1193 lines
65 KiB
XML
1193 lines
65 KiB
XML
|
<!DOCTYPE appendix PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
|
|||
|
|
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
|
|||
|
|
|
|||
|
|
<appendix id='dev-manual-bsp-appendix'>
|
|||
|
|
|
|||
|
|
<title>Development Cases</title>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
Many development cases exist for which you can use the Yocto Project.
|
|||
|
|
However, for the purposes of this manual we are going to focus on two common development cases or groupings:
|
|||
|
|
System Development and User Application Development.
|
|||
|
|
System Development covers Board Support Package (BSP) development and kernel modification.
|
|||
|
|
User Application Development covers development of applications that you intend to run on some
|
|||
|
|
target hardware.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
[WRITERS NOTE: What is undetermined at this point is how much of the entire development process
|
|||
|
|
we include in this particular chapter.
|
|||
|
|
In other words, do we cover debugging and emulation steps here on a case-specific basis?
|
|||
|
|
Or, do we capture that information in the appropriate subsequent chapter by case?]
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<section id='system-development-app'>
|
|||
|
|
<title>System Development</title>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
System development involves modification or creation of an image that you want to run on
|
|||
|
|
a specific hardware target.
|
|||
|
|
Usually when you want to create an image that runs on embedded hardware the image does
|
|||
|
|
not require the same amount of features that a full-fledged Linux distribution provides.
|
|||
|
|
Thus, you can create a much smaller image that is designed to just use the hardware
|
|||
|
|
features for your particular hardware.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
To help you understand how system development works in the Yocto Project, this section
|
|||
|
|
covers two types of image development: BSP creation and kernel modification.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<section id='developing-a-board-support-package-bsp-app'>
|
|||
|
|
<title>Developing a Board Support Package (BSP)</title>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
A BSP is a package of recipes that when applied while building an image results in
|
|||
|
|
an image you can run on a particular board.
|
|||
|
|
Thus, the package, when compiled into the new image, supports the operation of the board.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<note>
|
|||
|
|
For a brief list of terms used when describing the development process in the Yocto Project,
|
|||
|
|
see <xref linkend='yocto-project-terms'>Yocto Project Terms</xref> in this manual.
|
|||
|
|
</note>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
Here are the basic steps involved in creating a BSP:
|
|||
|
|
<orderedlist>
|
|||
|
|
<listitem><para>Be sure your host development system is set up to support
|
|||
|
|
development using the Yocto Project.
|
|||
|
|
See
|
|||
|
|
<ulink url='http://www.yoctoproject.org/docs/1.1/yocto-project-qs/yocto-project-qs.html#the-linux-distro'>
|
|||
|
|
The Linux Distributions</ulink> section and
|
|||
|
|
<ulink url='http://www.yoctoproject.org/docs/1.1/yocto-project-qs/yocto-project-qs.html#packages'>
|
|||
|
|
The Packages</ulink> section both
|
|||
|
|
in the Yocto Project Quick Start for requirements.
|
|||
|
|
You will also need a release of Yocto Project installed on the host.</para></listitem>
|
|||
|
|
<listitem><para>Choose a BSP available with Yocto Project that most closely represents
|
|||
|
|
your hardware.</para></listitem>
|
|||
|
|
<listitem><para>Get set up with a base BSP.</para></listitem>
|
|||
|
|
<listitem><para>Make a copy of the existing BSP and isolate your work by creating a layer
|
|||
|
|
for your recipes.</para></listitem>
|
|||
|
|
<listitem><para>Make configuration and recipe changes to your new BSP layer.</para></listitem>
|
|||
|
|
<listitem><para>Prepare for the build.</para></listitem>
|
|||
|
|
<listitem><para>Select and configure the kernel.</para></listitem>
|
|||
|
|
<listitem><para>Identify the machine branch.</para></listitem>
|
|||
|
|
<listitem><para>Build the image.</para></listitem>
|
|||
|
|
</orderedlist>
|
|||
|
|
You can view a video presentation of the BSP creation process
|
|||
|
|
<ulink url='http://free-electrons.com/blog/elc-2011-videos'>here</ulink>.
|
|||
|
|
You can also find supplemental information in the
|
|||
|
|
<ulink url='http://yoctoproject.org/docs/1.1/bsp-guide/bsp-guide.html'>
|
|||
|
|
Board Support Package (BSP) Development Guide</ulink>.
|
|||
|
|
Finally, there is wiki page write up of the example located
|
|||
|
|
<ulink url='https://wiki.yoctoproject.org/wiki/Transcript:_creating_one_generic_Atom_BSP_from_another'>
|
|||
|
|
here</ulink> you might find helpful.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<section id='setting-up-yocto-project-app'>
|
|||
|
|
<title>Setting Up Yocto Project</title>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
You need to have the Yocto Project files available on your host system.
|
|||
|
|
You can get files through tarball extraction or by cloning the <filename>poky</filename>
|
|||
|
|
Git repository.
|
|||
|
|
Typically, cloning the Git repository is the method to use.
|
|||
|
|
This allows you to maintain a complete history of changes and facilitates you
|
|||
|
|
contributing back to the Yocto Project.
|
|||
|
|
However, if you just want a hierarchical file structure that contains the recipes
|
|||
|
|
and metadata that let you develop you can download tarballs from the
|
|||
|
|
<ulink url='http://yoctoproject.org/download'>download page</ulink>.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
Regardless of the method you use this manual will refer to the resulting
|
|||
|
|
hierarchical set of files as "the local Yocto Project files."
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
[WRITER'S NOTE: I need to substitute correct and actual filenames for the
|
|||
|
|
1.1 release throughout this example once they become available.]
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
If you download a tarball you can extract it into any directory you want using the
|
|||
|
|
tar command.
|
|||
|
|
For example, the following command extracts the Yocto Project 1.1 release tarball
|
|||
|
|
into the current working directory and sets up a file structure whose top-level
|
|||
|
|
directory is named <filename>poky-1.1</filename>:
|
|||
|
|
<literallayout class='monospaced'>
|
|||
|
|
$ tar xfj poky-1.1.tar.bz2
|
|||
|
|
</literallayout>
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
The following transcript shows how to clone the <filename>poky</filename> Git repository
|
|||
|
|
into the current working directory.
|
|||
|
|
The command creates the repository in a directory named <filename>poky</filename>:
|
|||
|
|
<literallayout class='monospaced'>
|
|||
|
|
$ git clone git://git.yoctoproject.org/poky
|
|||
|
|
Initialized empty Git repository in /home/scottrif/poky/.git/
|
|||
|
|
remote: Counting objects: 107624, done.
|
|||
|
|
remote: Compressing objects: 100% (37128/37128), done.
|
|||
|
|
remote: Total 107624 (delta 73393), reused 99851 (delta 67287)
|
|||
|
|
Receiving objects: 100% (107624/107624), 69.74 MiB | 483 KiB/s, done.
|
|||
|
|
Resolving deltas: 100% (73393/73393), done.
|
|||
|
|
</literallayout>
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
Once you have the local <filename>poky</filename> Git repository set up,
|
|||
|
|
you have many development branches from which you can work.
|
|||
|
|
From inside the repository you can see the branch names and the tag names used
|
|||
|
|
in the Git repository using either of the following two commands:
|
|||
|
|
<literallayout class='monospaced'>
|
|||
|
|
$ git branch -a
|
|||
|
|
$ git tag -l
|
|||
|
|
</literallayout>
|
|||
|
|
For this example we are going to use the Yocto Project 1.1 Release,
|
|||
|
|
which maps to the <filename>1.1</filename> branch in the repository.
|
|||
|
|
These commands create a local branch named <filename>1.1</filename>
|
|||
|
|
that tracks the remote branch of the same name.
|
|||
|
|
<literallayout class='monospaced'>
|
|||
|
|
|
|||
|
|
$ cd poky
|
|||
|
|
$ git checkout -b 1.1 origin/1.1
|
|||
|
|
Switched to a new branch '1.1'
|
|||
|
|
</literallayout>
|
|||
|
|
</para>
|
|||
|
|
</section>
|
|||
|
|
|
|||
|
|
<section id='choosing-a-base-bsp-app'>
|
|||
|
|
<title>Choosing a Base BSP</title>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
The Yocto Project ships with several BSPs that support various hardware.
