stm32之HAL库实现us延时方法
4 R" o% h8 m' x8 p! u. i  jHAL_Delay()源码为ms级别的延时如下：

1. /**
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2.   * @brief This function provides accurate delay (in milliseconds) based
   
3.   *        on variable incremented.
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4.   * @note In the default implementation , SysTick timer is the source of time base.
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5.   *       It is used to generate interrupts at regular time intervals where uwTick
   
6.   *       is incremented.
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7.   * @note This function is declared as __weak to be overwritten in case of other
   
8.   *       implementations in user file.
   
9.   *
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10.   * @param Delay: specifies the delay time length, in milliseconds.
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11.   * @retval None
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12.   */
    
13. __weak void HAL_Delay(__IO uint32_t Delay)
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14. {
    
15.   uint32_t tickstart = 0U;
    
16.   tickstart = HAL_GetTick();
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17.   while((HAL_GetTick() - tickstart) < Delay)
    
18.   {
    
19.   }
    
20. }

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+ Z2 b6 l7 M/ u8 |1 T& d% N  o下面是us级别的延时：
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1. void HAL_Delay_us(uint32_t nus)
   
2. {
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3. //将systic设置为1us中断
   
4. HAL_SYSTICK_Config(HAL_RCC_GetHCLKFreq()/1000000);
   
5. //延时nus
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6. HAL_Delay(nus-1);
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7. //恢复systic中断为1ms
   
8. HAL_SYSTICK_Config(HAL_RCC_GetHCLKFreq()/1000);
   
9. }

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3 g' S% a) @8 y另外需要注意的一点是stm32H7里面时钟配置如下：

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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：
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HAL_SYSTICK_Config(HAL_RCC_GetHCLKFreq()*2/1000000);
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