Custom board support
Pre-requisites: a Yocto Board Support Package (BSP) layer for your particular board. It should be compatible to the Yocto releases balenaOS supports.
Repositories used to build balenaOS host Operating System (OS) are typically named
balena-<board-family>. For example, consider balena-raspberrypi which is used for building the OS for Raspberryi Pi, or balena-intel repository which can be used to build a balena image for the Intel NUC boards.
Contributing support for a new board consist of creating a Yocto package that includes:
- general hardware support for the specific board,
- the balenaOS-specific software features,
- deployment-specific features (i.e. settings to create SD card images or self-flashing images)
The following documentation walks you through the steps of creating such a Yocto package. Because of the substantial difference between the hardware of many boards, this document provides general directions, and often it might be helpful to see the examples of already supported boards. The list of the relevant repositories is found the end of this document.
Board Support Repository Breakout
balena-<board-family> repositories use git submodules for including required Yocto layers from the relevant sub-projects.
The root directory shall contain 2 directory entries:
- balena-yocto-scripts git submodule.
Note: you add submodules by
git submodule add <url> <directory>, see the git documentation for more details.
The root directory generally also includes the following files:
and one or more files named
<yocto-machine-name>.coffee, one for each of the boards that the repository will add support for (eg.
raspberry-pi3.coffee for Raspberry Pi 3 in
balena-raspberrypi). This file contains information on the Yocto build for the specific board, in CoffeeScript format. A minimal version of this file, using Raspberry Pi 3 as the example, would be:
module.exports = yocto: machine: 'raspberrypi3' image: 'balena-image' fstype: 'balenaos-img' version: 'yocto-jethro' deployArtifact: 'balena-image-raspberrypi3.balenaos-img' compressed: true
layers directory contains the git submodules of the yocto layers used in the build process. This normally means the following components are present:
- poky at the version/revision required by the board BSP
- meta-openembedded at the revision poky uses
- meta-balena using the master branch
- meta-rust using the master branch
- Yocto BSP layer for the board (for example, the BSP layer for Raspberry Pi is meta-raspberrypi)
- any additional Yocto layers required by the board BSP (check the Yocto BSP layer of the respective board for instructions on how to build the BSP and what are the Yocto dependencies of that particular BSP layer)
In addition to the above git submodules, the "layers" directory also contains a
meta-balena-<board-family> directory (please note this directory is not a git submodule, but an actual directory in the ). This directory contains the required customization for making a board balena enabled. For example, the balena-raspberrypi repository contains the directory
layers/meta-balena-raspberrypi to supplement the BSP from
layers/meta-raspberrypi git submodule, with any changes that might be required by balenaOS.
The layout so far looks as follows:
├── CHANGELOG.md ├── LICENSE ├── README.md ├── VERSION ├── layers │ ├── meta-openembedded │ ├── meta-<board-family> │ ├── meta-balena │ ├── meta-balena-<board-family> │ ├── meta-rust │ └── poky ├── <board>.coffee └── balena-yocto-scripts
This directory contains:
COPYING.Apache-2.0file with the Apache Version 2.0 license,
README.mdfile specifying the supported boards
and a number of directories out of which the mandatory ones are:
confdirectory - contains the following files:
layer.conf, see the layer.conf from
meta-balena-raspberrypifor an example, and see Yocto documentation
samples/bblayers.conf.samplefile in which all the required Yocto layers are listed, see this bblayers.conf.sample from
meta-balena-raspberrypifor an example, and see the Yocto documentation
samples/local.conf.samplefile which defines part of the build configuration (see the meta-balena README.md for an overview of some of the variables use in the
local.conf.samplefile). An existing file can be used (e.g. local.conf.sample) but making sure the "Supported machines" area lists the appropriate machines this repository is used for. See also the Yocto documentation.
recipes-containers/docker-diskdirectory, which contains
balena-supervisor.bbappendthat shall define the following variable(s):
LED_FILE_<yocto-machine-name>: this variable should point to the Linux sysfs path of an unused LED if available for that particular board. This allows the unused LED to be flashed for quick visual device identification purposes. If no such unused LED exists, this variable shall not be used.
recipes-core/imagesdirectory, which contains at least a
balena-image.bbappendfile. Depending on the type of board you are adding support for, you should have your device support either just
balena-imageis for boards that boot directly from external storage (these boards do not have internal storage to install balena on).
balena-image-flasheris used when the targeted board has internal storage so this flasher image is burned onto an SD card or USB stick that is used for the initial boot. When booted, this flasher image will automatically install balena on internal storage.
balena-image.bbappendfile shall define the following variables:
IMAGE_FSTYPES_<yocto-machine-name>: this variable is used to declare the type of the produced image (it can be ext3, ext4, balenaos-img etc. The usual type for a board that can boot from SD card, USB, is "balenaos-img").
