L-813e.A8 Yocto Reference Manual

Table of Contents

L-813e.A8 Yocto Reference Manual
Document TitleL-813e.A8 Yocto Reference Manual
Document TypeYocto Reference Manual
Article NumberL813e.A8
Release Date2019/06/26
Is Branch ofL-813e.Ax Yocto Head
Compatible BSPsBSP Release TypeBSP Release DateBSP Status
AM335x PD19.1.1MinorMay 17th, 2019Released
i.MX6UL PD19.1.0MajorMay 29th, 2019Released
i.MX 8M PD19.1.0MajorDecember 16th, 2019Released

This manual applies to all sumo based PHYTEC releases:

The Yocto Project

Introduction

Yocto is the smallest SI metric system prefix. Like m stands for Milli = 10^-3, so is yocto y = 10^-24. Yocto is also a project working group of the Linux foundation and therefore backed up by several major companies in the field. On the project website http://www.yoctoproject.org/ you can read the official introduction:

"The Yocto Project is an open source collaboration project that provides templates, tools, and methods to help you create custom Linux-based systems for embedded products regardless of the hardware architecture. It was founded in 2010 as a collaboration among many hardware manufacturers, open-source operating systems vendors, and electronics companies to bring some order to the chaos of embedded Linux development."

As said, the project wants to provide toolsets for embedded developers. It builds on top of the long-lasting OpenEmbedded project. It is not a Linux distribution. It contains the tools to create a Linux distribution specially fitted to the product requirements. The most important step to bring order in the set of tools is to define a common versioning scheme and a reference system. All subprojects have then to comply to the reference system and have to comply with the versioning scheme.

The release process is similar to the Linux kernel. Yocto increases its version number every six months and gives the release a name. The release list can be found here:

https://wiki.yoctoproject.org/wiki/Releases

Core Components

The most important tools or subprojects of the Yocto Project are:

  • Bitbake: build engine, a task scheduler like make, interprets metadata
  • OpenEmbedded-Core, a set of base layers, containing metadata of software, no sources
  • Yocto kernel
    • Optimized for embedded devices
    • Includes many subprojects: rt-kernel, vendor patches
    • Infrastructure provided by Wind River
    • Alternative: classic kernel build → we use it to integrate our kernel into Yocto
  • Yocto Reference BSP: beagleboneblack, minnow max
  • Poky, the reference system, a collection of projects and tools, used to bootstrap a new distribution based on Yocto

Vocabulary

Recipes

Recipes contain information about the software project (author, homepage, and license). A recipe is versioned, defines dependencies, contains the URL of the source code, and describes how to fetch, configure and compile the sources. It describes how to package the software, e.g. into different.deb packages, which then contain the installation path. Recipes are basically written in Bitbake's own programming language, which has a simple syntax. However, a recipe can contain Python as well as bash code.

Classes

Classes combine functionality used inside recipes into reusable blocks.

Layers

A layer is a collection of recipes, classes, and configuration metadata. A layer can depend on other layers and can be included or excluded one by one. It encapsulates a specific functionality and fulfills a specific purpose. Each layer falls into a specific category:

  • Base
  • Machine (BSP)
  • Software
  • Distribution
  • Miscellaneous

Yocto's versioning scheme is reflected in every layer as version branches. For each Yocto version, every layer has a named branch in its Git repository. You can add one or many layers of each category in your build.

A collection of OpenEmbedded layers can be found here. The search function is very helpful to see if a software package can be retrieved and integrated easily:

http://layers.openembedded.org/layerindex/branch/sumo/layers/

Machine

Machines are configuration variables which describe the aspects of the target hardware.

Distribution (Distro)

Distribution describes the software configuration and comes with a set of software features.

Poky

Poky is the reference system to define Yocto Project compatibility. It combines several subprojects into releases:

  • Bitbake
  • Toaster
  • OpenEmbedded Core
  • Yocto Documentation
  • Yocto Reference BSP

Bitbake

Bitbake is the task scheduler. It is written in Python and interprets recipes which contain code in Bitbake's own programming language, Python, and bash code. The official documentation can be found here:

http://www.yoctoproject.org/docs/2.5/bitbake-user-manual/bitbake-user-manual.html

Toaster

Toaster is a web frontend for Bitbake to start and investigate builds. It provides information about the build history and statistics on created images. There are several use cases where the installation and maintenance of a Toaster instance is beneficial. PHYTEC did not add or remove any features to the upstream Toaster, provided by Poky. The best source for more information is the official documentation:

http://www.yoctoproject.org/docs/2.5/toaster-manual/toaster-manual.html#toaster-manual-intro

Official Documentation

For more general questions about Bitbake and Poky consult the mega-manual:

http://www.yoctoproject.org/docs/2.5/mega-manual/mega-manual.html

Compatible Linux Distributions

To build Yocto you need a compatible Linux host development machine. The list of supported distributions can be found in the reference manual:

http://www.yoctoproject.org/docs/2.5/ref-manual/ref-manual.html#detailed-supported-distros

PHYTEC BSP Introduction

BSP Structure

The BSP consists roughly of three parts. BSP management, BSP metadata, and BSP content. The management consists of Repo and phyLinux while the metadata depends on the SOC, which describes how to build the software. The content comprises PHYTEC's Git repositories and external sources.

BSP Management

Yocto is an umbrella project. Naturally, this will force the user to base their work on several external repositories. They need to be managed in a deterministic way. We use manifest files, which contain an xml data structure, to describe all git repositories with pinned down version. The Repo tool and our phyLinux wrapper script are used to manage the manifests and setup the BSP, as described in the manifest file.

phyLinux

phyLinux is a wrapper for Repo to handle downloading and setting up the BSP with an "out of the box" experience.

Repo

Repo is a wrapper around the Repo toolset. The phyLinux script will install the wrapper in a global path. This is only a wrapper, though. Whenever you run "repo init -u <url>", you first download the Repo tools from Googles Git server in a specific version to the .repo/repo directory. The next time you run Repo, all the commands will be available. Be aware that the Repo version in different build directories can differ over the years if you do not run Repo sync. Also if you store information for your archives, you need to include the complete .repo folder.

Repo expects a Git repository which will be parsed from the command line. In the PHYTEC BSP, it is called phy²octo. In this repository, all information about a software BSP release is stored in the form of a Repo XML manifest. This data structure defines URLs of Git servers (called "remotes") and Git repositories and their states (called "projects"). The Git repositories can be seen in different states. The revision field can be a branch, tag, or commit id of a repository. This means the state of the software is not necessarily unique and can change over time. That is the reason we use only tags or commit ids for our releases. The state of the working directory is then unique and does not change.

The manifests for the releases have the same name as the release itself. It is a unique identifier for the complete BSP. The releases are sorted by SOC platform. The selected SOC will define the branch of the phy²octo Git repository which will be used for the manifest selection.

BSP Metadata

We include several third-party layers in our BSP to get a complete Linux distribution up and running without the need to integrate external projects. All used repositories are described in the following section.

Poky

The PHYTEC BSP is built on top of Poky. It comes with a specific version, defined in the Repo manifest. Poky comes with a specific version of Bitbake. The OpenEmbedded-core layer "meta" is used as a base for our Linux system.

meta-openembedded

OpenEmbedded is a collection of different layers containing the meta description for many open-source software projects. We ship all OpenEmbedded layers with our BSP, but not all of them are activated. Our example images pull several software packages generated from OpenEmbedded recipes.

meta-qt5

This layer provides a community-supported integration of Qt5 in Poky-based root filesystem and is integrated into our BSP.

meta-nodejs

This is an application layer to add recent Node.js versions.

meta-gstreamer1.0

This is an application layer to add recent gstreamer versions.

meta-rauc

This layer contains tools required to build an update infrastructure with RAUC. A comparison with other update systems can be found here Yocto update tools.

meta-phytec

This layer contains all machines and common features for all our BSPs. It is PHYTEC's Yocto Board Support Package for all supported hardware (since fido) and designed to be standalone with Poky. Only these two parts are required if you want to integrate the PHYTEC's hardware into your existing Yocto workflow. The features are:

  • Bootloaders in recipes-bsp/barebox/
  • Kernels in recipes-kernel/linux/
  • Many machines in conf/machine/
  • Proprietary OpenGL ES/EGL user space libraries for AM335x and i.MX 6 platforms
  • Proprietary OpenCL libraries for i.MX 6 platforms

meta-yogurt

This is our example distribution and BSP layer. It extends the basic configuration of Poky with software projects described by all the other BSP components. It provides a base for your specific development scenarios. The current features are:

  • systemd init system
  • Qt5 with eglfs backend for PHYTEC's AM335x, i.MX 6 and RK3288 platforms
  • Two different images: phytec-headless-image for non-graphic applications and phytec-qt5demo-image for Qt5 and video applications
  • Camera integration with OpenCV and gstreamer examples for the i.MX 6 platform bundled in a phytec-vision-image
  • A Qt5 demo application demonstrating how to create a Qt5 project using QML widgets and a Bitbake recipe for the Yocto and systemd integration. It can be found at sources/meta-yogurt/recipes-qt/examples/phytec-qtdemo_git.bb
  • RAUC integration: we setup basic support for an over-the-air A-B system image update

BSP Content

The BSP content gets pulled from different online sources when you first start using Bitbake. All files will be downloaded and cloned in a local directory configured as DL_DIR in Yocto. If you backup you BSP with the complete content, those sources have to be backed up, too. How you can do this will be explained in the chapter "Generating Source Mirrors, working offline".

Build Configuration

The BSP initializes a build folder which will contain all files you create by running Bitbake commands. It contains a conf folder which handles build input variables.

