations involving other lan-
guages are covered elsewhere, namely the use of modules written in C and the MicroPython inline ARM Thumb-2
assembler.
The process of developing high performance code comprises the following stages which should be performed in the
order listed.
• Design for speed.
• Code and debug.
Optimisation steps:
• Identify the slowest section of code.
• Improve the efficiency of the Python code.
• Use the native code emitter.
• Use the viper code emitter.
Designing for speed
Performance issues should be considered at the outset. This involves taking a view on the sections of code which are
most performance critical and devoting particular attention to their design. The process of optimisation begins when
the code has been tested: if the design is correct at the outset optimisation will be straightforward and may actually be
unnecessary.
Algorithms
The most important aspect of designing any routine for performance is ensuring that the best algorithm is employed.
This is a topic for textbooks rather than for a MicroPython guide but spectacular performance gains can sometimes be
achieved by adopting algorithms known for their efficiency.
RAM Allocation
To design efficient MicroPython code it is necessary to have an understanding of the way the interpreter allocates
RAM. When an object is created or grows in size (for example where an item is appended to a list) the necessary
RAM is allocated from a block known as the heap. This takes a significant amount of time; further it will on occasion
trigger a process known as garbage collection which can take several milliseconds.
Consequently the performance of a function or method can be improved if an object is created once only and not
permitted to grow in size. This implies that the object persists for the duration of its use: typically it will be instantiated
in a class constructor and used in various methods.
This is covered in further detail Controlling garbage collection below.
Buffers
An example of the above is the common case where a buffer is required, such as one used for communication with
a device. A typical driver will create the buffer in the constructor and use it in its I/O methods which will be called
repeatedly.

The MicroPython libraries typically provide support for pre-allocated buffers. For example, objects which support
stream interface (e.g., file or UART) provide read() method which allocate new buffer for read data, but also a
readinto() method to read data into an existing buffer.
Floating Point
Some MicroPython ports allocate floating point numbers on heap. Some other ports may lack dedicated floating-point
coprocessor, and perform arithmetic operations on them in “software” at considerably lower speed than on integers.
Where performance is important, use integer operations and restrict the use of floating point to sections of the code
where performance is not paramount. For example, capture ADC readings as integers values to an array in one quick
go, and only then convert them to floating-point numbers for signal processing.
Arrays
Consider the use of the various types of array classes as an alternative to lists. The array module supports various
element types with 8-bit elements supported by Python’s built in bytes and bytearray classes. These data struc-
tures all store elements in contiguous memory locations. Once again to avoid memory allocation in critical code these
should be pre-allocated and passed as arguments or as bound objects.
When passing slices of objects such as bytearray instances, Python creates a copy which involves allocation of
the size proportional to the size of slice. This can be alleviated using a memoryview object. memoryview itself is
allocated on heap, but is a small, fixed-size object, regardless of the size of slice it points too.
ba = bytearray(10000) # big array
func(ba[30:2000]) # a copy is passed, ~2K new allocation
mv = memoryview(ba) # small object is allocated
func(mv[30:2000]) # a pointer to memory is passed
A memoryview can only be applied to objects supporting the buffer protocol - this includes arrays but not lists. Small
caveat is that while memoryview object is live, it also keeps alive the original buffer object. So, a memoryview isn’t
a universal panacea. For instance, in the example above, if you are done with 10K buffer and just need those bytes
30:2000 from it, it may be better to make a slice, and let the 10K buffer go (be ready for garbage collection), instead
of making a long-living memoryview and keeping 10K blocked for GC.
Nonetheless, memoryview is indispensable for advanced preallocated buffer management. .readinto() method
discussed above puts data at the beginning of buffer and fills in entire buffer. What if you need to put data in the middle
of existing buffer? Just create a memoryview into the needed section of buffer and pass it to .readinto().
Identifying the slowest section of code
This is a process known as profiling and is covered in textbooks and (for standard Python) supported by various
software tools. For the type of smaller embedded application likely to be running on MicroPython platforms the
slowest function or method can usually be established by judicious use of the timing ticks group of functions
documented here. Code execution time can be measured in ms, us, or CPU cycles.
The following enables any function or method to be timed by adding an @timed_function decorator:
def timed_function(f, *args, **kwargs):
myname = str(f).split(' ')[1]
def new_func(*args, **kwargs):
t = time.ticks_us()
result = f(*args, **kwargs)
delta = time.ticks_diff(time.ticks_us(), t)
print('Function {} Time = {:6.3f}ms'.format(myname, delta/1000))

