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poky/documentation/dev-manual/dev-manual-cases.xml
Scott Rifenbark be0aaef24f documentation/dev-manual/dev-manual-cases.xml: Docbook formatting completed. 
Initial content in and the formatting complete.  Some bad links fixed
also.

(From yocto-docs rev: 2461522b77c8240476a14aef8f3e94336419af56)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
2011-07-21 10:59:23 +01:00

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<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<chapter id='dev-manual-cases'>
<title>Development Cases</title>
<para>
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 image 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'>
<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'>
<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>
<para>
Packages consist of recipes.
Recipes are sets of instructions for building a package.
The recipes describe where to get source code and what patches to apply.
Recipes also describe dependencies for libraries or for other recipes.
They also contain configuration and compilation options.
Recipes are logical units of execution.
</para>
<para>
Here are the basic steps involved in creating a BSP:
<orderedlist>
<listitem><para>Be sure you are set up to use Yocto Project (see
<xref linkend='dev-manual-start'>Getting Started with the Yocto Project</xref>).</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. (WRITER'S NOTE: Not sure on this step).</para></listitem>
<listitem><para>Identify the machine branch in the Git repository.</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'>
<title>Setting Up Yocto Project</title>
<para>
For general host development system preparation such as package requirements and
operating system requirements, see
<xref linkend='dev-manual-start'>Getting Started with the Yocto Project</xref>)Chapter 2 of
this manual or the
<ulink url='http://www.yoctoproject.org/docs/1.1/yocto-project-qs/yocto-project-qs.html'>
Yocto Project Quick Start</ulink>.
</para>
<para>
You need to have the Yocto Project source tree available on your host system.
You can get that through tarball extraction or by initializing and checking out the
Yocto Project Git repository.
Typically, checking out 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 the source you can download the Yocto Project Release
tarball from the
<ulink url='http://yoctoproject.org/download'>download page</ulink>.
If you download the tarball you can extract it into any directory you want using the
tar command.
For example, the following commands extract the 1.0.1 release tarball into
<filename>/usr/local/yocto</filename> with the Yocto Project source directory as
<filename>poky.bernard.5.0.1.tar.bz2</filename>:
<literallayout class='monospaced'>
/usr/local/yocto$ tar xfj poky.bernard.5.0.1.tar.bz2
</literallayout>
</para>
<para>
The following transcript shows how to initialize a Git repository and checkout the
Yocto Project source tree:
<literallayout class='monospaced'>
/usr/local/yocto$ git init
Initialized empty Git repository in /usr/local/yocto/.git
/usr/local/yocto$ git remote add poky git://git.yoctoproject.org/poky.git
/usr/local/yocto$ git remote update
Fetching poky
remote: Counting objects: 106111, done.
remote: Compressing objects: 100% (36106/36106), done.
remote: Total 106111 (delta 72275), reused 99193 (delta 66808)
Receiving objects: 100% (106111/106111), 69.51 MiB | 518 KiB/s, done.
Resolving deltas: 100% (72275/72275), done.
From git://git.yoctoproject.org/poky
* [new branch] 1.1_M1 -> poky/1.1_M1
* [new branch] 1.1_M2 -> poky/1.1_M2
* [new branch] bernard -> poky/bernard
* [new branch] blinky -> poky/blinky
* [new branch] clyde -> poky/clyde
* [new branch] elroy -> poky/elroy
* [new branch] green -> poky/green
* [new branch] laverne -> poky/laverne
* [new branch] master -> poky/master
* [new branch] pinky -> poky/pinky
* [new branch] purple -> poky/purple
* [new tag] 1.1_M1.final -> 1.1_M1.final
* [new tag] 1.1_M2.rc1 -> 1.1_M2.rc1
* [new tag] bernard-5.0.1 -> bernard-5.0.1
* [new tag] pinky-3.1.2 -> pinky-3.1.2
From git://git.yoctoproject.org/poky
* [new tag] 1.1_M1.rc1 -> 1.1_M1.rc1
* [new tag] 1.1_M1.rc2 -> 1.1_M1.rc2
* [new tag] bernard-1.0rc1 -> bernard-1.0rc1
* [new tag] bernard-5.0 -> bernard-5.0
* [new tag] bernard-5.0-alpha -> bernard-5.0-alpha
* [new tag] bernard-5.0rc1 -> bernard-5.0rc1
* [new tag] bernard-5.0rc2 -> bernard-5.0rc2
* [new tag] laverne-4.0 -> laverne-4.0
* [new tag] laverne-4.0.1 -> laverne-4.0.1
* [new tag] m4 -> m4
* [new tag] purple-3.2 -> purple-3.2
* [new tag] purple-3.2.1 -> purple-3.2.1
</literallayout>
</para>
<para>
Once you have the repository set up, you have many development branches from which
you can work.
