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Building Wandboard Systems with Yocto

23 Apr 2016

Some notes on building systems for Wandboards using tools from the Yocto Project.

The meta-wandboard layer generates some basic systems with packages to support C, C++, Qt5, Perl and Python development.

I use this as a template when starting new Wandboard projects.

System Info

The Yocto version is 2.0.1 the [jethro] branch.

The 4.4.6 Linux kernel comes from the linux-stable repository.

The u-boot version is 2015.07.

These are sysvinit systems.

The Qt version is 5.5.1. There is no X11 and no desktop installed. Qt GUI applications can be run using the -platform linuxfb switch.

A light-weight X11 desktop can be added with minimal changes to the build configuration. (X11 is needed to run Java GUI apps.)

ZeroMQ version 4.1.3 with development headers and libs is included.

Perl 5.22 and Python 2.7.9 each with a number of modules is included.

The following device tree binaries (dtbs) from the linux-stable repository are built and installed

U-Boot should detect the correct dtb to load at boot time.

Ubuntu Setup

I primarily use Ubuntu 15.10 64-bit server installations. Other versions should work.

You will need at least the following packages installed

bc
build-essential
chrpath
diffstat
gawk
git
libncurses5-dev
pkg-config
subversion
texi2html
texinfo
u-boot-tools

You also want to change the default Ubuntu shell from dash to bash by running this command from a shell

sudo dpkg-reconfigure dash

Choose No to dash when prompted.

Fedora Setup

I have used Fedora 23 64-bit workstations.

The extra packages I needed to install for Yocto were

chrpath
perl-bignum
perl-Thread-Queue
texinfo

and the package group

Development Tools

There might be more packages required since I had already installed qt-creator and the Development Tools group before I did the first build with Yocto.

Fedora already uses bash as the shell.

Clone the dependency repositories

First the main Yocto project poky repository

scott@fractal:~ git clone -b jethro git://git.yoctoproject.org/poky.git poky-jethro

Then the meta-openembedded repository

scott@fractal:~$ cd poky-jethro
scott@fractal:~/poky-jethro$ git clone -b jethro git://git.openembedded.org/meta-openembedded

And the meta-qt5 repository

scott@fractal:~/poky-jethro$ git clone -b jethro https://github.com/meta-qt5/meta-qt5.git

I usually keep these repositories separated since they can be shared between projects and different boards.

Clone the meta-wandboard repository

Create a sub-directory for the meta-wandboard repository before cloning

scott@octo:~$ mkdir ~/wandboard
scott@octo:~$ cd ~/wanboard
scott@octo:~/wandboard$ git clone -b jethro git://github.com/jumpnow/meta-wandboard

The meta-wandboard/README.md file has the last commits from the dependency repositories that I tested. You can always checkout those commits explicitly if you run into problems.

Initialize the build directory

Much of the following are only the conventions that I use. All of the paths to the meta-layers are configurable.

First setup a build directory. I tend to do this on a per board and/or per project basis so I can quickly switch between projects. For this example I’ll put the build directory under ~/wandboard/ with the meta-wandboard layer.

You could manually create the directory structure like this

scott@fractal:~$ mkdir -p ~/wandboard/build/conf

Or you could use the Yocto environment script oe-init-build-env like this passing in the path to the build directory

scott@fractal:~$ source poky-jethro/oe-init-build-env ~/wandboard/build

The Yocto environment script will create the build directory if it does not already exist.

Customize the configuration files

There are some sample configuration files in the meta-wandboard/conf directory.

Copy them to the build/conf directory (removing the ‘-sample’)

scott@fractal:~/wandboard$ cp meta-wandboard/conf/local.conf-sample build/conf/local.conf
scott@fractal:~/wandboard$ cp meta-wandboard/conf/bblayers.conf-sample build/conf/bblayers.conf

If you used the oe-init-build-env script to create the build directory, it generated some generic configuration files in the build/conf directory.
It is okay to copy over them.

You may want to customize the configuration files before your first build.

Edit bblayers.conf

In bblayers.conf file replace ${HOME} with the appropriate path to the meta-layer repositories on your system if you modified any of the paths in the previous instructions.

For example, if your directory structure does not look exactly like this, you will need to modify bblayers.conf

~/poky-jethro/
     meta-openembedded/
     meta-qt5/
     ...

