Building your Own

Bake Your Own Image

In order to build your very own version of balenaOS for one of our supported boards, you will first need to make sure you have a working Yocto environment setup. Then pick the device type you want to build, in this example we will use the Raspberry Pi 3. So first we need to grab the balena-raspberrypi and initialise all its submodules.

git clone https://github.com/balena-os/balena-raspberrypi
cd balena-raspberrypi/
git submodule update --init --recursive

We can then use the helpful BARYS tool to setup up and start our build. To see all the functionality BARYS provides run ./balena-yocto-scripts/build/barys -h from with in the repo.

Now to actually build a development version of balenaOS for the Raspberry Pi 3, we can run the following:

./balena-yocto-scripts/build/barys -m raspberrypi3

Now sit tight and maybe go and make several cups of tea, this is going to take a little while.

By default, the images are created in the build/tmp/deploy/<yocto-machine-name> directory with the file extension .resinos-img or .balenaos-img. Rename the file extension to .img to flash the image to a SD card or USB drive using balenaEtcher.

Customer Board Support

Pre-requisites: a Yocto Board Support Package (BSP) layer for your particular board. It should be compatible with the Yocto releases balenaOS supports.

The repositories used to build the balenaOS host Operating System (OS) are typically called 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 balenaOS image for the Intel NUC boards.

Contributing support for a new board is a process that involves the following steps:

• Create the board support repository
• Contact balena to have the repository moved/mirrored and the build system jobs created
• Send a Pull Request for a hardware contract which describes the board's capabilities
• Maintaining the repository and OS updates

Step 1: Board Support Repository Breakout

The following documentation walks you through 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 at the end of this document.

There is a sample repo which we encourage you use as a starting base for your repository.

The balena-<board-family> repositories use git submodules for including required Yocto layers from the relevant sub-projects. Note: you add submodules by git submodule add <url> <directory>, see the git documentation for more details. The submodules have to be added using the https protocol.

The root directory structure contains the following directories:

├──.github
├──.versionbot
├── balena-yocto-scripts
└── layers

and files:

├── .gitignore
├── .gitmodules
├── CHANGELOG.md
├── LICENSE
├── README.md
├── VERSION
├── repo.yml
├── <board-name-1>.coffee
├── <board-name-2>.coffee
...
└── <board-name-x>.coffee

About coffee file(s)

One or more files named <board-name>.coffee, where <board-name> is the corresponding yocto machine name. Should add one for each of the boards that the repository adds support for (eg. raspberrypi3.coffee or rockpi-4b-rk3399.coffee). This file contains information on the Yocto build for the specific board, in CoffeeScript format.

Layers directory breakout

The typical layout for the layers directory is:

├── layers
│   ├── meta-balena
│   ├── meta-balena-<board-family>
│   ├── meta-<vendor>
│   ├── meta-openembedded
│   ├── meta-rust
│   └── poky

The layers directory contains the git submodules of the yocto layers used in the build process. The BSP git submodule(s) used should be publicly available repositories. All git submodules need to be cloned using the https protocol. This normally means the following components are present:

• meta-balena using the master branch
• meta-<vendor> : the Yocto BSP layer for the board (for example, the BSP layer for Raspberry Pi is meta-raspberrypi)
• meta-openembedded at the branch equivalent to the poky version
• meta-rust at the revision poky uses
• poky at the version/revision required by the board BSP (this fork must be used to not be rate-limited by the yocto project git when doing lots of builds)
• 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). These should be public repo(s).

In addition to the above git submodules, the layers directory requires a meta-balena-<board-family> directory (please note this directory is not a git submodule). This directory contains the required customization for making a board balena.io 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.

meta-balena-<board-family> breakout

We call this directory the balena integration directory. It is a Yocto layer that includes:

• balenaOS-specific software features,
• deployment-specific features (i.e., settings to create SD card, USB thumb drive, or self-flashing images)

This directory contains optional and mandatory directories:

conf directory - contains the following files:

1. layer.conf, see the layer.conf from meta-balena-raspberrypi for an example, and see Yocto documentation
2. samples/bblayers.conf.sample file in which all the required Yocto layers are listed, see this bblayers.conf.sample, and see the Yocto documentation
3. samples/local.conf.sample file 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.sample file). You can use as guide an existing sample (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-bsp

