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Version: 5.0

Build a Reference Image with Yocto Project/OpenEmbedded

Introduction

This hands-on document describes how to build our Reference Images for Yocto Project from scratch using OpenEmbedded-Core (OE-Core). For a conceptual article about the relationship between Toradex' Embedded Linux offerings and the Yocto Project, you must read Yocto Project. For building TorizonCore, additional instructions are provided on Build TorizonCore With Yocto Project.

OpenEmbedded (openembedded.org) is a build framework that creates kernel images, root filesystem images and installable packages from source code. It is used by the Yocto Project to build Embedded Linux images. For the sake of this document OpenEmbedded and Yocto Project are used interchangeably unless otherwise noted.

OpenEmbedded uses meta-information (called recipes) for downloading/compiling/deploying of software packages on a x86/x86_64 Linux build host for a target device. This meta-information is structured into so-called layers. Layers are directory trees with recipes that provide similar functionality, e.g. meta-lxde which provides recipes to build packages for the LXDE desktop.

Versions and Source-Code

Layers from git.toradex.com are used together with a number of other layers. The collection of Toradex and third-party layers used on a specific BSP release are provided in a repo manifest on toradex-manifest, and you will learn more about it later in this article.

There might be several concurrent versions available at a given point in time, learn more about this on the Toradex Embedded Linux Support Strategy. Versions of the Reference Images for Yocto Project and their correspondent distribution, OpenEmbedded codename, and Yocto Project releases are provided in the following table:

Toradex VersionStatusDistributionOpenEmbedded/Yocto Project CodenameYocto Project Release
2.1OutdatedÅngström v2013.06dylan1.4
2.2OutdatedÅngström v2013.12dora1.5
2.3OutdatedÅngström v2014.06daisy1.6
2.4OutdatedÅngström v2014.12dizzy1.7
2.5OutdatedÅngström v2015.06fido1.8
2.6 / 2.6.1OutdatedÅngström v2015.12jethro2.0
2.7OutdatedÅngström v2016.12morty2.2
2.8LTSÅngström v2017.12rocko2.4
3.0LTSPoky basedthud2.6
4.0.0 (deferred*)DeferredPoky basedzeus3.0
5.x.yLatestPoky baseddunfell3.1 LTS

* 4.0.0 is deferred, learn more on https://www.toradex.com/blog/torizon-yocto-project-long-term-support-alignment

A release matrix that summarizes versions of Yocto/OpenEmbedded, the Linux kernel and U-Boot, and release dates for Toradex Embedded Linux releases is provided in a separate article:

Release Notes

Concise, high-level release notes are published on the News section of toradex.com:

Comprehensive, detailed release notes are maintained on the following pages on the developer website:

Building a Reference Image with Yocto Project

BSP 5.0.0

Prerequisites

A Yocto Project build requires intensive computing power and specific software packages.

Computer for the Yocto Project Build

A powerful host machine is highly recommended to build a Yocto Project image. If the host system is a multi-core machine, you can configure the Yocto Project build system to decrease the time needed to build images significantly. There should be a minimum of 60 GBytes of free disk space. For some images, a 32-bit host with 4 GBytes of memory is enough, but to build applications such as the WebKit web engine, a 64-bit machine with at least 8 GBytes of RAM is recommended.

Operating System and Build Dependencies

Yocto Project Release 3.1 is officialy supported by the Yocto Project. The following Linux distributions are supported and you must use one of them on your development PC to build our BSPs:

You must install the required Yocto build dependencies on your host PC:

danger

make sure to follow only the steps on the Yocto Mega Manual to install the build dependencies. Do not go any further into the environment setup.

