🛠 Faire clignoter une LED sur la broche P8_03 avec libgpiod

Objectives

Control a pin on the P8/P9 headers using the modern libgpiod library: identify the correct GPIO controller (the AI-64 has several), understand that P8_03 corresponds to GPIO0_20 (muxmode 7 according to chapter 7 of the System Reference Manual), and blink an LED in Python.

Hardware

• 1 BeagleBone AI-64 with the official Debian image
• 1 breadboard, 1 LED, 1 330 Ω resistor, connecting wires
• Golden rule: ALL signals on P8/P9 are 3.3 V. Never apply 5 V to a pin, and never inject voltage into the pins when the board is powered off (back-powering through ESD diodes = destroyed processor, voided warranty).

Complete code

sudo apt install python3-gpiod gpiod
gpiodetect   # chercher la puce nommée 600000.gpio (contrôleur "main")
gpioinfo 600000.gpio | grep -i P8_03

#!/usr/bin/env python3
# blink.py — libgpiod v2, image Debian AI-64
import gpiod, time

# 4211000.gpio = wkup (petit contrôleur), 600000.gpio = main (broches P8/P9)
with gpiod.Chip("600000.gpio") as chip:
    line = chip.get_line(20)          # P8_03 == GPIO0_20
    line.request(consumer="blink", type=gpiod.line_request.DIRECTION_OUTPUT)
    try:
        while True:
            line.set_value(1); time.sleep(0.5)
            line.set_value(0); time.sleep(0.5)
    finally:
        line.release

Expected verification

The LED blinks at 1 Hz. During execution, gpioinfo shows line 20 of 600000.gpio as "output" with the consumer "blink". The script cleanly releases the pin upon Ctrl+C.

Common errors

• Choosing the wrong gpiochip: the wkup controller (4211000.gpio) does not expose the P8/P9 pins; verify with gpiodetect.
• libgpiod API: on images with gpiod 1.x, the call differs (gpiod.LINE_REQ_DIR_OUT); the code above is for the v2 API.
• Forgetting the resistor: a direct LED connection saturates the pin (respect the 3.3 V limit and pin current).
• Expecting hardware PWM: eHRPWM muxing to the headers is a known documentation blind spot on the AI-64 (issue #19) — for beginners, software PWM via libgpiod is sufficient.
• Wiring while the board is powered on without a common GND: erratic readings.