Getting started with EXTI

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This article explains the EXTI and its use, with examples.

1. External interrupt/event controller (EXTI)

The external interrupt/event controller consists of up to 23 edge detectors for generating event/interrupt requests. Each input line can be independently configured to select the type (interrupt or event) and the corresponding trigger event (rising, falling, or both).

2. Configure EXTI to turn on an LED when a user button is pressed

2.1. Objective

Configure the GPIO that is connected to the user Button as External Interrupt (EXTI) with falling edge trigger.
Learn how to configure the Interrupt Controller : the NVIC

2.2. How

Configure a GPIO and EXTI pin in STM32CubeIDE and generate code.
Add into a project: a callback function, and a function to turn on an LED.
Verify the correct functionality by pressing a button that turns on an LED.

2.3. Create project in STM32CubeIDE

File > New > STM32 Project in main panel.
Select NUCLEO-L476RG in board Selector.

File:GPIO3 EXTI.png

Configure an LED pin as GPIO_Output (PA5 on NucleoFL476RG). For other boards check their user manual.

File:LedPinGPIO1.png File:LED UM GPIO1.png

Configure a button pin as GPIO_EXTIX (PC13 on NucleoL467RG). For other boards check their user manual.

File:PC13.png

GPIO configuration check

File:Pc13 Config.png

Enable the interrupt for EXTI

The easiest way the generate the code is save your current project : Ctrl + S

The code is generated so you can see it in the left side of the screen in the project explorer
File:GPIO10.png

2.4. HAL Library workflow summary

File:EXTI HAL flowchart.png

2.5. Code the Interrupt

Create a function to handle the EXTI interrupts:

HAL callback function for EXTI: void HAL_GPIO_EXTI_Callback(uint16_t GPIO_Pin)
To turn an LED on we need to use the function: HAL_GPIO_WritePin

Put the functions into main.c

Information

Between /* USER CODE BEGIN 4 */ and /* USER CODE END 4 */ tags

/* USER CODE BEGIN 4 */
void HAL_GPIO_EXTI_Callback(uint16_t GPIO_Pin)
{
  if(GPIO_Pin == GPIO_PIN_0) {
    HAL_GPIO_WritePin(GPIOG, GPIO_PIN_14, GPIO_PIN_SET);
  } else {
      __NOP();
  }
}
/* USER CODE END 4 */

2.6. Compile and Flash

First of all, build your project File:GPIO14.png
Then debug it File:GPIO15.png
Finally, run it File:GPIO16.png

When you press the blue button on your board the LED must switch on.