|
|||
|
|
It is best to base your new BSP on an existing BSP rather than create all the
|
|||
|
|
recipes and configuration files from scratch.
|
|||
|
|
While it is possible to create everything from scratch, basing your new BSP
|
|||
|
|
on something that is close is much easier.
|
|||
|
|
Or, at a minimum, it gives you some structure with which to start.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
At this point you need to understand your target hardware well enough to determine which
|
|||
|
|
existing BSP it most closely matches.
|
|||
|
|
Things to consider are your hardware’s on-board features such as CPU type and graphics support.
|
|||
|
|
You should look at the README files for supported BSPs to get an idea of which one
|
|||
|
|
you could use.
|
|||
|
|
A generic Atom-based BSP to consider is the Crown Bay that does not support
|
|||
|
|
the Intel® Embedded Media Graphics Driver (EMGD).
|
|||
|
|
The remainder of this example uses that base BSP.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
To see the supported BSPs, go to the Yocto Project
|
|||
|
|
<ulink url='http://www.yoctoproject.org/download'>download page</ulink> and click
|
|||
|
|
on “BSP Downloads.”
|
|||
|
|
</para>
|
|||
|
|
</section>
|
|||
|
|
|
|||
|
|
<section id='getting-your-base-bsp-app'>
|
|||
|
|
<title>Getting Your Base BSP</title>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
You need to have the base BSP layer on your development system.
|
|||
|
|
Like the local Yocto Project files, you can get the BSP
|
|||
|
|
layer one of two ways:
|
|||
|
|
download the BSP tarball and extract it, or set up a local Git repository that
|
|||
|
|
has the Yocto Project BSP layers.
|
|||
|
|
You should use the same method that you used to get the local Yocto Project files earlier.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
If you are using tarball extraction, simply download the tarball for the base
|
|||
|
|
BSP you chose in the previous step and then extract it into any directory
|
|||
|
|
you choose using the tar command.
|
|||
|
|
Upon extraction, the BSP source directory (layer) will be named
|
|||
|
|
<filename>meta-<BSP_name></filename>.
|
|||
|
|
The following command extracts the Crown Bay BSP into the current directory and names it
|
|||
|
|
<filename>meta-crownbay</filename>:
|
|||
|
|
<literallayout class='monospaced'>
|
|||
|
|
$ tar xjf crownbay-noemgd-1.1.tar.bz2
|
|||
|
|
</literallayout>
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
If you cloned a <filename>poky</filename> Git repository
|
|||
|
|
then you need to set up a different local Git repository
|
|||
|
|
(<filename>meta-intel</filename>) for the BSP.
|
|||
|
|
The <filename>meta-intel</filename> Git repository contains all the metadata
|
|||
|
|
that supports BSP creation.
|
|||
|
|
When you set up the <filename>meta-intel</filename> Git repository you can
|
|||
|
|
set it up anywhere you want.
|
|||
|
|
We will set up the repository inside the
|
|||
|
|
<filename>poky</filename> Git repository in this example.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
The following transcript shows the steps to clone the <filename>meta-intel</filename>
|
|||
|
|
Git repository inside the <filename>poky</filename> Git repository created earlier in this
|
|||
|
|
example.
|
|||
|
|
<literallayout class='monospaced'>
|
|||
|
|
$cd poky
|
|||
|
|
$ git clone git://git.yoctoproject.org/meta-intel.git
|
|||
|
|
Initialized empty Git repository in /home/scottrif/poky/meta-intel/.git/
|
|||
|
|
remote: Counting objects: 1325, done.
|
|||
|
|
remote: Compressing objects: 100% (1078/1078), done.
|
|||
|
|
remote: Total 1325 (delta 546), reused 85 (delta 27)
|
|||
|
|
Receiving objects: 100% (1325/1325), 1.56 MiB | 330 KiB/s, done.
|
|||
|
|
Resolving deltas: 100% (546/546), done.
|
|||
|
|
</literallayout>
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
Because <filename>meta-intel</filename> is its own Git repository you will want
|
|||
|
|
to be sure you are in the appropriate branch for your work.
|
|||
|
|
For this example we are going to use the <filename>1.1</filename> branch.
|
|||
|
|
<literallayout class='monospaced'>
|
|||
|
|
$ cd meta-intel
|
|||
|
|
$ git checkout -b 1.1 origin/1.1
|
|||
|
|
Switched to a new branch 'bernard'
|
|||
|
|
</literallayout>
|
|||
|
|
</para>
|
|||
|
|
</section>
|
|||
|
|
|
|||
|
|
<section id='making-a-copy-of-the-base bsp-to-create-your-new-bsp-layer-app'>
|
|||
|
|
<title>Making a Copy of the Base BSP to Create Your New BSP Layer</title>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
Now that you have the local Yocto Project files and the base BSP files you need to create a
|
|||
|
|
new layer for your BSP.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
Layers are ideal for isolating and storing work for a given piece of hardware.
|
|||
|
|
A layer is really just a location or area in which you place the recipes for your BSP.
|
|||
|
|
In fact, a BSP is, in itself, a special type of layer.
|
|||
|
|
Consider an application as another example that illustrates a layer.
|
|||
|
|
Suppose you are creating an application that has library or other dependencies in
|
|||
|
|
order for it to compile and run.
|
|||
|
|
The layer, in this case, would be where all the recipes that define those dependencies
|
|||
|
|
are kept. The key point for a layer is that it is an isolated area that contains
|
|||
|
|
all the relevant information for the project that the Yocto Project build system knows about.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<note>
|
|||
|
|
The Yocto Project supports four BSPs that are part of the
|
|||
|
|
Yocto Project release: <filename>atom-pc</filename>, <filename>beagleboard</filename>,
|
|||
|
|
<filename>mpc8315e</filename>, and <filename>routerstationpro</filename>.
|
|||
|
|
The recipes and configurations for these four BSPs are located and dispersed
|
|||
|
|
within local Yocto Project files.
|
|||
|
|
Consequently, they are not totally isolated in the spirit of layers unless you think
|
|||
|
|
of <filename>meta-yocto</filename> as a layer itself.
|
|||
|
|
On the other hand, BSP layers for Crown Bay, Emenlow, Jasper Forest,
|
|||
|
|
N450, and Sugar Bay are isolated.
|
|||
|
|
</note>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
When you set up a layer for a new BSP you should follow a standard layout.
|
|||
|
|
This layout is described in the
|
|||
|
|
<ulink url='http://www.yoctoproject.org/docs/1.1/bsp-guide/bsp-guide.html#bsp-filelayout'>
|
|||
|
|
Example Filesystem Layout</ulink> section of the Board Support Package (BSP) Development
|
|||
|
|
Guide.
|
|||
|
|
In the standard layout you will notice a suggested structure for recipes and
|
|||
|
|
configuration information.
|
|||
|
|
You can see the standard layout for the Crown Bay BSP in this example by examining the
|
|||
|
|
directory structure of the <filename>meta-crownbay</filename> layer inside the
|
|||
|
|
local Yocto Project files.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
To create your BSP layer you simply copy the <filename>meta-crownbay</filename>
|
|||
|
|
layer to a new layer.
|
|||
|
|
For this example the new layer will be named <filename>meta-mymachine</filename>.
|
|||
|
|
The name must follow the BSP layer naming convention, which is
|
|||
|
|
<filename>meta-<name></filename>.
|
|||
|
|
The following example assumes your working directory is <filename>meta-intel</filename>
|
|||
|
|
inside the local Yocto Project files.
|
|||
|
|
If you downloaded and expanded a Crown Bay tarball then you simply copy the resulting
|
|||
|
|
<filename>meta-crownbay</filename> directory structure to a location of your choice.
