--- title: Porting Boards description: Guide on how to port new boards to RIOT-OS --- At some point you might need to port a new `BOARD` to `RIOT`, either because that specific development board is not yet supported or because you have a custom `BOARD` for your project. If you want to port a `BOARD` to `RIOT` you have two choices: doing it inside of `RIOTBASE` or outside. In either case the file structure is basically the same and moving from one to another is easy. This guide details the generic structure you need to add a new `BOARD` to `RIOT`, the different files as well as their functionality. :::note We assume here that your `CPU` and `CPU_MODEL` is already supported in `RIOT` so no peripheral or cpu implementation is needed. ::: # Porting Flowchart ![Porting flowchart](img/porting-boards.svg) # General Structure Like [applications](/advanced_tutorials/creating_applications/) or [modules](/advanced_tutorials/creating_modules), boards consist of a directory containing source files and Makefiles. Usually a `BOARD` directory has the following structure, although not all of the subdirectories or Makefiles have to be present for a board implementation to work. ``` board-foo/ |----dist/ |----scripts |----board.c |----doc.md |----include/ |----periph_conf.h |----board.h |----gpio_params.h |----Makefile |----Makefile.dep |----Makefile.features |----Makefile.include ``` ## Source Files Header files in `board-foo/include` define physical mappings or configurations. e.g: - `periph_conf.h`: defines configurations and mappings for peripherals as well as clock configurations. - `board.h`: holds board specific definitions or mappings, for example LEDs, buttons. It might as well override default drivers parameters (e.g.: assigning specific pin connections to a LCD screen, radio, etc.). - `gpio_params.h`: if the board supports [SAUL](https://doc.riot-os.org/group__drivers__saul.html) then its [saul_gpio_params_t](https://doc.riot-os.org/structsaul__gpio__params__t.html) is defined here. (Analogously, an `adc_params.h` can contain a [saul_adc_params_t](https://doc.riot-os.org/structsaul__adc__params__t.html) and `pwm_params.h` a [saul_pwm_rgb_params_t](https://doc.riot-os.org/structsaul__pwm__rgb__params__t.html) and a [saul_pwm_dimmer_params_t](https://doc.riot-os.org/structsaul__pwm__dimmer__params__t.html)). - other: other specific headers needed by one `BOARD` :::note Header files do not need to be defined in `include/`, but if defined somewhere else then they must be added to the include path in `Makefile.include`: `INCLUDES += -I//` ::: Board initialization functions are defined in `board.c`. This file can define a `board_init()` function that is called at startup. It is run before the scheduler is started, so it must not block (e.g. by performing I2C operations). ```c void board_init(void) { /* initialize GPIO or others... */ ... } ``` ## Makefiles ### Makefile A board's Makefile just needs to include `Makefile.base` in the RIOT repository and define the `MODULE` as `board` (see [modules](/advanced_tutorials/creating_modules) for more details) ```makefile MODULE = board include $(RIOTBASE)/Makefile.base ``` ### Makefile.dep Dependencies on other `MODULES` or `FEATURES` can be defined here. This might specify `MODULES` or dependencies that need to be pulled under specific configurations. e.g.: if your board has a sx1276 lora chip: ```makefile ifneq (,$(filter netdev_default,$(USEMODULE))) USEMODULE += sx1276 endif ``` :::note `Makefile.dep` is processed only once so you have to take care of adding the dependency block for your board *before* its dependencies pull in their own dependencies. ::: #### Default Configurations There are two pseudomodules that are used to indicate that certain drivers of devices present in the platform should be enabled. Each board (or CPU) has knowledge as to which drivers should be enabled in each case. The previous code snippet shows how a board which has a [Semtech SX1272 and SX1276 radio driver](https://doc.riot-os.org/group__drivers__sx127x.html) device, pulls in its driver when the default network interfaces are required. When the pseudomodule `saul_default` is enabled, the board should pull in all the drivers of the devices it has which provide a [[S]ensor [A]ctuator [U]ber [L]ayer](https://doc.riot-os.org/group__drivers__saul.html) interface. This is usually done as following: ```makefile ifneq (,$(filter saul_default,$(USEMODULE))) USEMODULE += saul_gpio USEMODULE += apds9960 USEMODULE += bmp280_i2c USEMODULE += lis3mdl USEMODULE += sht3x endif ``` ### Makefile.features This file defines all the features provided by the BOARD. These features might also need to be supported by the `CPU`. Here, define the `CPU` and `CPU_MODEL` (see [build system basics](/build-system/build_system_basics/) for more details on these variables). e.g.: ```makefile CPU = foo CPU_MODEL = foobar # Put defined MCU peripherals here (in alphabetical order) FEATURES_PROVIDED += periph_i2c FEATURES_PROVIDED += periph_spi FEATURES_PROVIDED += periph_uart ``` ### Makefile.include This file contains BSP or toolchain configurations for the `BOARD`. It should at least define the configuration needed for flashing (i.e. specify a default programmer) as well as the serial configuration (if one is available). The default serial port configuration is provided by `makefiles/tools/serial.inc.mk` and defines the following values for the serial port (depending on the host OS): ``` PORT_LINUX ?