.. _board_porting_guide: Board Porting Guide ################### To add Zephyr support for a new :term:`board`, you at least need a *board directory* with various files in it. Files in the board directory inherit support for at least one SoC and all of its features. Therefore, Zephyr must support your :term:`SoC` as well. Boards, SoCs, etc. ****************** Zephyr's hardware support hierarchy has these layers, from most to least specific: - Board: a particular CPU instance and its peripherals in a concrete hardware specification - SoC: the exact system on a chip the board's CPU is part of - SoC series: a smaller group of tightly related SoCs - SoC family: a wider group of SoCs with similar characteristics - CPU core: a particular CPU in an architecture - Architecture: an instruction set architecture You can visualize the hierarchy like this: .. figure:: ../../../../../../../zephyr/doc/hardware/porting/board/hierarchy.png :width: 500px :align: center :alt: Configuration Hierarchy Configuration Hierarchy Here are some examples. Notice how the SoC series and family levels are not always used. .. list-table:: :header-rows: 1 * - Board - SoC - SoC series - SoC family - CPU core - Architecture * - :ref:`nrf52dk_nrf52832 ` - nRF52832 - nRF52 - Nordic nRF5 - Arm Cortex-M4 - Arm * - :ref:`frdm_k64f ` - MK64F12 - Kinetis K6x - NXP Kinetis - Arm Cortex-M4 - Arm * - :ref:`stm32h747i_disco ` - STM32H747XI - STM32H7 - STMicro STM32 - Arm Cortex-M7 - Arm * - :ref:`rv32m1_vega_ri5cy ` - RV32M1 - (Not used) - (Not used) - RI5CY - RISC-V Make sure your SoC is supported ******************************* Start by making sure your SoC is supported by Zephyr. If it is, it's time to :ref:`create-your-board-directory`. If you don't know, try: - checking :ref:`boards` for names that look relevant, and reading individual board documentation to find out for sure. - asking your SoC vendor If you need to add SoC, CPU core, or even architecture support, this is the wrong page, but here is some general advice. Architecture ============ See :ref:`architecture_porting_guide`. CPU Core ======== CPU core support files go in ``core`` subdirectories under :zephyr_file:`arch`, e.g. :zephyr_file:`arch/x86/core`. See :ref:`gs_toolchain` for information about toolchains (compiler, linker, etc.) supported by Zephyr. If you need to support a new toolchain, :ref:`build_overview` is a good place to start learning about the build system. Please reach out to the community if you are looking for advice or want to collaborate on toolchain support. SoC === Zephyr SoC support files are in architecture-specific subdirectories of :zephyr_file:`soc`. They are generally grouped by SoC family. When adding a new SoC family or series for a vendor that already has SoC support within Zephyr, please try to extract common functionality into shared files to avoid duplication. If there is no support for your vendor yet, you can add it in a new directory ``zephyr/soc//``; please use self-explanatory directory names. .. _create-your-board-directory: Create your board directory *************************** Once you've found an existing board that uses your SoC, you can usually start by copy/pasting its board directory and changing its contents for your hardware. You need to give your board a unique name. Run ``west boards`` for a list of names that are already taken, and pick something new. Let's say your board is called ``plank`` (please don't actually use that name). Start by creating the board directory ``zephyr/boards//plank``, where ```` is your SoC's architecture subdirectory. (You don't have to put your board directory in the zephyr repository, but it's the easiest way to get started. See :ref:`custom_board_definition` for documentation on moving your board directory to a separate repository once it's working.) .. note:: The board directory name does not need to match the name of the board. Multiple boards can even defined be in one directory. For example, for boards with multi-core SoC, a logical board might be created for each core following the naming scheme `_`, with definitions for all of these different boards defined inside the same directory. This and similar schemes are common for upstream vendor boards. Your board directory should look like this: .. code-block:: none boards//plank ├── board.cmake ├── CMakeLists.txt ├── doc │   ├── plank.png │   └── index.rst ├── Kconfig.board ├── Kconfig.defconfig ├── plank_defconfig ├── plank.dts └── plank.yaml Replace ``plank`` with your board's name, of course. The mandatory files are: #. :file:`plank.dts`: a hardware description in :ref:`devicetree ` format. This declares your SoC, connectors, and any other hardware components such as LEDs, buttons, sensors, or communication peripherals (USB, BLE controller, etc). #. :file:`Kconfig.board`, :file:`Kconfig.defconfig`, :file:`plank_defconfig`: software configuration in :ref:`kconfig` formats. This provides default settings for software features and peripheral drivers. The optional files are: - :file:`board.cmake`: used for :ref:`flash-and-debug-support` - :file:`CMakeLists.txt`: if you need to add additional source files to your build. - :file:`doc/index.rst`, :file:`doc/plank.png`: documentation for and a picture of your board. You only need this if you're :ref:`contributing-your-board` to Zephyr. - :file:`plank.yaml`: a YAML file with miscellaneous metadata used by the :ref:`twister_script`. .. _default_board_configuration: Write your devicetree ********************* The devicetree file :file:`boards//plank/plank.dts` describes your board hardware in the Devicetree Source (DTS) format (as usual, change ``plank`` to your board's name). If you're new to devicetree, see :ref:`devicetree-intro`. In general, :file:`plank.dts` should look like this: .. code-block:: devicetree /dts-v1/; #include / { model = "A human readable name"; compatible = "yourcompany,plank"; chosen { zephyr,console = &your_uart_console; zephyr,sram = &your_memory_node; /* other chosen settings for your hardware */ }; /* * Your board-specific hardware: buttons, LEDs, sensors, etc. */ leds { compatible = "gpio-leds"; led0: led_0 { gpios = < /* GPIO your LED is hooked up to */ >; label = "LED 0"; }; /* ... other LEDs ... */ }; buttons { compatible = "gpio-keys"; /* ... your button definitions ... */ }; /* These aliases are provided for compatibility with samples */ aliases { led0 = &led0; /* now you support the blinky sample! */ /* other aliases go here */ }; }; &some_peripheral_you_want_to_enable { /* like a GPIO or SPI controller */ status = "okay"; }; &another_peripheral_you_want { status = "okay"; }; If you're in a hurry, simple hardware can usually be supported by copy/paste followed by trial and error. If you want to understand details, you will need to read the rest of the devicetree documentation and the devicetree specification. .. _dt_k6x_example: Example: FRDM-K64F and Hexiwear K64 =================================== .. Give the filenames instead of the full paths below, as it's easier to read. The cramped 'foo.dts' style avoids extra spaces before commas. This section contains concrete examples related to writing your board's devicetree. The FRDM-K64F and Hexiwear K64 board devicetrees are defined in :zephyr_file:`frdm_k64fs.dts ` and :zephyr_file:`hexiwear_k64.dts ` respectively. Both boards have NXP SoCs from the same Kinetis SoC family, the K6X. Common devicetree definitions for K6X are stored in :zephyr_file:`nxp_k6x.dtsi `, which is included by both board :file:`.dts` files. :zephyr_file:`nxp_k6x.dtsi` in turn includes :zephyr_file:`armv7-m.dtsi`, which has common definitions for Arm v7-M cores. Since :zephyr_file:`nxp_k6x.dtsi` is meant to be generic across K6X-based boards, it leaves many devices disabled by default using ``status`` properties. For example, there is a CAN controller defined as follows (with unimportant parts skipped): .. code-block:: devicetree can0: can@40024000 { ... status = "disabled"; ... }; It is up to the board :file:`.dts` or application overlay files to enable these devices as desired, by setting ``status = "okay"``. The board :file:`.dts` files are also responsible for any board-specific configuration of the device, such as adding nodes for on-board sensors, LEDs, buttons, etc. For example, FRDM-K64 (but not Hexiwear K64) :file:`.dts` enables the CAN controller and sets the bus speed: .. code-block:: devicetree &can0 { status = "okay"; bus-speed = <125000>; }; The ``&can0 { ... };`` syntax adds/overrides properties on the node with label ``can0``, i.e. the ``can@4002400`` node defined in the :file:`.dtsi` file. Other examples of board-specific customization is pointing properties in ``aliases`` and ``chosen`` to the right nodes (see :ref:`dt-alias-chosen`), and making