STM32CubeF0

/**
  @page RCC_ClockConfig RCC Clock Config example
  
  @verbatim
  ******************** (C) COPYRIGHT 2016 STMicroelectronics *******************
  * @file    RCC/RCC_ClockConfig/readme.txt 
  * @author  MCD Application Team
  * @brief   Description of the RCC Clock Config example.
  ******************************************************************************
  *
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  * are permitted provided that the following conditions are met:
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  *      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
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  * 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 

Configuration of the system clock (SYSCLK) and modification of the clock settings in Run mode, using the RCC HAL API. 

In this example, after startup SYSCLK is configured to the max frequency using the PLL with
HSE as clock source, the User push-button (connected to EXTI_Line0) will be 
used to change the PLL source: 
- from HSI to HSE
- from HSE to HSI

Each time the User push-button is pressed; EXTI_Line0 interrupt is generated and in the ISR
the PLL oscillator source is checked using __HAL_RCC_GET_PLL_OSCSOURCE() macro:

- If the HSE oscillator is selected as PLL source, the following steps will be followed to switch 
   the PLL source to HSI oscillator:
     a- Switch the system clock source to HSE to allow modification of the PLL configuration
     b- Enable HSI Oscillator, select it as PLL source and finally activate the PLL
     c- Select the PLL as system clock source and configure the HCLK and PCLK1 clocks dividers
     d- Disable the HSE oscillator (optional, if the HSE is no more needed by the application)


- If the HSI oscillator is selected as PLL source, the following steps will be followed to switch 
   the PLL source to HSE oscillator:
     a- Switch the system clock source to HSI to allow modification of the PLL configuration
     b- Enable HSE Oscillator, select it as PLL source and finally activate the PLL
     c- Select the PLL as system clock source and configure the HCLK and PCLK1 clocks dividers
     d- Disable the HSI oscillator (optional, if the HSI is no more needed by the application)

In this example the SYSCLK  is outputted on the MCO1 pin(PA.08).

LED3 is toggled with a timing defined by the HAL_Delay() API.

@note Care must be taken when using HAL_Delay(), this function provides accurate delay (in milliseconds)
      based on variable incremented in SysTick ISR. This implies that if HAL_Delay() is called from
      a peripheral ISR process, then the SysTick interrupt must have higher priority (numerically lower)
      than the peripheral interrupt. Otherwise the caller ISR process will be blocked.
      To change the SysTick interrupt priority you have to use HAL_NVIC_SetPriority() function.
      
@note The application need to ensure that the SysTick time base is always set to 1 millisecond
      to have correct HAL operation.

@par Directory contents 

  - RCC/RCC_ClockConfig/Inc/stm32f0xx_hal_conf.h    HAL configuration file
  - RCC/RCC_ClockConfig/Inc/stm32f0xx_it.h          Interrupt handlers header file
  - RCC/RCC_ClockConfig/Inc/main.h                  Header for main.c module  
  - RCC/RCC_ClockConfig/Src/stm32f0xx_it.c          Interrupt handlers
  - RCC/RCC_ClockConfig/Src/main.c                  Main program
  - RCC/RCC_ClockConfig/Src/system_stm32f0xx.c      STM32F0xx system source file

@par Hardware and Software environment

  - This example runs on STM32F030x8 devices.
    
  - This example has been tested with STM32F0308-Discovery RevA 
    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>
 */