qmk-firmware/tmk_core/common/mbed/timer.c

#include "cmsis.h"
#include "timer.h"

/* Mill second tick count */
volatile uint32_t timer_count = 0;

/* Timer interrupt handler */
void SysTick_Handler(void)  {
    timer_count++;
}

void timer_init(void)
{
    timer_count = 0;
    SysTick_Config(SystemCoreClock / 1000); /* 1ms tick */
}

void timer_clear(void)
{
    timer_count = 0;
}

uint16_t timer_read(void)
{
    return (uint16_t)(timer_count & 0xFFFF);
}

uint32_t timer_read32(void)
{
    return timer_count;
}

uint16_t timer_elapsed(uint16_t last)
{
    return TIMER_DIFF_16(timer_read(), last);
}

uint32_t timer_elapsed32(uint32_t last)
{
    return TIMER_DIFF_32(timer_read32(), last);
}