~/wandboard/
    meta-wandboard/
    build/
        conf/

Edit local.conf

The variables you may want to customize are the following:

The defaults for all of these work fine. Adjustments are optional.

TMPDIR

This is where temporary build files and the final build binaries will end up. Expect to use at least 35GB. You probably want at least 50GB available.

The default location is in the build directory, in this example ~/wandboard/build/tmp.

If you specify an alternate location as I do in the example conf file make sure the directory is writable by the user running the build.

DL_DIR

This is where the downloaded source files will be stored. You can share this among configurations and build files so I created a general location for this outside my home directory. Make sure the build user has write permission to the directory you decide on.

The default location is in the build directory, ~/wandboard/build/sources.

SSTATE_DIR

This is another Yocto build directory that can get pretty big, greater then 5GB. I often put this somewhere else other then my home directory as well.

The default location is in the build directory, ~/wandboard/build/sstate-cache.

Run the build

You need to source the Yocto environment into your shell before you can use bitbake. The oe-init-build-env will not overwrite your
customized conf files.

scott@fractal:~$ source poky-jethro/oe-init-build-env ~/wandboard/build

### Shell environment set up for builds. ###

You can now run 'bitbake '

Common targets are:
    core-image-minimal
    core-image-sato
    meta-toolchain
    meta-toolchain-sdk
    adt-installer
    meta-ide-support

You can also run generated qemu images with a command like 'runqemu qemux86'
scott@fractal:~/wandboard/build$

I don’t use those Common targets, but instead use my own custom image recipes.

There are two custom images available in the meta-wandboard layer. The recipes for the images can be found in meta-wandboard/images/

You should add your own custom images to this same directory.

console-image

A basic console developer image. See the recipe meta-wandboard/images/console-image.bb for specifics, but some of the installed programs are

gcc/g++ and associated build tools
git
ssh/scp server and client
perl and python
zeromq

The console-image has a line

inherit core-image

which is poky-jethro/meta/classes/core-image.bbclass and pulls in some required base packages. This is useful to know if you create your own image recipe.

qt5-image

This image includes the console-image and adds Qt5 with the associated development headers and qmake.

Build

To build the console-image run the following command

scott@fractal:~/wandboard/build$ bitbake console-image

You may occasionally run into build errors related to packages that either failed to download or sometimes out of order builds. The easy solution is to clean the failed package and rerun the build again.

For instance if the build for zip failed for some reason, I would run this

scott@fractal:~/wandboard/build$ bitbake -c cleansstate zip
scott@fractal:~/wandboard/build$ bitbake zip

And then continue with the full build.

scott@fractal:~/wandboard/build$ bitbake console-image

To build the qt5-image it would be

scott@fractal:~/wandboard/build$ bitbake qt5-image

The cleansstate command (with two s’s) works for image recipes as well.

The image files won’t get deleted from the TMPDIR until the next time you build.

Copying the binaries to an SD card

After the build completes, the bootloader, kernel and rootfs image files can be found in <TMPDIR>/deploy/images/wandboard/.

The meta-wandboard/scripts directory has some helper scripts to format and copy the files to a microSD card.

mk2parts.sh

This script will partition an SD card with the minimal 2 partitions required for the boards. The script leaves a 4 MB empty region before the first partition for use as explained below.

Insert the microSD into your workstation and note where it shows up.

lsblk is convenient for finding the microSD card.

For example

scott@fractal:~/wandboard/meta-wandboard$ lsblk
NAME    MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sda       8:0    0 931.5G  0 disk
|-sda1    8:1    0  93.1G  0 part /
|-sda2    8:2    0  93.1G  0 part /home
|-sda3    8:3    0  29.8G  0 part [SWAP]
|-sda4    8:4    0     1K  0 part
|-sda5    8:5    0   100G  0 part /oe5
|-sda6    8:6    0   100G  0 part /oe6
|-sda7    8:7    0   100G  0 part /oe7
|-sda8    8:8    0   100G  0 part /oe8
|-sda9    8:9    0   100G  0 part /oe9
`-sda10   8:10   0 215.5G  0 part /oe10
sdb       8:16   1   7.4G  0 disk
|-sdb1    8:17   1    64M  0 part
`-sdb2    8:18   1   7.3G  0 part

I would use sdb for the format and copy script parameters on this machine.

