RPi2040 C Code Interrupt Example

RPi2040 C Code Interrupt Example
  • An Interrupt is just that - an interrupt of a running program to handle an event (mouse click, keyboard, video, hard drive - etc.)
  • Interrupts actually have a long history. You can read about the history of the interrupt for the PC DOS from many years  ago.
DOS API - Wikipedia

I noticed that there was literally next to no working (or scarce, and I need to google for  this all day) examples of Interrupt Handlers for the RPi2040 in terms of the C language.

  • So. write this guide and put it all together for reference purposes.

If you are looking for a basic primer of how to write a interrupt handler in Python:

Because micropython execution speeds are estimated to be about 100 - 250x slower than embedded C. Micropython is great for some tinker projects like triggering on a button - but we want to get to the raw speed of the microcontroller - so we need to work in C, but that also makes development considerably more complex until you get used to it.

Writing an Interrupt Handler in C:

  • Before you can compile C code for the RPi2040 there are some background work on setting up your Cmake / Development environment.  The  guide below will get you up and going!
Coding in C Into the RPi2040 Zone with Console Simplified
In this comprehensive guide we explain the meat and potatoes of effectively coding in C for the raspberry pi pico.

Luckily for us the authors of the Raspberry pi made the most simplest example from the github page:

pico-examples/gpio/hello_gpio_irq/hello_gpio_irq.c at master · raspberrypi/pico-examples
Contribute to raspberrypi/pico-examples development by creating an account on GitHub.

Going over the code of the main block:

#include <stdio.h>
#include "pico/stdlib.h"
#include "hardware/gpio.h"

void gpio_callback(uint gpio, uint32_t events) {
    // Put the GPIO event(s) that just happened into event_str
    // so we can print it
    gpio_event_string(event_str, events);
    printf("GPIO %d %s\n", gpio, event_str);

int main() {

    printf("Hello GPIO IRQ\n");
    gpio_set_irq_enabled_with_callback(2, GPIO_IRQ_EDGE_RISE | GPIO_IRQ_EDGE_FALL, true, &gpio_callback);

    // Wait forever
    while (1);
  • gpio_set_irq_enabled_with_callback passes it's parameters to the &gpio_callback assigned function defined above it (ok that's confusing..)
  • Explaining this again gpio_set_irq_enabled_with_callback is a function assigning the handler function when the target GPIO pin has a trigger where it goes from high-to-low or GPIO_IRQ_EDGE_FALL.

Searching the internet for the potential values that can be passed are:

  • So naturally if you have a constantly low pin and you set GPIO_IRQ_LEVEL_LOW - it is going to trip and call the interrupt handler function constantly..  Fair enough!
  • The gpio_set_irq_enabled_with_callback is defined as:
void gpio_set_irq_enabled_with_callback (uint gpio, uint32_t event_mask, bool enabled, gpio_irq_callback_t callback)

Breaking this down:

  • gpio - specify which pin will activate this IRQ.
  • event_mask  - one or more of GPIO_IRQ_LEVEL_LOW etc etc, separated by a C OR function ( | );
  • bool enabled (pass true or false)
  • gpio_irq_callback_t callback - specify the function to handle the callback.

Another example:

gpio_set_irq_enabled_with_callback(3, GPIO_IRQ_EDGE_RISE | GPIO_IRQ_EDGE_FALL, true, my_handler_function);

From page 60 of the documentation however we see the one catch/gotcha - you are allowed 1 interrupt per GPIO bank?  

Expanding from This:

It needs to be understood that there is only [one] IRQ handler for the entire bank, as discussed in this thread:


Solves this issue with the following code example:

  • Set one IRQ for one pin of one of the four monitor states that you want to monitor.
  • Add for each pin that you want to monitor with:
gpio_set_irq_enabled(1, GPIO_IRQ_EDGE_RISE | GPIO_IRQ_EDGE_FALL, true);
  • With the associate handlers:
void irqhandler1() {
    if (gpio_get_irq_event_mask(1) & GPIO_IRQ_EDGE_RISE | GPIO_IRQ_EDGE_FALL) {
        gpio_acknowledge_irq(1, GPIO_IRQ_EDGE_RISE | GPIO_IRQ_EDGE_FALL);

void irqhandler2() {
    if (gpio_get_irq_event_mask(4) & GPIO_IRQ_EDGE_RISE | GPIO_IRQ_EDGE_FALL) {
        gpio_acknowledge_irq(4, GPIO_IRQ_EDGE_RISE | GPIO_IRQ_EDGE_FALL);

In this instance if there is a GPIO_IRQ_EDGE_RISE or GPIO_IRQ_EDGE_FALL on either pin 1, or 4 it will call the respective irqhandler1(), and irqhandler2().

Compilation Errors:

  • You may reach a point where your project stops making the elf2uf2 file!  
  • Inside your pico-sdk/elf2uf2 folder is a small converter/ compiler application:
  • You can copy this as a standalone to your working directory to convert your elf to uf2 binaries that the RPi2040 can work with!
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