Getting started with EXTI

This message will disappear after all relevant tasks have been resolved.

Semantic MediaWiki

There are 1 incomplete or pending task to finish installation of Semantic MediaWiki. An administrator or user with sufficient rights can complete it. This should be done before adding new data to avoid inconsistencies.

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

1. What is an external interrupt/event controller (EXTI)

The external interrupt/event controller consists of up to 40 edge detectors for generating event/interrupt requests, for (STM32L47x/L48x devices),. 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

Learn how to use the external interrupt and turn ON a LED when user button is pressed.

Configure the GPIO that is connected to the user Button as External Interrupt (EXTI) with falling edge trigger using STM32CubeIDE
Learn how to configure the Interrupt Controller : the NVIC
Verify the correct functionality by pressing a button that turns on an LED

2.2. Create the project in STM32CubeIDE

File > New > STM32 Project in main panel.

In this example the NUCLEO-L476RG board is used.

Select NUCLEO-L476RG in board Selector.

Configure the 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 File:Blue button PC13.png

GPIO configuration check

Information

Make sure to select 'External interrupt mode with Falling edge trigger detection as GPIO Mode!

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:EXTTI project.png

2.3. HAL Library workflow summary

The HAL library provides a high-level access to STM32 peripherals like the EXTI.
The HAL_EXTI0_IRQHandler and EXTI0_IRQHandler are inside stm32l4xx_it.c file.
You must define the Callback function in the main.c : HAL_GPIO_EXTI_Callback.
.

File:EXTI HAL flowchart.png

2.4. Configure 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

Insert your code 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(GPIOA, GPIO_PIN_5, GPIO_PIN_SET);
  } else {
      __NOP();
  }
}
/* USER CODE END 4 */

2.5. Compile and flash

Click on Build button
Click on Debug button (to run step by step)
Or on Run button (to execute)

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