|
|||
|
|
Good practice for a Git repository, however, is to just copy the new layer alongside
|
|||
|
|
the existing
|
|||
|
|
BSP layers in the <filename>meta-intel</filename> Git repository:
|
|||
|
|
<literallayout class='monospaced'>
|
|||
|
|
$ cp -a meta-crownbay/ meta-mymachine
|
|||
|
|
</literallayout>
|
|||
|
|
</para>
|
|||
|
|
</section>
|
|||
|
|
|
|||
|
|
<section id='making-changes-to-your-bsp-app'>
|
|||
|
|
<title>Making Changes to Your BSP</title>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
Right now you have two identical BSP layers with different names:
|
|||
|
|
<filename>meta-crownbay</filename> and <filename>meta-mymachine</filename>.
|
|||
|
|
You need to change your configurations so that they work for your new BSP and
|
|||
|
|
your particular hardware.
|
|||
|
|
We will look first at the configurations, which are all done in the layer’s
|
|||
|
|
<filename>conf</filename> directory.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
First, since in this example the new BSP will not support EMGD we will get rid of the
|
|||
|
|
<filename>crownbay.conf</filename> file and then rename the
|
|||
|
|
<filename>crownbay-noemgd.conf</filename> file to <filename>mymachine.conf</filename>.
|
|||
|
|
Much of what we do in the configuration directory is designed to help the Yocto Project
|
|||
|
|
build system work with the new layer and to be able to find and use the right software.
|
|||
|
|
The following two commands result in a single machine configuration file named
|
|||
|
|
<filename>mymachine.conf</filename>.
|
|||
|
|
<literallayout class='monospaced'>
|
|||
|
|
$ rm meta-mymachine/conf/machine/crownbay.conf
|
|||
|
|
$ mv meta-mymachine/conf/machine/crownbay-noemgd.conf \
|
|||
|
|
meta-mymachine/conf/machine/mymachine.conf
|
|||
|
|
</literallayout>
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
The next step makes changes to <filename>mymachine.conf</filename> itself.
|
|||
|
|
The only changes needed for this example are changes to the comment lines.
|
|||
|
|
Here we simply substitute the Crown Bay name with an appropriate name.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
Note that inside the <filename>mymachine.conf</filename> is the
|
|||
|
|
<filename>PREFERRED_PROVIDER_virtual/kernel</filename> statement.
|
|||
|
|
This statement identifies the kernel that the BSP is going to use.
|
|||
|
|
In this case the BSP is using <filename>linux-yocto</filename>, which is the
|
|||
|
|
current Linux Yocto kernel based on the Linux 2.6.37 release.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
The next configuration file in the new BSP layer we need to edit is <filename>layer.conf</filename>.
|
|||
|
|
This file identifies build information needed for the new layer.
|
|||
|
|
You can see the
|
|||
|
|
<ulink url='http://www.yoctoproject.org/docs/1.1/bsp-guide/bsp-guide.html#bsp-filelayout-layer'>
|
|||
|
|
Layer Configuration File</ulink> section in the Board Support Packages (BSP) Development Guide
|
|||
|
|
for more information on this configuration file.
|
|||
|
|
Basically, we are changing the existing statements to work with our BSP.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
The file contains these statements that reference the Crown Bay BSP:
|
|||
|
|
<literallayout class='monospaced'>
|
|||
|
|
BBFILE_COLLECTIONS += "crownbay"
|
|||
|
|
BBFILE_PATTERN_crownbay := "^${LAYERDIR}/"
|
|||
|
|
BBFILE_PRIORITY_crownbay = "6"
|
|||
|
|
</literallayout>
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
Simply substitute the machine string name <filename>crownbay</filename>
|
|||
|
|
with the new machine name <filename>mymachine</filename> to get the following:
|
|||
|
|
<literallayout class='monospaced'>
|
|||
|
|
BBFILE_COLLECTIONS_mymachine += "mymachine"
|
|||
|
|
BBFILE_PATTERN_mymachine := "^${LAYERDIR}/"
|
|||
|
|
BBFILE_PRIORITY_mymachine = "6"
|
|||
|
|
</literallayout>
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
Now we will take a look at the recipes in your new layer.
|
|||
|
|
The standard BSP structure has areas for BSP, graphics, core, and kernel recipes.
|
|||
|
|
When you create a BSP you use these areas for appropriate recipes and append files.
|
|||
|
|
Recipes take the form of <filename>.bb</filename> files.
|
|||
|
|
If you want to leverage the existing recipes the Yocto Project build system uses
|
|||
|
|
but change those recipes you can use <filename>.bbappend</filename> files.
|
|||
|
|
All new recipes and append files for your layer must go in the layer’s
|
|||
|
|
<filename>recipes-bsp</filename>, <filename>recipes-kernel</filename>,
|
|||
|
|
<filename>recipes-core</filename>, and
|
|||
|
|
<filename>recipes-graphics</filename> directories.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
First, let's look at <filename>recipes-bsp</filename>.
|
|||
|
|
For this example we are not adding any new BSP recipes.
|
|||
|
|
And, we only need to remove the formfactor we do not want and change the name of
|
|||
|
|
the remaining one that doesn't support EMGD.
|
|||
|
|
These commands take care of the <filename>recipes-bsp</filename> recipes:
|
|||
|
|
<literallayout class='monospaced'>
|
|||
|
|
$ rm ‐rf meta-mymachine/recipes-graphics/xorg-xserver/*emgd*
|
|||
|
|
$ mv meta-mymachine/recipes-bsp/formfactor/formfactor/crownbay-noemgd/ \
|
|||
|
|
meta-mymachine/recipes-bsp/formfactor/formfactor/mymachine
|
|||
|
|
</literallayout>
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
Now let's look at <filename>recipes-graphics</filename>.
|
|||
|
|
For this example we want to remove anything that supports EMGD and
|
|||
|
|
be sure to rename remaining directories appropriately.
|
|||
|
|
The following commands clean up the <filename>recipes-graphics</filename> directory:
|
|||
|
|
<literallayout class='monospaced'>
|
|||
|
|
$ rm ‐rf meta-mymachine/recipes-graphics/xorg-xserver/xserver-xf86-emgd*
|
|||
|
|
$ rm ‐rf meta-mymachine/recipes-graphics/xorg-xserver/xserver-xf86-config/crownbay
|
|||
|
|
$ mv meta-mymachine/recipes-graphics/xorg-xserver/xserver-xf86-config/crownbay-noemgd \
|
|||
|
|
meta-mymachine/recipes-graphics/xorg-xserver/xserver-xf86-config/mymachine
|
|||
|
|
</literallayout>
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
At this point the <filename>recipes-graphics</filename> directory just has files that
|
|||
|
|
support Video Electronics Standards Association (VESA) graphics modes and not EMGD.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
Now let's look at changes in <filename>recipes-core</filename>.
|
|||
|
|
The file <filename>task-core-tools.bbappend</filename> in
|
|||
|
|
<filename>recipes-core/tasks</filename> appends the similarly named recipe
|
|||
|
|
located in the local Yocto Project files at
|
|||
|
|
<filename>meta/recipes-core/tasks</filename>.
|
|||
|
|
The "append" file in our layer right now is Crown Bay-specific and supports
|
|||
|
|
EMGD and non-EMGD.
|
|||
|
|
Here are the contents of the file:
|
|||
|
|
<literallayout class='monospaced'>
|
|||
|
|
RRECOMMENDS_task-core-tools-profile_append_crownbay = " systemtap"
|
|||
|
|
RRECOMMENDS_task-core-tools-profile_append_crownbay-noemgd = " systemtap"
|
|||
|
|
</literallayout>
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
The <filename>RRECOMMENDS</filename> statements list packages that
|
|||
|
|
extend usability.
|
|||
|
|
The first <filename>RRECOMMENDS</filename> statement can be removed, while the
|
|||
|
|
second one can be changed to reflect <filename>meta-mymachine</filename>:
|
|||
|
|
<literallayout class='monospaced'>
|
|||
|
|
RRECOMMENDS_task-core-tools-profile_append_mymachine = " systemtap"
|
|||
|
|
</literallayout>
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
Finally, let's look at <filename>recipes-kernel</filename> changes.
|
|||
|
|
Recall that the BSP uses the <filename>linux-yocto</filename> kernel as determined
|
|||
|
|
earlier in the <filename>mymachine.conf</filename>.
