STM32CubeF4/Projects/STM32F411RE-Nucleo/Examples_LL/RCC/RCC_UseHSEasSystemClock

/**
  @page RCC_UseHSEasSystemClock RCC Clock Config example
  
  @verbatim
  ******************** (C) COPYRIGHT 2017 STMicroelectronics *******************
  * @file    Examples_LL/RCC/RCC_UseHSEasSystemClock/readme.txt 
  * @author  MCD Application Team
  * @brief   Description of the RCC HSE start example.
  ******************************************************************************
  * @attention
  *
  * Copyright (c) 2017 STMicroelectronics.
  * All rights reserved.
  *
  * This software is licensed under terms that can be found in the LICENSE file
  * in the root directory of this software component.
  * If no LICENSE file comes with this software, it is provided AS-IS.
  *
  ******************************************************************************
   @endverbatim

@par Example Description 
This example describes how to use the RCC LL API how to start the HSE 
and use it as system clock.

At start-up, HSI clock is used as system clock (default clock after reset) and then Systick is 
configured at 1 ms using HSI_VALUE define.

Then, HSE is started and we wait for ready state. System clock is set to HSE thanks to IT 
triggered by HSE ready.
- LED2 is turned ON to indicate that HSE is ready.
- LED2 is toggled with a timing of 1 second in case of error to switch SYSCLK to HSE or if HSE CSS
failure is detected (through NMI IT).

 @note In HSE bypass mode, input clock will come from the MCO from
       ST_LINK MCU. This frequency cannot be changed, and it is fixed
       at 8 MHz. To use MCO from ST_LINK you need to check the Board
       User Manual to know how to connect the MCO pin to the STM32 device.

@par Keywords

System, RCC, PLL, PLLCLK, SYSCLK, HSE, Clock, Oscillator, HSI

@par Directory contents 

  - RCC/RCC_UseHSEasSystemClock/Inc/stm32f4xx_it.h          Interrupt handlers header file
  - RCC/RCC_UseHSEasSystemClock/Inc/main.h                  Header for main.c module
  - RCC/RCC_UseHSEasSystemClock/Inc/stm32_assert.h          Template file to include assert_failed function
  - RCC/RCC_UseHSEasSystemClock/Src/stm32f4xx_it.c          Interrupt handlers
  - RCC/RCC_UseHSEasSystemClock/Src/main.c                  Main program
  - RCC/RCC_UseHSEasSystemClock/Src/system_stm32f4xx.c      STM32F4xx system source file

@par Hardware and Software environment

  - This example runs on STM32F411xE devices.
    
  - This example has been tested with NUCLEO-F411RE 
    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


 */