qmk_firmware/tmk_core/common/chibios/timer.c

#include "ch.h"

#include "timer.h"

static systime_t last_systime    = 0;
static systime_t overflow        = 0;
static uint32_t  current_time_ms = 0;

void timer_init(void) { timer_clear(); }

void timer_clear(void) {
    last_systime    = chVTGetSystemTime();
    overflow        = 0;
    current_time_ms = 0;
}

uint16_t timer_read(void) { return (uint16_t)timer_read32(); }

uint32_t timer_read32(void) {
    // Note: We assume that the timer update is called at least once betweeen every wrap around of the system time
    systime_t current_systime = chVTGetSystemTime();
    systime_t elapsed         = current_systime - last_systime + overflow;
    uint32_t  elapsed_ms      = ST2MS(elapsed);
    current_time_ms += elapsed_ms;
    overflow     = elapsed - MS2ST(elapsed_ms);
    last_systime = current_systime;

    return current_time_ms;
}

uint16_t timer_elapsed(uint16_t last) { return timer_read() - last; }

uint32_t timer_elapsed32(uint32_t last) { return timer_read32() - last; }