Solution how to fix broken RTC on Nucleo_F103RB / STM32F103 BluePill etc..
Fork of Nucleo_RTC_battery_bkup_pwr_off_okay by
Experimental fork https://os.mbed.com/users/kenjiArai/code/Nucleo_RTC_battery_bkup_pwr_off_okay/ to fix broken RTC on Nucleo_F103RB / STM32F103 BluePill etc..
At this moment (7/11/17) use forked mbed-dev https://os.mbed.com/users/maxxir/code/mbed-dev/.
Or require patch for ./mbed-dev/targets/TARGET_STM/rtc_api.c.
You can manual add to your project fresh mbed-dev and change file mbed-dev\targets\TARGET_STM\rtc_api.c from root project patched rtc_api.c.stm32f10x.txt.
Exploring origin errors, I saw that something wrong with HAL API on STM32F1xx with this functions:
HAL_RTC_GetTime(&RtcHandle, &timeStruct, RTC_FORMAT_BIN); HAL_RTC_GetDate(&RtcHandle, &dateStruct, RTC_FORMAT_BIN); HAL_RTC_SetDate(&RtcHandle, &dateStruct, RTC_FORMAT_BIN); HAL_RTC_SetTime(&RtcHandle, &timeStruct, RTC_FORMAT_BIN);
Look here (as I understand it possible broken on STM32CUBE HAL level now):
So I use direct RTC register manipulation for STM32F1xx:
rtc_read(), rtc_write() (native rtc_init() - works good).
Also added stub for non-working on STM32F1xx rtc_read_subseconds().
Now the stm32F103 can survive power off, and allows you to get and set the time.
Tested OK on boards:
NUCLEO STM32F103RB, DIY STM32F100CB (forked from DISCO_F100RB)