  • bblayers.conf defines activated meta-layers,
  • local.conf defines build input variables specific to your build
  • site.conf defines build input variables specific to the development host

The two topmost build input variables are DISTRO and MACHINE. They are preconfigured in local.conf when you check out the BSP using phyLinux.

We use "Yogurt" as DISTRO with our BSP. This distribution will be preselected and gives you a starting point for implementing your own configuration.

A MACHINE defines a binary image which supports specific hardware combinations of module and baseboard. Check the machine.conf file or our webpage for a description of the hardware.

Prebuild Images

For each BSP we provide prebuild target images which can be downloaded from the PHYTEC FTP server:

https://download.phytec.de/Software/Linux/

These images are also used for the BSP tests, which are flashed to the boards during production. You can use the provided .sdcard images to create a bootable SD card at any time. Identify your hardware and flash the downloaded image file to an empty SD card using dd. Please see section Images for information about the correct usage of the command.

BSP Workspace Installation

Setting Up the Host

You need to have a running Linux distribution. It should be running on a powerful machine as a lot of compiling will need to be done. Yocto needs a handful of additional packages on your host. For Ubuntu 16.04 you need:

host$ sudo apt-get install gawk wget git-core diffstat unzip texinfo gcc-multilib build-essential chrpath socat libsdl1.2-dev xterm 

For other distributions you can find information in the Yocto Quick Build:

https://www.yoctoproject.org/docs/2.5/brief-yoctoprojectqs/brief-yoctoprojectqs.html

Git Configuration

The BSP is heavily based on Git. Git needs some information from you as a user to identify who made changes. If you do not have one, create a ~/.gitconfig:

[user]
	name = <Your Name>
	email = <Your Mail>
[core]
	editor = vim
[merge]
	tool = vimdiff
[alias]
	co = checkout
	br = branch
	ci = commit
	st = status
	unstage = reset HEAD --
	last = log -1 HEAD
[push]
	default = current
[color]
	ui = auto

You should set name and email in your Git configuration, otherwise Bitbake will complain during the first build. You can use the two commands to set them directly without editing ~/.gitconfig manually:

host$ git config --global user.email "your_email@example.com"
host$ git config --global user.name "name surname"

site.conf Setup

Before starting the Yocto build, it is advisable to configure the development setup. Two things are most important: the download directory and the cache directory. PHYTEC strongly recommends configuring the setup as it will reduce the compile time of consequent builds.

A download directory is a place where Yocto stores all sources fetched from the internet. It can contain tar.gz, Git mirror, etc. It is very useful to set this to a common shared location on the machine. Create this directory with 777 access rights. To share this directory with different users, all files need to have group write access. This will most probably be in conflict with default umask settings. One possible solution would be to use ACLs for this directory:

host$ sudo apt-get install acl
host$ sudo setfacl -R -d -m g::rwx <dl_dir>

If you have already created a download directory and want to fix the permissions afterwards, you can do so with:

host$ sudo find /home/share/  -perm /u=r ! -perm /g=r -exec chmod g+r \{\} \;
host$ sudo find /home/share/  -perm /u=w ! -perm /g=w -exec chmod g+w \{\} \;
host$ sudo find /home/share/  -perm /u=x ! -perm /g=x -exec chmod g+x \{\} \;

The cache directory stores all stages of the build process. Poky has quite an involved caching infrastructure. It is advisable to create a shared directory, as all builds can access this cache directory, called shared state cache.

Create the two directories on a drive where you have approximately 50 GB of space and assign the two variables in your build/conf/local.conf.

DL_DIR ?= "<your_directory>/yocto_downloads"
SSTATE_DIR ?= "<your_directory>/yocto_sstate"

If you want to know more about configuring your build, see the documented example settings:

sources/poky/meta-yocto/conf/local.conf.sample
sources/poky/meta-yocto/conf/local.conf.sample.extended

phyLinux Documentation

The phyLinux script is a basic management tool for PHYTEC Yocto BSP releases written in Python. It is mainly a helper to get started with the BSP structure. You can get all the BSP sources without the need of interacting with Repo or Git.

The phyLinux script has only one real dependency. It requires the wget tool installed on your host. It will also install the Repo tool in a global path (/usr/local/bin) on your host PC. You can install it to a different location manually. Repo will be automatically detected by phyLinux if it is found in the PATH. The Repo tool will be used to manage the different Git repositories of the Yocto BSP.

Get phyLinux

The phyLinux script can be found on the PHYTEC ftp server:

ftp://ftp.phytec.de/pub/Software/Linux/Yocto/Tools/phyLinux

Basic Usage

For the basic usage of phyLinux, type:

host$ ./phyLinux --help

which will result in:

usage: phyLinux init [-h] [--verbose] [--no-init] [-o REPOREPO] [-x XML]
                     [-u URL] [-p PLATFORM] [-r RELEASE]
 
optional arguments:
  -h, --help   show this help message and exit
  --verbose
  --no-init    dont execute init after fetch
  -o REPOREPO  Use repo tool from another url
  -x XML       Use a local XML manifest
  -u URL       Manifest git url
  -p PLATFORM  Processor platform
  -r RELEASE   Release version

Initialization

Create a fresh project folder:

host$ mkdir ~/yocto

and run phyLinux from the new folder:

host$ ./phyLinux init

A clean folder is important because phyLinux will clean its working directory. Calling phyLinux from an directory that isn't empty will result in the following warning:

This current directory is not empty. It could lead to errors in the BSP configuration
 process if you continue from here. At the very least, you have to check your build directory
 for settings in bblayers.conf and local.conf, which will not be handled correctly in
 all cases. It is advisable to start from an empty directory of call:
 $ ./phyLinux clean
 Do you really want to continue from here?
 [yes/no]:

On the first initialization, the phyLinux script will ask you to install the Repo tool in your /usr/local/bin directory. During the execution of the init command, you need to choose your processor platform (SoC), PHYTEC's BSP release number, and the hardware you are working on:

***************************************************
* Please choose one of the available SoC Platforms:
*
*   1: am335x
*   2: imx6
*   3: imx6ul
*   4: imx8
*   5: imx8m
*   6: nightly
*   7: rk3288
*   8: topic
*
 
# Exemplary output for choosen am335x
***************************************************
* Please choose one of the available Releases:
*
*   1: PD14.1-rc1
*   2: PD15.1-rc1
*   3: PD15.1-rc2
*   4: PD15.1.0
*   5: PD15.1.1
*   6: PD15.1.2
*   7: PD15.2-rc1
*   8: PD15.2.0
*   9: PD15.2.1
*   10: PD15.2.2
*   11: PD15.3-rc1
*   12: PD15.3.0
*   13: PD15.3.1
*   14: PD15.3.2
*   15: PD16.1-rc1
*   16: PD16.1.0
*   17: PD16.2.0
*   18: PD17.1.0
*   19: PD17.1.1
*   20: PD17.1.2
*   21: PD17.1.3-rc1
*   22: PD17.1.3
*   23: PD17.2-rc2
*   24: PD17.2.0
*   25: PD17.2.1
*   26: PD17.2.2
*   27: PD19.1-rc1
*   28: PD19.1.0
 
# Exemplary output for choosen PD19.1.0
*********************************************************************
* Please choose one of the available builds:
*
no:          machine: description and article number
                      distro: supported yocto distribution
                      target: supported build target
 
 1: phyboard-regor-am335x-1: PHYTEC phyBOARD-REGOR AM335x 512MiB RAM
                      512MiB NAND, 8MiB SPI flash
                      PB-01802-001.A5
                      distro: yogurt-rt
                      target: phytec-headless-image
 2: phyboard-wega-am335x-1: PHYTEC phyBOARD-WEGA AM335x 256MiB RAM
                      128MiB NAND flash, PEB-AV-01
                      PB-00802-0101C.A1, PB-00802-0200C.A2
                      distro: yogurt
                      target: phytec-headless-image
                      target: phytec-qt5demo-image
...
...
...
16: phycore-r2-am335x-5: PHYTEC phyCORE-AM335x R2 1GiB RAM
                      1GiB NAND flash, 8MiB SPI flash, PCM-953
                      PCM-060-43102F10I.A1
                      distro: yogurt
                      target: phytec-qt5demo-image
17: phycore-r2-am335x-6: PHYTEC phyCORE-AM335x R2 1GiB RAM
                      1GiB NAND flash, PCM-953
                      PCM-060-43002F10I.A0
                      distro: yogurt
                      target: phytec-qt5demo-image

If you cannot identify your board with the information given in the selector, have a look at the invoice of the product. After the configuration is done, you can always run:

host$ ./phyLinux info
 
# Exemplary output
**********************************************
* The current BSP configuration is:  
*
* SoC:  refs/heads/am335x
* Release:  PD19.1.0
*
**********************************************

to see which SoC and Release is selected in the current workspace. If you do not want to use the selector, phyLinux also supports command line arguments for the several settings:

host$ MACHINE=phyboard-wega-am335x-1 ./phyLinux init -p am335x -r PD19.1.0

or view the help command for more information:

host$ ./phyLinux  init --help 
 
usage: phyLinux init [-h] [--verbose] [--no-init] [-o REPOREPO] [-x XML]
                     [-u URL] [-p PLATFORM] [-r RELEASE]
 
optional arguments:
  -h, --help   show this help message and exit
  --verbose
  --no-init    dont execute init after fetch
  -o REPOREPO  Use repo tool from another url
  -x XML       Use a local XML manifest
  -u URL       Manifest git url
  -p PLATFORM  Processor platform
  -r RELEASE   Release version

After the execution of the init command, phyLinux will print a few important notes as well as information for the next steps in the build process.

