STM32F030 使用内部时钟和外部时钟

static void SetSysClock(void)

{

  __IO uint32_t StartUpCounter = 0, HSEStatus = 0;

  /* SYSCLK, HCLK, PCLK configuration ----------------------------------------*/

#if defined (PLL_SOURCE_HSI)

  /* At this stage the HSI is already enabled */

  /* 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 = (HSI/2) * 12 = ~48 MHz */

  RCC->CFGR &= (uint32_t)((uint32_t)~(RCC_CFGR_PLLSRC | RCC_CFGR_PLLXTPRE | RCC_CFGR_PLLMULL));

  RCC->CFGR |= (uint32_t)(RCC_CFGR_PLLSRC_HSI_Div2 | RCC_CFGR_PLLXTPRE_PREDIV1 | RCC_CFGR_PLLMULL12);

  /* 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 defined (PLL_SOURCE_HSE)

  /* Enable HSE */    

  RCC->CR |= ((uint32_t)RCC_CR_HSEON);

 #elif defined (PLL_SOURCE_HSE_BYPASS)

  /* HSE oscillator bypassed with external clock */    

  RCC->CR |= (uint32_t)(RCC_CR_HSEON | RCC_CR_HSEBYP);

 #endif /* PLL_SOURCE_HSE */

  /* Wait till HSE is ready and if Time out is reached exit */

  do

  {

    HSEStatus = RCC->CR & RCC_CR_HSERDY;

    StartUpCounter++;  

  } while((HSEStatus == 0) && (StartUpCounter != HSE_STARTUP_TIMEOUT));

  if ((RCC->CR & RCC_CR_HSERDY) != RESET)

  {

    HSEStatus = (uint32_t)0x01;

  }

  else

  {

    HSEStatus = (uint32_t)0x00;

  }  

  if (HSEStatus == (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 */

    RCC->CFGR &= (uint32_t)((uint32_t)~(RCC_CFGR_PLLSRC | RCC_CFGR_PLLXTPRE | RCC_CFGR_PLLMULL));

    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 HSE fails to start-up, the application will have wrong clock 

         configuration. User can add here some code to deal with this error */

  }  

#endif /* PLL_SOURCE_HSI */  

}