/**
  @page GPIO_EXTI GPIO EXTI example started by Linux Remote Processor Framework

  @verbatim
  ******************** (C) COPYRIGHT 2019 STMicroelectronics *******************
  * @file    GPIO/GPIO_EXTI/Remoteproc/README
  * @author  MCD Application Team
  * @brief   How to run example using Linux Remote Processor Framework
  ******************************************************************************
  * @attention
  *
  * <h2><center>&copy; Copyright (c) 2019 STMicroelectronics.
  * All rights reserved.</center></h2>
  *
  * This software component is licensed by ST under BSD 3-Clause license,
  * the "License"; You may not use this file except in compliance with the
  * License. You may obtain a copy of the License at:
  *                        opensource.org/licenses/BSD-3-Clause
  *
  ******************************************************************************
  @endverbatim

@par Description of M4 Cube example with Linux Remote Processor Framework

When Cube firmware is running on Cortex-M4, System Clock tree and regulators(vrefbuf) are configured by Cortex-A7
Besides, clock source for each peripheral assigned to Cortex-M4 is done by Cortex-A7.


@par How to use it ?

In order to make the program work with Linux running on Cortex-A7, you must do the following :
Before running M4 Cube example, you have to
1) interrupt uboot
2) choose the right configuration to make sure that M4 resources are assigned to Linux Resource Manager driver

Then,
 - Start example using the following command: "fw_cortex_m4.sh start" under example directory installed in userfs partition
     * it will load and start firmware using Linux Remote Processor
 - Stop example using the following command: "fw_cortex_m4.sh stop" under example directory installed in userfs partition
     * it will stop firmware using Linux Remote Processor

@par Example Description
How to configure external interrupt lines.

In this example, one EXTI line (EXTI14) is configured to generate
an interrupt on each falling edge.
In the interrupt routine a led connected to a specific GPIO pin is toggled.

In this example:
    - EXTI14 is connected to PA.14 pin
    - GPIO is connected to PA.13 pin

On STM32MP15x-phyBOARD-Sargas:
    - EXTI14 is connected to USER "S5" push-button
      - when falling edge is detected on EXTI14 by pressing USER "S5" push-button, LED2 (Red LED) toggles once

The System clock source is configured by the SystemClock_Config() function in case of Engineering Mode, this clock configuration is done
by the Firmware running on the Cortex-A7 in case of Production Mode.

@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 example needs to ensure that the SysTick time base is always set to 1 millisecond
      to have correct HAL operation.

@par Keywords

System, GPIO, EXTI, Output, Alternate function, Push-pull, Toggle

@par Directory contents 

  - GPIO/GPIO_EXTI/Inc/stm32mp1xx_hal_conf.h    HAL configuration file
  - GPIO/GPIO_EXTI/Inc/stm32mp1xx_it.h          Interrupt handlers header file
  - GPIO/GPIO_EXTI/Inc/main.h                  Header for main.c module  
  - GPIO/GPIO_EXTI/Src/stm32mp1xx_it.c          Interrupt handlers
  - GPIO/GPIO_EXTI/Src/stm32mp1xx_hal_msp.c     HAL MSP file
  - GPIO/GPIO_EXTI/Src/main.c                  Main program
  - GPIO/GPIO_EXTI/Src/system_stm32mp1xx.c      STM32MP1xx system source file

@par Hardware and Software environment

  - This example runs on STM32MP157CACx devices.
    
  - This example has been tested with phyBOARD-Sargas 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>
 */