GPIO/pinmux assignments. Write Kconfig files ******************* Zephyr uses the Kconfig language to configure software features. Your board needs to provide some Kconfig settings before you can compile a Zephyr application for it. Setting Kconfig configuration values is documented in detail in :ref:`setting_configuration_values`. There are three mandatory Kconfig files in the board directory for a board named ``plank``: .. code-block:: none boards//plank ├── Kconfig.board ├── Kconfig.defconfig └── plank_defconfig :file:`Kconfig.board` Included by :zephyr_file:`boards/Kconfig` to include your board in the list of options. This should at least contain a definition for a ``BOARD_PLANK`` option, which looks something like this: .. code-block:: kconfig config BOARD_PLANK bool "Plank board" depends on SOC_SERIES_YOUR_SOC_SERIES_HERE select SOC_PART_NUMBER_ABCDEFGH :file:`Kconfig.defconfig` Board-specific default values for Kconfig options. The entire file should be inside an ``if BOARD_PLANK`` / ``endif`` pair of lines, like this: .. code-block:: kconfig if BOARD_PLANK # Always set CONFIG_BOARD here. This isn't meant to be customized, # but is set as a "default" due to Kconfig language restrictions. config BOARD default "plank" # Other options you want enabled by default go next. Examples: config FOO default y if NETWORKING config SOC_ETHERNET_DRIVER default y endif # NETWORKING endif # BOARD_PLANK :file:`plank_defconfig` A Kconfig fragment that is merged as-is into the final build directory :file:`.config` whenever an application is compiled for your board. You should at least select your board's SOC and do any mandatory settings for your system clock, console, etc. The results are architecture-specific, but typically look something like this: .. code-block:: cfg CONFIG_SOC_${VENDOR_XYZ3000}=y # select your SoC CONFIG_SYS_CLOCK_HW_CYCLES_PER_SEC=120000000 # set up your clock, etc CONFIG_SERIAL=y :file:`plank_x_y_z.conf` A Kconfig fragment that is merged as-is into the final build directory :file:`.config` whenever an application is compiled for your board revision ``x.y.z``. Build, test, and fix ******************** Now it's time to build and test the application(s) you want to run on your board until you're satisfied. For example: .. code-block:: console west build -b plank samples/hello_world west flash For ``west flash`` to work, see :ref:`flash-and-debug-support` below. You can also just flash :file:`build/zephyr/zephyr.elf`, :file:`zephyr.hex`, or :file:`zephyr.bin` with any other tools you prefer. .. _porting-general-recommendations: General recommendations *********************** For consistency and to make it easier for users to build generic applications that are not board specific for your board, please follow these guidelines while porting. - Unless explicitly recommended otherwise by this section, leave peripherals and their drivers disabled by default. - Configure and enable a system clock, along with a tick source. - Provide pin and driver configuration that matches the board's valuable components such as sensors, buttons or LEDs, and communication interfaces such as USB, Ethernet connector, or Bluetooth/Wi-Fi chip. - If your board uses a well-known connector standard (like Arduino, Mikrobus, Grove, or 96Boards connectors), add connector nodes to your DTS and configure pin muxes accordingly. - Configure components that enable the use of these pins, such as configuring an SPI instance to use the usual Arduino SPI pins. - If available, configure and enable a serial output for the console using the ``zephyr,console`` chosen node in the devicetree. - If your board supports networking, configure a default interface. - Enable all GPIO ports connected to peripherals or expansion connectors. - If available, enable pinmux and interrupt controller drivers. - It is recommended to enable the MPU by default, if there is support for it in hardware. For boards with limited memory resources it is acceptable to disable it. When the MPU is enabled, it is recommended to also enable hardware stack protection (CONFIG_HW_STACK_PROTECTION=y) and, thus, allow the kernel to detect stack overflows when the system is running in privileged mode. .. _flash-and-debug-support: Flash and debug support *********************** Zephyr supports :ref:`west-build-flash-debug` via west extension commands. To add ``west flash`` and ``west