path: root/documentation/dev-manual/dev-manual-bsp-appendix.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>BSP Development Example</title>

<para>
    This appendix provides a complete BSP 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 from.</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.  
        See the bulleted item
        <link linkend='local-yp-release'>Yocto Project Release</link> in
        <xref linkend='getting-setup'>Getting Setup</xref> earlier in this manual
        for information on how to get these files.
    </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 is code
        named "edison". 
        These commands create a local branch named <filename>edison</filename>
        that tracks the remote branch of the same name.
        <literallayout class='monospaced'>
     $ cd poky
     $ git checkout -b edison origin/edison
     Switched to a new branch 'edison'
        </literallayout>
    </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>.
    </para>

    <para>
        For information on how to choose a base BSP, see
        <xref linkend='developing-a-board-support-package-bsp'>Developing a Board Support Package (BSP)</xref>
        earlier in this manual.
    </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 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.
        See <xref linkend='getting-setup'>Getting Setup</xref> earlier in this manual
        for information on how to get the BSP files.
    </para>
        
    <para>
        This example assumes the local <filename>meta-intel</filename> Git repository is
        inside the local <filename>poky</filename> Git repository.
        The <filename>meta-intel</filename> Git repository contains all the metadata 
        that supports BSP creation.
    </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>edison</filename> branch. 
        <literallayout class='monospaced'>
     $ cd meta-intel
     $ git checkout -b edison origin/edison
     Switched to a new branch 'edison'
        </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 must follow the BSP layer naming convention, which is 
        <filename>meta-&lt;name&gt;</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.
        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>
            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 3.0 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  
            <ulink url='http://www.yoctoproject.org/docs/1.1/bsp-guide/bsp-guide.html'>The Board 
            Support Packages (BSP) Development Guide</ulink>
            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.  
            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 <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-graphics/xorg-xserver/*emgd*
     $ 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 <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-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>
        </section>

        <section id='changing-recipes-core'>
            <title>Changing <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 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>
        </section>

        <section id='changing-recipes-kernel'>
            <title>Changing <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.
            </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 
                is appended 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 ?= \
        "67a46a608f47c19f16995be7de7b272025864b1b"

     SRCREV_machine_pn-linux-yocto_crownbay-noemgd ?= \
        "2247da9131ea7e46ed4766a69bb1353dba22f873"
     SRCREV_meta_pn-linux-yocto_crownbay-noemgd ?= \
        "67a46a608f47c19f16995be7de7b272025864b1b"
                </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.
                Here are the final <filename>SRCREV</filename> statements:
                <literallayout class='monospaced'>
     SRCREV_machine_pn-linux-yocto_mymachine ?= \ 
        "06c798f25a19281d7fa944b14366dd75820ba009"
     SRCREV_meta_pn-linux-yocto_mymachine ?= \ 
        "67a46a608f47c19f16995be7de7b272025864b1b"
                </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-3.0</filename> kernel at
                <ulink url='http://git.yoctoproject.org/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>.
                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/mymachine"
     KERNEL_FEATURES_append_mymachine += " cfg/smp.scc"

     SRCREV_machine_pn-linux-yocto_mymachine ?= \
        "06c798f25a19281d7fa944b14366dd75820ba009"
     SRCREV_meta_pn-linux-yocto_mymachine ?= \
        "67a46a608f47c19f16995be7de7b272025864b1b"
                </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-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>

<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>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>
        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>
</section>
</appendix>


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