Advanced Usage

phyLinux can be used to transport software states over any medium. The state of the software is uniquely identified by the manifest.xml. You can create a manifest, send it to another place and recover the software state with:

host$ ./phyLinux init -x manifest.xml

You can also create a Git repository containing your software states. The Git repository needs to have branches other than master, as we reserved the master branch for a different usage. Use phyLinux to check out the states:

host$ ./phyLinux -u <url-of-your-git-repo>

Working with Poky and Bitbake

Start the Build

After you downloaded all the metadata with phyLinux init, you have to set up the shell environment variables. This needs to be done every time you open a new shell for starting builds. We use the shell script provided by Poky in its default configuration. From the root of your project directory type:

host$ source sources/poky/oe-init-build-env

The abbreviation for the source command is a single dot.

host$ . sources/poky/oe-init-build-env

The current working directory of the shell should change to build/. Before building for the first time, you should take a look at the main configuration file:

host$ vim conf/local.conf

Your local modifications for the current build are stored here. Depending on the SoC, you might need to accept license agreements. For example, to build the image for Freescale/NXP processors you need to accept the GPU and VPU binary license agreements. You have to uncomment the corresponding lines.

Now you are ready to build your first image. We suggest starting with our smaller non-graphical image phytec-headless-image to see if everything is working correctly:

host$ bitbake phytec-headless-image

The first compile process takes about 40 minutes on a modern Intel Core i7. All subsequent builds will use the filled caches and should take about 3 minutes.

Images

If everything worked, the images can be found under:

host$ cd deploy/images/<MACHINE>

The easiest way to test your image is to configure your board for SD card boot and to flash the build image to the SD card:

host$ sudo dd if=phytec-headless-image-<MACHINE>.sdcard of=/dev/<your_device> bs=1M conv=fsync

Here <your_device> could be "sde", for example, depending on your system. Be very careful when selecting the right drive! Selecting the wrong drive can erase your hard drive! The parameter conv=fsync forces a data buffer write to the device before dd returns.

After booting you can login using a serial cable or over ssh. There is no root password. That is because of the debug settings in conf/local.conf. If you uncomment the line:

#EXTRA_IMAGE_FEATURES = "debug-tweaks"

the debug settings, like setting an empty root password, will not be applied.

Accessing Development States between Releases

Special release manifests exist to give you access to current development states of the Yocto BSP. They will not be displayed in the phyLinux selection menu but need to be selected manually. This can be done using the following command line:

host$ ./phyLinux init -p master -r sumo

This will initialize a BSP which will track the latest development state. From now on running:

host$ repo sync

in this folder will pull all the latest changes from our Git repositories.

Inspect your Build Configuration

Poky includes several tools to inspect your build layout. You can inspect the commands of the layer tool:

host$ bitbake-layers

It can, for example, be used to view in which layer a specific recipe gets modified:

host$ bitbake-layers show-appends

Before running a build you can also launch Toaster to be able to inspect the build details with the Toaster web GUI:

host$ source toaster start

You can then point your browser to http://0.0.0.0:8000/ and continue working with Bitbake. All build activity can be monitored and analyzed from this web server. If you want to learn more about Toaster, look at:

http://www.yoctoproject.org/docs/2.5/toaster-manual/toaster-manual.html#toaster-manual-intro

To shut down the Toaster web GUI again, execute:

host$ source toaster stop

BSP Features of meta-phytec and meta-yogurt

Buildinfo

The buildinfo task is a feature in our recipes which prints instructions to fetch the source code from the public repositories. So you do not have to look into the recipes yourself. To see the instructions, e.g. for the barebox package, execute:

host$ bitbake barebox -c buildinfo

in your shell. This will print something like:

(mini) HOWTO: Use a local git repository to build barebox:
 
To get source code for this package and version (barebox-2018.11.0-phy2), execute
 
$ mkdir -p ~/git
$ cd ~/git
$ git clone git://git.phytec.de/barebox barebox
$ cd ~/git/barebox
$ git checkout -b v2018.11.0-phy2-local-development 9a40cd5eb3e5286f9c8ca186475380acf262f2ed
 
You now have two possible workflows for your changes:
 
1. Work inside the git repository:
Copy and paste the following snippet to your "local.conf":
 
SRC_URI_pn-barebox = "git:///${HOME}/git/barebox;branch=${BRANCH}"
SRCREV_pn-barebox = "${AUTOREV}"
BRANCH_pn-barebox = "v2018.11.0-phy2-local-development"
 
After that you can recompile and deploy the package with
 
$ bitbake barebox -c compile
$ bitbake barebox -c deploy
 
Note: You have to commit all your changes. Otherwise yocto doesn't pick them up!
 
2. Work and compile from the local working directory
To work and compile in an external source directoy we provide the
externalsrc.bbclass. To use it copy and paste the following snippet to your
"local.conf":
 
INHERIT += "externalsrc"
EXTERNALSRC_pn-barebox = "${HOME}/git/barebox"
EXTERNALSRC_BUILD_pn-barebox = "${HOME}/git/barebox"
 
Note: All the compiling is done in the EXTERNALSRC directory. Everytime
you build an Image, the package will be recompiled and build.
 
NOTE: Tasks Summary: Attempted 1 tasks of which 0 didn't need to be rerun and all succeeded.
NOTE: Writing buildhistory

As you can see, everything is explained in the output.

Warning

Using externalsrc breaks a lot of Yocto′s internal dependency mechanism. It is not guaranteed that any changes to the source directory are automatically picked up by the build process and incorporated into the root filesystem or SD card image. You have to always use --force. E.g. to compile barebox and redeploy it to deploy/images/<machine> execute:

host$ bitbake barebox -c compile --force
host$ bitbake barebox -c deploy

To update the SD card image with a new kernel or image first force the compilation of it and then force a rebuild of the root filesystem. Use:

host$ bitbake phytec-qt5demo-image -c rootfs --force

Note that the buildsystem is not modifying the external source directory. If you want to apply all patches the Yocto recipe is carrying to the external source directory, run the line:

SRCTREECOVEREDTASKS="" BB_ENV_EXTRAWHITE="$BB_ENV_EXTRAWHITE SRCTREECOVEREDTASKS" bitbake <recipe> -c patch

BSP Customization

To get you started with the BSP, we have summarized some basic tasks from the Yocto official documentation. It describes how to add additional software to the image, change the kernel and bootloader configuration, and integrate patches for kernel and bootloader.

Minor modifications, such as adding software, are done in the file build/conf/local.conf. There you can overwrite global configuration variables and make small modifications to recipes.

There are 2 ways to make major changes:

  1. Either create your own layer and use bbappend files.
  2. Add everything to PHYTEC's Distro layer meta-yogurt.

Creating your own layer is described in section Create your own Layer.

Disable Qt Demo

By default, the BSP image phytec-qt5demo-image starts a Qt5 Demo application on the attached display or monitor. If you want to stop the demo and use the Linux framebuffer console behind it, connect to the target via serial cable or ssh and execute the shell command:

target$ systemctl stop phytec-qtdemo.service

This command stops the demo temporarily. To start it again, reboot the board or execute:

target$ systemctl start phytec-qtdemo.service

You can disable the service permanently, so it does not start on boot:

target$ systemctl disable phytec-qtdemo.service

Tip

The last command only disables the service. It does not stop it immediately. To see the current status execute:

target$ systemctl status phytec-qtdemo.service

If you want to disable the service by default, edit the file build/conf/local.conf and add the following line:

# file build/conf/local.conf
SYSTEMD_AUTO_ENABLE_pn-phytec-qtdemo = "disable"

After that, rebuild the image:

host$ bitbake phytec-qt5demo-image

Framebuffer Console

On boards with a display interface, the framebuffer console is enabled per default. You can attach a USB keyboard and login. To change the keyboard layout from the English default to German, type:

target$ loadkeys /usr/share/keymaps/i386/qwertz/de-latin1.map.gz

To detach the framebuffer console, run:

target$ echo 0 > sys/class/vtconsole/vtcon1/bind

To completely deactivate the framebuffer console, disable the following kernel configuration option:

Device Drivers->Graphics Support->Support for framebuffer devices->Framebuffer Console Support

More information can be found at:

https://www.kernel.org/doc/Documentation/fb/fbcon.txt

Tools Provided in the Prebuild Image

RAM Benchmark

Performing RAM and cache performance tests can best be done by using pmbw (Parallel Memory Bandwidth Benchmark/Measurement Tool). Pmbw runs several assembly routines which all use different access patterns to the caches and RAM of the SoC. Before running the test, make sure that you have about 2 MiB of space left on the device for the log files. We also lower the level of the benchmark to ask the kernel more aggressively for resources. The benchmark test will take several hours.

To start the test type:

target$ nice -n -2 pmbw

Upon completion of the test run, the log file can be converted to a gnuplot script with:

target$ stats2gnuplot stats.txt > run1.gnuplot

Now you can transfer the file to the host machine and install any version of gnuplot:

host$ sudo apt-get install gnuplot
host$ gnuplot run1.gnuplot

The generated plots-<machine>.pdf file contains all plots. To render single plots as png file for any web output you can use Ghostscript:

host$ sudo apt-get install ghostscript
host$ gs -dNOPAUSE -dBATCH -sDEVICE=png16m -r150 -sOutputFile='page-%00d.png' plots-phyboard-wega-am335x-1.pdf

Add Additional Software for the BSP Image

To add additional software to the image, look at the OpenEmbedded layer index:

http://layers.openembedded.org/layerindex/branch/sumo/layers/

First, select the Yocto version of the BSP you have from the drop-down list in the top left corner and click Recipes. Now you can search for a software project name and find which layer it is in. In some cases, the program is in meta-openembedded, openembedded-core, or Poky which means that the recipe is already in your build tree. This section describes how to add additional software when this is the case. If the package is in another layer, see the next section.