|
|||
|
|
The recipe for that kernel is not located in the
|
|||
|
|
BSP layer but rather in the local Yocto Project files at
|
|||
|
|
<filename>meta/recipes-kernel/linux</filename> and is
|
|||
|
|
named <filename>linux-yocto-2.6.37.bb</filename>.
|
|||
|
|
The <filename>SRCREV_machine</filename> and <filename>SRCREV_meta</filename>
|
|||
|
|
statements point to the exact commits used by the Yocto Project development team
|
|||
|
|
in their source repositories that identify the right kernel for our hardware.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
However, in the <filename>meta-mymachine</filename> layer in
|
|||
|
|
<filename>recipes-kernel/linux</filename> resides a <filename>.bbappend</filename>
|
|||
|
|
file named <filename>linux-yocto-2.6.37.bbappend</filename> that
|
|||
|
|
is appended to the recipe of the same name in <filename>meta/recipes-kernel/link</filename>.
|
|||
|
|
Thus, the <filename>SRCREV</filename> statements in the "append" file override
|
|||
|
|
the more general statements found in <filename>meta</filename>.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
The <filename>SRCREV</filename> statements in the "append" file currently identify
|
|||
|
|
the kernel that supports the Crown Bay BSP with and without EMGD support.
|
|||
|
|
Here are the statements:
|
|||
|
|
<literallayout class='monospaced'>
|
|||
|
|
SRCREV_machine_pn-linux-yocto_crownbay ?= \
|
|||
|
|
"372c0ab135978bd8ca3a77c88816a25c5ed8f303"
|
|||
|
|
SRCREV_meta_pn-linux-yocto_crownbay ?= \
|
|||
|
|
"d5d3c6480d61f83503ccef7fbcd765f7aca8b71b"
|
|||
|
|
|
|||
|
|
SRCREV_machine_pn-linux-yocto_crownbay-noemgd ?= \
|
|||
|
|
"372c0ab135978bd8ca3a77c88816a25c5ed8f303"
|
|||
|
|
SRCREV_meta_pn-linux-yocto_crownbay-noemgd ?= \
|
|||
|
|
"d5d3c6480d61f83503ccef7fbcd765f7aca8b71b"
|
|||
|
|
</literallayout>
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
You will notice that there are two pairs of <filename>SRCREV</filename> statements.
|
|||
|
|
The top pair identifies the kernel that supports
|
|||
|
|
EMGD, which we don’t care about in this example.
|
|||
|
|
The bottom pair identifies the kernel that we will use:
|
|||
|
|
<filename>linux-yocto</filename>.
|
|||
|
|
At this point though, the unique commit strings all are still associated with
|
|||
|
|
Crown Bay and not <filename>meta-mymachine</filename>.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
To fix this situation in <filename>linux-yocto-2.6.37.bbappend</filename>
|
|||
|
|
we delete the two <filename>SRCREV</filename> statements that support
|
|||
|
|
EMGD (the top pair).
|
|||
|
|
We also change the remaining pair to specify <filename>mymachine</filename>
|
|||
|
|
and insert the commit identifiers to identify the kernel in which we
|
|||
|
|
are interested, which will be based on the <filename>atom-pc-standard</filename>
|
|||
|
|
kernel.
|
|||
|
|
Here are the final <filename>SRCREV</filename> statements:
|
|||
|
|
<literallayout class='monospaced'>
|
|||
|
|
SRCREV_machine_pn-linux-yocto-_mymachine ?= \
|
|||
|
|
"fce17f046d3756045e4dfb49221d1cf60fcae329"
|
|||
|
|
SRCREV_meta_pn-linux-yocto-stable_mymachine ?= \
|
|||
|
|
"84f1a422d7e21fbc23a687035bdf9d42471f19e0"
|
|||
|
|
</literallayout>
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
If you are familiar with Git repositories you probably won’t have trouble locating the
|
|||
|
|
exact commit strings in the Yocto Project source repositories you need to change
|
|||
|
|
the <filename>SRCREV</filename> statements.
|
|||
|
|
You can find all the <filename>machine</filename> and <filename>meta</filename>
|
|||
|
|
branch points (commits) for the <filename>linux-yocto-2.6.37</filename> kernel
|
|||
|
|
<ulink url='http://git.yoctoproject.org/cgit/cgit.cgi/linux-yocto-2.6.37'>here</ulink>.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
If you need a little more assistance after going to the link then do the following:
|
|||
|
|
<orderedlist>
|
|||
|
|
<listitem><para>Expand the list of branches by clicking <filename>[…]</filename></para></listitem>
|
|||
|
|
<listitem><para>Click on the <filename>yocto/standard/common-pc/atom-pc</filename>
|
|||
|
|
branch</para></listitem>
|
|||
|
|
<listitem><para>Click on the commit column header to view the top commit</para></listitem>
|
|||
|
|
<listitem><para>Copy the commit string for use in the
|
|||
|
|
<filename>linux-yocto-2.6.37.bbappend</filename> file</para></listitem>
|
|||
|
|
</orderedlist>
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
For the <filename>SRCREV</filename> statement that points to the <filename>meta</filename>
|
|||
|
|
branch use the same procedure except expand the <filename>meta</filename>
|
|||
|
|
branch in step 2 above.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
Also in the <filename>linux-yocto-2.6.37.bbappend</filename> file are
|
|||
|
|
<filename>COMPATIBLE_MACHINE</filename>, <filename>KMACHINE</filename>,
|
|||
|
|
and <filename>KERNEL_FEATURES</filename> statements.
|
|||
|
|
Two sets of these exist: one set supports EMGD and one set does not.
|
|||
|
|
Because we are not interested in supporting EMGD those three can be deleted.
|
|||
|
|
The remaining three must be changed so that <filename>mymachine</filename> replaces
|
|||
|
|
<filename>crownbay-noemgd</filename> and <filename>crownbay</filename>.
|
|||
|
|
Here is the final <filename>linux-yocto-2.6.37.bbappend</filename> file after all
|
|||
|
|
the edits:
|
|||
|
|
<literallayout class='monospaced'>
|
|||
|
|
FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
|
|||
|
|
|
|||
|
|
COMPATIBLE_MACHINE_mymachine = "mymachine"
|
|||
|
|
KMACHINE_mymachine = "yocto/standard/mymachine"
|
|||
|
|
KERNEL_FEATURES_append_mymachine += " cfg/smp.scc"
|
|||
|
|
|
|||
|
|
SRCREV_machine_pn-linux-yocto_mymachine ?= \
|
|||
|
|
"fce17f046d3756045e4dfb49221d1cf60fcae329"
|
|||
|
|
SRCREV_meta_pn-linux-yocto_mymachine ?= \
|
|||
|
|
"84f1a422d7e21fbc23a687035bdf9d42471f19e0"
|
|||
|
|
</literallayout>
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
In summary, the edits to the layer’s recipe files result in removal of any files and
|
|||
|
|
statements that do not support your targeted hardware in addition to the inclusion
|
|||
|
|
of any new recipes you might need.
|
|||
|
|
In this example, it was simply a matter of ridding the new layer
|
|||
|
|
<filename>meta-machine</filename> of any code that supported the EMGD features
|
|||
|
|
and making sure we were identifying the kernel that supports our example, which
|
|||
|
|
is the <filename>atom-pc-standard</filename> kernel.
|
|||
|
|
We did not introduce any new recipes to the layer.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
Finally, it is also important to update the layer’s <filename>README</filename>
|
|||
|
|
file so that the information in it reflects your BSP.
|
|||
|
|
</para>
|
|||
|
|
</section>
|
|||
|
|
|
|||
|
|
<section id='preparing-for-the-build-app'>
|
|||
|
|
<title>Preparing for the Build</title>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
Once you have made all the changes to your BSP layer there remains a few things
|
|||
|
|
you need to do for the Yocto Project build system in order for it to create your image.
|
|||
|
|
You need to get the build environment ready by sourcing an environment setup script
|
|||
|
|
and you need to be sure two key configuration files are configured appropriately.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
The entire process for building an image is overviewed in the
|
|||
|
|
<ulink url='http://www.yoctoproject.org/docs/1.1/yocto-project-qs/yocto-project-qs.html#building-image'>
|
|||
|
|
Building an Image</ulink> section of the Yocto Project Quick Start.