return result
return new_func
MicroPython code improvements
The const() declaration
MicroPython provides a const() declaration. This works in a similar way to #define in C in that when the code
is compiled to bytecode the compiler substitutes the numeric value for the identifier. This avoids a dictionary lookup
at runtime. The argument to const() may be anything which, at compile time, evaluates to an integer e.g. 0x100
or 1 << 8.
Caching object references
Where a function or method repeatedly accesses objects performance is improved by caching the object in a local
variable:
class foo(object):
def __init__(self):
ba = bytearray(100)
def bar(self, obj_display):
ba_ref = self.ba
fb = obj_display.framebuffer
# iterative code using these two objects
This avoids the need repeatedly to look up self.ba and obj_display.framebuffer in the body of the method
bar().
Controlling garbage collection
When memory allocation is required, MicroPython attempts to locate an adequately sized block on the heap. This may
fail, usually because the heap is cluttered with objects which are no longer referenced by code. If a failure occurs, the
process known as garbage collection reclaims the memory used by these redundant objects and the allocation is then
tried again - a process which can take several milliseconds.
There are benefits in pre-empting this by periodically issuing gc.collect(). Firstly doing a collection before it is
actually required is quicker - typically on the order of 1ms if done frequently. Secondly you can determine the point
in code where this time is used rather than have a longer delay occur at random points, possibly in a speed critical
section. Finally performing collections regularly can reduce fragmentation in the heap. Severe fragmentation can lead
to non-recoverable allocation failures.
Accessing hardware directly
This comes into the category of more advanced programming and involves some knowledge of the target MCU.
Consider the example of toggling an output pin on the Pyboard. The standard approach would be to write
mypin.value(mypin.value() ^ 1) # mypin was instantiated as an output pin
This involves the overhead of two calls to the Pin instance’s value() method. This overhead can be eliminated by
performing a read/write to the relevant bit of the chip’s GPIO port output data register (odr). To facilitate this the stm
module provides a set of constants providing the addresses of the relevant registers. A fast toggle of pin P4 (CPU pin
A14) - corresponding to the green LED - can be performed as follows:

BIT14 = const(1 << 14)

stm.mem16[stm.GPIOA + stm.GPIO_ODR] ^= BIT14
The Native code emitter
This causes the MicroPython compiler to emit ARM native opcodes rather than bytecode. It covers the bulk of the
Python language so most functions will require no adaptation (but see below). It is invoked by means of a function
decorator:
@micropython.native
def foo(self, arg):
buf = self.linebuf # Cached object
# code
There are certain limitations in the current implementation of the native code emitter.
• Context managers are not supported (the with statement).
• Generators are not supported.
• If raise is used an argument must be supplied.
The trade-off for the improved performance (roughly twices as fast as bytecode) is an increase in compiled code size.
The Viper code emitter
The optimisations discussed above involve standards-compliant Python code. The Viper code emitter is not fully
compliant. It supports special Viper native data types in pursuit of performance. Integer processing is non-compliant
because it uses machine words: arithmetic on 32 bit hardware is performed modulo 2**32.
Like the Native emitter Viper produces machine instructions but further optimisations are performed, substantially
increasing performance especially for integer arithmetic and bit manipulations. It is invoked using a decorator:
@micropython.viper
def foo(self, arg: int) -> int:
# code
As the above fragment illustrates it is beneficial to use Python type hints to assist the Viper optimiser. Type hints
provide information on the data types of arguments and of the return value; these are a standard Python language
feature formally defined here PEP0484. Viper supports its own set of types namely int, uint (unsigned integer),
ptr, ptr8, ptr16 and ptr32. The ptrX types are discussed below. Currently the uint type serves a single
purpose: as a type hint for a function return value. If such a function returns 0xffffffff Python will interpret the
result as 2**32 -1 rather than as -1.
In addition to the restrictions imposed by the native emitter the following constraints apply:
• Functions may have up to four arguments.
• Default argument values are not permitted.
• Floating point may be used but is not optimised.
Viper provides pointer types to assist the optimiser. These comprise
• ptr Pointer to an object.
• ptr8 Points to a byte.
• ptr16 Points to a 16 bit half-word.
• ptr32 Points to a 32 bit machine word.

The concept of a pointer may be unfamiliar to Python programmers. It has similarities to a Python memoryview
object in that it provides direct access to data stored in memory. Items are accessed using subscript notation, but slices
are not supported: a pointer can return a single item only. Its purpose is to provide fast random access to data stored in
contiguous memory locations - such as data stored in objects which support the buffer protocol, and memory-mapped
peripheral registers in a microcontroller. It should be noted that programming using pointers is hazardous: bounds
checking is not performed and the compiler does nothing to prevent buffer overrun errors.
Typical usage is to cache variables:
@micropython.viper
def foo(self, arg: int) -> int:
buf = ptr8(self.linebuf) # self.linebuf is a bytearray or bytes object
for x in range(20, 30):
bar = buf[x] # Access a data item through the pointer
# code omitted
In this instance the compiler “knows” that buf is the address of an array of bytes; it can emit code to rapidly com-
pute the address of buf[x] at runtime. Where casts are used to convert objects to Viper native types these should
be performed at the start of the function rather than in critical timing loops as the cast operation can take several
microseconds. The rules for casting are as follows:
• Casting operators are currently: int, bool, uint, ptr, ptr8, ptr16 and ptr32.
• The result of a cast will be a native Viper variable.
• Arguments to a cast can be a Python object or a native Viper variable.
• If argument is a native Viper variable, then cast is a no-op (i.e. costs nothing at runtime) that just changes the
type (e.g. from uint to ptr8) so that you can then store/load using this pointer.
• If the argument is a Python object and the cast is int or uint, then the Python object must be of integral type
and the value of that integral object is returned.
• The argument to a bool cast must be integral type (boolean or integer); when used as a return type the viper
function will return True or False objects.
• If the argument is a Python object and the cast is ptr, ptr, ptr16 or ptr32, then the Python object must
either have the buffer protocol with read-write capabilities (in which case a pointer to the start of the buffer is
returned) or it must be of integral type (in which case the value of that integral object is returned).
The following example illustrates the use of a ptr16 cast to toggle pin X1 n times:
BIT0 = const(1)
@micropython.viper
def toggle_n(n: int):
odr = ptr16(stm.GPIOA + stm.GPIO_ODR)
for _ in range(n):
odr[0] ^= BIT0
A detailed technical description of the three code emitters may be found on Kickstarter here Note 1 and here Note 2
5.3.4 MicroPython on Microcontrollers
MicroPython is designed to be capable of running on microcontrollers. These have hardware limitations which may
be unfamiliar to programmers more familiar with conventional computers. In particular the amount of RAM and non-
volatile “disk” (flash memory) storage is limited. This tutorial offers ways to make the most of the limited resources.
Because MicroPython runs on controllers based on a variety of architectures, the methods presented are generic: in
some cases it will be necessary to obtain detailed information from platform specific documentation.