Virtual Machines, Containers and Cloud Builds

Toradex does not go on about doing a Toradex Reference Image build on a VM, Container, or a public cloud provider as AWS or Azure. Nevertheless, it is possible. Therefore if you feel like doing it, you may consider studying your options. Find some generic remarks for a simplified overview:

  • VM: a Yocto Project build is resource-intensive, it may not be a good idea to use a VM, because a VM may introduce a performance penalty that will make the build longer.
  • Container: it has a negligible performance penalty. Pay attention to using bind-mounts or volumes to keep persistent data; otherwise, you may lose time on every build. Containers theoretically allow you to do a Yocto Project build from a Windows PC.
    • Toradex supports a container environment for building TorizonCore with the Yocto Project, read the article Build TorizonCore With Yocto for details. You may use it for building Reference Images but do it at your own risk since building Reference Images is not officially supported.
  • Cloud: the cloud has powerful machines that make it possible to run a full Yocto Project build in less than half an hour if you disregard setup and pre-requisites installation time. Similar to containers, you should plan how to store the output of a build. Also, don't forget to evaluate the cost of this approach!

Repo and Git

Since OpenEmbedded requires several git repositories to build our images, starting with V2.1 images, we use a utility called 'repo'. The repo manifest manages the various git repositories and their branches. (more on repo: http://code.google.com/p/git-repo/)

Install the repo bootstrap binary:

$  mkdir ~/bin
$ export PATH=~/bin:$PATH
$ curl https://commondatastorage.googleapis.com/git-repo-downloads/repo > ~/bin/repo
$ chmod a+x ~/bin/repo

Alternatively, in Ubuntu, repo may be installed as part of the 'phablet-tools' package.

Repo uses Git. Make sure you have it installed and your user name and e-mail address configured. Below is an example for Debian-based systems:

$ sudo apt install git
$ git config --global user.name "John Doe"
$ git config --global user.email johndoe@example.com

Installation

This section has two major sub-sections you have to choose:

  • First-time Configuration: if you are doing a build for the first time.
  • Update an Existing Configuration: if you have a build already set up and want to update it.

First-time Configuration

Create a directory for your OE-Core setup to live in and clone the meta-information:

caution

Please be sure to have Python installed on your machine. For the command "repo init" to work, the executable "python" must be available, "python" can be a symbolic link to "python3". In addition, remember to have the PATH variable exported on the terminal you're currently using.

$ mkdir ${HOME}/oe-core
$ cd ${HOME}/oe-core
$ repo init -u https://git.toradex.com/toradex-manifest.git -b dunfell-5.x.y -m tdxref/default.xml
$ repo sync

Source the file export to setup the environment. On the first invocation, this also copies a sample configuration to build/conf/*.conf.

$ . export

Note: Sourcing export configures the shell environment for the current shell session. You must enter this command whenever you open a new shell session for use with OpenEmbedded.

Adjust the settings in the local.conf file

Adapt build/conf/local.conf to your needs.

The MACHINE variable specifies the target device for the image. Set this variable to the module type you are planning to build for.

Our BSP layers provide the following machines:

Machine NameCorresponding Toradex Module
apalis-imx6Apalis iMX6
apalis-imx8Apalis iMX8
apalis-imx8xApalis iMX8X V1.1B and newer
apalis-imx8x-v11aApalis iMX8X V1.1A only
apalis-tk1Apalis TK1
colibri-imx6Colibri iMX6
colibri-imx6ullColibri iMX6ULL 512MB (equipped with raw NAND flash)
colibri-imx6ull-emmcColibri iMX6ULL 1GB (equipped with eMMC flash) [1]
colibri-imx7Colibri iMX7S 256MB and iMX7D 512MB (equipped with raw NAND flash)
colibri-imx7-emmcColibri iMX7D 1GB (equipped with eMMC flash)
colibri-imx8xColibri iMX8X V1.0C or newer [2]
verdin-imx8mmVerdin iMX8M Mini
verdin-imx8mpVerdin iMX8M Plus

[1] added on the 5.4.0-devel-202109 (September 2021 monthly pre-release)


[2] the machine `colibri-imx8x-v10b` for V1.0B latest supported version is BSP 5.4.0. It was removed in 5.5.0 onward.

e.g. set in local.conf

    MACHINE ?= "colibri-imx6"

Note: You can explicitly override the MACHINE setting on the command line. To do that, set the variable MACHINE when calling the bitbake command (e.g. MACHINE=apalis-imx6 bitbake...)

