This is a RTC additional function. This is only for Nucleo F401RE & F411RE mbed(Added L152RE, F334R8, L476RG & F746xx). If you connected battery backup circuit for internal RTC, you can make a power-off and reset condition. RTC still has proper time and date.
Please refer following NOTE information.
Revisions of rtc_api_L476.c
|13:44e5327acb05||2016-05-27||Added L476RG mbed.Changed SetRTC and rtc_api.c for F401RE & F411RE, F334R8 based on latest mbed-dev revision (141).||File Diff Annotate|