path: root/documentation/dev-manual/dev-manual-bsp-appendix.xml

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[<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] >

<appendix id='dev-manual-bsp-appendix'>

<title>BSP Development Example</title>

<para>
    This appendix provides a complete BSP development example.
    The example assumes the following:
    <itemizedlist>
        <listitem><para>No previous preparation or use of the Yocto Project.</para></listitem>
        <listitem><para>Use of the Crown Bay Board Support Package (BSP) as a "base" BSP from 
            which to work.  
            The example begins with the Crown Bay BSP as the starting point
            but ends by building a new 'atom-pc' BSP, which was based on the Crown Bay BSP.
            </para></listitem>  
        <listitem><para>Shell commands assume <filename>bash</filename></para></listitem>
        <listitem><para>Example was developed on an Intel-based Core i7 platform running 
            Ubuntu 10.04 LTS released in April of 2010.</para></listitem>        
    </itemizedlist>             
</para>

<section id='getting-local-yocto-project-files-and-bsp-files'>
    <title>Getting Local Yocto Project Files and BSP Files</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.
        The following paragraphs describe both methods.
        For additional information, see the bulleted item
        "<link linkend='local-yp-release'>Yocto Project Release</link>".
    </para> 

    <para>
        As mentioned, one way to get the Yocto Project files is to use Git to clone the 
        <filename>poky</filename> repository. 
        These commands create a local copy of the Git repository.
        By default, the top-level directory of the repository is named <filename>poky</filename>:
        <literallayout class='monospaced'>
     $ git clone git://git.yoctoproject.org/poky
     $ cd poky
        </literallayout> 
        Alternatively, you can start with the downloaded Poky "edison" tarball.
        These commands unpack the tarball into a Yocto Project File directory structure.
        By default, the top-level directory of the file structure is named
        <filename>poky-&YOCTO_POKY;</filename>:
        <literallayout class='monospaced'>
     $ tar xfj &YOCTO_POKY_TARBALL;
     $ cd &YOCTO_POKY;
        </literallayout> 
        <note><para>If you're using the tarball method, you can ignore all the following steps that
        ask you to carry out Git operations.  
        You already have the results of those operations
        in the form of the edison release tarballs.
        Consequently, there is nothing left to do other than extract those tarballs into the 
        proper locations.</para>

        <para>Once you expand the released tarball, you have a snapshot of the Git repository
        that represents a specific release.
        Fundamentally, this is different than having a local copy of the Yocto Project 
        Git repository.  
        Given the tarball method, changes you make are building on top of a release.
        With the Git repository method you have the ability to track development
        and keep changes in revision control.
        See the 
        "<link linkend='repositories-tags-and-branches'>Repositories, Tags, and Branches</link>" section
        for more discussion around these differneces.</para></note>
    </para>

    <para>
        With the local <filename>poky</filename> Git repository set up, 
        you have all the development branches available to you from which you can work. 
        Next, you need to be sure that your local repository reflects the exact
        release in which you are interested.
        From inside the repository you can see the development branches that represent
        areas of development that have diverged from the main (master) branch
        at some point, such as a branch to track a maintenance release's development.  
        You can also see the tag names used to mark snapshots of stable releases or 
        points in the repository.
        Use the following commands to list out the branches and the tags in the repository, 
        respectively.
        <literallayout class='monospaced'>
     $ git branch -a
     $ git tag -l
        </literallayout> 
        For this example, we are going to use the Yocto Project &DISTRO; Release, which is code
        named "&DISTRO_NAME;". 
        To make sure we have a local area (branch in Git terms) on our machine that 
        reflects the &DISTRO; release, we can use the following commands:
        <literallayout class='monospaced'>
     $ cd ~/poky
     $ git fetch --tags
     $ git checkout &DISTRO_NAME;-&POKYVERSION; -b &DISTRO_NAME;
     Switched to a new branch '&DISTRO_NAME;'
        </literallayout>
        The <filename>git fetch --tags</filename> is somewhat redundant since you just set 
        up the repository and should have all the tags.
        The <filename>fetch</filename> command makes sure all the tags are available in your
        local repository.
        The Git <filename>checkout</filename> command with the <filename>-b</filename> option
        creates a local branch for you named <filename>&DISTRO_NAME;</filename>.
        Your local branch begins in the same state as the Yocto Project &DISTRO; released tarball 
        marked with the <filename>&DISTRO_NAME;-&POKYVERSION;</filename> tag in the source repositories.
    </para>
</section> 

