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_F746.c
|14:78e453d7bb85||2016-07-02||Added F746xx and modified main.c||File Diff Annotate|