调用接口system_sleep_enable(); 使能休眠后，休眠不停地在进入退出，进入退出；进入休眠前打印s;退出休眠打印w；看到不停地在打印swsw

NVIC_SystemReset();
头文件：core_cm3.h
/**
\brief System Reset
\details Initiates a system reset request to reset the MCU.
/
__STATIC_INLINE void NVIC_SystemReset(void)
{
__DSB(); / Ensure all outstanding memory accesses included
buffered write are completed before reset /
SCB->AIRCR = (uint32_t)((0x5FAUL << SCB_AIRCR_VECTKEY_Pos) |
(SCB->AIRCR & SCB_AIRCR_PRIGROUP_Msk) |
SCB_AIRCR_SYSRESETREQ_Msk ); / Keep priority group unchanged /
__DSB(); / Ensure completion of memory access */

for(;;)                                                           /* wait until reset */
{
    __NOP();
}

}