//系统进入待机模式

PWR_EnterSTANDBYMode();       
void PWR_EnterSTANDBYMode(void)
{
  /* Select STANDBY mode */
  PWR->CR |= PWR_CR_PDDS;

  /* Set SLEEPDEEP bit of Cortex System Control Register */
  SCB->SCR |= SCB_SCR_SLEEPDEEP_Msk;         //请问大家这个操作的是什么寄存器？我看SCB这个结构体定义在core_cm4.h   

  /* This option is used to ensure that store operations are completed */
#if defined ( __CC_ARM   )
  __force_stores();
#endif
  /* Request Wait For Interrupt */
  __WFI();
}