If you have lots of disk space and want to browse the unpacked sources, consider commenting on the INHERIT += "rm_work" line.

If you already have a download directory with sources from a previous OE setup, consider moving that directory into oe-core/build/download or change local.conf to point to your standard download location. DL_DIR.

If you want to build for a machine based on an NXP based SoM, some downloads require you to read and accept the NXP®/Freescale EULA available in layers/meta-freescale/EULA. You have to state your acceptance by adding the following line to your local.conf file:

ACCEPT_FSL_EULA = "1"

If this line is missing, the relevant packages will produce an ERROR similar to:

ERROR: To use 'imx-vpu' you need to accept the NXP®/Freescale EULA at 'layers/meta-freescale/EULA'. Please read it and in case you accept it, write: ACCEPT_FSL_EULA = "1" in your local.conf.

When the setup finishes, continue with the Building chapter.

Update an Existing Configuration

If you need to update the installation, you first update the repo manifest to the version you want to work with and then sync all layers. Check the known issues section below before starting the update.

If you did local changes to the individual layers, merge conflicts may occur, which you will have to resolve in the respective layer.

Update to the HEAD Revision
info

You cannot update from BSP 4.0.0 or older to 5.0.0 or newer, because a different Git repository is used!

A list of available branches is available in the repository: http://git.toradex.com/cgit/toradex-manifest.git/refs/heads

$ repo init -u https://git.toradex.com/toradex-manifest.git -b dunfell-5.x.y -m tdxref/default.xml
$ repo sync
Update to a Specific Version by Using its Tag

If you need to update to a specific version, a list of available tags is available in the manifest repository: https://git.toradex.com/cgit/toradex-manifest.git/refs/tags

As an example:

$ repo init -u https://git.toradex.com/toradex-manifest.git -b refs/tags/5.1.0-devel-202011 -m tdxref/default.xml
$ repo sync

Building the BSP from our Nightly Platform

caution

This is for development and testing only, to validate the latest changes/bugfixes from Toradex at BSP 5. Do not use it for production.

In some cases, you may want to experience our latest additions to the BSP, so to try a fix or even an improvement.

That can be done with a repository set to use the tdxref/integration.xml manifest:

repo init -u https://git.toradex.com/toradex-manifest.git -b dunfell-5.x.y -m tdxref/integration.xml

You can then sync it, to get the resources:

repo sync

In addition, you have to add the following parameter to your conf/local.conf file:

MACHINEOVERRIDES =. "use-head-next:"

After that, you can build your image using bitbake as instructed in Build an Image below.

Known Issues During repo Setup

If your repo command succeeds, you can directly proceed with the instructions in the chapter Building below. See additional known issues notes at the end of this page.

Repo Sync Issues

Due to many company firewalls/proxies only permitting HTTP traffic, our default repo manifest is using. However, the OpenEmbedded or Linaro repositories might show inconsistencies if fetched over HTTP, or their web servers might be under such heavy load. If you get any of the following repo fetch/sync issues:

    error: Unable to find d29dee17d9a95f2ec6b641c234870f3ccbe24102 under http://git.openembedded.org/meta-openembedded
Cannot obtain needed blob d29dee17d9a95f2ec6b641c234870f3ccbe24102

or:

    error: Unable to find 318f971bb4515a6dcbbb0b87f85f2bc58b6e314f under http://git.linaro.org/git-ro/openembedded/meta-linaro.git
Cannot obtain needed commit 318f971bb4515a6dcbbb0b87f85f2bc58b6e314f

or:

    fatal: loose object 8807fd141bb73d6b405eff223b3b105613bc809a (stored in /home/user/oe-core/.repo/projects/layers/meta-openembedded.git/objects/88/07fd141bb73d6b405eff223b3b105613bc809a) is corrupt
error: http://git.openembedded.org/meta-openembedded did not send all necessary objects

First, try repo syncing again. It might only have been a connection glitch.