Flash Memory
On the Pyboard the simple way to address the limited capacity is to fit a micro SD card. In some cases this is
impractical, either because the device does not have an SD card slot or for reasons of cost or power consumption;
hence the on-chip flash must be used. The firmware including the MicroPython subsystem is stored in the onboard
flash. The remaining capacity is available for use. For reasons connected with the physical architecture of the flash
memory part of this capacity may be inaccessible as a filesystem. In such cases this space may be employed by
incorporating user modules into a firmware build which is then flashed to the device.
There are two ways to achieve this: frozen modules and frozen bytecode. Frozen modules store the Python source
with the firmware. Frozen bytecode uses the cross compiler to convert the source to bytecode which is then stored
with the firmware. In either case the module may be accessed with an import statement:
import mymodule
The procedure for producing frozen modules and bytecode is platform dependent; instructions for building the
firmware can be found in the README files in the relevant part of the source tree.
In general terms the steps are as follows:
• Clone the MicroPython repository.
• Acquire the (platform specific) toolchain to build the firmware.
• Build the cross compiler.
• Place the modules to be frozen in a specified directory (dependent on whether the module is to be frozen as
source or as bytecode).
• Build the firmware. A specific command may be required to build frozen code of either type - see the platform
documentation.
• Flash the firmware to the device.
RAM
When reducing RAM usage there are two phases to consider: compilation and execution. In addition to memory
consumption, there is also an issue known as heap fragmentation. In general terms it is best to minimise the repeated
creation and destruction of objects. The reason for this is covered in the section covering the heap.
Compilation Phase
When a module is imported, MicroPython compiles the code to bytecode which is then executed by the MicroPython
virtual machine (VM). The bytecode is stored in RAM. The compiler itself requires RAM, but this becomes available
for use when the compilation has completed.
If a number of modules have already been imported the situation can arise where there is insufficient RAM to run the
compiler. In this case the import statement will produce a memory exception.
If a module instantiates global objects on import it will consume RAM at the time of import, which is then unavailable
for the compiler to use on subsequent imports. In general it is best to avoid code which runs on import; a better
approach is to have initialisation code which is run by the application after all modules have been imported. This
maximises the RAM available to the compiler.
If RAM is still insufficient to compile all modules one solution is to precompile modules. MicroPython has a cross
compiler capable of compiling Python modules to bytecode (see the README in the mpy-cross directory). The result-
ing bytecode file has a .mpy extension; it may be copied to the filesystem and imported in the usual way. Alternatively
some or all modules may be implemented as frozen bytecode: on most platforms this saves even more RAM as the
bytecode is run directly from flash rather than being stored in RAM.

Execution Phase
There are a number of coding techniques for reducing RAM usage.

Constants
MicroPython provides a const keyword which may be used as follows:
from micropython import const
ROWS = const(33)
_COLS = const(0x10)
a = ROWS
b = _COLS
In both instances where the constant is assigned to a variable the compiler will avoid coding a lookup to the name
of the constant by substituting its literal value. This saves bytecode and hence RAM. However the ROWS value will
occupy at least two machine words, one each for the key and value in the globals dictionary. The presence in the
dictionary is necessary because another module might import or use it. This RAM can be saved by prepending the
name with an underscore as in _COLS: this symbol is not visible outside the module so will not occupy RAM.
The argument to const() may be anything which, at compile time, evaluates to an integer e.g. 0x100 or 1 << 8.
It can even include other const symbols that have already been defined, e.g. 1 << BIT.
Constant data structures
Where there is a substantial volume of constant data and the platform supports execution from Flash, RAM may be
saved as follows. The data should be located in Python modules and frozen as bytecode. The data must be defined as
bytes objects. The compiler ‘knows’ that bytes objects are immutable and ensures that the objects remain in flash
memory rather than being copied to RAM. The ustruct module can assist in converting between bytes types and
other Python built-in types.
When considering the implications of frozen bytecode, note that in Python strings, floats, bytes, integers and complex
numbers are immutable. Accordingly these will be frozen into flash. Thus, in the line
mystring = "The quick brown fox"
the actual string “The quick brown fox” will reside in flash. At runtime a reference to the string is assigned to the
variable mystring. The reference occupies a single machine word. In principle a long integer could be used to store
constant data:
bar = 0xDEADBEEF0000DEADBEEF
As in the string example, at runtime a reference to the arbitrarily large integer is assigned to the variable bar. That
reference occupies a single machine word.
It might be expected that tuples of integers could be employed for the purpose of storing constant data with minimal
RAM use. With the current compiler this is ineffective (the code works, but RAM is not saved).
foo = (1, 2, 3, 4, 5, 6, 100000)
At runtime the tuple will be located in RAM. This may be subject to future improvement.
Needless object creation
There are a number of situations where objects may unwittingly be created and destroyed. This can reduce the usability
of RAM through fragmentation. The following sections discuss instances of this.
String concatenation
Consider the following code fragments which aim to produce constant strings:

