Simple parallel out with RP2040 PIO

parallel_pio.c

#include <stdio.h>

#include "hardware/clocks.h"
#include "hardware/pio.h"
#include "hardware/timer.h"
#include "main.pio.h"
#include "pico/stdlib.h"

#define START_PIN 10
#define ROW_PINS 4

// PIO program is a simple pull and shift out
// simply copy & paste the following into main.pio file
// .program main
//     pull
//     out pins, 4

void main_program_init(PIO pio, uint sm, uint offset, uint pin) {
    // Initialize ROW_PINS amount of pins, starting from function input value pin
    for(int i = 0; i < ROW_PINS; i++) {
        pio_gpio_init(pio, pin + i);
    }
    pio_sm_set_consecutive_pindirs(pio, sm, pin, ROW_PINS, true);
    
    // Start building PIO config
    pio_sm_config c = main_program_get_default_config(offset);
    
    // NOTE: You have to config out and set pins separately, or they just won't write anything
    sm_config_set_out_pins(&c, pin, ROW_PINS);
    sm_config_set_out_shift(&c, true, false, 16);
    
    // Begin PIO state machine
    pio_sm_init(pio, sm, offset, &c);
}

int main() {
    stdio_init_all();

    PIO pio = pio0;
    uint offset = pio_add_program(pio, &main_program);
    uint sm = pio_claim_unused_sm(pio, true);
    main_program_init(pio, sm, offset, START_PIN);
    pio_sm_set_clkdiv(pio, sm, 20);
    pio_sm_set_enabled(pio, sm, true);

    uint8_t counter = 0;
    while(1) {
        pio_sm_put(pio, sm, (uint32_t)counter);
        sleep_us(5);
        counter++;
    }
}