debug`` support for your board, you need to create a :file:`board.cmake` file in your board directory. This file's job is to configure a "runner" for your board. (There's nothing special you need to do to get ``west build`` support for your board.) "Runners" are Zephyr-specific Python classes that wrap :ref:`flash and debug host tools ` and integrate with west and the zephyr build system to support ``west flash`` and related commands. Each runner supports flashing, debugging, or both. You need to configure the arguments to these Python scripts in your :file:`board.cmake` to support those commands like this example :file:`board.cmake`: .. code-block:: cmake board_runner_args(jlink "--device=nrf52" "--speed=4000") board_runner_args(pyocd "--target=nrf52" "--frequency=4000000") include(${ZEPHYR_BASE}/boards/common/nrfjprog.board.cmake) include(${ZEPHYR_BASE}/boards/common/jlink.board.cmake) include(${ZEPHYR_BASE}/boards/common/pyocd.board.cmake) This example configures the ``nrfjprog``, ``jlink``, and ``pyocd`` runners. .. warning:: Runners usually have names which match the tools they wrap, so the ``jlink`` runner wraps Segger's J-Link tools, and so on. But the runner command line options like ``--speed`` etc. are specific to the Python scripts. .. note:: Runners and board configuration should be created without being targeted to a single operating system if the tool supports multiple operating systems, nor should it rely upon special system setup/configuration. For example; do not assume that a user will have prior knowledge/configuration or (if using Linux) special udev rules installed, do not assume one specific ``/dev/X`` device for all platforms as this will not be compatible with Windows or macOS, and allow for overriding of the selected device so that multiple boards can be connected to a single system and flashed/debugged at the choice of the user. For more details: - Run ``west flash --context`` to see a list of available runners which support flashing, and ``west flash --context -r `` to view the specific options available for an individual runner. - Run ``west debug --context`` and ``west debug --context `` to get the same output for runners which support debugging. - Run ``west flash --help`` and ``west debug --help`` for top-level options for flashing and debugging. - See :ref:`west-runner` for Python APIs. - Look for :file:`board.cmake` files for other boards similar to your own for more examples. To see what a ``west flash`` or ``west debug`` command is doing exactly, run it in verbose mode: .. code-block:: sh west --verbose flash west --verbose debug Verbose mode prints any host tool commands the runner uses. The order of the ``include()`` calls in your :file:`board.cmake` matters. The first ``include`` sets the default runner if it's not already set. For example, including ``nrfjprog.board.cmake`` first means that ``nrfjprog`` is the default flash runner for this board. Since ``nrfjprog`` does not support debugging, ``jlink`` is the default debug runner. .. _porting_board_revisions: Multiple board revisions ************************ See :ref:`application_board_version` for basics on this feature from the user perspective. To create a new board revision for the ``plank`` board, create these additional files in the board folder: .. code-block:: none boards//plank ├── plank_.conf # optional ├── plank_.overlay # optional └── revision.cmake When the user builds for board ``plank@``: - The optional Kconfig settings specified in the file :file:`plank_.conf` will be merged into the board's default Kconfig configuration. - The optional devicetree overlay :file:`plank_.overlay` will be added to the common :file:`plank.dts` devicetree file - The :file:`revision.cmake` file controls how the Zephyr build system matches the ``@`` string specified by the user when building an application for the board. Currently, ```` can be either a numeric ``MAJOR.MINOR.PATCH`` style revision like ``1.5.0``, an integer number like ``1``, or single letter like ``A``, ``B``, etc. Zephyr provides a CMake board extension function, ``board_check_revision()``, to make it easy to match either style from :file:`revision.cmake`. Valid board revisions may be specified as arguments to the ``board_check_revision()`` function, like: .. code-block:: cmake board_check_revision(FORMAT MAJOR.MINOR.PATCH VALID_REVISIONS 0.1.0 0.3.0 ... ) .. note:: ``VALID_REVISIONS`` can be omitted if all valid revisions have specific Kconfig fragments, such as ``_0_1_0.conf``, ``_0_3_0.conf``. This allows you to just place Kconfig revision fragments in the board folder and not have to keep the corresponding ``VALID_REVISIONS`` in sync. The following sections describe how to support these styles of revision numbers. MAJOR.MINOR.PATCH revisions =========================== Let's say you want to add support for revisions ``0.5.0``, ``1.0.0``, and ``1.5.0`` of the ``plank`` board with both Kconfig fragments and devicetree overlays. Create :file:`revision.cmake` with ``board_check_revision(FORMAT MAJOR.MINOR.PATCH)``, and create the following additional files in the board directory: .. code-block:: none boards//plank ├── plank_0_5_0.conf ├── plank_0_5_0.overlay ├── plank_1_0_0.conf ├── plank_1_0_0.overlay ├── plank_1_5_0.conf ├── plank_1_5_0.overlay └── revision.cmake Notice how the board files have changed periods (".") in the revision number to underscores ("_"). Fuzzy revision matching ----------------------- To support "fuzzy" ``MAJOR.MINOR.PATCH`` revision matching for the ``plank`` board, use the following code in :file:`revision.cmake`: .. code-block:: cmake board_check_revision(FORMAT MAJOR.MINOR.PATCH) If the user selects a revision between those available, the closest revision number that is not larger than the user's choice is used. For example, if the user builds for ``plank@0.7.0``, the build system will target revision ``0.5.0``. The build system will print this at CMake configuration time: .. code-block:: console -- Board: plank, Revision: 0.7.0 (Active: 0.5.0) This allows you to only create revision configuration files for board revision numbers that introduce incompatible changes. Any revision less than the minimum defined will be treated as an error. You may use ``0.0.0`` as a minimum revision to build for by creating the file :file:`plank_0_0_0.conf` in the board directory. This will be used for any revision lower than ``0.5.0``, for example if the user builds for ``plank@0.1.0``. Exact revision matching ----------------------- Alternatively, the ``EXACT`` keyword can be given to ``board_check_revision()`` in :file:`revision.cmake` to allow exact matches only, like this: .. code-block:: cmake board_check_revision(FORMAT MAJOR.MINOR.PATCH EXACT) With this :file:`revision.cmake`, building for ``plank@0.7.0`` in the above example will result in the following error message: .. code-block:: console Board revision `0.7.0` not found. Please specify a valid board revision. Letter revision matching ======================== Let's say instead that you need to support revisions ``A``, ``B``, and ``C`` of the ``plank`` board. Create the following additional files in the board directory: .. code-block:: none boards//plank ├── plank_A.conf ├── plank_A.overlay ├── plank_B.conf ├── plank_B.overlay ├── plank_C.conf ├── plank_C.overlay └── revision.cmake And add the following to :file:`revision.cmake`: .. code-block:: cmake board_check_revision(FORMAT LETTER) Number revision matching ======================== Let's say instead that you need to support revisions ``1``, ``2``, and ``3`` of the ``plank`` board. Create the following additional files in the board directory: .. code-block:: none boards//plank ├── plank_1.conf ├── plank_1.overlay ├── plank_2.conf ├── plank_2.overlay ├── plank_3.conf ├── plank_3.overlay └── revision.cmake And add the following to :file:`revision.cmake`: .. code-block:: cmake board_check_revision(FORMAT NUMBER) board_check_revision() details ============================== .. code-block:: cmake board_check_revision(FORMAT [OPTIONAL EXACT] [DEFAULT_REVISION ] [HIGHEST_REVISION ] [VALID_REVISIONS [ ...]] ) This function supports the following arguments: * ``FORMAT LETTER``: matches single letter revisions from ``A`` to ``Z`` only * ``FORMAT NUMBER``: matches integer revisions * ``FORMAT MAJOR.MINOR.PATCH``: matches exactly three digits. The command line allows for loose typing, that is ``-DBOARD=@1`` and ``-DBOARD=@1.0`` will be handled as ``-DBOARD=@1.0.0``. Kconfig fragment and devicetree overlay files must use full numbering to avoid ambiguity, so only :file:`_1_0_0.conf` and :file:`_1_0_0.overlay` are allowed. * ``OPTIONAL``: if given, a revision is not required to be specified. If the revision is not supplied, the base board is used with no