var = "foo" + "bar"

var1 = "foo" "bar"
var2 = """\
foo\
bar"""
Each produces the same outcome, however the first needlessly creates two string objects at runtime, allocates more
RAM for concatenation before producing the third. The others perform the concatenation at compile time which is
more efficient, reducing fragmentation.
Where strings must be dynamically created before being fed to a stream such as a file it will save RAM if this is done
in a piecemeal fashion. Rather than creating a large string object, create a substring and feed it to the stream before
dealing with the next.
The best way to create dynamic strings is by means of the string format method:
var = "Temperature {:5.2f} Pressure {:06d}\n".format(temp, press)
Buffers
When accessing devices such as instances of UART, I2C and SPI interfaces, using pre-allocated buffers avoids the
creation of needless objects. Consider these two loops:
while True:
var = spi.read(100)
# process data
buf = bytearray(100)
while True:
spi.readinto(buf)
# process data in buf
The first creates a buffer on each pass whereas the second re-uses a pre-allocated buffer; this is both faster and more
efficient in terms of memory fragmentation.
Bytes are smaller than ints
On most platforms an integer consumes four bytes. Consider the two calls to the function foo():
def foo(bar):
for x in bar:
print(x)
foo((1, 2, 0xff))
foo(b'\1\2\xff')
In the first call a tuple of integers is created in RAM. The second efficiently creates a bytes object consuming the
minimum amount of RAM. If the module were frozen as bytecode, the bytes object would reside in flash.
Strings Versus Bytes
Python3 introduced Unicode support. This introduced a distinction between a string and an array of bytes. MicroPy-
thon ensures that Unicode strings take no additional space so long as all characters in the string are ASCII (i.e. have a
value < 126). If values in the full 8-bit range are required bytes and bytearray objects can be used to ensure that
no additional space will be required. Note that most string methods (e.g. strip()) apply also to bytes instances
so the process of eliminating Unicode can be painless.
s = 'the quick brown fox' # A string instance
b = b'the quick brown fox' # a bytes instance
Where it is necessary to convert between strings and bytes the string encode and the bytes decode methods can be
used. Note that both strings and bytes are immutable. Any operation which takes as input such an object and produces

another implies at least one RAM allocation to produce the result. In the second line below a new bytes object is
allocated. This would also occur if foo were a string.
foo = b' empty whitespace'
foo = foo.lstrip()
Runtime compiler execution

The Python keywords eval and exec invoke the compiler at runtime, which requires significant amounts of RAM.
Note that the pickle library employs exec. It may be more RAM efficient to use the json library for object
serialisation.
Storing strings in flash
Python strings are immutable hence have the potential to be stored in read only memory. The compiler can place in
flash strings defined in Python code. As with frozen modules it is necessary to have a copy of the source tree on the PC
and the toolchain to build the firmware. The procedure will work even if the modules have not been fully debugged,
so long as they can be imported and run.
After importing the modules, execute:
micropython.qstr_info(1)
Then copy and paste all the Q(xxx) lines into a text editor. Check for and remove lines which are obviously invalid.
Open the file qstrdefsport.h which will be found in stmhal (or the equivalent directory for the architecture in use).
Copy and paste the corrected lines at the end of the file. Save the file, rebuild and flash the firmware. The outcome can
be checked by importing the modules and again issuing:
micropython.qstr_info(1)
The Q(xxx) lines should be gone.
The Heap
When a running program instantiates an object the necessary RAM is allocated from a fixed size pool known as the
heap. When the object goes out of scope (in other words becomes inaccessible to code) the redundant object is known
as “garbage”. A process known as “garbage collection” (GC) reclaims that memory, returning it to the free heap. This
process runs automatically, however it can be invoked directly by issuing gc.collect().
The discourse on this is somewhat involved. For a ‘quick fix’ issue the following periodically:
gc.collect()
gc.threshold(gc.mem_free() // 4 + gc.mem_alloc())
Fragmentation
Say a program creates an object foo, then an object bar. Subsequently foo goes out of scope but bar remains. The
RAM used by foo will be reclaimed by GC. However if bar was allocated to a higher address, the RAM reclaimed
from foo will only be of use for objects no bigger than foo. In a complex or long running program the heap can
become fragmented: despite there being a substantial amount of RAM available, there is insufficient contiguous space
to allocate a particular object, and the program fails with a memory error.
The techniques outlined above aim to minimise this. Where large permanent buffers or other objects are required it is
best to instantiate these early in the process of program execution before fragmentation can occur. Further improve-
ments may be made by monitoring the state of the heap and by controlling GC; these are outlined below.