|
|||
|
|
You might want to reference this information.
|
|||
|
|
The remainder of this section will apply to our example of the
|
|||
|
|
<filename>meta-mymachine</filename> layer.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
To get ready to build your image that uses the new layer you need to do the following:
|
|||
|
|
<orderedlist>
|
|||
|
|
<listitem><para>Get the environment ready for the build by sourcing the environment
|
|||
|
|
script.
|
|||
|
|
The environment script is in the top-level of the local Yocto Project files
|
|||
|
|
directory structure.
|
|||
|
|
The script has the string
|
|||
|
|
<filename>init-build-env</filename> in the file’s name.
|
|||
|
|
For this example, the following command gets the build environment ready:
|
|||
|
|
<literallayout class='monospaced'>
|
|||
|
|
$ source oe-init-build-env yocto-build
|
|||
|
|
</literallayout>
|
|||
|
|
When you source the script a build directory is created in the current
|
|||
|
|
working directory.
|
|||
|
|
In our example we were in the <filename>poky</filename> directory.
|
|||
|
|
Thus, entering the previous command created the <filename>yocto-build</filename> directory.
|
|||
|
|
If you do not provide a name for the build directory it defaults to
|
|||
|
|
<filename>build</filename>.
|
|||
|
|
The <filename>yocot-build</filename> directory contains a
|
|||
|
|
<filename>conf</filename> directory that has
|
|||
|
|
two configuration files you will need to check: <filename>bblayers.conf</filename>
|
|||
|
|
and <filename>local.conf</filename>.</para></listitem>
|
|||
|
|
<listitem><para>Check and edit the resulting <filename>local.conf</filename> file.
|
|||
|
|
This file minimally identifies the machine for which to build the image by
|
|||
|
|
configuring the <filename>MACHINE</filename> variable.
|
|||
|
|
For this example you must set the variable to mymachine as follows:
|
|||
|
|
<literallayout class='monospaced'>
|
|||
|
|
MACHINE ??= “mymachine”
|
|||
|
|
</literallayout>
|
|||
|
|
You should also be sure any other variables in which you are interested are set.
|
|||
|
|
Some variables to consider are <filename>BB_NUMBER_THREADS</filename>
|
|||
|
|
and <filename>PARALLEL_MAKE</filename>, both of which can greatly reduce your build time
|
|||
|
|
if you are using a multi-threaded development system (e.g. values of
|
|||
|
|
<filename>8</filename> and <filename>j 6</filename>, respectively are optimal
|
|||
|
|
for a development machine that has four available cores).</para></listitem>
|
|||
|
|
<listitem><para>Update the <filename>bblayers.conf</filename> file so that it includes
|
|||
|
|
the path to your new BSP layer.
|
|||
|
|
In this example you need to include the pathname to <filename>meta-mymachine</filename>.
|
|||
|
|
For this example the
|
|||
|
|
<filename>BBLAYERS</filename> variable in the file would need to include the following path:
|
|||
|
|
<literallayout class='monospaced'>
|
|||
|
|
$HOME/poky/meta-intel/meta-mymachine
|
|||
|
|
</literallayout></para></listitem>
|
|||
|
|
</orderedlist>
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
The appendix
|
|||
|
|
<ulink url='http://www.yoctoproject.org/docs/1.1/poky-ref-manual/poky-ref-manual.html#ref-variables-glos'>
|
|||
|
|
Reference: Variables Glossary</ulink> in the Yocto Project Reference Manual has more information
|
|||
|
|
on configuration variables.
|
|||
|
|
</para>
|
|||
|
|
</section>
|
|||
|
|
|
|||
|
|
<section id='building-the-image-app'>
|
|||
|
|
<title>Building the Image</title>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
The Yocto Project uses the BitBake tool to build images based on the type of image
|
|||
|
|
you want to create.
|
|||
|
|
You can find more information on BitBake
|
|||
|
|
<ulink url='http://bitbake.berlios.de/manual/'>here</ulink>.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
The build process supports several types of images to satisfy different needs.
|
|||
|
|
When you issue the BitBake command you provide a “top-level” recipe that essentially
|
|||
|
|
starts the process off of building the type of image you want.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
[WRITER'S NOTE: Consider moving this to the Poky Reference Manual.]
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
You can find these recipes in the <filename>meta/recipes-core/images</filename> and
|
|||
|
|
<filename>meta/recipes-sato/images</filename> directories of your local Yocto Project
|
|||
|
|
file structure (Git repository or extracted release tarball).
|
|||
|
|
Although the recipe names are somewhat explanatory, here is a list that describes them:
|
|||
|
|
<itemizedlist>
|
|||
|
|
<listitem><para><emphasis>Base</emphasis> – A foundational basic image without support
|
|||
|
|
for X that can be reasonably used for customization.</para></listitem>
|
|||
|
|
<listitem><para><emphasis>Core</emphasis> – A foundational basic image with support for
|
|||
|
|
X that can be reasonably used for customization.</para></listitem>
|
|||
|
|
<listitem><para><emphasis>Direct Disk</emphasis> – An image that you can copy directory to
|
|||
|
|
the disk of the target device.</para></listitem>
|
|||
|
|
<listitem><para><emphasis>Live</emphasis> – An image you can run from a USB device or from
|
|||
|
|
a CD without having to first install something.</para></listitem>
|
|||
|
|
<listitem><para><emphasis>Minimal</emphasis> – A small image without a GUI.
|
|||
|
|
This image is not much more than a kernel with a shell.</para></listitem>
|
|||
|
|
<listitem><para><emphasis>Minimal Development</emphasis> – A Minimal image suitable for
|
|||
|
|
development work.</para></listitem>
|
|||
|
|
<listitem><para><emphasis>Minimal Direct Disk</emphasis> – A Minimal Direct Disk image.</para></listitem>
|
|||
|
|
<listitem><para><emphasis>Minimal RAM-based Initial Root Filesystem</emphasis> – A minimal image
|
|||
|
|
that has the <filename>initramfs</filename> as part of the kernel, which allows the
|
|||
|
|
system to find the first “init” program more efficiently.</para></listitem>
|
|||
|
|
<listitem><para><emphasis>Minimal Live</emphasis> – A Minimal Live image.</para></listitem>
|
|||
|
|
<listitem><para><emphasis>Minimal MTD Utilities</emphasis> – A minimal image that has support
|
|||
|
|
for the MTD utilities, which let the user interact with the MTD subsystem in
|
|||
|
|
the kernel to perform operations on flash devices.</para></listitem>
|
|||
|
|
<listitem><para><emphasis>Sato</emphasis> – An image with Sato support, a mobile environment
|
|||
|
|
and visual style that works well with mobile devices.</para></listitem>
|
|||
|
|
<listitem><para><emphasis>Sato Development</emphasis> – A Sato image suitable for
|
|||
|
|
development work.</para></listitem>
|
|||
|
|
<listitem><para><emphasis>Sato Direct Disk</emphasis> – A Sato Direct Disk image.</para></listitem>
|
|||
|
|
<listitem><para><emphasis>Sato Live</emphasis> – A Sato Live image.</para></listitem>
|
|||
|
|
<listitem><para><emphasis>Sato SDK</emphasis> – A Sato image that includes the Yocto Project
|
|||
|
|
toolchain and development libraries.</para></listitem>
|
|||
|
|
<listitem><para><emphasis>Sato SDK Direct Disk</emphasis> – A Sato SDK Direct
|
|||
|
|
Disk image.</para></listitem>
|
|||
|
|
<listitem><para><emphasis>Sato SDK Live</emphasis> – A Sato SDK Live image.</para></listitem>
|
|||
|
|
</itemizedlist>
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
The remainder of this section applies to our example of the <filename>meta-mymachine</filename> layer.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
To build the image for our <filename>meta-mymachine</filename> BSP enter the following command
|
|||
|
|
from the same shell from which you ran the setup script.
|
|||
|
|
You should run the <filename>bitbake</filename> command without any intervening shell commands.