Then, if the error(s) persist, try using git's garbage collection on the failing repository before attempting to sync again, e.g., if the error indicates an issue in the meta-openembedded repository:

$ cd .repo/projects/layers/meta-openembedded.git
$ git gc

If the error(s) persist try removing your local git/repo cache before attempting to sync again, e.g. if the error indicates an issue in the meta-openembedded repository:

$ rm -rf .repo/projects/layers/meta-openembedded.git
$ rm -rf .repo/project-objects/meta-openembedded.git

Additionally, you can limit the number of downloads of git repositories in parallel using the additional parameter -jX. e.g., to download one repository at a time:

$ repo sync -j1

Additionally, the Ångström Distribution reports the following tweak to your IP settings helpful:

$ sudo sysctl -w net.ipv4.tcp_window_scaling=0

If your Internet connection permits you might also try switching those failing repositories to using the git protocol instead by modifying your .repo/manifest.xml as follows:

    <remote fetch="git://git.openembedded.org" name="oe"/>
<remote fetch="git://git.linaro.org/openembedded" name="linaro"/>
Bitbake Build Issues

There are no bitbake build issues reported for the latest BSPs; you can consult the Legacy section at the end of this article to see Bitbake build issues for older releases.

Building

This section goes on about build steps.

Setup the Environment

Every time you open a new terminal, go to the OpenEmbedded directory and setup the environment:

$ . export

Directory Structure

OE-Core installation, configuration, and build will setup the following directory structure:

    oe-core/
+-- build
¦ +-- conf
¦ +-- downloads
¦ +-- tmp
¦ +-- sstate-cache
¦ +-- deploy
¦ +-- images
¦ ¦ +-- <machine 1...n>
¦ +-- ipk
¦ +-- licenses
¦ +-- sdk
+-- layers
+-- meta-browser
+-- meta-freescale
(... other layers)
+-- openembedded-core
  • layers: stores metadata, as machine and distro information, but also the recipes for building all components of an embedded Linux image.
  • build: keeps build configuration, downloaded source codes, intermediate build output, generated packages (IPK, DEB, RPM), SDKs.
    • conf: this is the only subdirectory that you must preserve under build. All other subdirectories are regenerated when you start a new build if they don't exist yet.
    • deploy: the final images, ready to install (flash) into a computer on module. The packages that compose an image, in our case packaged as IPK, since we use the OPKG package manager. Licenses for all the software installed. The SDK, if you build one.

Openembedded uses several places for configurations.

  • General files from e.g. bitbake folder.
  • Distro (from Layer/conf/distro/<distro-name>.conf)
  • Machine (from Layer/conf/machine/<machine-name>.conf)
  • Local Build (from <build-directory>/conf/local.conf)
Distro

A Linux distribution (often abbreviated as distro) is a software collection based upon the Linux kernel. It comprises the Linux Kernel, tools, libraries and additional software.

Openembedded / Yocto gets the distribution policy from a configuration file which is set by the DISTRO variable in local.conf.

This policy for example defines the libc variant, the init system, the ARM vs. THUMB instruction set, or the package manager used. Also, it can set distro features which the individual recipes can then evaluate to configure their build, e.g. if polkit is used/available or what display server protocol is available.

Toradex provides several distribution policy files based on the Poky one. We provide distro variants for different kernel configurations, summarized in the table below. Even though all distributions set the policy for the graphics stack, for example Weston/Wayland + XWayland, not all images include the graphics libraries: for instance, the Reference Minimal Image is a console-only image.

If you want to know exactly what is defined for each distro, follow the links as they point to the relevant configuration files.