Reporting
A number of library functions are available to report on memory allocation and to control GC. These are to be found
in the gc and micropython modules. The following example may be pasted at the REPL (ctrl e to enter paste
mode, ctrl d to run it).
import gc
import micropython
gc.collect()
micropython.mem_info()
print('-----------------------------')
print('Initial free: {} allocated: {}'.format(gc.mem_free(), gc.mem_alloc()))
def func():
a = bytearray(10000)
gc.collect()
print('Func definition: {} allocated: {}'.format(gc.mem_free(), gc.mem_alloc()))
func()
print('Func run free: {} allocated: {}'.format(gc.mem_free(), gc.mem_alloc()))
gc.collect()
print('Garbage collect free: {} allocated: {}'.format(gc.mem_free(), gc.mem_alloc()))
print('-----------------------------')
micropython.mem_info(1)
Methods employed above:

• gc.collect() Force a garbage collection. See footnote.
• micropython.mem_info() Print a summary of RAM utilisation.
• gc.mem_free() Return the free heap size in bytes.
• gc.mem_alloc() Return the number of bytes currently allocated.
• micropython.mem_info(1) Print a table of heap utilisation (detailed below).
The numbers produced are dependent on the platform, but it can be seen that declaring the function uses a small
amount of RAM in the form of bytecode emitted by the compiler (the RAM used by the compiler has been reclaimed).
Running the function uses over 10KiB, but on return a is garbage because it is out of scope and cannot be referenced.
The final gc.collect() recovers that memory.
The final output produced by micropython.mem_info(1) will vary in detail but may be interpreted as follows:
Symbol Meaning
. free block
h head block
= tail block
m marked head block
T tuple
L list
D dict
F float
B byte code
M module
Each letter represents a single block of memory, a block being 16 bytes. So each line of the heap dump represents
0x400 bytes or 1KiB of RAM.

Control of Garbage Collection
A GC can be demanded at any time by issuing gc.collect(). It is advantageous to do this at intervals, firstly to
pre-empt fragmentation and secondly for performance. A GC can take several milliseconds but is quicker when there
is little work to do (about 1ms on the Pyboard). An explicit call can minimise that delay while ensuring it occurs at
points in the program when it is acceptable.
Automatic GC is provoked under the following circumstances. When an attempt at allocation fails, a GC is performed
and the allocation re-tried. Only if this fails is an exception raised. Secondly an automatic GC will be triggered if the
amount of free RAM falls below a threshold. This threshold can be adapted as execution progresses:
gc.collect()
gc.threshold(gc.mem_free() // 4 + gc.mem_alloc())
This will provoke a GC when more than 25% of the currently free heap becomes occupied.
In general modules should instantiate data objects at runtime using constructors or other initialisation functions. The
reason is that if this occurs on initialisation the compiler may be starved of RAM when subsequent modules are
imported. If modules do instantiate data on import then gc.collect() issued after the import will ameliorate the
problem.
String Operations
MicroPython handles strings in an efficient manner and understanding this can help in designing applications to run
on microcontrollers. When a module is compiled, strings which occur multiple times are stored once only, a process
known as string interning. In MicroPython an interned string is known as a qstr. In a module imported normally
that single instance will be located in RAM, but as described above, in modules frozen as bytecode it will be located
in flash.
String comparisons are also performed efficiently using hashing rather than character by character. The penalty for
using strings rather than integers may hence be small both in terms of performance and RAM usage - a fact which may
come as a surprise to C programmers.
Postscript
MicroPython passes, returns and (by default) copies objects by reference. A reference occupies a single machine word
so these processes are efficient in RAM usage and speed.
Where variables are required whose size is neither a byte nor a machine word there are standard libraries which can
assist in storing these efficiently and in performing conversions. See the array, ustruct and uctypes modules.
Footnote: gc.collect() return value
On Unix and Windows platforms the gc.collect() method returns an integer which signifies the number of
distinct memory regions that were reclaimed in the collection (more precisely, the number of heads that were turned
into frees). For efficiency reasons bare metal ports do not return this value.


CHAPTER
SIX
INDICES AND TABLES
• genindex
• modindex
• search
113
114 Chapter 6. Indices and tables

PYTHON MODULE INDEX
a
array, 12
b
btree, 31
e
esp, 54
f
framebuf, 33
g
gc, 12
m
machine, 35
math, 12
micropython, 48
n
network, 49
s
sys, 15
u
ubinascii, 16
ucollections, 17
uctypes, 52
uhashlib, 17
uheapq, 18
uio, 18
ujson, 20
uos, 20
ure, 22
usocket, 23
ussl, 26
ustruct, 27
utime, 27
uzlib, 30
115
116 Python Module Index

INDEX
Symbols bytearray_at() (in module uctypes), 53

__call__() (machine.Pin method), 41 byteorder (in module sys), 15
__contains__() (btree.btree method), 32 bytes (built-in class), 10
__detitem__() (btree.btree method), 32 bytes_at() (in module uctypes), 53
__getitem__() (btree.btree method), 32 BytesIO (class in uio), 20
__iter__() (btree.btree method), 32
__setitem__() (btree.btree method), 32 C
calcsize() (in module ustruct), 27
A callable() (built-in function), 10
a2b_base64() (in module ubinascii), 16 cancel() (machine.RTC method), 44
abs() (built-in function), 10 ceil() (in module math), 13
accept() (usocket.socket method), 24 chdir() (in module uos), 20
acos() (in module math), 13 chr() (built-in function), 10
acosh() (in module math), 13 classmethod() (built-in function), 10
active() (network.wlan method), 50 close() (btree.btree method), 32
addressof() (in module uctypes), 53 close() (usocket.socket method), 24
alarm() (machine.RTC method), 44 collect() (in module gc), 12
alarm_left() (machine.RTC method), 44 compile() (built-in function), 10
all() (built-in function), 10 compile() (in module ure), 22
alloc_emergency_exception_buf() (in module micropy- complex (built-in class), 10
thon), 48 config() (network.wlan method), 51
any() (built-in function), 10 connect() (network.wlan method), 50
any() (machine.UART method), 46 connect() (usocket.socket method), 24
append() (array.array.array method), 12 const() (in module micropython), 48
argv (in module sys), 15 copysign() (in module math), 13
array (module), 12 cos() (in module math), 13
array.array (class in array), 12 cosh() (in module math), 13
asin() (in module math), 13
asinh() (in module math), 13 D
atan() (in module math), 13 DEBUG (in module ure), 22
atan2() (in module math), 13 decompress() (in module uzlib), 30
atanh() (in module math), 13 deepsleep() (in module esp), 55
deepsleep() (in module machine), 36
B degrees() (in module math), 13
b2a_base64() (in module ubinascii), 16 deinit() (machine.I2C method), 37
BIG_ENDIAN (in module uctypes), 53 deinit() (machine.RTC method), 44
bin() (built-in function), 10 deinit() (machine.SPI method), 45
bind() (usocket.socket method), 24 deinit() (machine.Timer method), 46
blit() (framebuf.FrameBuffer method), 34 deinit() (machine.UART method), 46
bool (built-in class), 10 delattr() (built-in function), 10
btree (module), 31 DESC (in module btree), 33
bytearray (built-in class), 10 dict (built-in class), 10
117
digest() (uhashlib.hash method), 18 get() (btree.btree method), 32

