STM32CubeF0

@verbatim
******************** (C) COPYRIGHT 2016 STMicroelectronics *******************
* @file RCC/RCC_CRS_Synchronization_Polling/readme.txt
* @author MCD Application Team
* @brief Description of the RCC Clock Recovery Service example.
******************************************************************************
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@endverbatim

@par Example Description

Configuration of the clock recovery service (CRS) in Polling mode, using the RCC HAL API.

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 48 MHz.

Then, HSI48 and LSE oscillators are enabled. In this example CRS will use LSE
oscillator 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.
- LED3 power on means that a timeout occurred during polling procedure. It may
due to an issue with LSE synchronization frequency.
- LED1 will finally power on if SYNC OK is returned by CRS.

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

@par Directory contents

- RCC/RCC_CRS_Synchonization_Polling/Inc/stm32f0xx_hal_conf.h HAL configuration file
- RCC/RCC_CRS_Synchonization_Polling/Inc/stm32f0xx_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/stm32f0xx_it.c Interrupt handlers
- RCC/RCC_CRS_Synchonization_Polling/Src/main.c Main program
- RCC/RCC_CRS_Synchonization_Polling/Src/system_stm32f0xx.c STM32F0xx system source file

@par Hardware and Software environment

- This example runs on STM32F042x6, STM32F071xB, STM32F072xB, STM32F078xB and STM32F091xC Devices.

- This example has been tested with STM32072B-EVAL 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