circuitpython/stm/systick.c

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#include <stm32f4xx.h>
#include "misc.h"
#include "systick.h"
volatile uint32_t sys_tick_counter;
void sys_tick_init() {
// sys-tick interrupt called at 1ms intervals
sys_tick_counter = 0;
SysTick_Config(SystemCoreClock / 1000);
}
// called on SysTick interrupt
void SysTick_Handler() {
sys_tick_counter++;
}
void sys_tick_delay_ms(uint32_t delay_ms) {
sys_tick_wait_at_least(sys_tick_counter, delay_ms);
}
// waits until at least delay_ms milliseconds have passed from the sampling of sys_tick_counter in stc
// handles overflow properl
// assumes stc was taken from sys_tick_counter some time before calling this function
// eg stc <= sys_tick_counter for the case of no wrap around of sys_tick_counter
void sys_tick_wait_at_least(uint32_t stc, uint32_t delay_ms) {
// stc_wait is the value of sys_tick_counter that we wait for
uint32_t stc_wait = stc + delay_ms;
if (stc_wait < stc) {
// stc_wait wrapped around
while (stc <= sys_tick_counter || sys_tick_counter < stc_wait) {
}
} else {
// stc_wait did not wrap around
while (stc <= sys_tick_counter && sys_tick_counter < stc_wait) {
}
}
}
bool sys_tick_has_passed(uint32_t stc, uint32_t delay_ms) {
// stc_wait is the value of sys_tick_counter that we wait for
uint32_t stc_wait = stc + delay_ms;
if (stc_wait < stc) {
// stc_wait wrapped around
return !(stc <= sys_tick_counter || sys_tick_counter < stc_wait);
} else {
// stc_wait did not wrap around
return !(stc <= sys_tick_counter && sys_tick_counter < stc_wait);
}
}