|
|||
|
|
For example, moving your working directory around could cause problems.
|
|||
|
|
Here is the command for this example:
|
|||
|
|
<literallayout class='monospaced'>
|
|||
|
|
$ bitbake –k core-image-sato-live
|
|||
|
|
</literallayout>
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
This command specifies an image that has Sato support and that can be run from a USB device or
|
|||
|
|
from a CD without having to first install anything.
|
|||
|
|
The build process takes significant time and includes thousands of tasks, which are reported
|
|||
|
|
at the console.
|
|||
|
|
If the build results in any type of error you should check for misspellings in the
|
|||
|
|
files you changed or problems with your host development environment such as missing packages.
|
|||
|
|
</para>
|
|||
|
|
</section>
|
|||
|
|
</section>
|
|||
|
|
|
|||
|
|
<section id='modifying-a-kernel-kernel-example-app'>
|
|||
|
|
<title>Modifying a Kernel</title>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
Kernel modification involves changing or adding configurations to an existing kernel, or
|
|||
|
|
adding recipes to the kernel that are needed to support specific hardware features.
|
|||
|
|
The process is similar to creating a Board Support Package (BSP) except that it does not
|
|||
|
|
involve a BSP layer.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
This section presents a brief overview of the kernel structure and then provides a simple
|
|||
|
|
example that shows how to modify the kernel.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<section id='yocto-project-kernel-app'>
|
|||
|
|
<title>Yocto Project Kernel Overview</title>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
When one thinks of the source files for a kernel they usually think of a fixed structure
|
|||
|
|
of files that contain kernel patches.
|
|||
|
|
The Yocto Project, however, employs mechanisims that in a sense result in a kernel source
|
|||
|
|
generator.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
The Yocto Project uses the source code management (SCM) tool Git to manage and track Yocto
|
|||
|
|
Project files.
|
|||
|
|
Git employs branching strategies that effectively produce a tree-like structure whose
|
|||
|
|
branches represent diversions from more general code.
|
|||
|
|
For example, suppose two kernels are basically identical with the exception of a couple
|
|||
|
|
different features in each.
|
|||
|
|
In the Yocto Project source repositories managed by Git a main branch can contain the
|
|||
|
|
common or shared
|
|||
|
|
parts of the kernel source and two branches that diverge from that common branch can
|
|||
|
|
each contain the features specific to the respective kernel.
|
|||
|
|
The result is a managed tree whose "leaves" represent the end of a specific path that yields
|
|||
|
|
a set of kernel source files necessary for a specific piece of hardware and its features.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
A big advantage to this scheme is the sharing of common features by keeping them in
|
|||
|
|
"larger" branches that are further up the tree.
|
|||
|
|
This practice eliminates redundant storage of similar features shared among kernels.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
When you build the kernel on your development system all files needed for the build
|
|||
|
|
are taken from the Yocto Project source repositories pointed to by the
|
|||
|
|
<filename>SRC_URI</filename> variable and gathered in a temporary work area
|
|||
|
|
where they are subsequently used to create the unique kernel.
|
|||
|
|
Thus, in a sense, the process constructs a local source tree specific to your
|
|||
|
|
kernel to generate the new kernel image - a source generator if you will.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
For a complete discussion of the Yocto Project kernel's architcture and its branching strategy,
|
|||
|
|
see the <ulink url='http://www.yoctoproject.org/docs/1.1/kernel-manual/kernel-manual.html'>
|
|||
|
|
The Yocto Project Kernel Architecture and Use Manual</ulink>.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
You can find a web interface to the Yocto Project source repository at
|
|||
|
|
<ulink url='http://git.yoctoproject.org/'></ulink>.
|
|||
|
|
Within the interface you will see groups of related source code, each of which can
|
|||
|
|
be cloned using Git to result in a working Git repository on your local system
|
|||
|
|
(referred to as the "local Yocto Project files" in this manual).
|
|||
|
|
The Yocto Project supports four types of kernels in its source repositories at
|
|||
|
|
<ulink url='http://git.yoctoproject.org/'></ulink>:
|
|||
|
|
<itemizedlist>
|
|||
|
|
<listitem><para><emphasis><filename>linux-yocto-2.6.34</filename></emphasis> - The
|
|||
|
|
stable Linux Yocto kernel that is based on the Linux 2.6.34 release.</para></listitem>
|
|||
|
|
<listitem><para><emphasis><filename>linux-yocto-2.6.37</filename></emphasis> - The current
|
|||
|
|
Linux Yocto kernel that is based on the Linux 2.6.37 release.</para></listitem>
|
|||
|
|
<listitem><para><emphasis><filename>linux-yocto-dev</filename></emphasis> - A development
|
|||
|
|
kernel based on the Linux 2.6.39-rc1 release.</para></listitem>
|
|||
|
|
<listitem><para><emphasis><filename>linux-2.6</filename></emphasis> - A kernel based on
|
|||
|
|
minimal Linux mainline tracking.
|
|||
|
|
[WRITER'S NOTE: I don't know which Git repository the user needs to clone to get this
|
|||
|
|
repository on their development system.]</para></listitem>
|
|||
|
|
</itemizedlist>
|
|||
|
|
</para>
|
|||
|
|
</section>
|
|||
|
|
|
|||
|
|
<section id='modifying-a-kernel-example-app'>
|
|||
|
|
<title>Modifying a Kernel Example</title>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
This section presents a simple example that illustrates kernel modification
|
|||
|
|
based on the <filename>linux-yocto-2.6.37</filename> kernel.
|
|||
|
|
The example uses the audio and mixer capabilities supported by the
|
|||
|
|
<ulink url='http://www.alsa-project.org/main/index.php/Main_Page'>Advanced Linux
|
|||
|
|
Sound Architecture (ALSA) Project</ulink>.
|
|||
|
|
As the example progresses you will see how to do the following:
|
|||
|
|
<itemizedlist>
|
|||
|
|
<listitem><para>Iteratively modify a base kernel locally.</para></listitem>
|
|||
|
|
<listitem><para>Provide a recipe-based solution for your modified kernel.
|
|||
|
|
</para></listitem>
|
|||
|
|
<listitem><para>Proved an "in-tree" solution for your modified kernel
|
|||
|
|
(i.e. make the modifcations part of the Yocto Project).</para></listitem>
|
|||
|
|
</itemizedlist>
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
The example flows as follows:
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
<itemizedlist>
|
|||
|
|
<listitem><para>Be sure your host development system is set up to support
|
|||
|
|
development using the Yocto Project.
|
|||
|
|
See
|
|||
|
|
<ulink url='http://www.yoctoproject.org/docs/1.1/yocto-project-qs/yocto-project-qs.html#the-linux-distro'>
|
|||
|
|
The Linux Distributions</ulink> section and
|
|||
|
|
<ulink url='http://www.yoctoproject.org/docs/1.1/yocto-project-qs/yocto-project-qs.html#packages'>
|
|||
|
|
The Packages</ulink> section both
|
|||
|
|
in the Yocto Project Quick Start for requirements.
|
|||
|
|
You will also need a release of Yocto Project installed on the host.</para></listitem>
|
|||
|
|
<listitem><para>Set up your environment for optimal local kernel development.
|
|||
|
|
</para></listitem>
|
|||
|
|
<listitem><para>Create a layer to isolate your kernel work.</para></listitem>
|
|||
|
|
<listitem><para>Next item.</para></listitem>
|
|||
|
|
<listitem><para>Next item.</para></listitem>
|
|||
|
|
<listitem><para>Next item.</para></listitem>
|
|||
|
|
<listitem><para>Next item.</para></listitem>
|
|||
|
|
</itemizedlist>
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<section id='setting-up-yocto-project-kernel-example-app'>
|
|||
|
|
<title>Setting Up Yocto Project</title>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
You need to have the Yocto Project files available on your host system.
|
|||
|
|
The process is identical to that described in getting the files in section
|
|||
|
|
<xref linkend='setting-up-yocto-project-app'>"Setting Up Yocto Project"</xref> for
|
|||
|
|
the BSP development case.
|
|||
|
|
Be sure to either set up a local Git repository for <filename>poky</filename>
|
|||
|
|
or download and unpack the Yocto Project release tarball.
