OpenEmbedded / Angstrom : build from sources
How to build Angstrom for AT91
Note that building an entire distribution is a long process. It also requires a big amount of free disk space ; at least :
- ~650 MByte of source archives downloaded for Internet
- ~5 GByte of compiled packages and tools
This documentation is largely inspired by the following resources :
To build the binary found in the OpenEmbeddedAngstromGet page, you will have to go through the following steps.
Pre-requires
Here are the reference pages for setting up an OpenEmbedded building environment.
Note however that most of time, on a development host, those packages are often already installed.
Building environment
A step-by-step comprehensive installation is explained in the OpenEmbedded Getting Started page. The following lines have to be considered as an add-on that is AT91 specific or that can facilitate your setup.
Have a look at the OEDirectoryTree to figure out what your working environment tree will look like. In the following procedure, each time we speak about the base directory, we refer to the stuff directory.
Getting BitBake
Take it through the BitBake build tool website and take the latest archive tarball. follow the advice: simply install it in your OEDirectoryTree and make a generic link:
tar xvzf bitbake-1.8.18.tar.gz ln -s bitbake-1.8.18 bitbake
Getting OpenEmbedded
Once in your OEDirectoryTree, download a snapshot of the OpenEmbedded database using the GIT Souce Code Management tool.
git clone git://git.openembedded.org/openembedded openembedded
or using HTTP protocol:
git clone http://repo.or.cz/r/openembedded.git openembedded
Make sure to call the directory where you will clone the GIT source openembedded. This name will be used in the following procedure and in the site.conf configuration file.
Then create a local branch based on OpenEmbedded stable/2009 branch:
cd openembedded git checkout -b stable_2009_mybranch origin/stable/2009 cd ..
For demo root filesystems available in the GettingStarted page, we used the following commit ID :a646269c2ada7691d8a7f7455ba4528c7cca3483 . The stable/2009 branch should be stable enough to be able to build using those instructions even with a more recent HEAD for this branch.
AT91 OpenEmbedded overlay tree
In addition to the upstream recipes, we also have a set of our own recipes or modifications of the original ones. So, the following overlay tree will modify current OE original recipes.
note however that the goal of those recipes is to merge the most of it bits into the mainstream OE tree.
Then download and install the overlay tree archive, be sure to be in your OEDirectoryTree and:
wget ftp://ftp.linux4sam.org/pub/oe/linux4sam_x.y/oe_at91sam.tgz tar xvzf oe_at91sam.tgz
This archive contains the configuration files, recipes that will overload the original ones from the OpenEmbedded project. The oe_env.sh script will allow you to setup local configuration variables needed for your rootfs to build.
Setup local configuration
The local configuration is located in oe_at91sam/conf/local.conf . This configuration file will overload theopenembedded/conf/local.conf one.
Read comments in it as it will bring you valuable information and allow you to adapt it to your own environment and building host (directory structure for example). Choose the proper machine type: we will use at91sam9m10g45ek for this setup:
MACHINE ?= "at91sam9m10g45ek"
Start building
Be sure to always be in your OEDirectoryTree.
To start the building, source the oe_env.sh script:
source ./oe_env.sh
Then begin building the distribution with a little set of packages:
bitbake base-image
even a minimal image will require a big amount of time because of the cross-toolchain building process.
The console and graphical images are built using the following recipes respectively:
bitbake console-at91sam9-image bitbake x11-at91sam9-image
Or for AT91SAM9M10 based boards:
bitbake x11-at91sam9m10-image
This will allow you to take advantage of video features of this chip. This image will include kernel and Gstreamer components needed to use the hardware video decoder.
Tips & tricks
OE Link collection
From the BUG community, here is a very good link collection :
Three Steps for OpenEmbedded N00Bs
Wonder how to customize an OpenEmbedded building based on AT91 SOCs? Here is a simple and clear step by step blog:
Customizing OpenEmbedded
BitBake
BitBake usage:
http://www.uv-ac.de/openembedded/openembedded-3.html#ss3.2 BitBake User Manuallist tasks provided by a package:
bitbake -c listtasks <package_name>
You can use one of those tasks to have a fine grained control over the package building.
The structure of a BitBake file explained: BitBake Metadata
Hello World examples
The OpenMoko way:
http://wiki.openmoko.org/wiki/Building_a_hello_world_application
http://wiki.openmoko.org/wiki/Application_Development_Crash_Course#Your_First_Application
If you build additional packages, do not forget to run 
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