For this example we are going to use the Yocto Project 1.0.1 Release,
which maps to the <filename>Bernard 5.0.1</filename> tag in Git.
<literallayout class='monospaced'>
/usr/local/yocto$ git checkout -b Bernard-5.0.1 bernard-5.0.1
Switched to a new branch 'bernard-5.0.1'
</literallayout>
</para>
</section>
<section id='choosing-a-base-bsp'>
<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 most closely matches it.
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 with no Intel® Embedded Media
Graphics Driver (EMGD) support.
That is the BSP that this example is going to use.
</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'>
<title>Getting Your Base BSP</title>
<para>
You need to have the base BSP layer on your development system.
Like the Yocto Project source tree you can get the BSP layer one of two ways:
download the tarball and extract it, or initialize a Git repository and check out the BSP.
You should use the same method that you used for the Yocto Project source tree.
</para>
<para>
If you are using tarball extraction then 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-&lt;BSP_name&gt;</filename>.
The following command extracts the Crown Bay BSP into a directory named
<filename>meta-crownbay</filename>:
<literallayout class='monospaced'>
/usr/local$ tar xjf crownbay-noemgd-bernard-5.0.1.tar.bz2
</literallayout>
</para>
<para>
If you initialized a Yocto Project Git repository then you need to do the same for the
BSP, which is located in the meta-intel Git repository.
The meta-intel repository contains all the metadata that supports BSP creation.
</para>
<para>
The following transcript shows the steps to create and set up the meta-intel Git
repository inside the Yocto Project Git repository:
<literallayout class='monospaced'>
/usr/local/yocto$ mkdir meta-intel
/usr/local/yocto$ cd meta-intel
/usr/local/yocto/meta-intel$ git init
Initialized empty Git repository in /usr/local/yocto/meta-intel/.git/
/usr/local/yocto/meta-intel$ git remote add meta-intel \ git://git.yoctoproject.org/meta-intel.git
/usr/local/yocto/meta-intel$ git remote update
Fetching meta-intel
remote: Counting objects: 1240, done.
remote: Compressing objects: 100% (1008/1008), done.
remote: Total 1240 (delta 513), reused 85 (delta 27)
Receiving objects: 100% (1240/1240), 1.55 MiB | 510 KiB/s, done.
Resolving deltas: 100% (513/513), done.
From git://git.yoctoproject.org/meta-intel
* [new branch] 1.1_M1 -> meta-intel/1.1_M1
* [new branch] 1.1_M2 -> meta-intel/1.1_M2
* [new branch] bernard -> meta-intel/bernard
* [new branch] dvhart/n450 -> meta-intel/dvhart/n450
* [new branch] laverne -> meta-intel/laverne
* [new branch] master -> meta-intel/master
</literallayout>
</para>
<para>
Once you have the repository set up, you have many development branches from
which you can work.
For this example we are going to use Bernard 5.0.
<literallayout class='monospaced'>
/usr/local/yocto/meta-intel$ git checkout -b Bernard-5.0.1 meta-intel/bernard
Branch Bernard-5.0.1 set up to track remote branch bernard from meta-intel.
Switched to a new branch 'bernard-5.0.1'
</literallayout>
</para>
</section>
<section id='making-a-copy-of-the-base bsp-to-create-your-new-bsp-layer'>
<title>Making a Copy of the Base BSP to Create Your New BSP Layer</title>
<para>
Now that you have the Yocto Project and base BSP source 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 <filename>meta</filename>, which can be found in the Yocto Project source directory.
Consequently, they are not totally isolated in the spirit of layers unless you think
of <filename>meta</filename> as a layer itself.
On the other hand, the Yocto Project has isolated BSP layers within
<filename>meta-intel</filename> for the Crown Bay, Emenlow, Jasper Forest, N450, and
Sugar Bay.
[WRITER'S NOTE: <filename>meta-yocto</filename>, <filename>meta</filename>, and
<filename>meta-intel</filename> need some explanation.
Not sure about the relationship of meta-yocto as compared to meta-intel.]
</note>
<para>
When you set up a layer for a new BSP you should follow a standard layout.
This layout is described in
<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 hierarchy for BSP kernel recipes,
graphics recipes, and configuration information.
You can see the standard layout for the Crown Bay BSP in this example by examining the
directory structure of <filename>meta-crownbay</filename>.
