Extended Clock Recovery System Control functions
[RCCEx Exported Functions]

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                ##### Extended Clock Recovery System Control functions  #####
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    [..]
      For devices with Clock Recovery System feature (CRS), RCC Extention HAL driver can be used as follows:

      (#) In System clock config, HSI48 needs to be enabled

      (#) Enable CRS clock in IP MSP init which will use CRS functions

      (#) Call CRS functions as follows:
          (##) Prepare synchronization configuration necessary for HSI48 calibration
              (+++) Default values can be set for frequency Error Measurement (reload and error limit)
                        and also HSI48 oscillator smooth trimming.
              (+++) Macro __HAL_RCC_CRS_RELOADVALUE_CALCULATE can be also used to calculate 
                        directly reload value with target and sychronization frequencies values
          (##) Call function HAL_RCCEx_CRSConfig which
              (+++) Resets CRS registers to their default values.
              (+++) Configures CRS registers with synchronization configuration 
              (+++) Enables automatic calibration and frequency error counter feature
           Note: When using USB LPM (Link Power Management) and the device is in Sleep mode, the
           periodic USB SOF will not be generated by the host. No SYNC signal will therefore be
           provided to the CRS to calibrate the HSI48 on the run. To guarantee the required clock
           precision after waking up from Sleep mode, the LSE or reference clock on the GPIOs
           should be used as SYNC signal.

          (##) A polling function is provided to wait for complete synchronization
              (+++) Call function HAL_RCCEx_CRSWaitSynchronization()
              (+++) According to CRS status, user can decide to adjust again the calibration or continue
                        application if synchronization is OK
              
      (#) User can retrieve information related to synchronization in calling function
            HAL_RCCEx_CRSGetSynchronizationInfo()

      (#) Regarding synchronization status and synchronization information, user can try a new calibration
           in changing synchronization configuration and call again HAL_RCCEx_CRSConfig.
           Note: When the SYNC event is detected during the downcounting phase (before reaching the zero value), 
           it means that the actual frequency is lower than the target (and so, that the TRIM value should be 
           incremented), while when it is detected during the upcounting phase it means that the actual frequency 
           is higher (and that the TRIM value should be decremented).

      (#) In interrupt mode, user can resort to the available macros (__HAL_RCC_CRS_XXX_IT). Interrupts will go 
          through CRS Handler (CRS_IRQn/CRS_IRQHandler)
              (++) Call function HAL_RCCEx_CRSConfig()
              (++) Enable CRS_IRQn (thanks to NVIC functions)
              (++) Enable CRS interrupt (__HAL_RCC_CRS_ENABLE_IT)
              (++) Implement CRS status management in the following user callbacks called from 
                   HAL_RCCEx_CRS_IRQHandler():
                   (+++) HAL_RCCEx_CRS_SyncOkCallback()
                   (+++) HAL_RCCEx_CRS_SyncWarnCallback()
                   (+++) HAL_RCCEx_CRS_ExpectedSyncCallback()
                   (+++) HAL_RCCEx_CRS_ErrorCallback()

      (#) To force a SYNC EVENT, user can use the function HAL_RCCEx_CRSSoftwareSynchronizationGenerate().
          This function can be called before calling HAL_RCCEx_CRSConfig (for instance in Systick handler)