dir() (built-in function), 10 getattr() (built-in function), 10
disable() (in module gc), 12 getcwd() (in module uos), 20
disable_irq() (in module machine), 35 getvalue() (uio.BytesIO method), 20
disconnect() (network.wlan method), 50 globals() (built-in function), 10
divmod() (built-in function), 10 group() (ure.match method), 22
drive() (machine.Pin method), 41
dumps() (in module ujson), 20 H
hasattr() (built-in function), 10
E hash() (built-in function), 10
e (in module math), 14 heap_lock() (in module micropython), 48
enable() (in module gc), 12 heap_unlock() (in module micropython), 48
enable_irq() (in module machine), 35 heapify() (in module uheapq), 18
enumerate() (built-in function), 10 heappop() (in module uheapq), 18
erf() (in module math), 13 heappush() (in module uheapq), 18
erfc() (in module math), 13 hex() (built-in function), 10
esp (module), 54 hexdigest() (uhashlib.hash method), 18
eval() (built-in function), 10 hexlify() (in module ubinascii), 16
exec() (built-in function), 10 hline() (framebuf.FrameBuffer method), 34
exit() (in module sys), 15
exp() (in module math), 13 I
expm1() (in module math), 13 I2C (class in machine), 37
extend() (array.array.array method), 12 id() (built-in function), 10
idle() (in module machine), 35
F ifconfig() (network.wlan method), 51
fabs() (in module math), 13 ilistdir() (in module uos), 20
feed() (machine.wdt method), 47 implementation (in module sys), 15
FileIO (class in uio), 20 INCL (in module btree), 33
fill() (framebuf.FrameBuffer method), 34 init() (machine.I2C method), 37
fill_rect() (framebuf.FrameBuffer method), 34 init() (machine.Pin method), 40
filter() (built-in function), 10 init() (machine.RTC method), 43
flash_erase() (in module esp), 55 init() (machine.SPI method), 44
flash_id() (in module esp), 55 input() (built-in function), 10
flash_read() (in module esp), 55 int (built-in class), 11
flash_write() (in module esp), 55 irq() (machine.Pin method), 41
float (built-in class), 10 irq() (machine.RTC method), 44
floor() (in module math), 13 isconnected() (network.wlan method), 51
flush() (btree.btree method), 32 isfinite() (in module math), 14
fmod() (in module math), 13 isinf() (in module math), 14
framebuf (module), 33 isinstance() (built-in function), 11
framebuf.GS4_HMSB (in module framebuf), 35 isnan() (in module math), 14
framebuf.MONO_HLSB (in module framebuf), 34 issubclass() (built-in function), 11
framebuf.MONO_HMSB (in module framebuf), 35 items() (btree.btree method), 32
framebuf.MONO_VLSB (in module framebuf), 34 iter() (built-in function), 11
framebuf.RGB565 (in module framebuf), 35
FrameBuffer (class in framebuf), 33 K
freq() (in module machine), 35 kbd_intr() (in module micropython), 48
frexp() (in module math), 13 keys() (btree.btree method), 32
from_bytes() (int class method), 11
frozenset (built-in class), 10 L
ldexp() (in module math), 14
G len() (built-in function), 11
gamma() (in module math), 13 lgamma() (in module math), 14
gc (module), 12
118 Index
line() (framebuf.FrameBuffer method), 34 off() (machine.Signal method), 43

