2020年02月22日 | STM32F4设置系统时钟源为内部HSI

最近项目需要在调试STM32时遇到外部晶振时钟不稳定，查看RCC_CR寄存器的第17位始终处于0，表示外部晶振始终处于不稳定状态：

当HSE开启时，如果HSERDY一直处于0时，则芯片会启动内部16Mhz晶振,但是此时PLL分频无效，整个系统降到了16Mhz，无法忍受，立刻启动内部时钟源HSI为系统时钟， 同时通过配置PLL，将系统时钟配置到168Mhz,

由于系统设置时钟源是在系统起来厚，main函数之前设置的，在SetSysClock（），首先需要自己设置HSI为系统时钟源，代码如下：

/**

  * @brief  Configures HSI as the System clock source

  **/  

void HSI_SetSysClock()

{

  __IO uint32_t HSIStartUpStatus = 0;

  RCC_DeInit();

  //set HSI

  RCC_HSICmd(ENABLE);

  HSIStartUpStatus = RCC->CR & RCC_CR_HSIRDY;

  if (HSIStartUpStatus == RCC_CR_HSIRDY)

  {    

    /* Select regulator voltage output Scale 1 mode */

     RCC->APB1ENR |= RCC_APB1ENR_PWREN;

     PWR->CR |= PWR_CR_VOS;

     // HCLK = SYSCLK / 1

     RCC_HCLKConfig(RCC_SYSCLK_Div1);

    /* HCLK = SYSCLK / 1*/

    RCC->CFGR |= RCC_CFGR_HPRE_DIV1;

#if defined(STM32F40_41xxx) || defined(STM32F427_437xx) || defined(STM32F429_439xx) ||  defined(STM32F412xG) || defined(STM32F446xx) || defined(STM32F469_479xx)    

    /* PCLK2 = HCLK / 2*/

    RCC->CFGR |= RCC_CFGR_PPRE2_DIV2;

    /* PCLK1 = HCLK / 4*/

    RCC->CFGR |= RCC_CFGR_PPRE1_DIV4;

#endif /* STM32F40_41xxx || STM32F427_437x || STM32F429_439xx  || STM32F412xG || STM32F446xx || STM32F469_479xx */

#if defined(STM32F401xx) || defined(STM32F413_423xx)

    /* PCLK2 = HCLK / 1*/

    RCC->CFGR |= RCC_CFGR_PPRE2_DIV1;

    /* PCLK1 = HCLK / 2*/

    RCC->CFGR |= RCC_CFGR_PPRE1_DIV2;

#endif /* STM32F401xx || STM32F413_423xx */

    #if defined(STM32F40_41xxx) || defined(STM32F427_437xx) || defined(STM32F429_439xx) || defined(STM32F401xx) || defined(STM32F469_479xx)    

    /* Configure the main PLL */

    RCC->PLLCFGR = HSI_PLL_M | (PLL_N << 6) | (((PLL_P >> 1) -1) << 16) |

                   (RCC_PLLCFGR_PLLSRC_HSI) | (PLL_Q << 24);

#endif /* STM32F40_41xxx || STM32F401xx || STM32F427_437x || STM32F429_439xx || STM32F469_479xx */

#if  defined(STM32F412xG) || defined(STM32F413_423xx) || defined(STM32F446xx)

    /* Configure the main PLL */

    RCC->PLLCFGR = HSI_PLL_M | (PLL_N << 6) | (((PLL_P >> 1) -1) << 16) |

                   (RCC_PLLCFGR_PLLSRC_HSI) | (PLL_Q << 24) | (PLL_R << 28);

#endif /* STM32F412xG || STM32F413_423xx || STM32F446xx */

    /* Enable the main PLL */

    RCC->CR |= RCC_CR_PLLON;

    /* Wait till the main PLL is ready */

    while (RCC_GetFlagStatus(RCC_FLAG_PLLRDY) == RESET) {

    }

    #if defined(STM32F427_437xx) || defined(STM32F429_439xx) || defined(STM32F446xx) || defined(STM32F469_479xx)

    /* Enable the Over-drive to extend the clock frequency to 180 Mhz */

    PWR->CR |= PWR_CR_ODEN;

    while((PWR->CSR & PWR_CSR_ODRDY) == 0)

    {

    }

    PWR->CR |= PWR_CR_ODSWEN;

    while((PWR->CSR & PWR_CSR_ODSWRDY) == 0)

    {

    }      

    /* Configure Flash prefetch, Instruction cache, Data cache and wait state */

    FLASH->ACR = FLASH_ACR_PRFTEN | FLASH_ACR_ICEN |FLASH_ACR_DCEN |FLASH_ACR_LATENCY_5WS;

#endif /* STM32F427_437x || STM32F429_439xx || STM32F446xx || STM32F469_479xx */

#if defined(STM32F40_41xxx)  || defined(STM32F412xG)  

    /* Configure Flash prefetch, Instruction cache, Data cache and wait state */

    FLASH->ACR = FLASH_ACR_PRFTEN | FLASH_ACR_ICEN |FLASH_ACR_DCEN |FLASH_ACR_LATENCY_5WS;

#endif /* STM32F40_41xxx  || STM32F412xG */

#if defined(STM32F413_423xx)  

    /* Configure Flash prefetch, Instruction cache, Data cache and wait state */

    FLASH->ACR = FLASH_ACR_PRFTEN | FLASH_ACR_ICEN |FLASH_ACR_DCEN |FLASH_ACR_LATENCY_3WS;

#endif /* STM32F413_423xx */

#if defined(STM32F401xx)

    /* Configure Flash prefetch, Instruction cache, Data cache and wait state */

    FLASH->ACR = FLASH_ACR_PRFTEN | FLASH_ACR_ICEN |FLASH_ACR_DCEN |FLASH_ACR_LATENCY_2WS;

#endif /* STM32F401xx */

    /* Select the main PLL as system clock source */

    RCC->CFGR &= (uint32_t)((uint32_t)~(RCC_CFGR_SW));

    RCC->CFGR |= RCC_CFGR_SW_PLL;

    /* Wait till the main PLL is used as system clock source */

    while ((RCC->CFGR & (uint32_t)RCC_CFGR_SWS ) != RCC_CFGR_SWS_PLL);

    {

    }

  }

}

将上述代码添加到，设置外部时钟源失败异常处理流程SetSysClock（）函数中：

系统恢复如初，系统时钟源恢复到168Mhz,很happy