BALENA_BOOT_PARTITION_FILES_<yocto-machine-name>: this allows adding files from the build's deploy directory into the vfat formatted resin-boot partition (can be used to add bootloader config files, first stage bootloader, initramfs or anything else needed for the booting process to take place for your particular board). If the board uses different bootloader configuration files when booting from either external media (USB thumb drive, SD card etc.) or from internal media (mSATA, eMMC etc) then you would want make use of this variable to make sure the different bootloader configuration files get copied over and further manipulated as needed (see
INTERNAL_DEVICE_BOOTLOADER_CONFIG_PATH_<yocto-machine-name>below). Please note that you only reference these files here, it is the responsibility of a
.bbappendto provide and deploy them (for bootloader config files this is done with an append typically in
recipes-bsp/<your board's bootloader>/<your board's bootloader>.bbappend, see balena-intel grub bbappend for an example)
It is a space separated list of items with the following format: FilenameRelativeToDeployDir:FilenameOnTheTarget. If FilenameOnTheTarget is omitted then the FilenameRelativeToDeployDir will be used.
For example to have the Intel NUC
bzImage-intel-corei7-64.bincopied from deploy directory over to the boot partition, renamed to
BALENA_BOOT_PARTITION_FILES_nuc = "bzImage-intel-corei7-64.bin:vmlinuz"
balena-image-flasher.bbappendfile shall define the following variables:
BALENA_BOOT_PARTITION_FILES_<yocto-machine-name>(see above). For example, if the board uses different bootloader configuration files for booting from SD/USB and internal storage (see below the use of
INTERNAL_DEVICE_BOOTLOADER_CONFIGvariable), then make sure these files end up in the boot partition (i.e. they should be listed in this
recipes-kernel/linux directory: shall contain a
.bbappendto the kernel recipe used by the respective board. This kernel
.bbappendmust "inherit kernel-resin" in order to add the necessary kernel configs for using with balena.
recipes-support/resin-initdirectory - shall contain a
resin-init-flasher.bbappendfile if you intend to install balena to internal storage and hence use the flasher image. This shall define the following variables:
INTERNAL_DEVICE_KERNEL_<yocto-machine-name>: this variable is used to identify the internal storage where balena will be written to.
INTERNAL_DEVICE_BOOTLOADER_CONFIG_<yocto-machine-name>: this variable is used to specify the filename of the bootloader configuration file used by your board when booting from internal media (must be the same with the FilenameOnTheTarget parameter of the bootloader internal config file used in the
INTERNAL_DEVICE_BOOTLOADER_CONFIG_PATH_<yocto-machine-name>: this variable is used to specify the relative path (including filename) to the resin-boot partition where
INTERNAL_DEVICE_BOOTLOADER_CONFIG_<yocto-machine-name>will be copied to.
For example, setting
INTERNAL_DEVICE_BOOTLOADER_CONFIG_intel-corei7-64 = "grub.cfg_internal"
INTERNAL_DEVICE_BOOTLOADER_CONFIG_PATH_intel-corei7-64 = "/EFI/BOOT/grub.cfg"
will result that after flashing the file
grub.cfg_internal is copied with the name
grub.cfgto the /EFI/BOOT/ directory on the resin-boot partition.
The directory structure then looks similar to this:
├── COPYING.Apache-2.0 ├── README.md ├── conf │ ├── layer.conf │ └── samples │ ├── bblayers.conf.sample │ └── local.conf.sample ├── recipes-bsp │ └── bootfiles ├── recipes-containers │ └── docker-disk │ └── balena-supervisor.bbappend ├── recipes-core │ ├── images │ │ └── balena-image.bbappend ├── recipes-kernel │ └── linux │ ├── linux-<board-family>-<version> │ │ └── <patch files> │ ├── linux-<board-family>_%.bbappend │ └── linux-<board>_<version>.bbappend └── recipes-support └── resin-init ├── files │ └── resin-init-board └── resin-init-board.bbappend
See the meta-balena Readme on how to build the new balenaOS image after setting up the new board package as defined above.
For specific examples on how board support is provided for existing devices, see the repositories in the Supported Boards section.