/**
  @page RCC_UseHSI_PLLasSystemClock RCC example
  
  @verbatim
  ******************** (C) COPYRIGHT 2017 STMicroelectronics *******************
  * @file    Examples_LL/RCC/RCC_UseHSI_PLLasSystemClock/readme.txt 
  * @author  MCD Application Team
  * @brief   Description of the RCC_UseHSI_PLLasSystemClock 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 shows how to modify the PLL parameters in run time.

In this example, the toggling frequency of the green LED1 depends on the system clock 
frequency and, each time the user-button is pressed, the PLL switches between two configurations.
This make the LED1 blinking speed to highlight the system clock frequency changes.

In this example, after start-up, SYSCLK is configured to the max frequency using the PLL with
HSE as clock source.
Then, at user-button press, an automatic switch is done between PLL with HSI as clock source (SYSCLK
set to 40MHz) and PLL with HSI as clock source (SYSCLK set to 120MHz). 
LED1 will toggle differently between the 2 configurations (quick toggle with HSI configuration at 120MHz).
NUCLEO-F207ZG LED1 can be used to monitor system clock frequency changes:
- LED1 blinks quickly ( 200ms) to indicate that the system clock is set to RCC_FREQUENCY_HIGH (120 Mhz)
- LED1 blinks slowly ( 500 ms) to indicate that the system clock is set to RCC_FREQUENCY_Low (40 Mhz)

To detect a problem with PLL configuration, switch USE_TIMEOUT can be enabled. Then in case of issues, 
LED1 will toggle every 1 second.
Note: "uwFrequency" variable can be added in LiveWatch to monitor the system clock frequency.

User can monitor the different system clock configurations using an oscilloscope connected 
to pin PC9 (pin4 on CN8 connector)


@par Directory contents 

  - RCC/RCC_UseHSI_PLLasSystemClock/Inc/stm32f2xx_it.h          Interrupt handlers header file
  - RCC/RCC_UseHSI_PLLasSystemClock/Inc/main.h                  Header for main.c module
  - RCC/RCC_UseHSI_PLLasSystemClock/Inc/stm32_assert.h          Template file to include assert_failed function
  - RCC/RCC_UseHSI_PLLasSystemClock/Src/stm32f2xx_it.c          Interrupt handlers
  - RCC/RCC_UseHSI_PLLasSystemClock/Src/main.c                  Main program
  - RCC/RCC_UseHSI_PLLasSystemClock/Src/system_stm32f2xx.c      STM32F2xx system source file


@par Hardware and Software environment

  - This example runs on STM32F207xx devices.
    
  - This example has been tested with NUCLEO-F207ZG 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>
 */