<section id='choosing-a-base-bsp-app'>
    <title>Choosing a Base BSP</title>

    <para>
        For this example, the base BSP is the <trademark class='registered'>Intel</trademark>
        <trademark class='trade'>Atom</trademark> Processor E660 with Intel Platform 
        Controller Hub EG20T Development Kit, which is otherwise referred to as "Crown Bay."
        The BSP layer is <filename>meta-crownbay</filename>.  
        The base BSP is simply the BSP
        we will be using as a starting point, so don't worry if you don't actually have Crown Bay
        hardware.
        The remainder of the example transforms the base BSP into a BSP that should be
        able to boot on generic atom-pc (netbook) hardware.
    </para>

    <para>
        For information on how to choose a base BSP, see
        "<link linkend='developing-a-board-support-package-bsp'>Developing a Board Support Package (BSP)</link>".
    </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.  
        Similar to the local Yocto Project files, you can get the BSP 
        layer in a couple of different 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.
        See "<link linkend='getting-setup'>Getting Setup</link>" for information on how to get 
        the BSP files.
    </para>

    <para>
        This example assumes the BSP layer will be located within a directory named
        <filename>meta-intel</filename> contained within the <filename>poky</filename>
        parent directory.  
        The following steps will automatically create the
        <filename>meta-intel</filename> directory and the contained 
        <filename>meta-crownbay</filename> starting point in both the Git and the tarball cases.
    </para>

    <para>
        If you're using the Git method, you could do the following to create
        the starting layout after you have made sure you are in the <filename>poky</filename>
        directory created in the previous steps:
        <literallayout class='monospaced'>
     $ git clone git://git.yoctoproject.org/meta-intel.git
     $ cd meta-intel
        </literallayout> 
        Alternatively, you can start with the downloaded Crown Bay tarball.
        You can download the edison version of the BSP tarball from the
        <ulink url='&YOCTO_HOME_URL;/download'>Download</ulink> page of the 
        Yocto Project website. 
        Here is the specific link for the tarball needed for this example:
        <ulink url='&YOCTO_MACHINES_DL_URL;/crownbay-noemgd/crownbay-noemgd-&DISTRO_NAME;-6.0.0.tar.bz2'></ulink>.
        Again, be sure that you are already in the <filename>poky</filename> directory
        as described previously before installing the tarball:
        <literallayout class='monospaced'>
     $ tar xfj crownbay-noemgd-&DISTRO_NAME;-6.0.0.tar.bz2
     $ cd meta-intel
        </literallayout> 
    </para>
        
    <para>
        The <filename>meta-intel</filename> directory contains all the metadata 
        that supports BSP creation.  
        If you're using the Git method, the following
        step will switch to the edison metadata.
        If you're using the tarball method, you already have the correct metadata and can 
        skip to the next step.
        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>&DISTRO_NAME;</filename> branch. 
        <literallayout class='monospaced'>
     $ git checkout -b &DISTRO_NAME; origin/&DISTRO_NAME;
     Switched to a new branch '&DISTRO_NAME;'
        </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.
        To create your BSP layer, you simply copy the <filename>meta-crownbay</filename>
        layer to a new layer.
    </para>

    <para>  
        For this example, the new layer will be named <filename>meta-mymachine</filename>.  
        The name should follow the BSP layer naming convention, which is 
        <filename>meta-&lt;name&gt;</filename>.  
        The following assumes your working directory is <filename>meta-intel</filename> 
        inside the local Yocto Project files.  
        To start your new layer, just copy the new layer alongside the existing
        BSP layers in the <filename>meta-intel</filename> directory:
        <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.
        The following sections look at each of these areas of the BSP.
    </para>

    <section id='changing-the-bsp-configuration'>
        <title>Changing the BSP Configuration</title>
   
        <para>  
            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>
            Next, we need to make changes to the <filename>mymachine.conf</filename> itself.
            The only changes we want to make for this example are to the comment lines.  
            Changing comments, of course, is never strictly necessary, but it's alway good form to make
            them reflect reality as much as possible.

