stm32之HAL库实现us延时方法

HAL_Delay()源码为ms级别的延时如下：

/**
  * @brief This function provides accurate delay (in milliseconds) based 
  *        on variable incremented.
  * @note In the default implementation , SysTick timer is the source of time base.
  *       It is used to generate interrupts at regular time intervals where uwTick
  *       is incremented.
  * @note This function is declared as __weak to be overwritten in case of other
  *       implementations in user file.
  * 
  * @param Delay: specifies the delay time length, in milliseconds.
  * @retval None
  */
__weak void HAL_Delay(__IO uint32_t Delay)
{
  uint32_t tickstart = 0U;
  tickstart = HAL_GetTick();
  while((HAL_GetTick() - tickstart) < Delay)
  {
  }
}

下面是us级别的延时：

void HAL_Delay_us(uint32_t nus)
{
//将systic设置为1us中断
HAL_SYSTICK_Config(HAL_RCC_GetHCLKFreq()/1000000);
//延时nus
HAL_Delay(nus-1);
//恢复systic中断为1ms
HAL_SYSTICK_Config(HAL_RCC_GetHCLKFreq()/1000);
}

另外需要注意的一点是stm32H7里面时钟配置如下：

其中systic是系统时钟直接给systic的而不是HCLK，HAL_RCC_GetHCLKFreq()正好是系统时钟的1/2所以上面配置1us时钟源要改为如下：

HAL_SYSTICK_Config(HAL_RCC_GetHCLKFreq()*2/1000000);