🛠 GPIO avec libgpiod : faire clignoter une LED et lire un bouton

Objectives

Learn the GPIOs of the ZERO 3W as of 2026: no sysfs (deprecated), but libgpiod, the recommended path in Radxa documentation. The 40-pin connector is electrically compatible with Raspberry Pi (3.3 V logic, never 5 V on the pins!), with its specific pitfalls: pins 3, 5, 27, and 28 are unusable as GPIOs due to I2C pull-up resistors, and pins 8/10 = U-Boot serial console. You will write a blink program in C and an interrupt-driven button in Python.

Hardware

• 1 Radxa ZERO 3W (the 40-pin connector is unsoldered on base SKUs — plan for a soldering iron or higher-tier SKUs where it is soldered)
• 1 LED + 330 Ω resistor; 1 push button
• Breadboard jumper wires; stable 5 V/2 A power supply
• sudo apt install gcc libgpiod-dev gpiod python3-libgpiod

Pinout rules (source: official hardware-interface)

• All GPIO logic is 3.3 V (absolute maximum 3.63 V) — never inject 5 V into a pin.
• Pins 3, 5, 27, 28: additional I2C pull-ups, “behave abnormally as GPIO” — do not use them as digital I/O.
• Pins 8/10 (TX/RX): this is UART2_M0, the U-Boot console — see the dedicated serial tutorial.
• Pin 35 = GPIO3_A4; pin 11 = GPIO3_A1. Rockchip rule: bank 3 → gpiochip3, letter A=0/B=8 + offset → line 4 for A4.

Blink in C (pin 35, GPIO3_A4)

/* blink.c — compile : gcc blink.c -o blink -lgpiod */
#include <gpiod.h>
#include <stdio.h>
int main(void) {
    struct gpiod_chip *chip = gpiod_chip_open_by_name("gpiochip3");
    if (!chip) { perror("gpiochip3"); return 1; }
    struct gpiod_line *line = gpiod_chip_get_line(chip, 4);   /* A4 = ligne 4 */
    if (gpiod_line_request_output(line, "blink", 0) < 0) { perror("request"); return 1; }
    for (int i = 0; i < 10; i++) {          /* 5 cycles ON/OFF */
        gpiod_line_set_value(line, 1); sleep(1);
        gpiod_line_set_value(line, 0); sleep(1);
    }
    gpiod_line_release(line); gpiod_chip_close(chip);
    return 0;
}

Without compiling: gpioset -m signal $(gpiofind GPIO3_A4)=1 — gpiofind avoids hardcoding chip/line.

Event-driven button (pin 11, GPIO3_A1)

#!/usr/bin/env python3  # apt install python3-libgpiod gpiod
# Bouton : broche 11 -> 3V3 ; pull-down (flag gpiod ou résistance externe vers GND)
import gpiod
chip = gpiod.Chip("gpiochip3")
line = chip.get_line(1)                      # A1 = ligne 1
line.request(consumer="bouton", type=gpiod.LINE_REQ_EV_RISING_EDGE)
while True:
    if line.event_wait(sec=None): line.event_read; print("appui")

Expected verification

gcc blink.c -o blink -lgpiod && ./blink makes the LED blink 5 times. The Python script prints “press” on each button press, without polling (kernel blocking). gpioinfo gpiochip3 shows your requested lines.

Common errors

• Using pins 3/5/27/28 as GPIO: the board’s I2C pull-ups distort everything — the official documentation is explicit.
• Counting like on a Pi (BCM GPIO): here you reason in chip/line (gpiochip3, line 4) or kernel name via gpiofind GPIO3_A4.
• Forgetting that the connector is not soldered on entry-level SKUs: check your order before buying wires!
• 5 V on a pin: the absolute maximum is 3.63 V — direct 5 V can destroy the pin.
• Requesting a line already occupied by an overlay: request fails — list active overlays (sudo rsetup) and the gpioinfo of each chip.
• Connecting to pins 8/10 thinking you are doing safe GPIO: you short-circuit the U-Boot console (see the UART tutorial).