STM32CubeF3

@verbatim
******************** (C) COPYRIGHT 2016 STMicroelectronics *******************
* @file GPIO/GPIO_EXTI/readme.txt
* @author MCD Application Team
* @brief Description of the GPIO EXTI example.
******************************************************************************
* @attention
*
* <h2><center>&copy; Copyright (c) 2016 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 Example Description

How to configure external interrupt lines.

In this example, an EXTI line (EXTI0) when using the STM32F3-Discovery is configured
to generate an interrupt on each rising edge. In the interrupt routine leds
connected to a specific GPIO pin are toggled.

In this example:
- EXTI0 is mapped to PA0.

- when rising edge is detected on EXTI0 by pressing User button, LED3, LED6, LED7
and LED10 toggle.

On STM32F3-DK:
- EXTI0 is connected to User push-button

In this example, HCLK is configured at 72 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 Directory contents

- GPIO/GPIO_EXTI/Inc/stm32f3xx_hal_conf.h HAL configuration file
- GPIO/GPIO_EXTI/Inc/stm32f3xx_it.h Interrupt handlers header file
- GPIO/GPIO_EXTI/Inc/main.h Header for main.c module
- GPIO/GPIO_EXTI/Src/stm32f3xx_it.c Interrupt handlers
- GPIO/GPIO_EXTI/Src/main.c Main program
- GPIO/GPIO_EXTI/Src/system_stm32f3xx.c STM32F3xx system source file

@par Hardware and Software environment

- This example runs on STM32F303xC devices.

- This example has been tested with STM32F3-DK Rev x 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