This directory should contain the changes to the bootloader recipes used by your board. For example, for u-boot based boards, it must define the following, and it must include at least a patch to the u-boot bootcmd that changes the default boot command to include balena required setup. See this example, or if you use a newer u-boot you can simply use config fragments to alter the bootcmd like done here.

recipes-core/images directory

This directory contains at least a balena-image.bbappend file. Depending on the type of board you are adding support for, you should have your device support either just balena-image or both balena-image-flasher and balena-image. Generally, balena-image is for boards that run directly from external storage (these boards do not have internal storage to install balenaOS on). balena-image-flasher is 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 balenaOS on internal storage.

The balena-image.bbappend file shall define the following variable(s):

• 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 to 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_<yocto-machine-name> and INTERNAL_DEVICE_BOOTLOADER_CONFIG_PATH_<yocto-machine-name> below). Please note that you only reference these files here. It is the responsibility of a .bb or .bbappend to 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.bin copied from the deploy directory over to the boot partition, renamed to vmlinuz:

BALENA_BOOT_PARTITION_FILES_nuc = "bzImage-intel-corei7-64.bin:vmlinuz"

The balena-image-flasher.bbappend file shall define the following variable(s):

• 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 for the use of INTERNAL_DEVICE_BOOTLOADER_CONFIG variable), then make sure these files end up in the boot partition (i.e. they should be listed in this BALENA_BOOT_PARTITION_FILES_<yocto-machine-name> variable)

recipes-kernel/linux directory

Shall contain a .bbappend to the kernel recipe used by the respective board. This kernel .bbappend must "inherit kernel-balena" in order to add the necessary kernel configs for balenaOS

recipes-support/resin-init directory

Shall contain a resin-init-flasher.bbappend file if you intend to install balenaOS to internal storage and hence use the flasher image.

resin-init-flasher.bbappend should define the following variables:

• INTERNAL_DEVICE_KERNEL_<yocto-machine-name>: used to identify the internal storage where balenaOS will be written to.
• if required - INTERNAL_DEVICE_BOOTLOADER_CONFIG_<yocto-machine-name>: used to specify the filename of the bootloader configuration file used by your board when booting from internal media. Must be the same as the FilenameOnTheTarget parameter of the bootloader internal config file used in the BALENA_BOOT_PARTITION_FILES_<yocto-machine-name> variable from recipes-core/images/balena-image-flasher.bbappend.

• if required - INTERNAL_DEVICE_BOOTLOADER_CONFIG_PATH_<yocto-machine-name>: 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" and 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.cfg to the /EFI/BOOT/ directory on the resin-boot partition.

• BOOTLOADER_FLASH_DEVICE: used to identify the internal storage which the bootloader needs to be flashed to. This is only the case usually when the bootloader needs to be in a SPI flash-like memory where the bootrom code expects it to read it from raw disk instead from a partition. Note that if BOOTLOADER_FLASH_DEVICE is set, then also BOOTLOADER_IMAGE, BOOTLOADER_BLOCK_SIZE_OFFSET and BOOTLOADER_SKIP_OUTPUT_BLOCKS need to be set.
• BOOTLOADER_IMAGE: used to specify the name of the bootloader binary, from the resin-boot partition, that is to be written to BOOTLOADER_FLASH_DEVICE.
• BOOTLOADER_BLOCK_SIZE_OFFSET: used to specify the block size with which BOOTLOADER_IMAGE is to be written to BOOTLOADER_FLASH_DEVICE.

• BOOTLOADER_SKIP_OUTPUT_BLOCKS: used to specify how many blocks of size BOOTLOADER_BLOCK_SIZE_OFFSET need to be skipped from BOOTLOADER_FLASH_DEVICE when writing BOOTLOADER_IMAGE to it.

