This is a hh:mm:ss clock that runs from the time contained in NMEA RMC sentences. The code is targeted at an Atmel ATTiny13A.

Notes:

• As the target microcontroller doesn't have enough RAM to store a full NMEA sentence, this project uses a custom parser that only reads RMC ("Recommended Minimum") sentences from a UART and extracts the time from that (seenmea.c).

• The ATTiny13A lacks SPI and UART peripherals, so these are implemented in software.

Schematic and construction details can be found on this project's hackaday.io page.

The avr-gcc toolchain is required to build, but there are no other external dependencies.

# Build
make

# Flash with programmer configured in Makefile
make flash

The simple test suite for NMEA RMC sentence decoding can be run manually with:

make test