LL_RTC_WaitForSynchro() function

The RTC Resynchronization mode is write protected, use the LL_RTC_DisableWriteProtection before calling this function. To read the calendar through the shadow registers after calendar initialization, calendar update or after wakeup from low power modes the software must first clear the RSF flag. The software must then wait until it is set again before reading the calendar, which means that the calendar registers have been correctly copied into the RTC_TR and RTC_DR shadow registers.