            Here, simply substitute the Crown Bay name with an appropriate name for the BSP 
            (<filename>mymachine</filename> in this case) and change the description to 
            something that describes your hardware.
        </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 3.0 release. 
        </para>

        <para>
            The next configuration file in the new BSP layer we need to edit is
            <filename>meta-mymachine/conf/layer.conf</filename>.
            This file identifies build information needed for the new layer.  
            You can see the 
            "<ulink url='&YOCTO_DOCS_BSP_URL;#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"
     BBFILE_PATTERN_mymachine := "^${LAYERDIR}/"
     BBFILE_PRIORITY_mymachine = "6"
            </literallayout>
        </para>
    </section>

    <section id='changing-the-recipes-in-your-bsp'>
        <title>Changing the Recipes in Your BSP</title>

        <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, while append files take
            the form of <filename>.bbappend</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>

        <section id='changing-recipes-bsp'>
            <title>Changing&nbsp;&nbsp;<filename>recipes-bsp</filename></title>

            <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-bsp/formfactor/formfactor/crownbay
     $ mv meta-mymachine/recipes-bsp/formfactor/formfactor/crownbay-noemgd/ \
     meta-mymachine/recipes-bsp/formfactor/formfactor/mymachine
                </literallayout>
            </para>
        </section>

        <section id='changing-recipes-graphics'>
            <title>Changing&nbsp;&nbsp;<filename>recipes-graphics</filename></title>

            <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-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>
        </section>

        <section id='changing-recipes-core'>
            <title>Changing&nbsp;&nbsp;<filename>recipes-core</filename></title>

            <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 <link linkend='yocto-project-files'>Yocto Project Files</link> 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>
        </section>

        <section id='changing-recipes-kernel'>
            <title>Changing&nbsp;&nbsp;<filename>recipes-kernel</filename></title>

            <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_3.0.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.
                In other words, the <filename>SRCREV</filename> values are simply Git commit 
                IDs that identify which commit on each
                of the kernel branches (machine and meta) will be checked out and used to build
                the kernel.
            </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_3.0.bbappend</filename> that 
                appends information to the recipe of the same name in <filename>meta/recipes-kernel/linux</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 ?= \
        "2247da9131ea7e46ed4766a69bb1353dba22f873"
     SRCREV_meta_pn-linux-yocto_crownbay ?= \
        "d05450e4aef02c1b7137398ab3a9f8f96da74f52"

     SRCREV_machine_pn-linux-yocto_crownbay-noemgd ?= \
        "2247da9131ea7e46ed4766a69bb1353dba22f873"
     SRCREV_meta_pn-linux-yocto_crownbay-noemgd ?= \
        "d05450e4aef02c1b7137398ab3a9f8f96da74f52"
                </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_3.0.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.
                In this case, because we're working with the edison branch of everything, we
                need to use the <filename>SRCREV</filename> values for the atom-pc branch
                that are associated with the edison release.  
                To find those values, we need to find the <filename>SRCREV</filename>
                values that edison uses for the atom-pc branch, which we find in the
                <filename>poky/meta-yocto/recipes-kernel/linux/linux-yocto_3.0.bbappend</filename>
                file.
            </para>

            <para>  
                The machine <filename>SRCREV</filename> we want is in the 
                <filename>SRCREV_machine_atom-pc</filename> variable.  
                The meta <filename>SRCREV</filename> isn't specified in this file, so it must be 
                specified in the base kernel recipe in the
                <filename>poky/meta/recipes-kernel/linux/linux-yocto_3.0.bb</filename>
                file, in the <filename>SRCREV_meta variable</filename> found there.  
                It happens to be the same as the value we already inherited from the 
                <filename>meta-crownbay</filename> BSP.
                Here are the final <filename>SRCREV</filename> statements:
                <literallayout class='monospaced'>
     SRCREV_machine_pn-linux-yocto_mymachine ?= \ 
        "1e18e44adbe79b846e382370eb29bc4b8cd5a1a0"
     SRCREV_meta_pn-linux-yocto_mymachine ?= \ 
        "d05450e4aef02c1b7137398ab3a9f8f96da74f52"
                </literallayout>
            </para>

