RTC does not survive power cycle

[LaurentLouf]

Description

• Target STM32F103RCT6
• GNU ARM 7-2017-q4-major
• mbed-cli 1.7.3
• 603c4f9 (HEAD -> master) Merge pull request littlefs: Fixed issue with cleanup in mount function on error #7851 from geky/fix-littlefs-mount-cleanup

Steps to reproduce are pretty easy :

1. Read time and display it
2. Set time using the set_time function
3. Read time and display it
4. Power cycle the target

On my target, it gives me the following output :

[V] ******* Welcome ! ********
[V] Entering state BOOT
[V] Current time before RTC set : 56997
[V] Current time after RTC set : 1541173796
[V] Exiting previous state
[V] ******* Welcome ! ********
[V] Entering state BOOT
[V] Current time before RTC set : 56997
[V] Current time after RTC set : 1541173796

I have checked the electrical part and everything seems correct : the Vbat pin has a tension around 3V and oscillators are in place. I have been googling and found that it seems to be a known issue. Someone has even created a patch for it here https://os.mbed.com/users/maxxir/code/Nucleo_F103RB_RTC_battery_bkup_pwr_off_o/ but based on pretty old version of mbed (around 1 year ago). I have taken a look at the code and try to figure out what are the important differences between this version and the one in mbed-os repository, but so far haven't found anything. Biggest difference found so far is direct manipulation of registers, but IMHO, that does not seem to be the problem since I can write and read time without problem, it just doesn't survive a power cycle. Any thoughts ?

Issue request type

[ ] Question
[ ] Enhancement
[X] Bug

[LaurentLouf]

Well, from the mbed-os-5.10.2 release notes, it may seem that all I have to do is to update my version of mbed-os. Will test that immediately and close issue if it solves the problem.

[LaurentLouf]

Fixed the issue.