Initialization and de-initialization functions
[RTC Exported Functions]

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              ##### Initialization and de-initialization functions #####
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   [..] This section provide functions allowing to initialize and configure the 
         RTC Prescaler (Synchronous and Asynchronous), RTC Hour format, disable 
         RTC registers Write protection, enter and exit the RTC initialization mode,
         RTC registers synchronization check and reference clock detection enable.
         (#) The RTC Prescaler is programmed to generate the RTC 1Hz time base.
             It is split into 2 programmable prescalers to minimize power consumption.
             (++) A 7-bit asynchronous prescaler and a 15-bit synchronous prescaler.
             (++) When both prescalers are used, it is recommended to configure the 
                 asynchronous prescaler to a high value to minimize power consumption.
         (#) All RTC registers are Write protected. Writing to the RTC registers
             is enabled by writing a key into the Write Protection register, RTC_WPR.
         (#) To configure the RTC Calendar, user application should enter 
             initialization mode. In this mode, the calendar counter is stopped
             and its value can be updated. When the initialization sequence is 
             complete, the calendar restarts counting after 4 RTCCLK cycles.
         (#) 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. The HAL_RTC_WaitForSynchro() function 
             implements the above software sequence (RSF clear and RSF check).