= /dev/ttyACM0 PORT_DARWIN ?= $(firstword $(sort $(wildcard /dev/tty.usbmodem*))) ``` So if the board is also using this, there's no need to redefine these variables in the board configuration. For example a board that is using a custom serial port (via an USB to serial adapter) and that is flashed using OpenOCD by default would have the following content in its `Makefile.include`: ```makefile # Define the default port depending on the host OS PORT_LINUX ?= /dev/ttyUSB0 PORT_DARWIN ?= $(firstword $(sort $(wildcard /dev/tty.usbserial*))) # this board uses OpenOCD PROGRAMMER ?= openocd ``` ## Timer Configurations When using the high level timer `ztimer` there is an overhead in calling the [ztimer_sleep](https://doc.riot-os.org/group__sys__ztimer.html#gade98636e198f2d571c8acd861d29d360) and [ztimer_set](https://doc.riot-os.org/group__sys__ztimer.html#ga8934a79a89e35d58673418a1e4a2e69c) functions. This offset can be compensated for. It can be measured by running `tests/sys/ztimer_overhead` on your board, i.e: ```bash $ BOARD=my-new-board make -C tests/sys/ztimer_overhead flash term main(): This is RIOT! ZTIMER_USEC auto_adjust params: ZTIMER_USEC->adjust_set = xx ZTIMER_USEC->adjust_sleep = xx ZTIMER_USEC auto_adjust params cleared zitmer_overhead_set... min=6 max=7 avg_diff=6 zitmer_overhead_sleep... min=21 max=21 avg_diff=21 ZTIMER_USEC adjust params for my-new-board: CONFIG_ZTIMER_USEC_ADJUST_SET 6 CONFIG_ZTIMER_USEC_ADJUST_SLEEP 21 ``` The last two lines can be added as defines to the new board `board.h`: ```c /** * @name ztimer configuration values * @{ */ #define CONFIG_ZTIMER_USEC_ADJUST_SET 6 #define CONFIG_ZTIMER_USEC_ADJUST_SLEEP 21 /** @} */ ``` Alternatively, the pseudomodule [ztimer_auto_adjust](https://doc.riot-os.org/group__pseudomodule__ztimer__auto__adjust.html) can be used in an application to enable automatic timer offset compensation at board startup. This however incurs overhead both in the text segment and at bootup time. ## doc.md Although not explicitly needed, if upstreamed and as a general good practice, this file holds all `BOARD` documentation. This can include datasheet reference, documentation on how to flash, etc. The documentation must be under the proper doxygen group, you can compile the documentation by calling `make doc` and then open the generated html file on any browser. ```markdown @defgroup boards_foo FooBoard @ingroup boards @brief Support for the foo board @author FooName BarName ### User Interface ... ### Using UART ... ### Flashing the device ... ``` Previously documentation was contained in `doc.txt` files with C-style comment blocks. This style has been deprecated in favor of using `doc.md` files in Markdown format, which eliminates formatting and interpretation issues. Old style files will continually be replaced by the new format. Up to version `0.9.2` the [riotgen](https://pypi.org/project/riotgen/) tool will generate `doc.txt` files instead of `doc.md` files. You can upgrade it to the latest version with ```bash pip install --upgrade riotgen ``` # Helper Tools To help you start porting a board, the RIOT build system provides the `generate-board` make target. It is a wrapper around the [riotgen](https://pypi.org/project/riotgen/) command line tool that is helpful when starting to port a board: all required files are generated with copyright headers, doxygen groups, etc, so you can concentrate on the port. The board source files are created in the `boards/` directory. ## Usage From the RIOT base directory, run: ```bash make generate-board ``` Then answer a few questions about the driver: - Board name: Enter a name for your board. It will be used as the name of the board directory under `boards`. - Board displayed name: Enter the name of the board, as displayed in the Doxygen documentation. - CPU name: Enter the name of the CPU embedded on the board. - CPU model name: Enter the precise model name of the CPU. - Features provided: CPU features provided (and configured) for this board. Other global information (author name, email, organization) should be retrieved