You can also search the list of available recipes:

host$ bitbake -s | grep <program name>  # fill in program name, like in
host$ bitbake -s | grep lsof 

When the recipe for the program is already in the Yocto build, you can simply add it by appending a configuration option to your file build/conf/local.conf. The general syntax to add additional software to an image is:

# file build/conf/local.conf
IMAGE_INSTALL_append = " <package1> <package2>"

For example, the line:

# file build/conf/local.conf
IMAGE_INSTALL_append = " ldd strace file lsof"

installs some helper programs on the target image.

Warning

The leading whitespace is essential for the append command.

All configuration options in local.conf apply to all images. Consequently, the tools are now included in both images phytec-headless-image and phytec-qt5demo-image.

Notes about Packages and Recipes

You are adding packages to the IMAGE_INSTALL variable. Those are not necessarily equivalent to the recipes in your meta-layers. A recipe defines per default a package with the same name. But a recipe can set the PACKAGES variable to something different and is able to generate packages with arbitrary names. Whenever you look for software, you have to search for the package name and, strictly speaking, not for the recipe. In the worst case, you have to look at all PACKAGES variables. A tool such as Toaster can be helpful in some cases.

If you can not find your software in the layers provided in the folder sources/, see the next section to include another layer into the Yocto build.

References: Yocto 2.5 Docu - Customizing Images Using local.conf

Add an Additional Layer

This is a step by step guide how to add another layer to your Yocto build and install additional software from it. As an example, we include the network security scanner nmap in the layer meta-security. First, you must locate in the layer which software is hosted. Check out the OpenEmbedded MetaData Index and guess a little bit. The network scanner nmap is in the meta-security layer. See meta-security on layers.openembedded.org. To integrate it into the Yocto build, you have to checkout out the repository and then switch to the correct stable branch. Since the BSP is based on the Yocto 'sumo' build, you should try to use the 'sumo' branch in the layer, too.

host$ cd sources
host$ git clone git://git.yoctoproject.org/meta-security
host$ cd meta-security
host$ git branch -r

All available remote branches will show up. Usually there should be 'fido', 'jethro', 'krogoth', 'master', ...:

host$ git checkout sumo

Now we add the directory of the layer to the file build/conf/bblayers.conf by appending the line:

# file build/conf/bblayers.conf
BBLAYERS += "${BSPDIR}/sources/meta-security"

to the end of the file. After that, you can check if the layer is available in the build configuration by executing:

host$ bitbake-layers show-layers

If there is an error like:

ERROR: Layer 'security' depends on layer 'perl-layer', but this layer is not enabled in your configuration

the layer that you want to add (here meta-security), depends on another layer, which you need to enable first. E.g. the dependency required here is a layer in meta-openembedded (in the PHYTEC BSP it is in the path sources/meta-openembedded/meta-perl/). To enable it, add the following line to build/conf/bblayers.conf:

# file build/conf/bblayers.conf
BBLAYERS += "${BSPDIR}/sources/meta-openembedded/meta-perl"

Now the command bitbake-layers show-layers should print a list of all layers enabled including meta-security and meta-perl. After the layer is included, you can install additional software from it as already described above. The easiest way is to add the following line (here the package nmap):

# file build/conf/local.conf
IMAGE_INSTALL_append = " nmap"

to your build/conf/local.conf. Do not forget to rebuild the image:

host$ bitbake phytec-qt5demo-image

Create your own Layer

Creating your layer should be one of the first tasks when customizing the BSP. You have two basic options. You can either copy and rename our meta-yogurt, or you can create a new layer which will contain your changes. The better option depends on your use case. meta-yogurt is our example of how to create a custom Linux distribution and will be updated in the future. If you want to benefit from those changes and are, in general, satisfied with the user space configuration, it could be the best solution to create your own layer on top of Yogurt. If you need to rework a lot of information and only need the basic hardware support from PHYTEC, it would be better to copy meta-yogurt, rename it, and adapt it to your needs. You can also have a look at the OpenEmbedded layer index to find different distribution layers. If you just need to add your own application to the image, create your own layer.

In the following chapter, we have an embedded project called "racer" which we will implement using our Yogurt Linux distribution. First, we need to create a new layer.

Yocto provides a script for that. If you set up the BSP and the shell is ready, type:

host$ bitbake-layers create-layer meta-racer

Default options are fine for now. Move the layer to the source directory:

host$ mv meta-racer ../sources/

Create a Git repository in this layer to track your changes:

host$ cd ../sources/meta-racer
host$ git init && git add . && git commit -s
Now you can add the layer directly to your build/conf/bblayers.conf:
BBLAYERS += "${BSPDIR}/sources/meta-racer"

or with a script provided by Yocto:

host$ bitbake-layers add-layer meta-racer

Kernel and Bootloader Recipe and Version

First, you need to know which kernel and version are used for your target machine. PHYTEC provides two kernel recipes linux-mainline and linux-ti. The first one provides support for PHYTEC's i.MX 6 modules and is based on the Linux kernel stable releases from kernel.org. The second one provides support for the PHYTEC's AM335x modules and is based on the TI vendor kernel.

The Git repositories URLs are:

To find your kernel provider, execute the following command:

host$ bitbake virtual/kernel -e | grep  "PREFERRED_PROVIDER_virtual/kernel"

The command prints the value of the variable PREFERRED_PROVIDER_virtual/kernel. The variable is used in the internal Yocto build process to select the kernel recipe to use. The following two lines are two different outputs you might see:

PREFERRED_PROVIDER_virtual/kernel="linux-mainline"
PREFERRED_PROVIDER_virtual/kernel="linux-ti"

To see which version is used, execute bitbake -s. For example:

host$ bitbake -s | egrep -e "linux-mainline|linux-ti|barebox"

The parameter -s prints the version of all recipes. The output contains the recipe name on the left and the version on the right.

barebox                                  :2018.11.0-phy2-r7.0                          
barebox-ipl                              :2018.11.0-phy2-r7.1                          
barebox-targettools                      :2018.11.0-phy2-r7.0                          
linux-mainline                             :4.14.78-phy4-r0.0 

As you can see, the recipe linux-mainline has the version 4.14.78-phy4-r0. In the PHYTEC's linux-mainline Git repository, you will find a corresponding tag v4.14.78-phy4. The version of the barebox recipe is 2018.11.0-phy2. If your machine has an AM335x module the output of bitbake -s contains a line starting with linux-ti.

Kernel and Bootloader Configuration

The bootloader used by PHYTEC, barebox, uses the same build system as the Linux kernel. Therefore, all commands in this section can be used to configure the kernel and bootloader. To configure the kernel or bootloader, execute one of the following commands:

host$ bitbake -c menuconfig virtual/kernel  # Using the virtual provider name 
host$ bitbake -c menuconfig linux-ti        # Or use the recipe name directly (If you use an AM335x Module)
host$ bitbake -c menuconfig linux-mainline  # Or use the recipe name directly (If you use an i.MX 6 or RK3288 Module)
host$ bitbake -c menuconfig barebox         # Or change the configuration of the bootloader

After that, you can recompile and redeploy the kernel or bootloader:

host$ bitbake virtual/kernel -c compile    # Or 'barebox' for the bootloader
host$ bitbake virtual/kernel -c deploy     # Or 'barebox' for the bootloader

Instead, you can also just rebuild the complete build output with:

host$ bitbake phytec-headless-image        # To update the kernel/bootloader, modules and the images

In the last command, you can replace the image name with the name of an image of your choice. The new images and binaries are in build/deploy/images/<machine>/.

Warning

The build configuration is not permanent yet. Executing bitbake virtual/kernel -c clean will remove everything.

To make your changes permanent in the build system, you have to integrate your configuration modifications into a layer. For the configuration you have two options:

  • Include only a configuration fragment (a minimal diff between the old and new configuration)
  • Complete default configuration (defconfig) after your modifications.

Having a set of configuration fragments makes what was changed at which stage more transparent. You can turn on and off the changes, you can manage configurations for different situations and it helps when porting changes to new kernel versions. You can also group changes together to reflect specific use cases. A fully assembled kernel configuration will be deployed in the directory build/deploy/images/<machine>. If you do not have any of those requirements, it might be simpler to just manage a separate defconfig file.

Add a Configuration Fragment to a Recipe

The following steps can be used for both kernel and bootloader. Just replace the recipe name linux-mainline in the commands with linux-ti, or barebox for the bootloader. If you did not already take care of this, start from a clean build. Otherwise, the diff of the configuration may be wrong:

host$ bitbake linux-mainline -c clean
host$ bitbake linux-mainline -c menuconfig

Make your configuration changes in the menu and generate a config fragment:

host$ bitbake linux-mainline -c diffconfig

which prints the path of the written file:

Config fragment has been dumped into:
  /home/<path>/build/tmp-glibc/work/phyflex_imx6_2-phytec-linux-gnueabi/linux-mainline/3.19.5-phy4-r0/fragment.cfg

All config changes are in the file fragment.cfgwhich should consist of only some lines. The following example shows how to create a bbappend file and how to add the necessary lines for the config fragment. You just have to adjust the directories and names for the specific recipe: linux-mainline, linux-ti, or barebox.

sources/<layer>/recipes-kernel/linux/linux-mainline_%.bbappend     # For the recipe linux-mainline
sources/<layer>/recipes-kernel/linux/linux-ti_%.bbappend           # For the recipe linux-ti
sources/<layer>/recipes-bsp/barebox/barebox_%.bbappend             # For the recipe barebox

Replace the string layer with your own layer created as shown above (e.g. meta-racer), or just use meta-yogurt. To use meta-yogurt, first create the directory for the config fragment and give it a new name (here enable-r8169.cfg) and move the fragment to the layer.

host$ mkdir -p sources/meta-yogurt/recipes-kernel/linux/features
# copy the path from the output of *diffconfig*
host$ cp /home/<path>/build/tmp-glibc/work/phyflex_imx6_2-phytec-linux-gnueabi/linux-mainline/3.19.5-phy4-r0/fragment.cfg \
    sources/meta-yogurt/recipes-kernel/linux/features/enable-r8169.cfg

Then open the bbappend file (in this case sources/meta-yogurt/recipes-kernel/linux/linux-mainline_%.bbappend) with your favorite editor and add the following lines:

# contents of the file linux-mainline_%.bbappend
FILESEXTRAPATHS_prepend := "${THISDIR}/features:"
SRC_URI_append = " \
   file://enable-r8169.cfg \
"

Warning

Do not forget to use the correct bbappend filenames: linux-ti_%.bbappend for the linux-ti recipe and barebox_%.bbappend for the bootloader in the folder recipes-bsp/barebox/!

