修改STM32F030 时钟源为内部晶振（HEI ）_stm32030内部晶振-优快云博客

本文介绍如何在STM32F0xx微控制器中修改系统时钟配置，将时钟源从外部高速振荡器(HSE)更改为内部高速振荡器(HSI)，并设置PLL以获得48MHz的系统时钟频率。

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修改 SetSysClock（）函数，将时钟源由默认的HSE改为内部HSI 时钟

system_stm32f0xx.c

static void SetSysClock(void)
{
  __IO uint32_t StartUpCounter = 0, HSIStatus = 0;
  
  /* SYSCLK, HCLK, PCLK configuration ----------------------------------------*/
  /* Enable HSI */    
  RCC->CR |= ((uint32_t)RCC_CR_HSION);//((uint32_t)RCC_CR_HSEON)
 
  /* Wait till HSI is ready and if Time out is reached exit */
  do
  {
    HSIStatus = RCC->CR & RCC_CR_HSIRDY;//RCC->CR & RCC_CR_HSERDY;
    StartUpCounter++;  
  } while((HSIStatus == 0) && (StartUpCounter != HSI_STARTUP_TIMEOUT));

  if ((RCC->CR & RCC_CR_HSIRDY) != RESET)//((RCC->CR & RCC_CR_HSERDY) != RESET
  {
    HSIStatus = (uint32_t)0x01;
  }
  else
  {
    HSIStatus = (uint32_t)0x00;
  }  

  if (HSIStatus == (uint32_t)0x01)
  {
    /* Enable Prefetch Buffer and set Flash Latency */
    FLASH->ACR = FLASH_ACR_PRFTBE | FLASH_ACR_LATENCY;
 
    /* HCLK = SYSCLK */
    RCC->CFGR |= (uint32_t)RCC_CFGR_HPRE_DIV1;
      
    /* PCLK = HCLK */
    RCC->CFGR |= (uint32_t)RCC_CFGR_PPRE_DIV1;
	/* PLL configuration = HSE * 6 = 48 MHz */
    /* PLL configuration = HSI/2 * 12 = 48 MHz */  
    RCC->CFGR &= (uint32_t)((uint32_t)~(RCC_CFGR_PLLSRC  | RCC_CFGR_PLLMULL));
    RCC->CFGR |= (uint32_t)(RCC_CFGR_PLLSRC_HSI_DIV2| RCC_CFGR_PLLMULL12);
	 // RCC->CFGR |= (uint32_t)(RCC_CFGR_PLLSRC_PREDIV1 | RCC_CFGR_PLLXTPRE_PREDIV1 | RCC_CFGR_PLLMULL6)


            
    /* Enable PLL */
    RCC->CR |= RCC_CR_PLLON;

    /* Wait till PLL is ready */
    while((RCC->CR & RCC_CR_PLLRDY) == 0)
    {
    }

    /* Select PLL as system clock source */
    RCC->CFGR &= (uint32_t)((uint32_t)~(RCC_CFGR_SW));
    RCC->CFGR |= (uint32_t)RCC_CFGR_SW_PLL;    

    /* Wait till PLL is used as system clock source */
    while ((RCC->CFGR & (uint32_t)RCC_CFGR_SWS) != (uint32_t)RCC_CFGR_SWS_PLL)
    {
    }
  }
  else
  { /* If HSI fails to start-up, the application will have wrong clock 
         configuration. User can add here some code to deal with this error */
  }  
}