automatically from your git configuration. # Using Common Code To avoid code duplication, common code across boards has been grouped in `boards/common`. e.g. `BOARD`s based on the same cpu (`boards/common/nrf52`) or `BOARD`s having the same layout `boards/common/nucleo64`. In the case of source files this means some functions like `board_init` can be already defined in the common code. Unless having specific configurations or initialization you might not need a `board.c` or `board.h`. Another common use case is common peripheral configurations, for example in the `cfg_timer_tim5.h`: ```c /** * @name Timer configuration * @{ */ static const timer_conf_t timer_config[] = { { .dev = TIM5, .max = 0xffffffff, .rcc_mask = RCC_APB1ENR_TIM5EN, .bus = APB1, .irqn = TIM5_IRQn } }; #define TIMER_0_ISR isr_tim5 #define TIMER_NUMOF ARRAY_SIZE(timer_config) /** @} */ ``` # Boards Outside of RIOTBASE All `BOARD`s in RIOT reside in `RIOTBOARD` (`RIOTBOARD` being a make variable set to `$(RIOTBOARD)/boards`). If one wants to use a `BOARD` outside of `RIOTBOARD`, the way to go is setting the `EXTERNAL_BOARD_DIRS` variable to the path to the directory containing your external boards, e.g.: `EXTERNAL_BOARD_DIRS=/home/external-boards/` (this would commonly be done in your application `Makefile` or your environment). You can specify multiple directories separated by spaces. ``` /home/ |----RIOT/ |---- ... |----external-boards/ |----board-foo/ |----dist/ |----scripts |----board.c |----doc.md |----include/ |----periph_conf.h |----board.h |----gpio_params.h |----Makefile |----Makefile.dep |----Makefile.features |----Makefile.include ``` If the external `BOARD` is very similar to a `BOARD` already present in `RIOTBOARD`, the external `BOARD` (`board-foo`) can inherit from that parent `BOARD` (e.g: `foo-parent`). In this case some special considerations must be taken with the makefiles: - `Makefile` - `MODULE` cannot be `board`: `foo-parent` will already define `MODULE = board`, so use any other name, lets say `MODULE = board-foo`. - Include the location of the parent `BOARD` to inherit from (if there is one): ```makefile DIRS += $(RIOTBOARD)/foo-parent ``` - `Makefile.include` - duplicate the include done by `$(RIOTBASE)/Makefile.include` to also include the parent board header. e.g: if inheriting from `foo-parent` ``INCLUDES += $(addprefix -I,$(wildcard $(RIOTBOARD)/foo-parent/include))` - `Makefile.dep`: `board` is added by default to `USEMODULE` but since `board-foo` is used for this `BOARD`, it must be explicitly included by adding `USEMODULE += board-foo`. - Then simply include in each `Makefile.*` the corresponding parent `BOARD` `Makefile.*`, just as it is done for common `BOARD` code (as explained in [Using Common Code](#using-common-code)). e.g: `include $(RIOTBOARD)/foo-parent/Makefile.*include*` An example can be found in [`tests/build_system/external_board_native`](https://github.com/RIOT-OS/RIOT/tree/master/tests/build_system/external_board_native). # Board Names and Aliases New boards should be named according to [RDM0003](https://github.com/RIOT-OS/RIOT/blob/master/doc/memos/rdm0003.md). Historically, some board names have not followed this structure. For backwards compatibility, RIOT supports board aliases that can be used in place of the actual board name in the environment or Make variable `BOARD`. A list of all existing board aliases can be found in [`makefiles/board_alias.inc.mk`](https://github.com/RIOT-OS/RIOT/blob/master/makefiles/board_alias.inc.mk). [`BOARD=native`](https://doc.riot-os.org/group__boards__common__native.html) is a special alias in that it resolves to either [`native32`](https://doc.riot-os.org/group__boards__native32.html) or [`native64`](https://doc.riot-os.org/group__boards__native64.html) depending on the host architecture. # Tools Some scripts and tools available to ease `BOARD` porting and testing: - Run `dist/tools/insufficient_memory/add_insufficient_memory_board.sh ` if your board has little memory. This updates the `Makefile.ci` lists to exclude the `BOARD` from automated compile-tests of applications that do not fit on the `BOARD`s `CPU`. - Run `dist/tools/compile_and_test_for_board/compile_and_test_for_board.py . --with-test-only` to run all automated tests on the new board. # Further Reference - [In her blog](https://blog.martine-lenders.eu/riot-board-en.html), Martine Lenders documented her approach of porting the [Adafruit Feather nRF52840 Express](https://doc.riot-os.org/group__boards__adafruit-feather-nrf52840-express.html) in February 2020. - [Over at HackMD][https://hackmd.io/njFHwQ33SNS3sQKAkLkNtQ], Akshai M documented his approach of porting the [Silicon Labs SLSTK3400A starter kit](https://doc.riot-os.org/group__boards__slstk3400a.html) in July 2020.