After saving the bbappend file, you have to rebuild the image. Yocto should pick up the recipe changes automatically and generate a new image:

host$ bitbake phytec-headless-image    # Or another image name

Add a Complete Default Configuration (defconfig) to a Recipe

This approach is similar to the one above, but instead of adding a fragment a defconfig is used. First, create the necessary folders in the layer you want to use, either your own layer or meta-yogurt:

host$ mkdir -p sources/meta-yogurt/recipes-kernel/linux/features/   # For both linux-mainline and linux-ti
host$ mkdir -p sources/meta-yogurt/recipes-bsp/barebox/features/    # Or for the bootloader

Then you have to create a suitable defconfig file. Make your configuration changes using menuconfig and then save the defconfig file to the layer:

host$ bitbake linux-mainline -c menuconfig    # Or use recipe name linux-ti or barebox
host$ bitbake linux-mainline -c savedefconfig # Create file 'defconfig.temp' in the work directory

This will print the path to the generated file:

Saving defconfig to ..../defconfig.temp

Then, as above, copy the generated file to your layer, rename it to defconfig, and add the following lines to the bbappend file (here sources/meta-yogurt/recipes-kernel/linux/linux-mainline_%.bbappend):

# contents of the file linux-mainline_%.bbappend
FILESEXTRAPATHS_prepend := "${THISDIR}/features:"
SRC_URI_append = " \
   file://defconfig \
"

Tip

Do not forget to use the correct bbappend filenames: linux-ti_%.bbappend for the linux-ti recipe and barebox_%.bbappend for the bootloader in the folder recipes-bsp/barebox/!

After that, rebuild your image as the changes are picked up automatically:

host$ bitbake phytec-headless-image    # Or another image name

Patch the Kernel or Bootloader with devtool

Apart from using the standard versions of kernel and bootloader which are provided in the recipes, you can modify the source code or use our own repositories to build your customized kernel.

PROCON
Standard workflow of the official Yocto documentationUses additional hard drive space as the sources get duplicated
Toolchain does not have to recompile everythingNo optimal cache usage, build overhead

Devtool is a set of helper scripts to enhance the user workflow of Yocto. It was integrated in version 1.8. It is available as soon as you set up your shell environment. Devtool can be used to:

  • modify existing sources
  • integrate software projects into your build setup
  • build software and deploy software modifications to your target

Here we will use devtool to patch the kernel. We use linux-ti as an example for the AM335x TI Kernel. The first command we use is devtool modify - x <recipe> <directory>:

host$ devtool modify -x linux-ti linux-ti

Devtool will create a layer in build/workspace where you can see all modifications done by devtool. It will extract the sources corresponding to the recipe to the specified directory. A bbappend will be created in the workspace directing the SRC_URI to this directory. Building an image with Bitbake will now use the sources in this directory. Now you can modify lines in the kernel:

host$ vim linux-ti/arch/arm/boot/dts/am335x-phycore-som.dtsi
      -> make a change
host$ bitbake phytec-qt5demo-image

Your changes will now be recompiled and added to the image. If you want to store your changes permanently, it is advisable to create a patch from the changes, then store and backup only the patch. You can go into the linux-ti directory and create a patch using Git. How to create a patch is described in the middle of the next section and is the same for all methods.

If you want to learn more about devtool, visit:

Patch the Kernel or Bootloader using "Temporary Method"

PROCON
No overhead, no extra configurationChanges are easily overwritten by Yocto (Everything is lost!!).
Toolchain does not have to recompile everything

It is possible to alter the source code before Bitbake configures and compiles the recipe. Use Bitbake's devshell command to jump into the source directory of the recipe. Here is the barebox recipe:

host$ bitbake barebox -c devshell    # or linux-mainline, linux-ti

After executing the command, a shell window opens. The current working directory of the shell will be changed to the source directory of the recipe inside the tmp folder. Here you can use your favorite editor, e.g. vim, emacs, or any other graphical editor, to alter the source code. When you are finished, exit the devshell by typing exit or hitting CTRL-D.

After leaving the devshell you can recompile the package:

host$ bitbake barebox -c compile --force    # or linux-mainline, linux-ti

The extra argument '--force' is important because Yocto does not recognize that the source code was changed.

Tip

You cannot execute the bitbake command in the devshell. You have to leave it first.

If the build fails, execute the devshell command again and fix it. If the build is successful, you can deploy the package and create a new SD card image.

host$ bitbake barebox -c deploy         # new barebox in e.g. deploy/images/phyflex-imx6-2/barebox.bin
host$ bitbake phytec-headless-image    # new sdcard image in e.g. deploy/images/phyflex-imx6-2/phytec-headless-image-phyflex-imx6-2.sdcard

Warning

If you execute a clean e.g bitbake barebox -c clean, or if Yocto refetches the source code, all your changes are lost!!!

To avoid this, you can create a patch and add it to a bbappend file. It is the same workflow as described in the section about changing the configuration.

You have to create the patch in the devshell if you use the temporary method, and in the subdirectory created by devtool if you used devtool.

host$ bitbake barebox -c devshell            # Or linux-mainline, linux-ti
host(devshell)$ git status                   # Show changes files
host(devshell)$ git add <file>               # Add a special file to the staging area
host(devshell)$ git commit -m "important modification"   # Creates a commit with a not so useful commit message
host(devshell)$ git format-patch -1 -o ~/    # Creates a patch of the last commit and saves it in your home folder
/home/<user>/0001-important-modification.patch  # Git prints the path of the written patch file
host(devshell)$ exit

After you have created the patch, you must create a bbappend file for it. The locations for the three different recipes - linux-mainline, linux-ti, and barebox - are:

sources/<layer>/recipes-kernel/linux/linux-mainline_%.bbappend     # For the recipe linux-mainline
sources/<layer>/recipes-kernel/linux/linux-ti_%.bbappend           # For the recipe linux-ti
sources/<layer>/recipes-bsp/barebox/barebox_%.bbappend             # For the recipe barebox

The following example is for the recipe barebox. You have to adjust the paths. First, create the folders and move the patch into it. Then create the bbappend file:

host$ mkdir -p sources/meta-yogurt/recipes-bsp/barebox/features   # Or use your own layer instead of *meta-yogurt*
host$ cp ~/0001-important-modification.patch sources/meta-yogurt/recipes-bsp/barebox/features  # copy patch
host$ touch sources/meta-yogurt/recipes-bsp/barebox/barebox_%.bbappend

Tip

Pay attention to your current work directory. You have to execute the commands in the BSP top level directory. Not in the build directory!

After that use your favorite editor to add the following snipped into the bbappend file (here sources/meta-yogurt/recipes-bsp/barebox/barebox_%.bbappend):

# contents of the file barebox_%.bbappend
FILESEXTRAPATHS_prepend := "${THISDIR}/features:"
SRC_URI_append = " \
    file://0001-important-modification.patch \
"

Save the file and rebuild the barebox recipe with:

host$ bitbake barebox -c clean    # Or linux-ti, linux-mainline
host$ bitbake barebox

If the build is successful, you can rebuild the final image with:

host$ bitbake phytec-headless-image    # Or another image name

Further Resources:

The Yocto Project has some documentation for software developers. Check the 'Kernel Development Manual' for more information about how to configure the kernel. Please note that not all of the information from the Yocto manual can be applied to the PHYTEC BSP as we use the classic kernel approach of Yocto and most of the documentation assumes the Yocto kernel approach.

Working with the Kernel and Bootloader using SRC_URI in local.conf

Here we present a third option to make kernel and bootloader changes. You have external checkouts of the linux-mainline, linux-ti, or barebox Git repositories. You will overwrite the URL of the source code fetcher, the variable SRC_URI, to point to your local checkout instead of the remote repositories.

PROCON
All changes are saved with GitMany working directories in build/tmp-glibc/work/<machine>/<package>/

You have to commit every change before recompiling

For each change the toolchain compiles everything from scratch (avoidable with ccache)

First, you need a local clone of the Git repository barebox or kernel. If you do not have one, use the commands:

host$ mkdir ~/git
host$ cd ~/git
host$ git clone git://git.phytec.de/barebox
host$ cd barebox
host$ git checkout -b v2015.02.0-phy remotes/origin/v2015.02.0-phy

Add the following snippet to the file build/conf/local.conf:

# Use your own path to the git repository
# NOTE: Branche name in variable "BRANCH_pn-barebox" should be the same as the 
# branch which is used in the repository folder. Otherwise your commits won't be recognized later.
BRANCH_pn-barebox = "v2015.02.0-phy"
SRC_URI_pn-barebox = "git:///${HOME}/git/barebox;branch=${BRANCH}"
SRCREV_pn-barebox = "${AUTOREV}"

You also have to set the correct BRANCH name in the file. Either you create your own branch in the Git repository, or you use the default (here "v2015.02.0-phy"). Now you should recompile barebox from your own source:

host$ bitbake barebox -c clean
host$ bitbake barebox -c compile

The build should be successful because the source was not changed yet.

