110 lines
3.1 KiB
ReStructuredText
110 lines
3.1 KiB
ReStructuredText
.. _button-sample:
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Button
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######
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Overview
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********
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A simple button demo showcasing the use of GPIO input with interrupts.
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The sample prints a message to the console each time a button is pressed.
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Requirements
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************
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The board hardware must have a push button connected via a GPIO pin. These are
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called "User buttons" on many of Zephyr's :ref:`boards`.
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The button must be configured using the ``sw0`` :ref:`devicetree <dt-guide>`
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alias, usually in the :ref:`BOARD.dts file <devicetree-in-out-files>`. You will
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see this error if you try to build this sample for an unsupported board:
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.. code-block:: none
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Unsupported board: sw0 devicetree alias is not defined
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You may see additional build errors if the ``sw0`` alias exists, but is not
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properly defined.
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The sample additionally supports an optional ``led0`` devicetree alias. This is
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the same alias used by the :ref:`blinky-sample`. If this is provided, the LED
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will be turned on when the button is pressed, and turned off off when it is
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released.
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Devicetree details
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==================
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This section provides more details on devicetree configuration.
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Here is a minimal devicetree fragment which supports this sample. This only
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includes a ``sw0`` alias; the optional ``led0`` alias is left out for
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simplicity.
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.. code-block:: devicetree
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/ {
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aliases {
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sw0 = &button0;
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};
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soc {
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gpio0: gpio@0 {
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status = "okay";
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gpio-controller;
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#gpio-cells = <2>;
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/* ... */
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};
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};
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buttons {
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compatible = "gpio-keys";
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button0: button_0 {
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gpios = < &gpio0 PIN FLAGS >;
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label = "User button";
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};
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/* ... other buttons ... */
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};
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};
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As shown, the ``sw0`` devicetree alias must point to a child node of a node
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with a "gpio-keys" :ref:`compatible <dt-important-props>`.
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The above situation is for the common case where:
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- ``gpio0`` is an example node label referring to a GPIO controller
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- ``PIN`` should be a pin number, like ``8`` or ``0``
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- ``FLAGS`` should be a logical OR of :ref:`GPIO configuration flags <gpio_api>`
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meant to apply to the button, such as ``(GPIO_PULL_UP | GPIO_ACTIVE_LOW)``
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This assumes the common case, where ``#gpio-cells = <2>`` in the ``gpio0``
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node, and that the GPIO controller's devicetree binding names those two cells
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"pin" and "flags" like so:
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.. code-block:: yaml
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gpio-cells:
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- pin
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- flags
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This sample requires a ``pin`` cell in the ``gpios`` property. The ``flags``
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cell is optional, however, and the sample still works if the GPIO cells
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do not contain ``flags``.
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Building and Running
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********************
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This sample can be built for multiple boards, in this example we will build it
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for the nucleo_f103rb board:
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.. zephyr-app-commands::
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:zephyr-app: samples/basic/button
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:board: nucleo_f103rb
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:goals: build
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:compact:
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After startup, the program looks up a predefined GPIO device, and configures the
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pin in input mode, enabling interrupt generation on falling edge. During each
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iteration of the main loop, the state of GPIO line is monitored and printed to
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the serial console. When the input button gets pressed, the interrupt handler
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will print an information about this event along with its timestamp.
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