</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 is named <filename>meta-mymachine</filename>.
The name must follow the BSP layer naming convention, which is
<filename>meta-&lt;name&gt;</filename>.
The following example assumes a meta-intel Git repository.
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:
<literallayout class='monospaced'>
/usr/local/yocto/meta-intel$ cp -a meta-crownbay/ meta-mymachine
</literallayout>
</para>
</section>
<section id='making-changes-to-your-bsp'>
<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'>
/usr/local/yocto/meta-intel$ rm meta-mymachine/conf/machine/crownbay.conf
/usr/local/yocto/meta-intel$ 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 and to the
Source Revision (<filename>SRCREV</filename>) lines at the bottom of the file.
</para>
<para>
For the comments the string <filename>crownbay-noemgd</filename> needs to be changed to
<filename>mymachine</filename>.
</para>
<para>
To understand how to complete the changes to the <filename>SRCREV</filename>
statements we need to know which kernel we are using.
The <filename>PREFERRED_PROVIDER_virtual/kernel</filename> statement in the file specifies
the kernel we are going to use.
We are going to use <filename>linux-yocto-stable</filename>.
The <filename>SRCREV</filename> statement pairs point to the exact machine branch
(commit) and <filename>meta</filename> branch in the Git repository.
Right now the <filename>SRCREV</filename> variables are as follows in
<filename>mymachine.conf</filename>:
<literallayout class='monospaced'>
SRCREV_machine_pn-linux-yocto_crownbay-noemgd ?= \ "56fe215d3f1a2cc3a5a26482ac9809ba44495695"
SRCREV_meta_pn-linux-yocto_crownbay-noemgd ?= \ "e1f85a470934a0cf6abde5d95533e74501822c6b"
SRCREV_machine_pn-linux-yocto-stable_crownbay-noemgd ?= \ "56fe215d3f1a2cc3a5a26482ac9809ba44495695"
SRCREV_meta_pn-linux-yocto-stable_crownbay-noemgd ?= \ "e1f85a470934a0cf6abde5d95533e74501822c6b"
</literallayout>
</para>
<para>
You will notice that there are two pairs of <filename>SRCREV</filename> statements.
The first pair points to a current development kernel, which we don’t care about
in this example.
The bottom pair points to the stable kernel that we will use:
<filename>linux-yocto-stable</filename>.
At this point though, the unique commit strings all are still associated with
Crown Bay.
So the next changes we make to the configuration file gets rid of the pair that points
to the development kernel and provides new commit strings that points to the
<filename>atom-pc-standard</filename>, which we are choosing for the initial build of this BSP.
Here are the final <filename>SRCREV</filename> statements:
<literallayout class='monospaced'>
SRCREV_machine_pn-linux-yocto-stable_mymachine ?= \ "72ca49ab08b8eb475cec82a10049503602325791"
SRCREV_meta_pn-linux-yocto-stable_mymachine ?= \ "ec26387cb168e9e0976999b528b5a9dd62e3157a"
</literallayout>
</para>
<para>
If you are familiar with Git repositories you probably won’t have trouble locating the
exact commit strings 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-2.6.34</filename> kernel
<ulink url='http://git.yoctoproject.org/cgit/cgit.cgi/linux-yocto-2.6.34'>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>atom-pc-standard</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>mymachine.conf</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>wrs_meta</filename>
branch in step 2 above.
</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 removing statements that support EMGD and changing the ones that support no EMGD.
</para>
<para>
First, remove these statements from the file:
<literallayout class='monospaced'>
BBFILE_COLLECTIONS_crownbayd += "crownbay"
BBFILE_PATTERN_crownbay := "^${LAYERDIR}/"
BBFILE_PRIORITY_crownbay = "6"
</literallayout>
</para>
<para>
This leaves three similar statements that we care about:
<literallayout class='monospaced'>
BBFILE_COLLECTIONS_crownbay-noemgd += "crownbay-noemgd"
BBFILE_PATTERN_crownbay-noemgd := "^${LAYERDIR}/"
BBFILE_PRIORITY_crownbay-noemgd = "6"
</literallayout>
</para>
<para>
Simply substitute the machine string name <filename>crownbay-noemgd</filename>
with the new machine name <filename>mymachine</filename> to get the following:
<literallayout class='monospaced'>
BBFILE_COLLECTIONS_mymachine += "mymachine"
BBFILE_PATTERN_mymachine := "^${LAYERDIR}/"
BBFILE_PRIORITY_mymachine = "6"
</literallayout>
</para>
<para>
Now we will take a look at the recipes in your new layer.
