In standby mode, the system can go into ultra-low-power mode, consuming only a few microamperes, while waiting to be reinitialized by an external event. Entering standby mode requires you to set the flag SCB_SCR_PDDS prior to invoking WFI or WFE. While the system is in standby, all the voltage regulators are off, with the exception of the low-speed oscillators, which are used to clock the independent watchdog timer and the real-time clock.
The procedure to enter standby mode is slightly different from the one used to enter stop mode. The SCB_SCR_PDDS flag is set to select standby mode as a deep-sleep variant. The flag SCB_SCR_LPDS is not activated in this case, because we know it has no effect in standby mode:
void enter_lowpower_mode(void) ...
