🛠 Faire clignoter une LED en C avec libgpiod sur Le Potato

Objectives

Blink an LED on the 40-pin connector of the Le Potato (AML-S905X-CC) in C using libgpiod, the interface officially recommended by Libre Computer — there is no wiringPi on this board and the vendor refuses to port it.

Hardware

• Le Potato AML-S905X-CC running Armbian (mainline kernel, meson-gxl)
• LED + 330 Ω resistor
• Physical pin 3 = GPIOAO_5 = gpiochip0 line 5; 3.3 V logic, no 5 V tolerant pins
• Ground on a GND pin (6, 9, 14, 20, 25, 30, 34 or 39)

Complete code

/* blink.c — gcc blink.c -o blink -lgpiod (paquet libgpiod-dev) */
#include <gpiod.h>
#include <stdio.h>
#include <unistd.h>
int main(void) {
    struct gpiod_chip *chip = gpiod_chip_open_by_number(0);
    if (!chip) { perror("gpiochip0"); return 1; }
    struct gpiod_line *line = gpiod_chip_get_line(chip, 5); /* broche 3 */
    if (!line || gpiod_line_request_output(line, "blink", 0)) {
        perror("request"); return 1;
    }
    for (int i = 0; i < 10; i++) {
        gpiod_line_set_value(line, i & 1);
        usleep(200000);
    }
    gpiod_line_release(line);
    gpiod_chip_close(chip);
    return 0;
}

Expected verification

./blink blinks the LED 10 times at 5 Hz. During execution, gpioinfo gpiochip0 shows line 5 (named "7J1 Header Pin3" in the device tree) as requested by the consumer "blink".

Common errors

• Confusing physical pin and GPIO line: pin 3 = line 5 (GPIOAO_5). Check with lgpio info 3 (libretech-wiring-tool) or gpioinfo.
• libgpiod 2.x API differs from 1.x (gpiod_line_request): adapt according to the distribution.
• Sending 5 V to a pin: no pin is 5 V tolerant, board damage.
• Permission denied: add your user to the gpio group or run as root.