The standard BSP structure has areas for BSP, graphics, and kernel recipes.
When you create a BSP you use these areas for appropriate recipes and append files.
Recipes take the form of <filename>.bb</filename> files.
If you want to leverage off of existing recipes elsewhere in the Yocto Project
source tree but change them you can use <filename>.bbappend</filename> files.
All new recipes and append files for your layer go in the layer’s
<filename>recipes-bsp</filename>, <filename>recipes-kernel</filename>, and
<filename>recipes-graphics</filename> directories.
</para>
<para>
For this example we are not adding any new BSP recipes.
And, we only need to remove the formfactor we do not want and change the name of
the remaining one that supports no EMGD.
These commands take care of the new layer’s BSP recipes:
<literallayout class='monospaced'>
/usr/local/yocto/meta-intel$ rm -rf \
meta-mymachine/recipes-bsp/formfactor/formfactor/crownbay
/usr/local/yocto/meta-intel$ mv \
meta-mymachine/recipes-bsp/formfactor/formfactor/crownbay-noemgd/ \
meta-mymachine/recipes-bsp/formfactor/formfactor/mymachine
</literallayout>
</para>
<para>
For this example we want to remove anything that supports EMGD.
The following command cleans up the <filename>recipes-graphics</filename> directory:
<literallayout class='monospaced'>
/usr/local/yocto/meta-intel$ rm –rf \
meta-mymachine/recipes-graphics/xorg-xserver/xserver-xf86-emgd*
</literallayout>
</para>
<para>
At this point the <filename>recipes-graphics</filename> directory just has files that
support Video Electronics Standards Association (VESA) graphics modes.
However, we still need to rename a directory in the layer.
This command applies the final change to the <filename>recipes-graphics</filename> directory:
<literallayout class='monospaced'>
/usr/local/yocto/meta-intel$ 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>
Finally, let us look at the <filename>recipes-kernel</filename> directory in the example.
The only file we are concerned with for the example is
<filename>linux-yocto-stable_git.bbappend</filename>.
The other files all support the EMGD feature of Crown Bay.
These commands clean up the directory:
<literallayout class='monospaced'>
/usr/local/yocto/meta-intel$ rm –rf meta-mymachine/recipes-kernel/linux/linux-yocto
/usr/local/yocto/meta-intel$ rm –rf \
meta-mymachine/recipes-kernel/linux/linux-yocto-stable
/usr/local/yocto/meta-intel$ rm \
meta-mymachine/recipes-kernel/linux/linux-yocto_git.bbappend
</literallayout>
</para>
<para>
The <filename>linux-yocto-stable_git.bbappend</filename> file appends a Yocto Project
recipe having the same name.
The changes we need to make are to remove the statements that support EMGD
and change the remaining Crown Bay strings to be <filename>mymachine</filename>.
We also do not need to include the pointer to the EMGD licenses patch at the end of
the file.
Here is the original file:
<literallayout class='monospaced'>
FILESEXTRAPATHS := “${THISDIR}/${PN}”
COMPATIBLE_MACHINE_crownbay = “crownbay”
KMACHINE_CROWNBAY = “CROWNBAY”
COMPATIBLE_MACHINE_crownbay-noemgd = “crownbay-noemgd”
KMACHINE_crownbay-noemgd = “crownbay”
SRC_URI += file://0001-crownbay-update-a-handful-of-EMGD-licenses.patch
</literallayout>
</para>
<para>
After editing the file it looks like this:
<literallayout class='monospaced'>
FILESEXTRAPATHS := “${THISDIR}/${PN}”
COMPATIBLE_MACHINE_mymachine = “mymachine”
KMACHINE_mymachine = “mymachine
</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.
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'>
<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 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 Yocto Project source directory and 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'>
/usr/local/yocto$ 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 Yocto Project source 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 build.
The build directory contains a <filename>conf</filename> directory that contains
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 example, if you created a Yocto Project Git repository named
<filename>yocto</filename> in <filename>/usr/local</filename> then the
<filename>BBLAYERS</filename> variable in the file would need to include the following path:
<literallayout class='monospaced'>
/usr/local/yocto/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'>
<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>
You can find these recipes in the <filename>meta/recipes-core/images</filename> and
<filename>meta/recipes-sato/images</filename> directories of the Yocto Project source
tree or Git repository.
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'>
/usr/local/yocto/yocto-build$ bitbake –k poky-image-sato-live
</literallayout>
</para>
<para>
This command requests an image that has Sato support and 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'>
<title>Modifying a Kernel</title>
<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 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>
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