This document discusses the SysTick timer in the ARM Cortex-M microcontroller.
[1] The SysTick timer is a 24-bit decrementing counter that runs off the bus clock, decrementing every 20.83 ns with a 48 MHz bus clock. It can be configured as a modulo counter to generate periodic interrupts.
[2] The SysTick timer registers include the STCSR for control and status, STRVR for reload value, and STCVR for current value.
[3] Initialization involves disabling the timer, setting the reload value, clearing the current value, and enabling the timer clock source with or without interrupts. The timer can then generate periodic delays through either polling or
This document discusses the SysTick timer in the ARM Cortex-M microcontroller.
[1] The SysTick timer is a 24-bit decrementing counter that runs off the bus clock, decrementing every 20.83 ns with a 48 MHz bus clock. It can be configured as a modulo counter to generate periodic interrupts.
[2] The SysTick timer registers include the STCSR for control and status, STRVR for reload value, and STCVR for current value.
[3] Initialization involves disabling the timer, setting the reload value, clearing the current value, and enabling the timer clock source with or without interrupts. The timer can then generate periodic delays through either polling or
This document discusses the SysTick timer in the ARM Cortex-M microcontroller.
[1] The SysTick timer is a 24-bit decrementing counter that runs off the bus clock, decrementing every 20.83 ns with a 48 MHz bus clock. It can be configured as a modulo counter to generate periodic interrupts.
[2] The SysTick timer registers include the STCSR for control and status, STRVR for reload value, and STCVR for current value.
[3] Initialization involves disabling the timer, setting the reload value, clearing the current value, and enabling the timer clock source with or without interrupts. The timer can then generate periodic delays through either polling or
This document discusses the SysTick timer in the ARM Cortex-M microcontroller.
[1] The SysTick timer is a 24-bit decrementing counter that runs off the bus clock, decrementing every 20.83 ns with a 48 MHz bus clock. It can be configured as a modulo counter to generate periodic interrupts.
[2] The SysTick timer registers include the STCSR for control and status, STRVR for reload value, and STCVR for current value.
[3] Initialization involves disabling the timer, setting the reload value, clearing the current value, and enabling the timer clock source with or without interrupts. The timer can then generate periodic delays through either polling or
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EE529 Embedded Systems
Lecture 6: SysTick Timer
6-1 SysTick Timer
Timer/Counter operation 24-bit counter decrements at bus clock frequency o With 48MHz bus clock, decrements every 20.83 ns Counting is from n 0 o Setting n appropriately will make the counter a modulo n+1 counter. That is: next_value = (current_value-1) mod (n+1) Sequence: n,n-1,n-2,n-3… 2,1,0,n,n-1…
6-2 SysTick Timer Address 31-24 23-17 16 15-3 2 1 0 Name 0xE000E010 0 0 COUNT 0 CLK_SRC INTEN ENABLE SYSTICK_STCSR 0xE000E014 0 24-bit RELOAD value SYSTICK_STRVR 0xE000E018 0 24-bit CURRENT value of SysTick counter SYSTICK_STCVR
Initialization (4 steps) Step1: Clear ENABLE to stop counter Step2: Specify the RELOAD value Step3: Clear the counter via SYSTICK_STCVR Step4: Set SYSTICK_STCSR o CLK_SRC = 1 (bus clock is the only option) o INTEN = 0 for no interrupts o ENABLE = 0 to enable
6-3 SysTick Timer in C (using Polling) void SysTick_Init(void){ SysTick->CTRL = 0; // 1) disable SysTick during setup SysTick->LOAD = 0x00FFFFFF; // 2) maximum reload value SysTick->VAL = 0; // 3) any write to current clears it SysTick->CTRL = 0x00000005; // 4) enable SysTick with core clock }
// The delay parameter is in units of the 48 MHz clock. (20.83 ns)
void SysTick_Wait(uint32_t delay){ SysTick->LOAD = delay-1; // number of counts to wait SysTick->VAL = 0; // any value written to counter clears while((SysTick->CTRL & 0x00010000) == 0){ // wait for count flag } }
SysTick->CTRL = 0; // 1) disable SysTick during setup SysTick->LOAD = period - 1; // 2) reload value sets period SysTick->VAL = 0; // 3) any write to current clears it SCB->SHP[11] = priority<<5; // set priority into top 3 bits of 8-bit register SysTick->CTRL = 0x00000007; // 4) enable SysTick with core clock and interrupts }