            <para>
                In this example, we're using the <filename>SRCREV</filename> values we 
                found already captured in the edison release because we're creating a BSP based on 
                edison.  
                If, instead, we had based our BSP on the master branches, we would want to use 
                the most recent <filename>SRCREV</filename> values taken directly from the kernel repo.
                We will not be doing that for this example.
                However, if you do base a future BSP on master and
                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-3.0</filename> kernel at
                <ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi/linux-yocto-3.0'></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_3.0.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_3.0.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>.
                Because we are using the atom-pc branch for this new BSP, we can also find
                the exact branch we need for the KMACHINE variable in our new BSP from the value
                we find in the
                <filename>poky/meta-yocto/recipes-kernel/linux/linux-yocto_3.0.bbappend</filename>
                file we looked at in a previous step.  
                In this case, the value we want is in the KMACHINE_atom-pc variable in that file.
                Here is the final <filename>linux-yocto_3.0.bbappend</filename> file after all 
                the edits:
                <literallayout class='monospaced'>
     FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"

     COMPATIBLE_MACHINE_mymachine = "mymachine"
     KMACHINE_mymachine  = "yocto/standard/common-pc/atom-pc"
     KERNEL_FEATURES_append_mymachine += " cfg/smp.scc"

     SRCREV_machine_pn-linux-yocto_mymachine ?= \
        "1e18e44adbe79b846e382370eb29bc4b8cd5a1a0"
     SRCREV_meta_pn-linux-yocto_mymachine ?= \
        "d05450e4aef02c1b7137398ab3a9f8f96da74f52"
                </literallayout>
            </para>
        </section>
    </section>

    <section id='bsp-recipe-change-summary'>
        <title>BSP Recipe Change Summary</title>

        <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-mymachine</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>

<section id='preparing-for-the-build-app'>
    <title>Preparing for the Build</title>

    <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>yocto-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 your development system supports multiple cores.
                For development systems that support multiple cores, a good rule of thumb is to set 
                both the <filename>BB_NUMBER_THREADS</filename> and <filename>PARALLEL_MAKE</filename> 
                variables to twice the number of cores your system supports.</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='&YOCTO_DOCS_REF_URL;#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 and Booting the Image</title>

    <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
        </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>

    <para>
        Finally, once you have an image, you can try booting it from a device
        (e.g. a USB device).
        To prepare a bootable USB device, insert a USB flash drive into your build system and
        copy the <filename>.hddimg</filename> file, located in the 
        <filename>poky/build/tmp/deploy/images</filename>
        directory after a successful build to the flash drive.  
        Assuming the USB flash drive takes device <filename>/dev/sdf</filename>, 
        use <filename>dd</filename> to copy the live image to it.  
        For example:
        <literallayout class='monospaced'>
     # dd if=core-image-sato-mymachine-20111101223904.hddimg of=/dev/sdf
     # sync
     # eject /dev/sdf
        </literallayout>
        You should now have a bootable USB flash device.  
    </para>

    <para>
        Insert the device
        into a bootable USB socket on the target, and power it on.  
        The system should boot to the Sato graphical desktop.
        <footnote><para>Because 
            this new image is not in any way tailored to the system you're
            booting it on, which is assumed to be some sort of atom-pc (netbook) system for this
            example, it might not be completely functional though it should at least boot to a text
            prompt.  
            Specifically, it might fail to boot into graphics without some tweaking.  
            If this ends up being the case, a possible next step would be to replace the 
            <filename>mymachine.conf</filename>
            contents with the contents of <filename>atom-pc.conf</filename> and replace 
            <filename>xorg.conf</filename> with <filename>atom-pc xorg.conf</filename>
            in <filename>meta-yocto</filename> and see if it fares any better.  
            In any case, following the previous steps will give you a buildable image that 
            will probably boot on most systems.
            Getting things working like you want
            them to for your hardware will normally require some amount of experimentation with
            configuration settings.</para></footnote> 
    </para>

    <para>
        For reference, the sato image produced by the previous steps for edison 
        should look like the following in terms of size.
        If your sato image is much different from this,
        you probably made a mistake in one of the above steps:
        <literallayout class='monospaced'>
     358715392 2011-11-01 19:11 core-image-sato-mymachine-20111101223904.hddimg
        </literallayout>
        <note>The previous instructions are also present in the README that was copied
        from meta-crownbay, which should also be updated to reflect the specifics of your
        new BSP.  
        That file and the <filename>README.hardware</filename> file in the top-level 
        <filename>poky</filename> directory
        also provides some suggestions for things to try if booting fails and produces
        strange error messages.</note>
    </para>
</section>
</appendix>


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