You can alter the source in ~/git/barebox or the default defconfig (e.g. ~/git/barebox/arch/arm/configs/imx_v7_defconfig). After you are satisfied with your changes, you have to make a dummy commit for Yocto. If you do not, Yocto will not notice that the source code was modified in your repository folder (e.g. ~/git/barebox/):

host$ git status  # show modified files
host$ git diff    # show changed lines
host$ git commit -a -m "dummy commit for yocto"   # This command is important!

Try to compile your new changes. Yocto will automatically notice that the source code was changed and fetches and configures everything from scratch.

host$ bitbake barebox -c compile

If the build fails, go back to the source directory, fix the problem, and recommit your changes. If the build was successful, you can deploy barebox and even create a new SD card image.

host$ bitbake barebox -c deploy   # new barebox in e.g. deploy/images/phyflex-imx6-2/barebox-phyflex-imx6-2.bin
host$ bitbake phytec-headless-image   # new sd-card image in e.g. deploy/images/phyflex-imx6-2/phytec-headless-image-phyflex-imx6-2.sdcard

If you want to make additional changes, just make another commit in the repository and rebuild barebox again.

Add Existing Software with "Sustainable Method"

Now that you have created your own layer, you have a second option to add existing software to existing image definitions. Our standard image is defined in meta-yogurt in:

meta-yogurt/recipes-images/images/phytec-headless-image.bb

In your layer, you can now modify the recipe with a bbappend without modifying any BSP code:

meta-racer/recipes-images/images/phytec-headless-image.bbappend

The append will be parsed together with the base recipe. As a result, you can easily overwrite all variables set in the base recipe, which is not always what you want. If we want to include additional software, we need to append to the IMAGE_INSTALL variable:

IMAGE_INSTALL_append = " rsync"

Add Linux Firmware Files to the Root Filesystem

It is a common task to add an extra firmware file to your root filesystem into /lib/firmware/. For example, WiFi adapters or PCIe Ethernet cards might need proprietary firmware. As a solution, we use a bbappend in our layer. To create the necessary folders, bbappend and copy the firmware file type:

host$ cd meta-racer   # go into your layer
host$ mkdir -p recipes-kernel/linux-firmware/linux-firmware/
host$ touch recipes-kernel/linux-firmware/linux-firmware_%.bbappend
host$ cp ~/example-firmware.bin recipes-kernel/linux-firmware/linux-firmware/    # adapt filename

Then add the following content to the bbappend file and replace every occurrence of example-firmware.bin with your firmware file name.

# file recipes-kernel/linux-firmware/linux-firmware_%.bbappend

FILESEXTRAPATHS_prepend := "${THISDIR}/linux-firmware:"
SRC_URI += "file://example-firmware.bin"

do_install_append () {
        install -m 0644 ${WORKDIR}/example-firmware.bin ${D}/lib/firmware/example-firmware.bin
}

# NOTE: Use "=+" instead of "+=". Otherwise file is placed into the linux-firmware package.
PACKAGES =+ "${PN}-example"
FILES_${PN}-example = "/lib/firmware/example-firmware.bin"

Now try to build the linux-firmware recipe:

host$ . sources/poky/oe-init-build-env
host$ bitbake linux-firmware

This should generate a new package deploy/ipk/all/linux-firmware-example.

As the final step, you have to install the firmware package to your image. You can do that in your local.conf or image recipe via:

# file local.conf or image recipe
IMAGE_INSTALL += "linux-firmware-example"

Warning

Ensure that you have adapted the package name linux-firmware-example with the name you assigned in linux-firmware_%.bbappend.

Change the barebox Environment via bbappend Files

Since BSP-Yocto-AM335x-16.2.0 and BSP-Yocto-i.MX6-PD16.1.0, the barebox environment handling in meta-phytec has changed. Now it is possible to add, change, and remove files in the barebox environment via the Python bitbake task do_env. There are two Python functions to change the environment. Their signatures are:

  • env_add(d, filename as string, file content as string): to add a new file or overwrite an existing file
  • env_rm(d, filename as string): to remove a file

The first example of a bbappend file in the custom layer meta-racer shows how to add a new non-volatile variable linux.bootargs.fb in the barebox environment folder /env/nv/:

# file meta-racer/recipes-bsp/barebox/barebox_2015.11.0-phy4.bbappend
python do_env_append() {
    env_add(d, "nv/linux.bootargs.fb", "imxdrm.legacyfb_depth=32\n")
}

The next example shows how to replace the network configuration file /env/network/eth0:

# file meta-racer/recipes-bsp/barebox/barebox_2015.11.0-phy4.bbappend
python do_env_append() {
    env_add(d, "network/eth0",
"""#!/bin/sh

# ip setting (static/dhcp)
ip=static
global.dhcp.vendor_id=barebox-${global.hostname}

# static setup used if ip=static
ipaddr=192.168.178.5
netmask=255.255.255.0
gateway=192.168.178.1
serverip=192.168.178.1
""")
}

In the above example, the Python multiline string syntax """ text """ is used to avoid adding multiple newline characters \n into the recipe Python code. The Python function env_add can add and overwrite environment files.

The next example shows how to remove an already added environment file, for example /env/boot/mmc:

# file meta-racer/recipes-bsp/barebox/barebox_2015.11.0-phy4.bbappend
python do_env_append() {
    env_rm(d, "boot/mmc")
}

Debugging the Environment

If you want to see all environment files that are added in the build process, you can enable a debug flag in the local.conf:

# file local.conf
ENV_VERBOSE = "1"

After that, you have to rebuild the barebox recipe to see the debugging output:

host$ bitbake barebox -c clean
host$ bitbake barebox -c configure

The output of the last command looks like:

[...]
WARNING: barebox-2015.11.0-phy4-r7.1 do_env_write: File 'nv/allow_color' content "false"
WARNING: barebox-2015.11.0-phy4-r7.1 do_env_write: File 'nv/linux.bootargs.base' content "consoleblank=0"
WARNING: barebox-2015.11.0-phy4-r7.1 do_env_write: File 'nv/linux.bootargs.fb' content "imxdrm.legacyfb_depth=32"
WARNING: barebox-2015.11.0-phy4-r7.1 do_env_write: File 'nv/linux.bootargs.rootfs' content "rootwait ro fsck.repair=yes"

Changing the Environment (depending on Machines)

If you need to apply some barebox environment modifications only to a single or only a few machines, you can use Bitbake's machine overwrite syntax. For the machine overwrite syntax, you append a machine name or SoC name (such as mx6, ti33x or rk3288) with an underscore to a variable or task:

DEPENDS_remove_mx6 = "virtual/libgl" or
python do_env_append_phyboard-mira-imx6-4().

The next example adds the environment variables only if the MACHINE is set to phyboard-mira-imx6-4:

# file meta-phytec/recipes-bsp/barebox/barebox_2015.11.0-phy4.bb
python do_env_append_phyboard-mira-imx6-4() {
    env_add(d, "nv/linux.bootargs.cma", "cma=64M\n")
}

Bitbake's override syntax for variables is explained in more detail at: https://www.yoctoproject.org/docs/latest/bitbake-user-manual/bitbake-user-manual.html#conditional-metadata

Upgrading the barebox Environment from Previous BSP Releases

Prior to BSP version BSP-Yocto-AM335x-16.2.0 and BSP-Yocto-i.MX6-PD16.1.0, barebox environment changes via bbappend file were done differently. For example, the directory structure in your meta layer (here meta-skeleton) may have looked like this:

$ tree -a sources/meta-skeleton/recipes-bsp/barebox/
sources/meta-skeleton/recipes-bsp/barebox
├── barebox
│   └── phyboard-wega-am335x-3
│       ├── boardenv
│       │   └── .gitignore
│       └── machineenv
│           └── nv
│               └── linux.bootargs.cma
└── barebox_%.bbappend

and the file barebox_%.bbappend contained:

# file sources/meta-skeleton/recipes-bsp/barebox/barebox_%.bbappend
FILESEXTRAPATHS_prepend := "${THISDIR}/barebox:"

In this example, all environment changes from the directory boardenv in the layer meta-phytec are ignored and the file nv/linux.bootargs.cma is added. For the new handling of the barebox environment you use the Python functions env_add and env_rm in the Python task do_env. Now the above example translates to a single Python function in the file barebox_%.bbappend that looks like:

# file sources/meta-skeleton/recipes-bsp/barebox/barebox_%.bbappend
FILESEXTRAPATHS_prepend := "${THISDIR}/barebox:"
python do_env_append() {
    # Removing files (previously boardenv)
    env_rm(d, "config-expansions")
    # Adding new files (previously machineenv)
    env_add(d, "nv/linux.bootargs.cma", "cma=64M\n")
}

Changing the Network Configuration

To tweak IP addresses, routes, and gateways at runtime you can use the tools ifconfig and ip. Some examples:

target$ ip addr                                         # Show all network interfaces
target$ ip route                                        # Show all routes
target$ ip addr add 192.168.178.11/24 dev eth0          # Add static ip and route to interface eth0
target$ ip route add default via 192.168.178.1 dev eth0 # Add default gateway 192.168.178.1
target$ ip addr del 192.168.178.11/24 dev eth0          # Remove static ip address from interface eth0

The network configuration is managed by systemd-networkd. To query the current status use:

target$ networkctl status
target$ networkctl list

The network daemon reads its configuration from the directories /etc/systemd/network/, /run/systemd/network/, and /lib/systemd/network/ (from higher to lower priority). A sample configuration in /lib/systemd/network/10-eth0.network looks like this:

# file /lib/systemd/network/10-eth0.network 
[Match]
Name=eth0

[Network]
Address=192.168.3.11/24
Gateway=192.168.3.10

These files *.network replace /etc/network/interfaces from other distributions. You can either edit the file 10-eth0.network in-place or copy it to /etc/systemd/network/ and make your changes there. After changing a file you must restart the daemon to apply your changes:

target$ systemctl restart systemd-networkd

To see the syslog message of the network daemon use:

target$ journalctl --unit=systemd-networkd.service

To modify the network configuration at build time, look at the recipe sources/meta-yogurt/recipes-core/systemd/systemd-machine-units.bb and the interface files in the folder meta-yogurt/recipes-core/systemd/systemd-machine-units/ where the static IP address configuration for eth0 (and optionally eth1) is done.

