stm32之HAL库实现us延时方法
. G8 L( j; F& l' [7 |HAL_Delay()源码为ms级别的延时如下：
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1. /**
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2.   * @brief This function provides accurate delay (in milliseconds) based
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3.   *        on variable incremented.
   
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.
   
7.   * @note This function is declared as __weak to be overwritten in case of other
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8.   *       implementations in user file.
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9.   *
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10.   * @param Delay: specifies the delay time length, in milliseconds.
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11.   * @retval None
    
12.   */
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13. __weak void HAL_Delay(__IO uint32_t Delay)
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14. {
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15.   uint32_t tickstart = 0U;
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16.   tickstart = HAL_GetTick();
    
17.   while((HAL_GetTick() - tickstart) < Delay)
    
18.   {
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19.   }
    
20. }

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1 K* V- X! k7 u+ r: t+ R* p9 Q下面是us级别的延时：

1. void HAL_Delay_us(uint32_t nus)
   
2. {
   
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
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8. HAL_SYSTICK_Config(HAL_RCC_GetHCLKFreq()/1000);
   
9. }

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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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