overlays. Can be combined with ``EXACT``, in which case providing the revision is optional, but if given the ``EXACT`` rules apply. Mutually exclusive with ``DEFAULT_REVISION``. * ``EXACT``: if given, the revision is required to be an exact match. Otherwise, the closest matching revision not greater than the user's choice will be selected. * ``DEFAULT_REVISION ``: if given, ```` is the default revision to use when user has not selected a revision number. If not given, the build system prints an error when the user does not specify a board revision. * ``HIGHEST_REVISION``: if given, specifies the highest valid revision for a board. This can be used to ensure that a newer board cannot be used with an older Zephyr. For example, if the current board directory supports revisions 0.x.0-0.99.99 and 1.0.0-1.99.99, and it is expected that the implementation will not work with board revision 2.0.0, then giving ``HIGHEST_REVISION 1.99.99`` causes an error if the user builds using ``@2.0.0``. * ``VALID_REVISIONS``: if given, specifies a list of revisions that are valid for this board. If this argument is not given, then each Kconfig fragment of the form ``_.conf`` in the board folder will be used as a valid revision for the board. .. _porting_custom_board_revisions: Custom revision.cmake files *************************** Some boards may not use board revisions supported by ``board_check_revision()``. To support revisions of any type, the file :file:`revision.cmake` can implement custom revision matching without calling ``board_check_revision()``. To signal to the build system that it should use a different revision than the one specified by the user, :file:`revision.cmake` can set the variable ``ACTIVE_BOARD_REVISION`` to the revision to use instead. The corresponding Kconfig files and devicetree overlays must be named :file:`_.conf` and :file:`_.overlay`. For example, if the user builds for ``plank@zero``, :file:`revision.cmake` can set ``ACTIVE_BOARD_REVISION`` to ``one`` to use the files :file:`plank_one.conf` and :file:`plank_one.overlay`. .. _contributing-your-board: Contributing your board *********************** If you want to contribute your board to Zephyr, first -- thanks! There are some extra things you'll need to do: #. Make sure you've followed all the :ref:`porting-general-recommendations`. They are requirements for boards included with Zephyr. #. Add documentation for your board using the template file :zephyr_file:`doc/templates/board.tmpl`. See :ref:`zephyr_doc` for information on how to build your documentation before submitting your pull request. #. Prepare a pull request adding your board which follows the :ref:`contribute_guidelines`. Board extensions **************** Boards already supported by Zephyr can be extended by downstream users, such as ``example-application`` or vendor SDKs. In some situations, certain hardware description or :ref:`choices ` can not be added in the upstream Zephyr repository, but they can be in a downstream project, where custom bindings or driver classes can also be created. This feature may also be useful in development phases, when the board skeleton lives upstream, but other features are developed in a downstream module. Board extensions are board fragments that can be present in an out-of-tree board root folder, under ``${BOARD_ROOT}/boards/extensions``. Here is an example structure of an extension for the ``plank`` board and its revisions: .. code-block:: none boards/extensions/plank ├── plank.conf # optional ├── plank_.conf # optional ├── plank.overlay # optional └── plank_.overlay # optional A board extension directory must follow the naming structure of the original board it extends. It may contain Kconfig fragments and/or devicetree overlays. Extensions are, by default, automatically loaded and applied on top of board files, before anything else. There is no guarantee on which order extensions are applied, in case multiple exist. This feature can be disabled by passing ``-DBOARD_EXTENSIONS=OFF`` when building. Note that board extensions need to follow the :ref:`same guidelines ` as regular boards. For example, it is wrong to enable extra peripherals or subsystems in a board extension. .. warning:: Board extensions are not allowed in any module referenced in Zephyr's ``west.yml`` manifest file. Any board changes are required to be submitted to the main Zephyr repository.