rtc_sleep_start() function

Enter deep or light sleep mode This function enters the sleep mode previously configured using rtc_sleep_init function. Before entering sleep, software should configure wake up sources appropriately (set up GPIO wakeup registers, timer wakeup registers, and so on). If deep sleep mode was configured using rtc_sleep_init, and sleep is not rejected by hardware (based on reject_opt flags), this function never returns. When the chip wakes up from deep sleep, CPU is reset and execution starts from ROM bootloader. If light sleep mode was configured using rtc_sleep_init, this function returns on wakeup, or if sleep is rejected by hardware.