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.. zephyr:code-sample:: blinky
   :name: Blinky
   :relevant-api: gpio_interface

   Blink an LED forever using the GPIO API.

The Blinky sample blinks an LED forever using the :ref:`GPIO API <gpio_api>`.

The source code shows how to:

1. Get a pin specification from the :ref:`devicetree <dt-guide>` as a :c:struct:`gpio_dt_spec`
2. Configure the GPIO pin as an output
3. Toggle the pin forever

See :zephyr:code-sample:`pwm-blinky` for a similar sample that uses the PWM API instead.

Your board must:

1. Have an LED connected via a GPIO pin (these are called "User LEDs" on many of Zephyr's :ref:`boards`).
2. Have the LED configured using the led0 devicetree alias.

Build and flash Blinky as follows, changing reel_board for your board:

.. zephyr-app-commands::
   :zephyr-app: samples/basic/blinky
   :board: reel_board
   :goals: build flash
   :compact:

After flashing, the LED starts to blink and messages with the current LED state are printed on the console. If a runtime error occurs, the sample exits without printing to the console.

You will see a build error at the source code line defining the struct gpio_dt_spec led variable if you try to build Blinky for an unsupported board.

On GCC-based toolchains, the error looks like this:

error: '__device_dts_ord_DT_N_ALIAS_led_P_gpios_IDX_0_PH_ORD' undeclared here (not in a function)

To add support for your board, add something like this to your devicetree:

/ {
     aliases {
             led0 = &myled0;
     };

     leds {
             compatible = "gpio-leds";
             myled0: led_0 {
                     gpios = <&gpio0 13 GPIO_ACTIVE_LOW>;
             };
     };
};

The above sets your board's led0 alias to use pin 13 on GPIO controller gpio0. The pin flags :c:macro:`GPIO_ACTIVE_HIGH` mean the LED is on when the pin is set to its high state, and off when the pin is in its low state.

Tips:

• See :dtcompatible:`gpio-leds` for more information on defining GPIO-based LEDs in devicetree.
• If you're not sure what to do, check the devicetrees for supported boards which use the same SoC as your target. See :ref:`get-devicetree-outputs` for details.
• See :zephyr_file:`include/zephyr/dt-bindings/gpio/gpio.h` for the flags you can use in devicetree.
• If the LED is built in to your board hardware, the alias should be defined in your :ref:`BOARD.dts file <devicetree-in-out-files>`. Otherwise, you can define one in a :ref:`devicetree overlay <set-devicetree-overlays>`.