For more information, see https://wiki.archlinux.org/index.php/Systemd-networkd and http://www.freedesktop.org/software/systemd/man/systemd.network.html.

Changing the Wireless Network Configuration

Connecting to a WLAN Network

  • First set the correct regulatory domain for your country:
target$ iw reg set DE
target$ iw reg get

You will see:

country DE: DFS-ETSI
   (2400 - 2483 @ 40), (N/A, 20), (N/A)
   (5150 - 5250 @ 80), (N/A, 20), (N/A), NO-OUTDOOR
   (5250 - 5350 @ 80), (N/A, 20), (0 ms), NO-OUTDOOR, DFS
   (5470 - 5725 @ 160), (N/A, 26), (0 ms), DFS
   (57000 - 66000 @ 2160), (N/A, 40), (N/A)
  • Set up the wireless interface:
target$ ip link    # list all interfaces. Search for wlan*
target$ ip link set up dev wlan0
  • Now you can scan for available networks:
targe$ iw wlan0 scan | grep SSID

You can use a cross-platform supplicant with support for WEP, WPA, and WPA2 called wpa_supplicant for an encrypted connection.

  • To do so, add the network-credentials to the file /etc/wpa_supplicant.conf:
country=DE
network={
    ssid="<SSID>"
    proto=WPA2
    psk="<KEY>"
}
  • Now a connection can be established:
target$ wpa_supplicant -Dnl80211 -c/etc/wpa_supplicant.conf -iwlan0 &

This should result in the following output:

...
ENT-CONNECTED - Connection to 88:33:14:5d:db:b1 completed [id=0 id_str=]

To finish the configuration you can configure DHCP to receive an IP address (supported by most WLAN access points). For other possible IP configuration, see section "How to change the Network Configuration".

  • First create the directory:
target$ mkdir -p /etc/systemd/network/
  • Then add the following configuration snippet in /etc/systemd/network/10-wlan0.network:
# file /etc/systemd/network/10-wlan0.network
[Match]
Name=wlan0

[Network]
DHCP=yes
  • Now, restart the network daemon so that the configuration takes effect:
target$ systemctl restart systemd-networkd

Creating a WLAN Access Point

This section provides a basic access point (AP) configuration for a secured WPA2 network.

  • Find the name of the WLAN interface with:
target$ ip link
  • Edit the configuration in /etc/hostapd.conf. It is strongly dependent on the use case. The following shows an example:
# file /etc/hostapd.conf
interface=wlan0
driver=nl80211
ieee80211d=1
country_code=DE
hw_mode=g
ieee80211n=1
ssid=Test-Wifi
channel=2
wpa=2
wpa_passphrase=12345678
wpa_key_mgmt=WPA-PSK
wpa_pairwise=CCMP
  • Set up and start the DHCP server for the network interface wlan0 via systemd-networkd:
target$ mkdir -p /etc/systemd/network/
target$ vi /etc/systemd/network/10-wlan0.network
  • Insert the following text into the file:
[Match]
Name=wlan0

[Network]
Address=192.168.0.1/24
DHCPServer=yes

[DHCPServer]
EmitDNS=yes
target$ systemctl restart systemd-networkd
target$ systemctl status  systemd-networkd -l   # check status and see errors
  • Start the user space daemon hostapd:
target$ systemctl start hostapd
target$ systemctl status hostapd -l   # check for errors

Now, you should see the WLAN network Test-Wifi on your terminal device (laptop, smart phone, etc.).

If there are problems with the access point, you can either check the log messages with:

target$ journalctl --unit=hostapd

or start the daemon in debugging mode from the command line:

target$ systemctl stop hostapd
target$ hostapd -d /etc/hostapd.conf -P /var/run/hostapd.pid

You should see:

...
wlan0: interface state UNINITIALIZED->ENABLED
wlan0: AP-ENABLED

Further information about AP settings and the user space daemon hostapd can be found at:

http://processors.wiki.ti.com/index.php/OMAP_Wireless_Connectivity_NLCP_WLAN_AP_Configuration_Scripts
https://wireless.wiki.kernel.org/en/users/documentation/hostapd
https://w1.fi/hostapd/

Add OpenCV Libraries and Examples

OpenCV (Opensource Computer Vision http://opencv.org/) is an open-source library for computer vision applications.

  • To install the libraries and examples edit the file conf/local.conf in the Yocto buildsystem and add:
# file conf/local.conf
# Installing OpenCV libraries and examples
LICENSE_FLAGS_WHITELIST += "commercial_libav"
LICENSE_FLAGS_WHITELIST += "commercial_x264"
IMAGE_INSTALL_append = " \
    opencv \
    opencv-samples \
    libopencv-calib3d2.4 \
    libopencv-contrib2.4 \
    libopencv-core2.4 \
    libopencv-flann2.4 \
    libopencv-gpu2.4 \
    libopencv-highgui2.4 \
    libopencv-imgproc2.4 \
    libopencv-legacy2.4 \
    libopencv-ml2.4 \
    libopencv-nonfree2.4 \
    libopencv-objdetect2.4 \
    libopencv-ocl2.4 \
    libopencv-photo2.4 \
    libopencv-stitching2.4 \
    libopencv-superres2.4 \
    libopencv-video2.4 \
    libopencv-videostab2.4 \
"
  • Then rebuild your image:
host$ bitbake phytec-qt5demo-image

Tip

Most examples do not work out of the box, because they depend on the GTK graphics library. The BSP only supports Qt5.

Add Minimal php web runtime with lightpd

This is one example of how to add a small runtime for php applications and a webserver on your target. Lighttpd can be used together with the php command line tool over cgi. This solution weights only 5.5 MiB of disk storage. It is already preconfigured in meta-yogurt. Just modify the build configuration to install it on the image:

# file conf/local.conf
# install lighttpd with php cgi module
IMAGE_INSTALL_append = " lighttpd"

After booting the image, you should find the example web content in /www/pages. For testing php, you can delete the index.html and replace it with a index.php file:

<html>
 <head>
  <title>PHP-Test</title>
 </head>
 <body>
  <?php phpinfo(); ?>
 </body>
</html>

On your host, you can point your browser to the board's i, (e.g. 192.168.3.11) and the phpinfo should show up.

Common Tasks

Debugging a User Space Application

The phytec-qt5demo-image can be cross debugged without any change. For cross-debugging, you just have to match the host sysroot with the image in use. So you need to create a toolchain for your image:

host$ bitbake -c populate_sdk phytec-qt5demo-image

Additionally, if you want to have full debug and backtrace capabilities for all programs and libraries in the image, you could add:

DEBUG_BUILD = "1"

to the conf/local.conf. This is not necessary in all cases. The compiler options will then be switched from FULL_OPTIMIZATION to DEBUG_OPTIMIZATION. Look at the Poky source code for the default assignment of DEBUG_OPTIMIZATION.

To start a cross debug session, install the SDK as mentioned previously, source the SDK environment, and run Qt Creator in the same shell. If you do not use Qt Creator, you can directly call the arm-<..>-gdb debugger instead which should be in your path after sourcing the environment script.

If you work with Qt Creator, have a look in the appropriate documentation delivered with your product (either QuickStart or Application Guide) for information on how to set up the toolchain.

When starting the debugger with your userspace application you will get a SIGILL, an illegal instruction from the libcrypto. Openssl probes for the system capabilities by trapping illegal instructions, which will trigger GDB. You can ignore this and hit Continue (c command). You can permanently ignore this stop by adding:

handle SIGILL nostop

to your GDB startup script or in the Qt Creator GDB configuration panel. Secondly, you might need to disable a security feature by adding:

set auto-load safe-path /

to the same startup script, which will enable automatic loading of libraries from any location.

If you need to have native debugging, you might want to install the debug symbols on the target. You can do this by adding the following line to your conf/local.conf:

EXTRA_IMAGE_FEATURES += "dbg-pkgs"

For cross-debugging, this is not required as the debug symbols will be loaded from the host side and the dbg-pkgs are included in the SDK of your image anyway.

Generating Source Mirrors, working Offline

Modify your site.conf (or local.conf if you do not use a site.conf) as follows:

#DL_DIR ?= "" don't set it! It will default to a directory inside /build
SOURCE_MIRROR_URL = "file:///home/share/yocto_downloads/"
INHERIT += "own-mirrors"
BB_GENERATE_MIRROR_TARBALLS = "1"

Now run:

host$ bitbake --runall=fetch <image>

for all images and for all machines you want to provide sources for. This will create all necessary tar archives. We can remove all SCM subfolders, as they are duplicated with the tarballs:

host$ rm -rf build/download/git2/
etc...

Please consider that we used a local source mirror for generating the dl_dir. Because of that, some archives will be linked locally.

