2019年03月18日 | STM32F4时钟配置

看了下时钟树按照http://blog.csdn.net/louyangyang91/article/details/51374924这个博文配置了，结果发现UART波特率不对，但是MOC1\2都是正常输出（168M/5分频输出），蒙了很久才发现 USART_Init(USART1, &USART_InitStructure); 这个函数内部会调用RCC_GetClocksFreq(&RCC_ClocksStatus);这个函数来得到PCLK1\PCLK2等系统时钟，进入这个函数看其内部发现它调用了一个HSE_VALUE的宏定义，继续定位发现居然是

#if !defined  (HSE_VALUE) 

  #define HSE_VALUE    ((uint32_t)8000000) /*!< Value of the External oscillator in Hz */

8M的频率。果断改成我使用的外部晶振12M，然后配置PLL系统时钟168M，再看UART波特率对了。问题解决、、、、

的void RCC_GetClocksFreq(RCC_ClocksTypeDef* RCC_Clocks)

{

  uint32_t tmp = 0, presc = 0, pllvco = 0, pllp = 2, pllsource = 0, pllm = 2;

  /* Get SYSCLK source -------------------------------------------------------*/

  tmp = RCC->CFGR & RCC_CFGR_SWS;

  switch (tmp)

  {

    case 0x00:  /* HSI used as system clock source */

      RCC_Clocks->SYSCLK_Frequency = HSI_VALUE;

      break;

    case 0x04:  /* HSE used as system clock  source */

      RCC_Clocks->SYSCLK_Frequency = HSE_VALUE;

      break;

    case 0x08:  /* PLL used as system clock  source */

      /* PLL_VCO = (HSE_VALUE or HSI_VALUE / PLLM) * PLLN

         SYSCLK = PLL_VCO / PLLP

         */    

      pllsource = (RCC->PLLCFGR & RCC_PLLCFGR_PLLSRC) >> 22;

      pllm = RCC->PLLCFGR & RCC_PLLCFGR_PLLM;

      if (pllsource != 0)

      {

        /* HSE used as PLL clock source */

        pllvco = (HSE_VALUE / pllm) * ((RCC->PLLCFGR & RCC_PLLCFGR_PLLN) >> 6);

      }

      else

      {

        /* HSI used as PLL clock source */

        pllvco = (HSI_VALUE / pllm) * ((RCC->PLLCFGR & RCC_PLLCFGR_PLLN) >> 6);      

      }

      pllp = (((RCC->PLLCFGR & RCC_PLLCFGR_PLLP) >>16) + 1 ) *2;

      RCC_Clocks->SYSCLK_Frequency = pllvco/pllp;

      break;

    default:

      RCC_Clocks->SYSCLK_Frequency = HSI_VALUE;

      break;

  }

  /* Compute HCLK, PCLK1 and PCLK2 clocks frequencies ------------------------*/

  /* Get HCLK prescaler */

  tmp = RCC->CFGR & RCC_CFGR_HPRE;

  tmp = tmp >> 4;

  presc = APBAHBPrescTable[tmp];

  /* HCLK clock frequency */

  RCC_Clocks->HCLK_Frequency = RCC_Clocks->SYSCLK_Frequency >> presc;

  /* Get PCLK1 prescaler */

  tmp = RCC->CFGR & RCC_CFGR_PPRE1;

  tmp = tmp >> 10;

  presc = APBAHBPrescTable[tmp];

  /* PCLK1 clock frequency */

  RCC_Clocks->PCLK1_Frequency = RCC_Clocks->HCLK_Frequency >> presc;

  /* Get PCLK2 prescaler */

  tmp = RCC->CFGR & RCC_CFGR_PPRE2;

  tmp = tmp >> 13;

  presc = APBAHBPrescTable[tmp];

  /* PCLK2 clock frequency */

  RCC_Clocks->PCLK2_Frequency = RCC_Clocks->HCLK_Frequency >> presc;

}

下面贴出时钟配置代码：

void SetSysClockProc(void)

{

ErrorStatus HSEStartUpStatus;

RCC_DeInit();                                

RCC_HSEConfig(RCC_HSE_ON);        

HSEStartUpStatus = RCC_WaitForHSEStartUp();        

if(HSEStartUpStatus==SUCCESS)                        

{    

RCC_HCLKConfig(RCC_SYSCLK_Div1);        

RCC_PCLK1Config(RCC_HCLK_Div4);                

RCC_PCLK2Config(RCC_HCLK_Div2);                

FLASH_SetLatency(FLASH_Latency_5);        

FLASH_PrefetchBufferCmd(ENABLE); 

//RCC_ADCCLKConfig(RCC_PCLK2_Div2);

RCC_PLLConfig(RCC_PLLSource_HSE,12,336,2,7);//168M

RCC_PLLCmd(ENABLE);

while(RCC_GetFlagStatus(RCC_FLAG_PLLRDY) == RESET)

{

}    

RCC_SYSCLKConfig(RCC_SYSCLKSource_PLLCLK); 

//  while(RCC_GetSYSCLKSource()!=0x08)

//    {

//    }

}   

}