The STM32F30X clock is initialized to HSI 64Mhz and uses PLLCLK as the system clock

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 */  

    }  

}