STM32F30X时钟初始化为HSI 64Mhz,并使用PLLCLK作为系统时钟

void SYSCLK_Config_HSI_64Mhz(void)
{
	__IO uint32_t StartUpCounter = 0, HSIStatus = 0;

	/* SYSCLK, HCLK, PCLK2 and PCLK1 configuration ---------------------------*/	
	/* Enable HSI */	
	RCC->CR |= ((uint32_t)RCC_CR_HSION);
	
	/* Wait till HSI is ready and if Time out is reached exit */
	do
	{
	  HSIStatus = RCC->CR & RCC_CR_HSIRDY;
	  StartUpCounter++;  
	} while((HSIStatus == 0) && (StartUpCounter != HSE_STARTUP_TIMEOUT));


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

	if (HSIStatus == (uint32_t)0x01)
	{
	  /* Enable Prefetch Buffer */
	  FLASH->ACR |= FLASH_ACR_PRFTBE;
	  
	  /* Flash 2 wait state */
	  FLASH->ACR &= (uint32_t)((uint32_t)~FLASH_ACR_LATENCY);
	  FLASH->ACR |= (uint32_t)FLASH_ACR_LATENCY_1;	
	   
	  /* HCLK = SYSCLK */
	  RCC->CFGR |= (uint32_t)RCC_CFGR_HPRE_DIV1;
		
	  /* PCLK2 = HCLK */
	  RCC->CFGR |= (uint32_t)RCC_CFGR_PPRE2_DIV1;
	  
	  /* PCLK1 = HCLK */
	  RCC->CFGR |= (uint32_t)RCC_CFGR_PPRE1_DIV2;
	  
	 

	   /* Clear PLL Source [16] and Multiplier [21:18] bits */
	   RCC->CFGR &= ~(RCC_CFGR_PLLMULL | RCC_CFGR_PLLSRC);
	   /*  PLL configuration: PLLCLK = HSI / 2 * 16 = 64 MHz */
	  RCC->CFGR |= (uint32_t)(RCC_CFGR_PLLSRC_HSI_Div2 | RCC_CFGR_PLLMULL16);
	   	  
	  /* 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)0x08)
	  {
	  }
	}
	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 */
	}


}

来自：http://blog.csdn.net/lan120576664?viewmode=contents