list (built-in class), 11 on() (machine.Signal method), 43
listdir() (in module uos), 21 open() (built-in function), 11
listen() (usocket.socket method), 24 open() (in module btree), 32
LITTLE_ENDIAN (in module uctypes), 53 open() (in module uio), 19
loads() (in module ujson), 20 opt_level() (in module micropython), 48
locals() (built-in function), 11 ord() (built-in function), 11
localtime() (in module utime), 28 OrderedDict() (in module ucollections), 17
log() (in module math), 14 out_value() (machine.Pin method), 41
log10() (in module math), 14
log2() (in module math), 14 P
pack() (in module ustruct), 27
M pack_into() (in module ustruct), 27
machine (module), 35 path (in module sys), 16
machine.DEEPSLEEP (in module machine), 36 phy_mode() (in module network), 49
machine.DEEPSLEEP_RESET (in module machine), 36 pi (in module math), 14
machine.HARD_RESET (in module machine), 36 Pin (class in machine), 39
machine.IDLE (in module machine), 36 Pin.ALT (in module machine), 42
machine.PIN_WAKE (in module machine), 36 Pin.ALT_OPEN_DRAIN (in module machine), 42
machine.PWRON_RESET (in module machine), 36 Pin.HIGH_POWER (in module machine), 42
machine.RTC_WAKE (in module machine), 36 Pin.IN (in module machine), 42
machine.SLEEP (in module machine), 36 Pin.IRQ_FALLING (in module machine), 42
machine.SOFT_RESET (in module machine), 36 Pin.IRQ_HIGH_LEVEL (in module machine), 42
machine.WDT_RESET (in module machine), 36 Pin.IRQ_LOW_LEVEL (in module machine), 42
machine.WLAN_WAKE (in module machine), 36 Pin.IRQ_RISING (in module machine), 42
makefile() (usocket.socket method), 25 Pin.LOW_POWER (in module machine), 42
map() (built-in function), 11 Pin.MED_POWER (in module machine), 42
match() (in module ure), 22 Pin.OPEN_DRAIN (in module machine), 42
match() (ure.regex method), 22 Pin.OUT (in module machine), 42
math (module), 12 Pin.PULL_DOWN (in module machine), 42
max() (built-in function), 11 Pin.PULL_UP (in module machine), 42
maxsize (in module sys), 15 pixel() (framebuf.FrameBuffer method), 34
mem_alloc() (in module gc), 12 platform (in module sys), 16
mem_free() (in module gc), 12 pow() (built-in function), 11
mem_info() (in module micropython), 48 pow() (in module math), 14
memoryview (built-in class), 11 print() (built-in function), 11
micropython (module), 48 print_exception() (in module sys), 15
min() (built-in function), 11 property() (built-in function), 11
mkdir() (in module uos), 21 pull() (machine.Pin method), 41
mktime() (in module utime), 28
mode() (machine.Pin method), 41 Q
modf() (in module math), 14 qstr_info() (in module micropython), 48
modules (in module sys), 16
R
N radians() (in module math), 14
namedtuple() (in module ucollections), 17 range() (built-in function), 11
NATIVE (in module uctypes), 53 read() (machine.SPI method), 45
network (module), 49 read() (machine.UART method), 47
next() (built-in function), 11 read() (usocket.socket method), 25
now() (machine.RTC method), 44 readfrom() (machine.I2C method), 38
readfrom_into() (machine.I2C method), 38
O readfrom_mem() (machine.I2C method), 38
object (built-in class), 11 readfrom_mem_into() (machine.I2C method), 38
oct() (built-in function), 11 readinto() (machine.I2C method), 38
Index 119
readinto() (machine.SPI method), 45 socket.socket() (in module usocket), 23

