doc/guides/porting/shields.rst - third_party/github/zephyrproject-rtos/zephyr - Git at Google

 .. _shields:

 Shields
 #######

 Shields, also known as "add-on" or "daughter boards", attach to a board
 to extend its features and services for easier and modularized prototyping.
 In Zephyr, the shield feature provides Zephyr-formatted shield
 descriptions for easier compatibility with applications.

 Shield porting and configuration
 ********************************

 Shield configuration files are available in the board directory
 under :zephyr_file:`/boards/shields`:

 .. code-block:: none

    boards/shields/<shield>
    ├── <shield>.overlay
    ├── Kconfig.shield
    └── Kconfig.defconfig

 These files provides shield configuration as follows:

 * **<shield>.overlay**: This file provides a shield description in devicetree
   format that is merged with the board's :ref:`devicetree <dt-guide>`
   before compilation.

 * **Kconfig.shield**: This file defines shield Kconfig symbols that will be
   used for default shield configuration. To ease use with applications,
   the default shield configuration here should be consistent with those in
   the :ref:`default_board_configuration`.

 * **Kconfig.defconfig**: This file defines the default shield configuration. It
   is made to be consistent with the :ref:`default_board_configuration`. Hence,
   shield configuration should be done by keeping in mind that features
   activation is application responsibility.

 Board compatibility
 *******************

 Hardware shield-to-board compatibility depends on the use of well-known
 connectors used on popular boards (such as Arduino and 96boards).  For
 software compatibility, boards must also provide a configuration matching
 their supported connectors.

 This should be done at two different level:

 * Pinmux: Connector pins should be correctly configured to match shield pins

 * Devicetree: A board :ref:`devicetree <dt-guide>` file,
   :file:`BOARD.dts` should define a node alias for each connector interface.
   For example, for Arduino I2C:

 .. code-block:: DTS

         #define arduino_i2c i2c1

         aliases {
                 arduino,i2c = &i2c1;
         };

 Note: With support of dtc v1.4.2, above will be replaced with the recently
 introduced overriding node element:

 .. code-block:: DTS

         arduino_i2c:i2c1{};

 Board specific shield configuration
 -----------------------------------

 If modifications are needed to fit a shield to a particular board or board
 revision, you can override a shield description for a specific board by adding
 board or board revision overriding files to a shield, as follows:

 .. code-block:: none

    boards/shields/<shield>
    └── boards
        ├── <board>_<revision>.overlay
        ├── <board>.overlay
        ├── <board>.defconfig
        ├── <board>_<revision>.conf
        └── <board>.conf


 Shield activation
 *****************

 Activate support for one or more shields by adding the matching -DSHIELD arg to
 CMake command

   .. zephyr-app-commands::
      :zephyr-app: your_app
      :shield: "x_nucleo_idb05a1 x_nucleo_iks01a1"
      :goals: build


 Alternatively, it could be set by default in a project's CMakeLists.txt:

 .. code-block:: none

 	set(SHIELD x_nucleo_iks01a1)

 Shield variants
 ***************

 Some shields may support several variants or revisions. In that case, it is
 possible to provide multiple version of the shields description:

 .. code-block:: none

    boards/shields/<shield>
    ├── <shield_v1>.overlay
    ├── <shield_v1>.defconfig
    ├── <shield_v2>.overlay
    └── <shield_v2>.defconfig

 In this case, a shield-particular revision name can be used:

   .. zephyr-app-commands::
      :zephyr-app: your_app
      :shield: shield_v2
      :goals: build

 You can also provide a board-specific configuration to a specific shield
 revision:

 .. code-block:: none

    boards/shields/<shield>
    ├── <shield_v1>.overlay
    ├── <shield_v1>.defconfig
    ├── <shield_v2>.overlay
    ├── <shield_v2>.defconfig
    └── boards
        └── <shield_v2>
            ├── <board>.overlay
            └── <board>.defconfig

 GPIO nexus nodes
 ****************

 GPIOs accessed by the shield peripherals must be identified using the
 shield GPIO abstraction, for example from the ``arduino-header-r3``
 compatible.  Boards that provide the header must map the header pins
 to SOC-specific pins.  This is accomplished by including a `nexus
 node`_ that looks like the following into the board devicetree file:

 .. _nexus node:
     https://github.com/devicetree-org/devicetree-specification/blob/4b1dac80eaca45b4babf5299452a951008a5d864/source/devicetree-basics.rst#nexus-nodes-and-specifier-mapping