|
|||
|
|
</para>
|
|||
|
|
</section>
|
|||
|
|
|
|||
|
|
<section id='create-a-git-repository-of-poky-extras-app'>
|
|||
|
|
<title>Create a Git Repository of <filename>poky-extras</filename></title>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
Everytime you change a configuration or add a recipe to the kernel you need to
|
|||
|
|
do a fetch from the Linux Yocto kernel source repositories.
|
|||
|
|
This can get tedious and time consuming if you need to fetch the entire
|
|||
|
|
Linux Yocto 2.6.37 Git repository down from the Internet everytime you make a change
|
|||
|
|
to the kernel.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
You can get around this by setting up a <filename>meta-kernel-dev</filename>
|
|||
|
|
area on your local system.
|
|||
|
|
This area contains "append" files for every kernel recipe, which also include
|
|||
|
|
a <filename>KSRC</filename> statement that points to the kernel source files.
|
|||
|
|
You can set up the environment so that the <filename>KSRC</filename> points to the
|
|||
|
|
<filename>meta-kernel-dev</filename>, thus pulling source from a local area.
|
|||
|
|
This setup can speed up development time.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
To get set up you need to do two things: create a local Git repository
|
|||
|
|
of the <filename>poky-extras</filename> repository, and create a bare clone of the
|
|||
|
|
Linux Yocto 2.6.37 kernel Git repository.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
The following transcript shows how to clone the <filename>poky-extras</filename>
|
|||
|
|
Git repository into the current working directory, which is <filename>poky</filename>
|
|||
|
|
in this example.
|
|||
|
|
The command creates the repository in a directory named <filename>poky-extras</filename>:
|
|||
|
|
<literallayout class='monospaced'>
|
|||
|
|
$ git clone git://git.yoctoproject.org/poky-extras
|
|||
|
|
Initialized empty Git repository in /home/scottrif/poky/poky-extras/.git/
|
|||
|
|
remote: Counting objects: 532, done.
|
|||
|
|
remote: Compressing objects: 100% (472/472), done.
|
|||
|
|
remote: Total 532 (delta 138), reused 307 (delta 39)
|
|||
|
|
Receiving objects: 100% (532/532), 534.28 KiB | 362 KiB/s, done.
|
|||
|
|
Resolving deltas: 100% (138/138), done.
|
|||
|
|
</literallayout>
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
This transcript shows how to clone a bare Git repository of the Linux Yocto
|
|||
|
|
2.6.37 kernel:
|
|||
|
|
<literallayout class='monospaced'>
|
|||
|
|
$ git clone --bare git://git.yoctoproject.org/linux-yocto-2.6.37
|
|||
|
|
Initialized empty Git repository in /home/scottrif/linux-yocto-2.6.37.git/
|
|||
|
|
remote: Counting objects: 1886034, done.
|
|||
|
|
remote: Compressing objects: 100% (314326/314326), done.
|
|||
|
|
remote: Total 1886034 (delta 1570202), reused 1870335 (delta 1554798)
|
|||
|
|
Receiving objects: 100% (1886034/1886034), 401.51 MiB | 714 KiB/s, done.
|
|||
|
|
Resolving deltas: 100% (1570202/1570202), done.
|
|||
|
|
</literallayout>
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
The bare clone of the Linux Yocto 2.6.37 kernel on your local system mirrors
|
|||
|
|
the upstream repository of the kernel.
|
|||
|
|
You can effectively point to this local clone now during development to avoid
|
|||
|
|
having to fetch the entire Linux Yocto 2.6.37 kernel every time you make a
|
|||
|
|
kernel change.
|
|||
|
|
</para>
|
|||
|
|
</section>
|
|||
|
|
|
|||
|
|
<section id='create-a-layer-for-your-kernel-work-app'>
|
|||
|
|
<title>Create a Layer for Your Kernel Work</title>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
It is always good to isolate your work using your own layer.
|
|||
|
|
Doing so allows you to experiment and easily start over should things go wrong.
|
|||
|
|
This example uses a layer named <filename>meta-amixer</filename>.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
When you set up a layer for kernel work you should follow the general layout
|
|||
|
|
guidelines as described for BSP layers.
|
|||
|
|
This layout is described in the
|
|||
|
|
<ulink url='http://www.yoctoproject.org/docs/1.1/bsp-guide/bsp-guide.html#bsp-filelayout'>
|
|||
|
|
Example Filesystem Layout</ulink> section of the Board Support Package (BSP) Development
|
|||
|
|
Guide.
|
|||
|
|
In the standard layout you will notice a suggested structure for recipes and
|
|||
|
|
configuration information.
|
|||
|
|
[WRITER'S NOTE: The <filename>meta-elc</filename> example uses an
|
|||
|
|
<filename>images</filename> directory.
|
|||
|
|
Currently, <filename>images</filename> is not part of the standard BSP layout.
|
|||
|
|
I need to find out from Darren if this directory is required for kernel work.]
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
[WRITER'S NOTE: I need a paragraph here describing how to set up the layer.
|
|||
|
|
I am not sure if you should copy an existing BSP layer and modify from there.
|
|||
|
|
Or, if you should just look at a BSP layer and then create your own files.
|
|||
|
|
Email to Darren on this but no answer yet.]
|
|||
|
|
</para>
|
|||
|
|
</section>
|
|||
|
|
|
|||
|
|
<section id='making-changes-to-your-kernel-layer-app'>
|
|||
|
|
<title>Making Changes to Your Kernel Layer</title>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
In the standard layer structure you have several areas that you need to examine or
|
|||
|
|
modify.
|
|||
|
|
For this example the layer contains four areas:
|
|||
|
|
<itemizedlist>
|
|||
|
|
<listitem><para><emphasis><filename>conf</filename></emphasis> - Contains the
|
|||
|
|
<filename>layer.conf</filename> that identifies the location of the recipe files.
|
|||
|
|
</para></listitem>
|
|||
|
|
<listitem><para><emphasis><filename>images</filename></emphasis> - Contains the
|
|||
|
|
image recipe file.
|
|||
|
|
This recipe includes the base image you will be using and specifies other
|
|||
|
|
packages the image might need.</para></listitem>
|
|||
|
|
<listitem><para><emphasis><filename>recipes-bsp</filename></emphasis> - Contains
|
|||
|
|
recipes specific to the hardware for which you are developing the kernel.
|
|||
|
|
</para></listitem>
|
|||
|
|
<listitem><para><emphasis><filename>recipes-kernel</filename></emphasis> - Contains the
|
|||
|
|
"append" files that add information to the main recipe kernel.
|
|||
|
|
</para></listitem>
|
|||
|
|
</itemizedlist>
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
Let's take a look at the <filename>layer.conf</filename> in the
|
|||
|
|
<filename>conf</filename> directory first.
|
|||
|
|
This configuration file enables the Yocto Project build system to locate and
|
|||
|
|
use the information in your new layer.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
The variable <filename>BBPATH</filename> needs to include the path to your layer
|
|||
|
|
as follows:
|
|||
|
|
<literallayout class='monospaced'>
|
|||
|
|
BBPATH := "${BBPATH}:${LAYERDIR}"
|
|||
|
|
</literallayout>
|
|||
|
|
And, the variable <filename>BBFILES</filename> needs to be modified to include your
|
|||
|
|
recipe and append files:
|
|||
|
|
<literallayout class='monospaced'>
|
|||
|
|
BBFILES := "${BBFILES} ${LAYERDIR}/images/*.bb \
|
|||
|
|
${LAYERDIR}/images/*.bbappend \
|
|||
|
|
${LAYERDIR}/recipes-*/*/*.bb \
|
|||
|
|
${LAYERDIR}/recipes-*/*/*.bbappend"
|
|||
|
|
</literallayout>
|
|||
|
|
Finally, you need to be sure to use your layer name in these variables at the
|
|||
|
|
end of the file:
|
|||
|
|
<literallayout class='monospaced'>
|
|||
|
|
BBFILE_COLLECTIONS += "elc"
|
|||
|
|
BBFILE_PATTERN_elc := "^${LAYERDIR}/"
|
|||
|
|
BBFILE_PRIORITY_elc = "9"
|
|||
|
|
</literallayout>
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
The <filename>images</filename> directory contains an append file that helps
|
|||
|
|
further define the image.