Distrokernel basekernel config
tdx-xwaylandDownstream kernel from SoC vendor (NXP)Default (without the PREEMPT_RT patch)
tdx-xwayland-rtDownstream kernel from SoC vendor (NXP)Fully preemptive (real-time Linux PREEMPT_RT patch)
tdx-xwayland-upstreamMainline kernelDefault (without the PREEMPT_RT patch)
tdx-xwayland-upstream-rtMainline kernelFully preemptive (real-time Linux PREEMPT_RT patch)
info

For all i.MX8 based machines we use the downstream kernel. The mainline kernel does (not yet) contain the features needed for production use.

upstream: marks that the kernel built will be close to mainline and that the userspace uses mainlinish/opensource userspace drivers (Mostly graphical components, e.g. Vivante closed source vs. etnaviv). Note that each <machine>.conf decides what that mainline kernel will be.

rt: Toradex also provides real-time kernel flavours for use in an OpenEmbedded-Core (Yocto Project) build, and related distros that use it. See the Real-Time Linux article with Real-Time Linux article, Yocto Recipe for more information.

The default distro is tdx-xwayland. You can select other distro by modifying the DISTRO variable on the oe-core/buildconf/local.conf file.

See the configuration files of the distro on the layers/meta-toradex-distro/conf/distro/ directory.

Build an Image

A image recipe list all packages which have to be built and installed into the final root file system. The build system will take care that any known dependent package will also be installed.

Toradex provides two reference image variants built on top of the distribution variants. Below we list the image variants and their description and some remarkable features. If you want to know exactly all the features, follow the links as they point to the relevant Yocto recipes.

ImageDescription
Reference Minimal Image
tdx-reference-minimal-image
Minimal image without graphical interface that just boots

- Network manager: connman
- Init system: systemd
- Base command-line packages included in packagegroup-tdx-cli.bb
Reference Multimedia Image
tdx-reference-multimedia-image
Image for BSP verification with Qt and multimedia features

- All that is included in the Reference Minimal Image
- Graphics stack: Weston / Wayland + XWayland
- Graphical User Interface framework: Qt
- Camera and Video framework: V4L2 and Gstreamer
- All command-line packages included in packagegroup-tdx-cli.bb
- All graphical packages included in packagegroup-tdx-graphical.bb
- All Qt5 packages included in packagegroup-tdx-qt5.bb

You can use them as a base for your project. Don't use them as-is because they are not ready to be deployed in production (not hardened, etc.). The available image recipes are located in layers/meta-toradex-demos/recipes-images/images/, also in our Git repository - just make sure to select the correct branch!

After you choose the image from the table above, you can build it:

$ bitbake <image>

Bitbake automatically logs console output to timestamped files in build/tmp/log/cooker/$MACHINE/.

info

With OE-Core you need to be in the directory 'build' when you execute bitbake.

info

This will at first build take hours, download lots of stuff and fill 'build/tmp', so have at least 60 GByte free.

info

Check available demo image recipes in layers/meta-toradex-demos/recipes-images/images/

If you are executing an unattended build, -k tells bitbake to keep going with independent packages even after an error occurred:

$ bitbake -k <image>

Bitbake Commands

See in this section other useful bitbake commands.

Build a Single Package

Build a single package and all the things it depends on.

$ bitbake samba
Build an SDK

Building an SDK for your image, pass the parameter -c populate_sdk (See also Linux SDKs)

$ bitbake <image> -c populate_sdk
Build the Linux kernel

There is a virtual recipe for building the Linux kernel for your machine regardless of its version:

$ bitbake virtual/kernel
Additional Logs
caution

the number of messages to stdout is huge!