  Note: Some hardware requires the use of a MLO (a.k.a. SPL - secondary program loader) that is to be copied in static RAM and executed from there (static RAM is small in size), and this first stage bootloader is responsible for initializing the regular RAM and then copying the regular bootloader to this regular RAM and passing execution to it. For this purpose, a second set of variables called BOOTLOADERFLASHDEVICE1, BOOTLOADERIMAGE1, BOOTLOADERBLOCKSIZEOFFSET1, and BOOTLOADERSKIPOUTPUTBLOCKS_1 can be used to accommodate this use case.

For example, setting:

BOOTLOADER_FLASH_DEVICE = "mtdblock0"
BOOTLOADER_IMAGE = "u-boot.imx"
BOOTLOADER_BLOCK_SIZE_OFFSET = "1024"
BOOTLOADER_SKIP_OUTPUT_BLOCKS = "3"

will result that the file u-boot.imx from the resin-boot partition is written to /dev/mtdblock0 with a block size of 1024 bytes and after the first 3 * 1024 bytes of /dev/mtdblock0.

recipes-support/hostapp-update-hooks directory

Shall contain a hostapp-update-hooks.bbappend with content based on if your board uses u-boot or grub. Then it may also need to include an additional hook for writing the bootloader(s) binary in the right place(s) when doing hostOS updates.

The optional directories in meta-balena-<board-family> are:

recipes-containers/docker-disk directory

Which contains balena-supervisor.bbappend that can 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.

The directory structure then looks similar to this:

├── conf
│   ├── layer.conf
│   └── samples
│       ├── bblayers.conf.sample
│       └── local.conf.sample
├── recipes-bsp
│   └── <bootloader recipes dir used by your board>
├── 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
    └── hostapp-update-hooks
        ├── files
        │   └── <bootloader update hook>
        └──  hostapp-update-hooks.bbappend
    └── resin-init
        └── resin-init-flasher.bbappend

Building

See the meta-balena Readme on building the new balenaOS image after setting up the new board package as defined above.

Step 2: Contact balena

When you have completed the development of the yocto board support repository as detailed in the previous step, please get in touch with balena to finish the process of having your board available in the balena dashboard.
This will mean your board repository would need to be hosted in balena-os GitHub organization. Depending on your needs and upon agreeing with balena, it can be hosted either as a public repository for everyone to access or hosted privately with access only to selected users.

Step 3: Hardware contract

Having a board supported by balena also means having a hardware contract describing that device type.
balena allows for public or private device types. Public device types can be used by all users while private device types are only accessible to selected users upon agreeing with balena. Note that public/private device type visibility mentioned here is independent of the GitHub repository visibility (you can choose to have any combination of these two).

For publicly available device types, the hardware contracts are located here and you must send a Pull Request to this public contract repository with the appropriate contract. See this as an example to base on.

For private device types, balena will make the necessary changes when supplied with the hardware contract.

Step 4: Maintaining the repository and OS updates

Once the board is supported in balena, it will receive automatic pull requests with updates of meta-balena as new releases of meta-balena get done. These automatic pull requests get merged if the CI builds succeed, so care must be taken from time to time to check that your code is still compatible with the latest meta-balena releases.

Maintaining / pushing updates to the code other than meta-balena updates need to be done through pull requests in the appropriate board repository in the balena-os GitHub org and will be reviewed by balena prior to merging. However, after new code gets merged (either through the automatic meta-balena updates or through contribution pull requests), in order for the new releases to be available in the dashboard, balena needs to be contacted about deploying the new releases.

Currently Supported Hardware Families

See the repositories below for specific examples on how board support is provided for existing devices.

ARM

• Beaglebone: balena-beaglebone
• Raspberry Pi: balena-raspberrypi
• Freescale/NXP: balena-fsl-arm
• ODROID: balena-odroid
• Parallella: balena-parallella
• Technologic Systems: balena-ts
• Toradex: balena-toradex
• VIA: balena-via-arm
• Zynq: balena-zc702
• Samsung Artik: balena-artik

x86

• Intel Edison: balena-edison
• Intel NUC: balena-intel

Other

• QEMU: balena-qemu

Troubleshooting

Kernel complains that CONFIG_AUFS was not activated

The versions before v2.0-beta.3 didn't support kernel sources that were not git repositories. Starting with this version, aufs patches will get applied on kernel recipes that use tar archives, for example as well. For the older version, this is considered a limitation.