|
|||
|
|
In our example, the base image is <filename>core-image-minimal</filename>.
|
|||
|
|
The image does, however, need some additional modules that we are using
|
|||
|
|
for this example.
|
|||
|
|
These modules support the amixer functionality.
|
|||
|
|
Here is the append file:
|
|||
|
|
<literallayout class='monospaced'>
|
|||
|
|
require recipes-core/images/poky-image-minimal.bb
|
|||
|
|
|
|||
|
|
IMAGE_INSTALL += "dropbear alsa-utils-aplay alsa-utils-alsamixer"
|
|||
|
|
IMAGE_INSTALL_append_qemux86 += " kernel-module-snd-ens1370 \
|
|||
|
|
kernel-module-snd-rawmidi kernel-module-loop kernel-module-nls-cp437 \
|
|||
|
|
kernel-module-nls-iso8859-1 qemux86-audio alsa-utils-amixer"
|
|||
|
|
|
|||
|
|
LICENSE = "MIT"
|
|||
|
|
</literallayout>
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
While the focus of this example is not on the BSP, it is worth mentioning that the
|
|||
|
|
<filename>recipes-bsp</filename> directory has the recipes and append files for
|
|||
|
|
features that the hardware requires.
|
|||
|
|
In this example, there is a script and a recipe to support the
|
|||
|
|
<filename>amixer</filename> functionality in QEMU.
|
|||
|
|
It is beyond the scope of this manual to go too deeply into the script.
|
|||
|
|
Suffice it to say that the script tests for the presence of the mixer, sets up
|
|||
|
|
default mixer values, enables the mixer, unmutes master and then
|
|||
|
|
sets the volume to 100.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
The recipe <filename>qemu86-audio.bb</filename> installs and runs the
|
|||
|
|
<filename>amixer</filename> when the system boots.
|
|||
|
|
Here is the recipe:
|
|||
|
|
<literallayout class='monospaced'>
|
|||
|
|
SUMMARY = "Provide a basic init script to enable audio"
|
|||
|
|
DESCRIPTION = "Set the volume and unmute the Front mixer setting during boot."
|
|||
|
|
SECTION = "base"
|
|||
|
|
LICENSE = "MIT"
|
|||
|
|
LIC_FILES_CHKSUM = "file://${POKYBASE}/LICENSE;md5=3f40d7994397109285ec7b81fdeb3b58"
|
|||
|
|
|
|||
|
|
PR = "r4"
|
|||
|
|
|
|||
|
|
inherit update-rc.d
|
|||
|
|
|
|||
|
|
RDEPENDS = "alsa-utils-amixer"
|
|||
|
|
|
|||
|
|
SRC_URI = "file://qemux86-audio"
|
|||
|
|
|
|||
|
|
INITSCRIPT_NAME = "qemux86-audio"
|
|||
|
|
INITSCRIPT_PARAMS = "defaults 90"
|
|||
|
|
|
|||
|
|
do_install() {
|
|||
|
|
install -d ${D}${sysconfdir} \
|
|||
|
|
${D}${sysconfdir}/init.d
|
|||
|
|
install -m 0755 ${WORKDIR}/qemux86-audio ${D}${sysconfdir}/init.d
|
|||
|
|
cat ${WORKDIR}/${INITSCRIPT_NAME} | \
|
|||
|
|
sed -e 's,/etc,${sysconfdir},g' \
|
|||
|
|
-e 's,/usr/sbin,${sbindir},g' \
|
|||
|
|
-e 's,/var,${localstatedir},g' \
|
|||
|
|
-e 's,/usr/bin,${bindir},g' \
|
|||
|
|
-e 's,/usr,${prefix},g' > ${D}${sysconfdir}/init.d/${INITSCRIPT_NAME}
|
|||
|
|
chmod 755 ${D}${sysconfdir}/init.d/${INITSCRIPT_NAME}
|
|||
|
|
}
|
|||
|
|
</literallayout>
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
The last area to look at is <filename>recipes-kernel</filename>.
|
|||
|
|
This area holds configuration fragments and kernel append files.
|
|||
|
|
The append file must have the same name as the kernel recipe, which is
|
|||
|
|
<filename>linux-yocto-2.6.37</filename> in this example.
|
|||
|
|
The file can <filename>SRC_URI</filename> statements to point to configuration
|
|||
|
|
fragments you might have in the layer.
|
|||
|
|
The file can also contain <filename>KERNEL_FEATURES</filename> statements that specify
|
|||
|
|
included kernel configurations that ship with the Yocto Project.
|
|||
|
|
</para>
|
|||
|
|
</section>
|
|||
|
|
</section>
|
|||
|
|
</section>
|
|||
|
|
</section>
|
|||
|
|
|
|||
|
|
</appendix>
|
|||
|
|
|
|||
|
|
|
|||
|
|
|
|||
|
|
|
|||
|
|
|
|||
|
|
<!--
|
|||
|
|
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
[WRITER'S NOTE: This section is a second example that focuses on just modifying the kernel.
|
|||
|
|
I don't have any information on this yet.
|
|||
|
|
</para>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
Here are some points to consider though:
|
|||
|
|
<itemizedlist>
|
|||
|
|
<listitem><para>Reference Darren's presentation
|
|||
|
|
<ulink url='http://events.linuxfoundation.org/events/embedded-linux-conference/hart'>
|
|||
|
|
here</ulink></para></listitem>
|
|||
|
|
<listitem><para>Reference <xref linkend='dev-manual-start'>Getting Started with the Yocto Project</xref>
|
|||
|
|
section to get set up at minimum.</para></listitem>
|
|||
|
|
<listitem><para>Are there extra steps I need specific to kernel development to get started?</para></listitem>
|
|||
|
|
<listitem><para>What do I do to get set up?
|
|||
|
|
Is it a matter of just installing YP and having some pieces together?
|
|||
|
|
What are the pieces?</para></listitem>
|
|||
|
|
<listitem><para>Where do I get the base kernel to start with?</para></listitem>
|
|||
|
|
<listitem><para>Do I install the appropriate toolchain?</para></listitem>
|
|||
|
|
<listitem><para>What kernel git repository do I use?</para></listitem>
|
|||
|
|
<listitem><para>What is the conversion script?
|
|||
|
|
What does it do?</para></listitem>
|
|||
|
|
<listitem><para>What do I have to do to integrate the kernel layer?</para></listitem>
|
|||
|
|
<listitem><para>What do I use to integrate the kernel layer?
|
|||
|
|
HOB?
|
|||
|
|
Do I just Bitbake it?</para></listitem>
|
|||
|
|
<listitem><para>Using the System Image Creator.]</para></listitem>
|
|||
|
|
</itemizedlist>
|
|||
|
|
</para>
|
|||
|
|
</section>
|
|||
|
|
</section>
|
|||
|
|
</section>
|
|||
|
|
|
|||
|
|
<section id='user-application-development'>
|
|||
|
|
<title>User Application Development</title>
|
|||
|
|
|
|||
|
|
<para>
|
|||
|
|
[WRITER'S NOTE: This section is the second major development case - developing an application.
|
|||
|
|
Here are points to consider:
|
|||
|
|
<itemizedlist>
|
|||
|
|
<listitem><para>User-space Application Development scenario overview.</para></listitem>
|
|||
|
|
<listitem><para>Using the Yocto Eclipse Plug-in.</para></listitem>
|
|||
|
|
<listitem><para>Back-door support.</para></listitem>
|
|||
|
|
<listitem><para>I feel there is more to this area than we have captured during our two
|
|||
|
|
review meetings.]</para></listitem>
|
|||
|
|
</itemizedlist>
|
|||
|
|
</para>
|
|||
|
|
</section>
|
|||
|
|
</chapter>
|
|||
|
|
-->
|
|||
|
|
|
|||
|
|
<!--
|
|||
|
|
vim: expandtab tw=80 ts=4
|
|||
|
|
-->
|