If you need to dig into what recipes and settings are used for, the following command outputs a bunch of environment settings and info about what is going on, use the parameter -e:

$ bitbake -e virtual/kernel
$ bitbake -e virtual/kernel | grep ^WORKDIR
Available Tasks for a Recipe

If you want to see all tasks which exist for a given recipe, use the parameter -c listtasks:

$ bitbake -c listtasks virtual/kernel

Build Artifacts

The output artifacts can be found here:

  • For images, u-boot, uImage, rootfs, deployable tarball: build/deploy/images/${MACHINE}/
  • For SDKs: build/deploy/sdk/
  • For ipk packages: build/deploy/ipk/<package-arch>/*.ipk

Install the Image on the Board

Get the deployable tarball image from the directory pointed in the previous section.

The image tarball, (e.g. Colibri-iMX6_LXDE-Image-Tezi_2.7-20180104.tar) has the same structure as the ones Toradex provides pre-built for download.

To update your computer on module with a newly built image, follow the procedure documented in the Toradex Easy Installer article.

First Steps Into Your Custom Build

The Yocto Project can be quite defying and hard to use. In the following documentation, we cover some basic functionality that is likely you will have to go through during your development:

It does not replace the official Yocto Project documentation, though. At the end of this page, we provide links to it, and you will most likely need to study it to some degree.

Production Programming

Since BSP 5.2.0, we have introduced an End User License Agreement (EULA) to our Reference Images. It prevents you to use the autoinstall feature of the Toradex Easy Installer, as suggested in the article Production Programming for Linux.

You must remove the license line from the image.json file included in the deployable tarball image resulting from the OpenEmbedded build to allow the autoinstall. It also means that you accept the EULA.

Failing Builds

An OpenEmbedded build sometimes fails. Below some recommended steps to follow when a task fails:

  • Reading through the error messages.
  • Restarting bitbake without deleting anything and see if it happens again.
  • Clean the task which failed and then restarts building the image, e.g. if python-native fails
$ bitbake -c clean python-native
$ bitbake <image>
  • Clean the task which failed, including deleting cached output and then restart building the image
$ bitbake -c cleansstate python-native
$ bitbake <image>
  • Clean the task which failed, including deleting cached output and the downloaded files and then restart building the image
$ bitbake -c cleanall python-native
$ bitbake <image>
  • Check the layer which provides the recipe if a newer commit exists which addresses the problem.

  • If there are many issues with fetching sources, you could first try to download all needed sources.

$ bitbake <image> --runall=fetch

Check the legacy section at the end of this page to find out about failing builds on older BSP versions.

Additional Layers

Recipes for even more software are available in additional layers. e.g. The Java layer provides recipes related to Java. Most layers are registered at openembedded.org. They provide a web interface to find layers or individual recipes.

Note that just because a layer or a recipe exists, that does not mean that these recipes will compile/execute. The layers/recipe might have a version conflict with what we use or might have never been used with or intended for the Arm architecture.

Refer to the following sections to see examples of how to add a new layer to our setup.

Adding the Qt Layer

Please refer to How to set up Qt Creator to cross-compile for embedded Linux.

Adding the Java Layer

Please refer to Java Virtual Machine.

Working with the Package Manager

Starting with BSP 3.0, we dropped the Ångström Distribution in favour of a Poky based distribution. For BSP 3.0 and newer based images, you cannot install packages from an online feed, only packages you build. However, if you use TorizonCore, you can use a container that makes it possible to use Debian feeds.

Further Reading

The Yocto Project Documentation, particularly the Complete Documentation Set and the Bitbake User Manual provides a lot of information. Two books we can recommend are: Embedded Linux Development with Yocto Project Embedded Linux Projects Using Yocto Project Cookbook

Webinar: Building Embedded Linux Images with the Yocto Project



Webinar: Criando Distribuições de Linux Embarcado com Yocto Project (Brazilian Portuguese)

Known Issues During repo Setup

If your repo command succeeds, you can directly proceed with the instructions in the chapter Building below.

Bitbake Build Issues

Download paths, checksums, and so on change over time. If you try to build an older image, you might experience errors that are caused by such modifications. Also, newer host tools, like the native compiler, can introduce build errors. Check the relevant layer git repo for a fix and cherry-pick/update to a commit that fixes your specific issue.

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