void RCC_Configuration(void)
{
   ErrorStatus HSEStartUpStatus;
  RCC_DeInit();
  RCC_HSEConfig(RCC_HSE_ON);
  HSEStartUpStatus = RCC_WaitForHSEStartUp();
  if(HSEStartUpStatus == SUCCESS)
  {
   RCC_HCLKConfig(RCC_SYSCLK_Div1);
   RCC_PCLK2Config(RCC_HCLK_Div1);
   RCC_PCLK1Config(RCC_HCLK_Div2);
   RCC_ADCCLKConfig(RCC_PCLK2_Div6);
//  FLASH_SetLatency(FLASH_Latency_2);
  // FLASH_PrefetchBufferCmd(FLASH_PrefetchBuffer_Enable);
   RCC_PLLConfig(RCC_PLLSource_HSE_Div1, RCC_PLLMul_9);  //PLL 72M  ...HSE_DIV1见RCC_CR寄存器，rcc_pllMUL_9见RDD_CFGR寄存器
   RCC_PLLCmd(ENABLE);
   while(RCC_GetFlagStatus(RCC_FLAG_PLLRDY) == RESET)
    {
    }
   RCC_SYSCLKConfig(RCC_SYSCLKSource_PLLCLK);
    while(RCC_GetSYSCLKSource() != 0x08)
    {
    }
  }
}