First we need to copy all files, resolving symbolic links into the new mirror directory:

host$ rsync -vaL <dl_dir> ${TOPDIR}/../src_mirror/

Now we clean the /build directory by deleting everything except /build/conf/ but including /build/conf/sanity. We change site.conf as follows:

SOURCE_MIRROR_URL = "file://${TOPDIR}/../src_mirror"
INHERIT += "own-mirrors" 
BB_NO_NETWORK = "1"
SCONF_VERSION = "1"

The BSP directory can now be compressed with:

host$ tar cfJ <filename>.tar.xz <folder>

where filename and folder should be the full BSP Name.

Compiling on the Target

To your local.conf add:

IMAGE_FEATURES_append = " tools-sdk dev-pkgs"

Different Toolchains

There are several ways to create a toolchain installer in Poky. One option is to run:

host$ bitbake meta-toolchain

This will generate a toolchain installer in build/deploy/sdk which can be used for cross compiling of target applications. However, the installer does not include libraries added to your image, so it is a bare GCC compiler only. This is suited for bootloader and kernel development.

Another you can run is:

host$ bitbake -c populate_sdk <your_image>

This will generate a toolchain installer containing all necessary development packages of the software installed on the root filesystem of the target. This installer can be handed over to the user space application development team and includes all necessary parts to develop an application. If the image contains the QT libraries, all of those will be available in the installer too.

The third option is to create the ADT (Application Development Toolkit) installer. It will contain the cross-toolchain and some tools to aid the software developers, for example an Eclipse plugin and a QEMU target simulator.

host$ bitbake adt-installer

The ADT is untested for our BSP at the moment.

Using the SDK

After generating the SDK with:

host$ source sources/poky/oe-init-build-env
host$ bitbake -c populate_sdk phytec-qt5demo-image  # or another image

run the generated binary with:

host$ deploy/sdk/yogurt-glibc-x86_64-phytec-qt5demo-image-cortexa9hf-vfp-neon-toolchain-i.MX6-PD15.3-rc.sh 
Enter target directory for SDK (default: /opt/yogurt/i.MX6-PD15.3-rc): 
You are about to install the SDK to "/opt/yogurt/i.MX6-PD15.3-rc". Proceed[Y/n]?
Extracting SDK...done
Setting it up...done
SDK has been successfully set up and is ready to be used.

You can activate the toolchain for your shell by sourcing the file environment-setup in the toolchain directory:

host$ source /opt/yogurt/i.MX6-PD15.3-rc/environment-setup-cortexa9hf-vfp-neon-phytec-linux-gnueabi

Then the necessary tools like cross compiler and linker are in your PATH. To compile a simple C program, use:

host$ $CC main.c -o main

The environment variable $CC contains the path to the arm cross compiler and other compiler arguments needed like -march, -sysroot and --mfloat-abi.

Tip

You cannot compile programs only with the compiler name like:

host$ arm-phytec-linux-gnueabi-gcc main.c -o main

It will fail in many cases. Always use CC, CFLAGS, LDFLAGS, and so on.

For convenience, the environment-setup exports other environment variables like CXX, LD, SDKTARGETSYSROOT, ….

A simple makefile compiling a C and C++ program may look like:

# Makefile
TARGETS=c-program cpp-program 

all: $(TARGETS)

c-program: c-program.c
	$(CC) $(CFLAGS) $(LDFLAGS) $< -o $@ 

cpp-program: cpp-program.cpp
	$(CXX) $(CXXFLAGS) $(LDFLAGS) $< -o $@

.PHONY: clean
clean:
	rm -f $(TARGETS)

To compile for the target, just source the toolchain in your shell before executing make:

host$ make     # Compiling with host CC, CXX for host architecture
host$ source /opt/yogurt/i.MX6-PD15.3-rc/environment-setup-cortexa9hf-vfp-neon-phytec-linux-gnueabi
host$ make     # Compiling with target CC, CXX for target architecture

If you need to specify additional included directories in the sysroot of the toolchain, you can use an '=' sign in the -I argument like:

-I=/usr/include/SDL

GCC replaces it by the sysroot path (here /opt/yogurt/i.MX6-PD15.3-rc/sysroots/cortexa9hf-vfp-neon-phytec-linux-gnueabi/). See the main page of GCC for more information.

Tip

The variables $CFLAGS and $CXXFLAGS contain the compiler debug flag '-g' by default. This includes debugging information in the binary and makes it bigger. Those should be removed in the production image. If you create a Bitbake recipe, the default behavior is to turn on '-g' too. The debugging symbols are used in the SDK rootfs to be able to get debugging information when invoking GDB from the host. Before installing the package to the target rootfs, Bitbake will invoke strip on the program which removes the debugging symbols. By default, they are not found nor required on the target root filesystem

Using the SDK with GNU Autotools

Yocto SDK is a straightforward too for a project that uses the GNU Autotools. The traditional compile steps for the host are usually:

host$ ./autogen.sh  # maybe not needed
host$ ./configure
host$ make
host$ make install DESTDIR=$PWD/build/

The commands to compile for the target machine with the Yocto SDK are quite similar. The following commands assume that the SDK was unpacked to directory /opt/phytec-yogurt/i.MX6-PD15.3.0/ (adapt the path as needed):

host$ source /opt/phytec-yogurt/i.MX6-PD15.3.0/environment-setup-cortexa9hf-vfp-neon-phytec-linux-gnueabi
host$ ./autogen.sh  # maybe not needed
host$ ./configure ${CONFIGURE_FLAGS}
host$ make
host$ make install DESTDIR=$PWD/build/

Refer to the official Yocto documentation for more information: http://www.yoctoproject.org/docs/latest/mega-manual/mega-manual.html#creating-and-running-a-project-based-on-gnu-autotools

Working with Kernel Modules

You will come to the point where you either need to set some options for a kernel module or you want to blacklist a module. Those things are handled by udev and go into *.conf files in:

/etc/modprobe.d/*.conf.

If you want to specify an option at build time, there are three relevant variables. If you just want to autoload a module which has no autoload capabilities, add it to:

KERNEL_MODULE_AUTOLOAD += "your-module"

either in the kernel recipe or in the global variable scope. If you need to specify options for a module, you can do so with:

KERNEL_MODULE_AUTOLOAD += "your-module" 
KERNEL_MODULE_PROBECONF += "your-module"
module_conf_your-module = "options your-module parametername=parametervalue"

if you want to blacklist a module from autoloading, you can do it intuitively with:

KERNEL_MODULE_AUTOLOAD += "your-module" 
KERNEL_MODULE_PROBECONF += "your-module"
module_conf_your-module = "blacklist your-module"

Working with udev

Udev (Linux dynamic device management) is a system daemon that handles dynamic device management in /dev. It is controlled by udev rules that are located in /etc/udev/rules.d (sysadmin configuration space) and /lib/udev/rules.d/ (vendor provided). Here is an example of an udev rule file:

# file /etc/udev/rules.d/touchscreen.rules
# Create a symlink to any touchscreen input device
SUBSYSTEM=="input", KERNEL=="event[0-9]*", ATTRS{modalias}=="input:*-e0*,3,*a0,1,*18,*", SYMLINK+="input/touchscreen0"
SUBSYSTEM=="input", KERNEL=="event[0-9]*", ATTRS{modalias}=="ads7846", SYMLINK+="input/touchscreen0"

See http://www.freedesktop.org/software/systemd/man/udev.html for more details about the syntax and usage. To get the list of attributes for a specific device that can be used in an udev rule you can use the udevadm info tool. It prints all existing attributes of the device node and its parents. The key value pairs from the output can be copied and pasted into a rule file. Some examples:

target$ udevadm info -a /dev/mmcblk0
target$ udevadm info -a /dev/v4l-subdev25
target$ udevadm info -a -p /sys/class/net/eth0

After changing an udev rule, you have to notify the daemon. Otherwise, your changes are not reflected. Use the following command:

target$ udevadm control --reload-rules

While developing udev rules you should monitor the events in order to see when devices are attached or unattached to the system. Use:

target$ udevadm monitor

Furthermore, it is very useful to monitor the system log in another shell, especially if the rule executes external scripts. Execute:

target$ journalctl -f

Tip

You cannot start daemons or heavy scripts in a RUN attribute. See http://www.freedesktop.org/software/systemd/man/udev.html#RUN{type}.

This can only be used for very short-running foreground tasks. Running an event process for a long period of time may block all further events for this or a dependent device. Starting daemons or other long-running processes is not appropriate for udev; the forked processes, detached or not, will be unconditionally killed after the event handling has finished. You can use the special attribute ENV{SYSTEMD_WANTS}="service-name.service" and a systemdservice instead.

See http://unix.stackexchange.com/questions/63232/what-is-the-correct-way-to-write-a-udev-rule-to-stop-a-service-under-systemd.

Troubleshooting

Setscene Task Warning

This warning occurs when the Yocto cache is in a dirty state.

WARNING: Setscene task X ([...]) failed with exit code '1' - real task

You should avoid canceling the build process or if you have to, press Ctrl-C once and wait until the build process has stopped. To remove all these warnings just clean the sstate cache and remove the build folders.

bitbake phytec-headless-image -c cleansstate && rm -rf tmp deploy/ipk

Yocto Documentation

The most important piece of the documentation for a BSP user is probably the developer manual.

http://www.yoctoproject.org/docs/2.5/dev-manual/dev-manual.html

The chapter about common tasks is a good starting point.

http://www.yoctoproject.org/docs/2.5/dev-manual/dev-manual.html#extendpoky

The complete documentation is available in one single html page, which is good for searching for a feature or a variable name.

http://www.yoctoproject.org/docs/2.5/mega-manual/mega-manual.html