/**
  @page RCC_CRS_Synchonization_Polling RCC Clock Recovery Service example
  
  @verbatim
  ******************** (C) COPYRIGHT 2014 STMicroelectronics *******************
  * @file    RCC/RCC_CRS_Synchonization_Polling/readme.txt 
  * @author  MCD Application Team
  * @version V1.0.0
  * @date    18-June-2014
  * @brief   Description of the RCC Clock Recovery Service example.
  ******************************************************************************
  *
  * Redistribution and use in source and binary forms, with or without modification,
  * are permitted provided that the following conditions are met:
  *   1. Redistributions of source code must retain the above copyright notice,
  *      this list of conditions and the following disclaimer.
  *   2. Redistributions in binary form must reproduce the above copyright notice,
  *      this list of conditions and the following disclaimer in the documentation
  *      and/or other materials provided with the distribution.
  *   3. Neither the name of STMicroelectronics nor the names of its contributors
  *      may be used to endorse or promote products derived from this software
  *      without specific prior written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
  * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *
  ******************************************************************************
  @endverbatim

@par Example Description 

This example describes how to use the RCC HAL API to configure Clock Recovery Service in 
using polling mode.

At the beginning of the main program the HAL_Init() function is called to reset 
all the peripherals, initialize the Flash interface and the systick.
Then the SystemClock_Config() function is used to configure the system
clock (SYSCLK) to run at 32 MHz.

Then, HSI48 and LSE oscillators are enabled. In this example CRS will use LSE 
oscillotor to calibrate HSI48 frequency.
When HSI48 and LSE are started, automatic calibration starts and program call the
polling function to wait for synchronization status.

In this test, there are results which could occur:
 - few loops occurs up to SYNC OK event (if SYNC WARN, HSI48 trimming value will be
 automatically modified)
 - in case of SYNC MISS or SYNC ERROR, there is an issue with synchronization input
 parameters. In this case, user need to apply new parameters after checking synchronization
 information and restart the synchronization.
 - LED4 power on means that a timeout occurred during polling procedure. It may
 due to an issue with LSE synchronization frequency
 - LED3 will finally power on if SYNC OK is returned by CRS.

Note: HSI48 frequency can be checked with oscilloscope in using MCO PIN PA.08

@par Directory contents 

  - RCC/RCC_CRS_Synchonization_Polling/Inc/stm32l0xx_hal_conf.h    HAL configuration file
  - RCC/RCC_CRS_Synchonization_Polling/Inc/stm32l0xx_it.h          Interrupt handlers header file
  - RCC/RCC_CRS_Synchonization_Polling/Inc/main.h                  Header for main.c module  
  - RCC/RCC_CRS_Synchonization_Polling/Src/stm32l0xx_it.c          Interrupt handlers
  - RCC/RCC_CRS_Synchonization_Polling/Src/main.c                  Main program
  - RCC/RCC_CRS_Synchonization_Polling/Src/system_stm32l0xx.c      STM32F0xx system source file

@par Hardware and Software environment

  - This example runs on STM32L051xx, STM32L052xx, STM32L053xx STM32L062xx and 
    STM32L063xx device lines RevZ
    
  - This example has been tested with STM32L0538-DISCO RevB  board and can be
    easily tailored to any other supported device and development board.    


@par How to use it ? 

In order to make the program work, you must do the following :
 - Open your preferred toolchain 
 - Rebuild all files and load your image into target memory
 - Run the example

 * <h3><center>&copy; COPYRIGHT STMicroelectronics</center></h3>
 */