It doesn’t matter if some partitions from the SD card are mounted. The mk2parts.sh script will unmount them.

BE CAREFUL with this script. It will format any disk on your workstation.

scott@fractal:~$ cd ~/wandboard/meta-wandboard/scripts
scott@fractal:~/wandboard/meta-wandboard/scripts$ sudo ./mk2parts.sh sdb

You only have to format the SD card once.

/media/card

You will need to create a mount point on your workstation for the copy scripts to use.

scott@fractal:~$ sudo mkdir /media/card

You only have to create this directory once.

copy_boot.sh

This script copies the bootloaders (MLO and u-boot) to the unpartitioned 4MB beginning section of the SD card.

The script also formats the first partition of the SD card as a FAT filesystem and copies the kernel (zImage) and a number of DTB files to it.

This script needs to know the TMPDIR to find the binaries. It looks for an environment variable called OETMP.

For instance, if I had this in the local.conf

TMPDIR = "/oe9/wand/tmp-jethro"

Then I would export this environment variable before running copy_boot.sh

scott@fractal:~/wandboard/meta-wandboard/scripts$ export OETMP=/oe9/wand/tmp-jethro

Then run the copy_boot.sh script passing the location of SD card

scott@fractal:~/wandboard/meta-wandboard/scripts$ ./copy_boot.sh sdb

This script should run very fast.

copy_rootfs.sh

This script formats the second partition of the SD card as an EXT4 filesystem and copies the operating system to it.

The script accepts an optional command line argument for the image type, for example console or qt5. The default is console if no argument is provided.

The script also accepts a hostname argument if you want the host name to be something other then the default wandboard.

Here’s an example of how you’d run copy_rootfs.sh

scott@fractal:~/wandboard/meta-wandboard/scripts$ ./copy_rootfs.sh sdb console

or

scott@fractal:~/wandboard/meta-wandboard/scripts$ ./copy_rootfs.sh sdb qt5 wandq

The copy_rootfs.sh script will take longer to run and depends a lot on the quality of your SD card. With a good Class 10 card it should take less then 30 seconds.

The copy scripts will NOT unmount partitions automatically. If an SD card partition is already mounted, the script will complain and abort. This is for safety, mine mostly, since I run these scripts many times a day on different machines and the SD cards show up in different places.

Here’s a realistic example session where I want to copy already built images to a second SD card that I just inserted.

scott@fractal:~$ sudo umount /dev/sdb1
scott@fractal:~$ sudo umount /dev/sdb2
scott@fractal:~$ export OETMP=/oe9/wand/tmp-jethro
scott@fractal:~$ cd wandboard/meta-wandboard/scripts
scott@fractal:~/wandboard/meta-wandboard/scripts$ ./copy_boot.sh sdb
scott@fractal:~/wandboard/meta-wandboard/scripts$ ./copy_rootfs.sh sdb console wandq2

Both copy_boot.sh and copy_rootfs.sh are simple scripts easily modified for custom use.

Some custom package examples

tspress is a Qt5 GUI application installed in /usr/bin with the qt5-image.

The bitbake recipe is here

meta-wandboard/recipes-qt/tspress/tspress.bb

Check the README in the tspress repository for usage.

Adding additional packages

To display the list of available packages from the meta- repositories included in bblayers.conf

scott@fractal:~$ source poky-jethro/oe-init-build-env ~/wandboard/build

scott@fractal:~/wandboard/build$ bitbake -s

Once you have the package name, you can choose to either

  1. Add the new package to the console-image or qt5-image, whichever you are using.

  2. Create a new image file and either include the console-image the way the qt5-image does or create a complete new image recipe. The console-image can be used as a template.

The new package needs to get included directly in the IMAGE_INSTALL variable or indirectly through another variable in the image file.

Customizing the Kernel

See this post for some ways to go about customizing and rebuilding the Wandboard kernel or generating a new device tree. Replace bbb with wandboard when reading.

Package management

The package manager for these systems is opkg. The other choices are rpm or apt. You can change the package manager with the PACKAGE_CLASSES variable in local.conf.

opkg is the most lightweight of the Yocto package managers and the one that builds packages the quickest.

To add or upgrade packages to the system, you might be interested in using the build workstation as a remote package repository.