🛠 Faire clignoter la LED bleue via le GPIO

Objectives

Discover the GPIO of the ODROID-C4 under the mainline kernel (Armbian current or DietPi) by blinking the embedded blue "status" LED. You will learn to identify the two exposed GPIO controllers (gpio and gpio_ao), understand the role of the heartbeat kernel trigger, and control a line using libgpiod v2 (Debian Bookworm syntax).

Hardware

• ODROID-C4 (2 or 4 GB) with a 12 V/2 A power supply on the 5.5/2.1 mm DC jack (the USB OTG port does not provide enough current)
• microSD card with Armbian "current" (kernel 6.6 mainline)
• HDMI screen or UART serial console 115200 8N1
• No external components: the status LED is soldered onto the board (pin GPIOAO_11, active high)

Complete code

#!/usr/bin/env bash
# blink-status.sh - clignoter la LED bleue (chip gpio_ao, ligne 11)
# 1) Vérifier la présence des deux chips GPIO

gpiodetect
# 2) Rendre la LED à l'espace utilisateur (désactive le trigger heartbeat)
echo none > /sys/class/leds/blue:status/trigger 2>/dev/null || true
# 3) Boucle de clignotement : 250 ms ON, 250 ms OFF
while true; do
  gpioset --time=250ms gpio_ao 11=1
  gpioset --time=250ms gpio_ao 11=0
done

Expected verification

gpiodetect must list two chips: gpio (GPIOA/GPIOH/GPIOX/BOOT banks) and gpio_ao (always-on bank). After launching the script, the blue LED blinks approximately twice per second. gpioget gpio_ao 11 returns 1 or 0 depending on the moment. Stop with Ctrl+C: the LED remains in its last state.

Common errors

• The LED refuses to obey because the heartbeat trigger is still active: write none to /sys/class/leds/blue:status/trigger before controlling the line.
• Trying to use wiringPi (gpio -g) as on Raspberry Pi: not guaranteed on Armbian mainline, prefer libgpiod.
• Confusing gpio and gpio_ao: the status LED is on gpio_ao line 11, not on the gpio chip.
• Forgetting sudo: access to GPIO lines requires root or appropriate group membership.