readinto() (machine.UART method), 47 sorted() (built-in function), 11
readinto() (usocket.socket method), 26 SPI (class in machine), 44
readline() (machine.UART method), 47 SPI.LSB (in module machine), 45
readline() (usocket.socket method), 26 SPI.MASTER (in module machine), 45
rect() (framebuf.FrameBuffer method), 34 SPI.MSB (in module machine), 45
recv() (usocket.socket method), 25 split() (ure.regex method), 22
recvfrom() (usocket.socket method), 25 sqrt() (in module math), 14
remove() (in module uos), 21 ssl.CERT_NONE (in module ussl), 26
rename() (in module uos), 21 ssl.CERT_OPTIONAL (in module ussl), 26
repr() (built-in function), 11 ssl.CERT_REQUIRED (in module ussl), 26
reset() (in module machine), 35 ssl.SSLError (in module ussl), 26
reset_cause() (in module machine), 35 ssl.wrap_socket() (in module ussl), 26
reversed() (built-in function), 11 stack_use() (in module micropython), 48
rmdir() (in module uos), 21 start() (machine.I2C method), 37
round() (built-in function), 11 stat() (in module uos), 21
RTC (class in machine), 43 staticmethod() (built-in function), 11
RTC.ALARM0 (in module machine), 44 status() (network.wlan method), 51
statvfs() (in module uos), 21
S stderr (in module sys), 16
scan() (machine.I2C method), 37 stdin (in module sys), 16
scan() (network.wlan method), 50 stdout (in module sys), 16
schedule() (in module micropython), 49 stop() (machine.I2C method), 38
scroll() (framebuf.FrameBuffer method), 34 str (built-in class), 11
search() (in module ure), 22 StringIO (class in uio), 20
search() (ure.regex method), 22 struct (class in uctypes), 53
send() (usocket.socket method), 24 sum() (built-in function), 11
sendall() (usocket.socket method), 24 super() (built-in function), 11
sendbreak() (machine.UART method), 47 sync() (in module uos), 21
sendto() (usocket.socket method), 25 sys (module), 15
set (built-in class), 11
set_native_code_location() (in module esp), 55 T
setattr() (built-in function), 11 tan() (in module math), 14
setblocking() (usocket.socket method), 25 tanh() (in module math), 14
setsockopt() (usocket.socket method), 25 text() (framebuf.FrameBuffer method), 34
settimeout() (usocket.socket method), 25 TextIOWrapper (class in uio), 20
Signal (class in machine), 42 ticks_add() (in module utime), 29
sin() (in module math), 14 ticks_cpu() (in module utime), 28
sinh() (in module math), 14 ticks_diff() (in module utime), 29
sizeof() (in module uctypes), 53 ticks_ms() (in module utime), 28
sleep() (in module machine), 35 ticks_us() (in module utime), 28
sleep() (in module utime), 28 time() (in module utime), 30
sleep_ms() (in module utime), 28 time_pulse_us() (in module machine), 36
sleep_type() (in module esp), 55 Timer (class in machine), 46
sleep_us() (in module utime), 28 Timer.ONE_SHOT (in module machine), 46
slice (built-in class), 11 Timer.PERIODIC (in module machine), 46
socket.AF_INET (in module usocket), 24 to_bytes() (int method), 11
socket.AF_INET6 (in module usocket), 24 trunc() (in module math), 14
socket.getaddrinfo() (in module usocket), 23 tuple (built-in class), 12
socket.IPPROTO_SEC (in module usocket), 24 type() (built-in function), 12
socket.IPPROTO_TCP (in module usocket), 24
socket.IPPROTO_UDP (in module usocket), 24 U
socket.SOCK_DGRAM (in module usocket), 24 UART (class in machine), 46
socket.SOCK_STREAM (in module usocket), 24 ubinascii (module), 16
120 Index
ucollections (module), 17
uctypes (module), 52
uhashlib (module), 17
uhashlib.md5 (class in uhashlib), 18
uhashlib.sha1 (class in uhashlib), 18
uhashlib.sha256 (class in uhashlib), 18
uheapq (module), 18
uio (module), 18
ujson (module), 20
unhexlify() (in module ubinascii), 16
unique_id() (in module machine), 36
unpack() (in module ustruct), 27
unpack_from() (in module ustruct), 27
uos (module), 20
update() (uhashlib.hash method), 18
urandom() (in module uos), 21
ure (module), 22
usocket (module), 23
ussl (module), 26
ustruct (module), 27
utime (module), 27
uzlib (module), 30
V
value() (machine.Pin method), 40
value() (machine.Signal method), 43
values() (btree.btree method), 32
version (in module sys), 16
version_info (in module sys), 16
vline() (framebuf.FrameBuffer method), 34
W
WDT (class in machine), 47
WLAN (class in network), 50
write() (machine.I2C method), 38
write() (machine.SPI method), 45
write() (machine.UART method), 47
write() (usocket.socket method), 26
write_readinto() (machine.SPI method), 45
writeto() (machine.I2C method), 38
writeto_mem() (machine.I2C method), 38
Z
zip() (built-in function), 12
Index 121

Micropython Esp8266

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Micropython Esp8266

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MicroPython Documentation

Damien P. George, Paul Sokolovsky, and contributors

May 26, 2017

1 Quick reference for the ESP8266 1

3 MicroPython Differences from CPython 57

4 MicroPython license information 71

5 MicroPython documentation contents 73

6 Indices and tables 113

Python Module Index 115

QUICK REFERENCE FOR THE ESP8266

The Adafruit Feather HUZZAH board (image attribution: Adafruit).

1.1 Installing MicroPython

1.2 General board control

machine.freq() # get the current frequency of the CPU

The esp module:

esp.osdebug(None) # turn off vendor O/S debugging messages

The network module:

wlan = network.WLAN(network.STA_IF) # create station interface

ap = network.WLAN(network.AP_IF) # create access-point interface

A useful function for connecting to your local WiFi network is:

1.4 Delay and timing

Use the time module:

time.sleep(1) # sleep for 1 second

2 Chapter 1. Quick reference for the ESP8266

The period is in milliseconds.

1.6 Pins and GPIO

Use the machine.Pin class:

p0 = Pin(0, Pin.OUT) # create output pin on GPIO0

p2 = Pin(2, Pin.IN) # create input pin on GPIO2

p4 = Pin(4, Pin.IN, Pin.PULL_UP) # enable internal pull-up resistor

1.7 PWM (pulse width modulation)

pwm0 = PWM(Pin(0)) # create PWM object from a pin

pwm2 = PWM(Pin(2), freq=500, duty=512) # create and configure in one go

1.8 ADC (analog to digital conversion)

adc = ADC(0) # create ADC object on ADC pin

1.9 Software SPI bus

# construct an SPI bus on the given pins

spi.init(baudrate=200000) # set the baudrate

spi.read(10) # read 10 bytes on MISO

buf = bytearray(50) # create a buffer

spi.write(b'12345') # write 5 bytes on MOSI

buf = bytearray(4) # create a buffer

1.10 Hardware SPI bus

hspi = SPI(1, baudrate=80000000, polarity=0, phase=0)

(SPI(0) is used for FlashROM and not available to users.)

4 Chapter 1. Quick reference for the ESP8266

1.11 I2C bus

# construct an I2C bus

i2c.readfrom(0x3a, 4) # read 4 bytes from slave device with address 0x3a

buf = bytearray(10) # create a buffer with 10 bytes

1.12 Deep-sleep mode

# configure RTC.ALARM0 to be able to wake the device

# check if the device woke from a deep sleep

# set RTC.ALARM0 to fire after 10 seconds (waking the device)

# put the device to sleep

1.13 OneWire driver

The OneWire driver is implemented in software and works on all pins:

ow = onewire.OneWire(Pin(12)) # create a OneWire bus on GPIO12

There is a specific driver for DS18S20 and DS18B20 devices: