STM32CubeF4

@verbatim
******************** (C) COPYRIGHT 2017 STMicroelectronics *******************
* @file GPIO/GPIO_EXTI/readme.txt
* @author MCD Application Team
* @brief Description of the GPIO EXTI example.
******************************************************************************
*
* Copyright (c) 2017 STMicroelectronics. All rights reserved.
*
* 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 Example Description

How to configure external interrupt lines.

In this example, one EXTI line (EXTI0) 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:
- EXTI0 is connected to PA.00 pin
- when falling edge is detected on EXTI0 by pressing Joystick sel-button, LED1 toggles once

On STM32412G-DISCOVERY:
- EXTI0 is connected to Joystick sel-button

In this example, HCLK is configured at 100 MHz.

@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 Keywords

System, GPIO, Output, Alternate function, EXTI, Toggle

@par Directory contents

- GPIO/GPIO_EXTI/Inc/stm32f4xx_hal_conf.h HAL configuration file
- GPIO/GPIO_EXTI/Inc/stm32f4xx_it.h Interrupt handlers header file
- GPIO/GPIO_EXTI/Inc/main.h Header for main.c module
- GPIO/GPIO_EXTI/Src/stm32f4xx_it.c Interrupt handlers
- GPIO/GPIO_EXTI/Src/main.c Main program
- GPIO/GPIO_EXTI/Src/system_stm32f4xx.c STM32F4xx system source file

@par Hardware and Software environment

- This example runs on STM32F412xx devices.

- This example has been tested with STM32412G-DISCOVERY 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