 .. code-block:: none

     arduino_header: connector {
             compatible = "arduino-header-r3";
             #gpio-cells = <2>;
             gpio-map-mask = <0xffffffff 0xffffffc0>;
             gpio-map-pass-thru = <0 0x3f>;
             gpio-map = <0 0 &gpioa 0 0>,    /* A0 */
                        <1 0 &gpioa 1 0>,    /* A1 */
                        <2 0 &gpioa 4 0>,    /* A2 */
                        <3 0 &gpiob 0 0>,    /* A3 */
                        <4 0 &gpioc 1 0>,    /* A4 */
                        <5 0 &gpioc 0 0>,    /* A5 */
                        <6 0 &gpioa 3 0>,    /* D0 */
                        <7 0 &gpioa 2 0>,    /* D1 */
                        <8 0 &gpioa 10 0>,   /* D2 */
                        <9 0 &gpiob 3 0>,    /* D3 */
                        <10 0 &gpiob 5 0>,   /* D4 */
                        <11 0 &gpiob 4 0>,   /* D5 */
                        <12 0 &gpiob 10 0>,  /* D6 */
                        <13 0 &gpioa 8 0>,   /* D7 */
                        <14 0 &gpioa 9 0>,   /* D8 */
                        <15 0 &gpioc 7 0>,   /* D9 */
                        <16 0 &gpiob 6 0>,   /* D10 */
                        <17 0 &gpioa 7 0>,   /* D11 */
                        <18 0 &gpioa 6 0>,   /* D12 */
                        <19 0 &gpioa 5 0>,   /* D13 */
                        <20 0 &gpiob 9 0>,   /* D14 */
                        <21 0 &gpiob 8 0>;   /* D15 */
     };

 This specifies how Arduino pin references like ``<&arduino_header 11
 0>`` are converted to SOC gpio pin references like ``<&gpiob 4 0>``.

 In Zephyr GPIO specifiers generally have two parameters (indicated by
 ``#gpio-cells = <2>``): the pin number and a set of flags.  The low 6
 bits of the flags correspond to features that can be configured in
 devicetree.  In some cases it's necessary to use a non-zero flag value
 to tell the driver how a particular pin behaves, as with:

 .. code-block:: none

     drdy-gpios = <&arduino_header 11 GPIO_ACTIVE_LOW>;

 After preprocessing this becomes ``<&arduino_header 11 1>``.  Normally
 the presence of such a flag would cause the map lookup to fail,
 because there is no map entry with a non-zero flags value.  The
 ``gpio-map-mask`` property specifies that, for lookup, all bits of the
 pin and all but the low 6 bits of the flags are used to identify the
 specifier.  Then the ``gpio-map-pass-thru`` specifies that the low 6
 bits of the flags are copied over, so the SOC GPIO reference becomes
 ``<&gpiob 4 1>`` as intended.

 See `nexus node`_ for more information about this capability.
	.. _shields:

	Shields
	#######

	Shields, also known as "add-on" or "daughter boards", attach to a board
	to extend its features and services for easier and modularized prototyping.
	In Zephyr, the shield feature provides Zephyr-formatted shield
	descriptions for easier compatibility with applications.

	Shield porting and configuration
	********************************

	Shield configuration files are available in the board directory
	under :zephyr_file:`/boards/shields`:

	.. code-block:: none

	boards/shields/<shield>
	├── <shield>.overlay
	├── Kconfig.shield
	└── Kconfig.defconfig

	These files provides shield configuration as follows:

	* <shield>.overlay: This file provides a shield description in devicetree
	format that is merged with the board's :ref:`devicetree <dt-guide>`
	before compilation.

	* Kconfig.shield: This file defines shield Kconfig symbols that will be
	used for default shield configuration. To ease use with applications,
	the default shield configuration here should be consistent with those in
	the :ref:`default_board_configuration`.

	* Kconfig.defconfig: This file defines the default shield configuration. It
	is made to be consistent with the :ref:`default_board_configuration`. Hence,
	shield configuration should be done by keeping in mind that features
	activation is application responsibility.

	Board compatibility
	*******************

	Hardware shield-to-board compatibility depends on the use of well-known
	connectors used on popular boards (such as Arduino and 96boards). For
	software compatibility, boards must also provide a configuration matching
	their supported connectors.

	This should be done at two different level:

	* Pinmux: Connector pins should be correctly configured to match shield pins

	* Devicetree: A board :ref:`devicetree <dt-guide>` file,
	:file:`BOARD.dts` should define a node alias for each connector interface.
	For example, for Arduino I2C:

	.. code-block:: DTS

	#define arduino_i2c i2c1

	aliases {
	arduino,i2c = &i2c1;
	};

	Note: With support of dtc v1.4.2, above will be replaced with the recently
	introduced overriding node element:

	.. code-block:: DTS

	arduino_i2c:i2c1{};

	Board specific shield configuration
	-----------------------------------

	If modifications are needed to fit a shield to a particular board or board
	revision, you can override a shield description for a specific board by adding
	board or board revision overriding files to a shield, as follows:

	.. code-block:: none

	boards/shields/<shield>
	└── boards
	├── <board>_<revision>.overlay
	├── <board>.overlay
	├── <board>.defconfig
	├── <board>_<revision>.conf
	└── <board>.conf


	Shield activation
	*****************

	Activate support for one or more shields by adding the matching -DSHIELD arg to
	CMake command

	.. zephyr-app-commands::
	:zephyr-app: your_app
	:shield: "x_nucleo_idb05a1 x_nucleo_iks01a1"
	:goals: build


	Alternatively, it could be set by default in a project's CMakeLists.txt:

	.. code-block:: none

	set(SHIELD x_nucleo_iks01a1)

	Shield variants
	***************

	Some shields may support several variants or revisions. In that case, it is
	possible to provide multiple version of the shields description:

	.. code-block:: none

	boards/shields/<shield>
	├── <shield_v1>.overlay
	├── <shield_v1>.defconfig
	├── <shield_v2>.overlay
	└── <shield_v2>.defconfig

	In this case, a shield-particular revision name can be used:

	.. zephyr-app-commands::
	:zephyr-app: your_app
	:shield: shield_v2
	:goals: build

	You can also provide a board-specific configuration to a specific shield
	revision:

	.. code-block:: none

	boards/shields/<shield>
	├── <shield_v1>.overlay
	├── <shield_v1>.defconfig
	├── <shield_v2>.overlay
	├── <shield_v2>.defconfig
	└── boards
	└── <shield_v2>
	├── <board>.overlay
	└── <board>.defconfig

	GPIO nexus nodes
	****************

	GPIOs accessed by the shield peripherals must be identified using the
	shield GPIO abstraction, for example from the ``arduino-header-r3``
	compatible. Boards that provide the header must map the header pins
	to SOC-specific pins. This is accomplished by including a `nexus
	node`_ that looks like the following into the board devicetree file:

	.. _nexus node:
	https://github.com/devicetree-org/devicetree-specification/blob/4b1dac80eaca45b4babf5299452a951008a5d864/source/devicetree-basics.rst#nexus-nodes-and-specifier-mapping

	.. code-block:: none

	arduino_header: connector {
	compatible = "arduino-header-r3";
	#gpio-cells = <2>;
	gpio-map-mask = <0xffffffff 0xffffffc0>;
	gpio-map-pass-thru = <0 0x3f>;
	gpio-map = <0 0 &gpioa 0 0>, /* A0 */
	<1 0 &gpioa 1 0>, /* A1 */
	<2 0 &gpioa 4 0>, /* A2 */
	<3 0 &gpiob 0 0>, /* A3 */
	<4 0 &gpioc 1 0>, /* A4 */
	<5 0 &gpioc 0 0>, /* A5 */
	<6 0 &gpioa 3 0>, /* D0 */
	<7 0 &gpioa 2 0>, /* D1 */
	<8 0 &gpioa 10 0>, /* D2 */
	<9 0 &gpiob 3 0>, /* D3 */
	<10 0 &gpiob 5 0>, /* D4 */
	<11 0 &gpiob 4 0>, /* D5 */
	<12 0 &gpiob 10 0>, /* D6 */
	<13 0 &gpioa 8 0>, /* D7 */
	<14 0 &gpioa 9 0>, /* D8 */
	<15 0 &gpioc 7 0>, /* D9 */
	<16 0 &gpiob 6 0>, /* D10 */
	<17 0 &gpioa 7 0>, /* D11 */
	<18 0 &gpioa 6 0>, /* D12 */
	<19 0 &gpioa 5 0>, /* D13 */
	<20 0 &gpiob 9 0>, /* D14 */
	<21 0 &gpiob 8 0>; /* D15 */
	};

	This specifies how Arduino pin references like ``<&arduino_header 11
	0>`` are converted to SOC gpio pin references like ``<&gpiob 4 0>``.

	In Zephyr GPIO specifiers generally have two parameters (indicated by
	``#gpio-cells = <2>``): the pin number and a set of flags. The low 6
	bits of the flags correspond to features that can be configured in
	devicetree. In some cases it's necessary to use a non-zero flag value
	to tell the driver how a particular pin behaves, as with:

	.. code-block:: none

	drdy-gpios = <&arduino_header 11 GPIO_ACTIVE_LOW>;

	After preprocessing this becomes ``<&arduino_header 11 1>``. Normally
	the presence of such a flag would cause the map lookup to fail,
	because there is no map entry with a non-zero flags value. The
	``gpio-map-mask`` property specifies that, for lookup, all bits of the
	pin and all but the low 6 bits of the flags are used to identify the
	specifier. Then the ``gpio-map-pass-thru`` specifies that the low 6
	bits of the flags are copied over, so the SOC GPIO reference becomes
	``<&gpiob 4 1>`` as intended.

	See `nexus node`_ for more information about this capability.