stm32 cubemx hal 工程中 微秒延迟 delay_us

/* USER CODE BEGIN 0 */
typedef uint8_t u8;
typedef uint32_t u32;

u8 fac_us;

void delay_init(u8 SYSCLK)
{
    #if SYSTEM_SUPPORT_OS //?????? OS.
        u32 reload;
    #endif
    
    HAL_SYSTICK_CLKSourceConfig(SYSTICK_CLKSOURCE_HCLK);
    //SysTick ??? HCLK
    fac_us=SYSCLK; //?????? OS,fac_us ?????
    
    #if SYSTEM_SUPPORT_OS //?????? OS.
        reload=SYSCLK; //???????? ??? K
        reload*=1000000/delay_ostickspersec; //?? delay_ostickspersec ??????
        //reload ? 24 ????,???:16777216,? 180M ?,?? 0.745s ??
        fac_ms=1000/delay_ostickspersec; //?? OS ?????????
        SysTick->CTRL|=SysTick_CTRL_TICKINT_Msk;//?? SYSTICK ??
        SysTick->LOAD=reload; //? 1/OS_TICKS_PER_SEC ?????
        SysTick->CTRL|=SysTick_CTRL_ENABLE_Msk; //?? SYSTICK
        #else
    #endif
}





void delay_us(u32 nus)
{
    u32 ticks;
    u32 told,tnow,tcnt=0;
    u32 reload=SysTick->LOAD; //LOAD ??
    ticks=nus*fac_us; //??????
    told=SysTick->VAL; //?????????
    while(1)
    {
        tnow=SysTick->VAL;
        if(tnow!=told)
        {
            if(tnow<told)tcnt+=told-tnow;//???? SYSTICK ??????????.
            else tcnt+=reload-tnow+told;
            told=tnow;
            if(tcnt>=ticks)break; //????/????????,???.
        }
    };
}
/* USER CODE END 0 */

int main(void)
{

  /* USER CODE BEGIN 1 */

  /* USER CODE END 1 */

  /* MCU Configuration----------------------------------------------------------*/

  /* Reset of all peripherals, Initializes the Flash interface and the Systick. */
  HAL_Init();

  /* Configure the system clock */
  SystemClock_Config();

  /* Initialize all configured peripherals */
  MX_GPIO_Init();

  /* USER CODE BEGIN 2 */
    delay_init(168);
  /* USER CODE END 2 */

  /* Infinite loop */
  /* USER CODE BEGIN WHILE */
  while (1)
  {
  /* USER CODE END WHILE */
    HAL_GPIO_WritePin(GPIOF, GPIO_PIN_7, GPIO_PIN_SET);
    delay_us(50);
    HAL_GPIO_WritePin(GPIOF, GPIO_PIN_7, GPIO_PIN_RESET);
    delay_us(50);
  /* USER CODE BEGIN 3 */

  }
  /* USER CODE END 3 */

}