Button

Downstream Copy!

This sample is a copy from Zephyr with identical name and will be used for further development, improvement and preparation of changes for Zephyr within Bridle. However, the original sample still lives within the Zephyr namespace under the exactly same name: Button.

Overview

A simple button demo showcasing the use of GPIO input using a dedicated polling thread, spawned by an init function. Alternatively, it can be configured to use interrupts instead. In either mode, pressing the button will light up an led.

Requirements

The board hardware must have a push button connected via a GPIO pin. These are called “User buttons” on many of Zephyr’s Supported Boards.

The button must be configured using the sw0 devicetree alias, usually in the BOARD.dts file. You will see this error if you try to build this sample for an unsupported board:

Unsupported board: sw0 devicetree alias is not defined

You may see additional build errors if the sw0 alias exists, but is not properly defined.

Additionally, the sample requires the led0 devicetree alias.

Devicetree details

This section provides more details on devicetree configuration.

Here is a minimal devicetree fragment which supports this sample, containing both an sw0 and an led0 alias.

/ {
     aliases {
             sw0 = &button0;
             led0 = &green_led_1;
     };

     soc {
             gpio0: gpio@0 {
                     status = "okay";
                     gpio-controller;
                     #gpio-cells = <2>;
                     /* ... */
             };
     };

     buttons {
             compatible = "gpio-keys";
             button0: button_0 {
                     gpios = < &gpio0 PIN FLAGS >;
                     label = "User button";
             };
             /* ... other buttons ... */
     };

     leds {
             compatible = "gpio-leds";
             green_led_1: led_1 {
                     gpios = <&gpiob 0 GPIO_ACTIVE_HIGH>;
                     label = "User LD1";
             };
             /* ... other leds ... */

};

As shown, the sw0 devicetree alias must point to a child node of a node with a “gpio-keys” compatible, and the led0 alias must point to a child node of one with a “gpio-leds” compatible.

The above situation is for the common case where:

• gpio0 is an example node label referring to a GPIO controller

• PIN should be a pin number, like 8 or 0

• FLAGS should be a logical OR of GPIO configuration flags meant to apply to the button, such as (GPIO_PULL_UP | GPIO_ACTIVE_LOW)

This assumes the common case, where #gpio-cells = <2> in the gpio0 node, and that the GPIO controller’s devicetree binding names those two cells “pin” and “flags” like so:

gpio-cells:
  - pin
  - flags

This sample requires a pin cell in the gpios property. The flags cell is optional, however, and the sample still works if the GPIO cells do not contain flags.

Building and Running

This sample can be built for multiple boards, in this example we will build it for the ST Nucleo F413ZH board:

1. polling thread

   west build -b nucleo_f413zh -p -d build/nucleo_f413zh-button-poll bridle/samples/button -- -DCONF_FILE=prj-poll.conf
   west flash -d build/nucleo_f413zh-button-poll
   

2. interrupt callback

   west build -b nucleo_f413zh -p -d build/nucleo_f413zh-button-event bridle/samples/button -- -DCONF_FILE=prj-event.conf
   west flash -d build/nucleo_f413zh-button-event
   

During startup, an init function look up predefined GPIO devices, and configures their pins in input and output mode, respectively. Depending on the build configuration, an additional init function either spawns a dedicated polling thread which continuously monitors the button state and adjusts the led state to match, or sets up an interrupt that does the same whenever the button is pressed or released.