flipperzero-firmware/firmware/targets/f4/api-hal/api-hal-delay.c

#include "api-hal-delay.h"
#include "assert.h"
#include "cmsis_os2.h"

static uint32_t clk_per_microsecond;

void delay_us_init_DWT(void) {
    CoreDebug->DEMCR |= CoreDebug_DEMCR_TRCENA_Msk;
    DWT->CTRL |= DWT_CTRL_CYCCNTENA_Msk;
    DWT->CYCCNT = 0U;
    clk_per_microsecond = SystemCoreClock / 1000000.0f;
}

void delay_us(float microseconds) {
    uint32_t start = DWT->CYCCNT;
    uint32_t time_ticks = microseconds * clk_per_microsecond;
    while((DWT->CYCCNT - start) < time_ticks) {
    };
}

// cannot be used in ISR
// TODO add delay_ISR variant
void delay(float milliseconds) {
    uint32_t ticks = milliseconds / (1000.0f / osKernelGetTickFreq());
    osStatus_t result = osDelay(ticks);
    (void)result;
    assert(result == osOK);
}