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C GPIO Toggle

View source on GitHub

This guide walks you through building and running the C GPIO toggle reference on Avocado OS. The app uses libgpiod v2 to toggle a GPIO line every second on a Raspberry Pi 5.

Prerequisites​

  • macOS 10.12+ or Linux (Ubuntu 22.04+, Fedora 39+)
  • Docker Desktop installed and running
  • The latest version of the Avocado CLI
  • Raspberry Pi 5
  • SD card

Initialize​

Clone the reference or initialize a new project from it:

avocado init --reference c-gpio c-gpio
cd c-gpio

Install​

Install the SDK toolchain, extension dependencies, and runtime packages:

avocado install -f

This pulls the SDK container image with the Meson build system, cross-compilation toolchain, and libgpiod-dev headers.

Build​

Build the extensions and assemble the runtime image:

avocado build

The build step runs app-compile.sh inside the SDK container, which generates Meson cross-compilation files from the SDK environment and runs meson setup + ninja to cross-compile gpio-toggle for aarch64. Then app-install.sh runs ninja install to copy the binary into the extension sysroot at /usr/bin/gpio-toggle.

Deploy​

SD card​

Insert your SD card and provision:

avocado provision -r dev --profile sd

Insert the SD card into the Raspberry Pi 5 and apply power.

Verify​

SSH into the Pi or connect via serial console. Log in as root with an empty password. The app service starts automatically on boot.

Check the service is running:

systemctl status app

Watch GPIO toggle logs:

journalctl -u app -f

You should see output like:

gpio-toggle starting
GPIO chips:
  gpiochip0 [pinctrl-bcm2712] (54 lines)
  gpiochip4 [pinctrl-rp1] (54 lines)
Opening /dev/gpiochip0, line 17
Toggling line 17 every 1s
[1711234567] line 17 = HIGH
[1711234568] line 17 = LOW

To verify the GPIO is toggling, attach an LED (with a resistor) or a multimeter to GPIO 17.

Customize​

Change the GPIO chip or line​

Edit app/src/main.c:

#define DEFAULT_CHIP "/dev/gpiochip0"
#define DEFAULT_LINE 17
#define TOGGLE_INTERVAL_S 1

Or pass them as command-line arguments by editing app/overlay/usr/lib/systemd/system/app.service:

ExecStart=/usr/bin/gpio-toggle /dev/gpiochip4 22

Rebuild after changes​

After any change, rebuild and reprovision:

avocado build
avocado provision -r dev --profile sd