Pi Pico C SDK example of reading IR codes from a 'standard' 44 key IR LED remote.

led_ir_example.c

#include "pico/stdlib.h"
#include "hardware/gpio.h"
#include "hardware/timer.h"
#include "stdio.h"
#include "pico/util/queue.h"

#define IR_PIN 16
#define BRIGHTNESS_UP 0x3A
#define BRIGHTNESS_DN 0xBA
#define PLAY 0x82
#define POWER 0x02
#define RED1 0x1A
#define GREEN1 0x9A
#define BLUE1 0xA2
#define WHITE1 0x22
#define RED2 0x2A
#define GREEN2 0xAA
#define BLUE2 0x92
#define WHITE2 0x12
#define RED3 0x0A
#define GREEN3 0x8A
#define BLUE3 0xB2
#define WHITE3 0x32
#define RED4 0x38
#define GREEN4 0xB8
#define BLUE4 0x78
#define WHITE4 0xF8
#define RED5 0x18
#define GREEN5 0x98
#define BLUE5 0x58
#define WHITE5 0xD8
#define RED_UP 0x28
#define GREEN_UP 0xA8
#define BLUE_UP 0x68
#define QUICK 0xE8
#define RED_DN 0x08
#define GREEN_DN 0x88
#define BLUE_DN 0x48
#define SLOW 0xC8
#define DIY1 0x30
#define DIY2 0xB0
#define DIY3 0x70
#define AUTO 0xF0
#define DIY4 0x10
#define DIY5 0x90
#define DIY6 0x50
#define FLASH 0xD0
#define JUMP3 0x20
#define JUMP7 0xA0
#define FADE3 0x60
#define FADE7 0xE0
volatile uint32_t ir_data = 0;
volatile int bit_index = 0;

volatile absolute_time_t last_fall_time;
queue_t ir_queue;

void gpio_callback(uint gpio, uint32_t events)
{
    if (gpio != IR_PIN || !(events & GPIO_IRQ_EDGE_FALL))
    {
        return;
    }

    absolute_time_t now = get_absolute_time();
    int64_t dt = absolute_time_diff_us(last_fall_time, now);
    last_fall_time = now;

    // The remote sends an 'attention' or frame reset which is a long pulse, which is ~9ms, then a short pulse of ~4.5ms,
    // which adds up to ~13ms between falling edges. So here we just filter for something in about the right range. This signals
    // that we are starting a new frame, and we need to reset the bit index and clear the ir_data.
    if (dt > 10000 && dt < 20000)
    {
        bit_index = 31;
        ir_data = 0;
    }
    else if (bit_index >= 0)
    {
        // Each bit: pulse ~562us, then space, which is either ~562us or ~1690us, so a
        // low to low spaces is 1124us for a 0, or 2252us for a 1 see: https://www.vishay.com/docs/80071/dataform.pdf (page 2)
        // So if dt is > 1700us, it's a 1, otherwise it's a 0 (1700 is roughtly half way between and a nice round number)
        if (dt > 1700)
        {
            // Long space → "1" bit
            ir_data |= (1UL << bit_index);
        }
        else
        {
            // Short space → "0" bit (already zeroed)
        }
        bit_index--;

        if (bit_index == -1)
        {
            // We've gotten all 32 bits, they are in the format 0xAABBCCDD, where AA is the address which is always
            // 0x00, BB is the inverse of AA, CC is the command, and DD is the inverse of CC.
            // So for example, POWER is 0x00FF02FD. We verify that 0xFF == ~0x00 and 0x02 == ~0xFD, and then we can just take the
            // command byte (0x02) and send it to the queue.
            // Technically we could just verify that the address is 0x00 and the inverst is 0xFF, but who knows, maybes
            // some day somebody will use the address bits.
            uint8_t *data = (uint8_t *)&ir_data;
            // check to make sure that the first two bytes equal the second two bytes inverted
            if (data[2] == (uint8_t)~data[3] && data[1] == (uint8_t)~data[0])
            {
                uint8_t code = data[1];
                queue_try_add(&ir_queue, &code);
            }
        }
    }
}

int main()
{
    stdio_init_all();
    gpio_init(IR_PIN);
    gpio_set_dir(IR_PIN, GPIO_IN);
    gpio_pull_up(IR_PIN);

    gpio_set_irq_enabled_with_callback(IR_PIN, GPIO_IRQ_EDGE_FALL, true, &gpio_callback);
    queue_init(&ir_queue, sizeof(uint8_t), 10);

    uint8_t received_code;
    while (1)
    {
        while (queue_try_remove(&ir_queue, &received_code))
        {
            switch (received_code)
            {
            case BRIGHTNESS_UP:
                printf("Brightness Up\n");
                break;
            case BRIGHTNESS_DN:
                printf("Brightness Down\n");
                break;
            case PLAY:
                printf("Play\n");
                break;
            case POWER:
                printf("Power\n");
                break;
            case RED1:
                printf("Red 1\n");
                break;
            case GREEN1:
                printf("Green 1\n");
                break;
            case BLUE1:
                printf("Blue 1\n");
                break;
            case WHITE1:
                printf("White 1\n");
                break;

            case RED2:
                printf("Red 2\n");
                break;
            case GREEN2:
                printf("Green 2\n");
                break;
            case BLUE2:
                printf("Blue 2\n");
                break;
            case WHITE2:
                printf("White 2\n");
                break;
            case RED3:
                printf("Red 3\n");
                break;
            case GREEN3:
                printf("Green 3\n");
                break;
            case BLUE3:
                printf("Blue 3\n");
                break;
            case WHITE3:
                printf("White 3\n");
                break;
            case RED4:
                printf("Red 4\n");
                break;
            case GREEN4:
                printf("Green 4\n");
                break;
            case BLUE4:
                printf("Blue 4\n");
                break;
            case WHITE4:
                printf("White 4\n");
                break;
            case RED5:
                printf("Red 5\n");
                break;
            case GREEN5:
                printf("Green 5\n");
                break;
            case BLUE5:
                printf("Blue 5\n");
                break;
            case WHITE5:
                printf("White 5\n");
                break;
            case RED_UP:
                printf("Red Up\n");
                break;
            case GREEN_UP:
                printf("Green Up\n");
                break;
            case BLUE_UP:

                printf("Blue Up\n");
                break;
            case QUICK:
                printf("Quick\n");
                break;
            case RED_DN:
                printf("Red Down\n");
                break;
            case GREEN_DN:
                printf("Green Down\n");
                break;
            case BLUE_DN:
                printf("Blue Down\n");
                break;
            case SLOW:
                printf("Slow\n");
                break;
            case DIY1:
                printf("DIY 1\n");
                break;
            case DIY2:
                printf("DIY 2\n");
                break;
            case DIY3:
                printf("DIY 3\n");
                break;
            case AUTO:
                printf("Auto\n");
                break;
            case DIY4:
                printf("DIY 4\n");
                break;
            case DIY5:
                printf("DIY 5\n");
                break;
            case DIY6:
                printf("DIY 6\n");
                break;
            case FLASH:
                printf("Flash\n");
                break;
            case JUMP3:
                printf("Jump 3\n");
                break;
            case JUMP7:
                printf("Jump 7\n");
                break;
            case FADE3:
                printf("Fade 3\n");
                break;
            case FADE7:
                printf("Fade 7\n");
                break;

            default:
                break;
            }
        }
    }
}