Rapsberry pi pico GPIO IRQ function for push button not working as expected

Question

I added a button to GPIO 4(board pin 6) in my pico board. GPIO pin is normally pulled up and button press will bring it to ground. I want to add a simple debounce logic to the button press in the IRQ callback function.

This is what I have so far (modified form the LED blinking sample project)

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

const uint LED_PIN = 25;

// #define PUSH_BUTTON_01  4
const uint PUSH_BUTTON_01 = 4;
int led_state = 0;

void button_debounce_01(){
    // debounce button and check if the button went from high to low and is staying low
    // 20 ms delay for H to L edge debounce
    bool push_btn_1_state;
    printf("button_debounce_01() entered\n");
    // sleep_ms(1);
    sleep_us(500);
    printf("sleep_ms() ended\n");
    if( gpio_get(PUSH_BUTTON_01) == 0){
        // debounce succesful, button press detected
        printf("01\n");
        if(led_state == 0){
          led_state = 1;
        } else{
          led_state = 0;
        }
    }
    else {
        printf("02\n");
        return;     // button press NOT detected
    }
    printf("03\n");
}

int main() {

  bi_decl(bi_program_description("This is a test binary."));
  bi_decl(bi_1pin_with_name(LED_PIN, "On-board LED"));

  stdio_init_all();

  while (!tud_cdc_connected()) {
      tight_loop_contents();
  }

  printf("hello button debounce test\n");

  gpio_init(LED_PIN);
  gpio_set_dir(LED_PIN, GPIO_OUT);

  gpio_init(PUSH_BUTTON_01);
  gpio_set_dir(PUSH_BUTTON_01, GPIO_IN);
  gpio_pull_up(PUSH_BUTTON_01);
  gpio_set_irq_enabled_with_callback(PUSH_BUTTON_01, GPIO_IRQ_EDGE_FALL , true, &button_debounce_01);

#if 0
  while (1) {
    gpio_put(LED_PIN, 0);
    sleep_ms(250);
    gpio_put(LED_PIN, 1);
    puts("Hello World\n");
    sleep_ms(1000);
  }
#endif

  while(1){
    gpio_put(LED_PIN, led_state);
  }
}

The program will only start running after I open a terminal program in PC (I am using Putty) and I am using the pico board's USB serial port. When I run the program and press the button I get the following output on serial terminal

hello button debounce test
button_debounce_01() entered  

Looks like the program doesn't go past the sleep_us(500); line in the IRQ function.

Am I doing something wrong? Is there a simple button debounce routine in one of the official examples?

Answer 1

There should be minimal processing in any interrupt service routine. Set a flag and exit is best.

Any system call is likely to screw the system. Don't sleep, don't call printf.

Debounce is not trivial.

See picod debounce