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<chapter id='dev-manual-model'>

<title>Common Development Models</title>

<para>
    Many development models exist for which you can use the Yocto Project. 
    This chapter overviews the following methods:
    <itemizedlist>
        <listitem><para><emphasis>System Development:</emphasis>
             System Development covers Board Support Package (BSP) development and kernel 
             modification or configuration.
             If you want to examine specific examples of the system development models, 
             see the "<link linkend='dev-manual-bsp-appendix'>BSP Development Example</link>" 
             appendix and the 
             "<link linkend='dev-manual-kernel-appendix'>Kernel Modification Example</link>" appendix.
             </para></listitem>
         <listitem><para><emphasis>User Application Development:</emphasis>
             User Application Development covers development of applications that you intend 
             to run on some target hardware.
             For information on how to set up your host development system for user-space
             application development, see the 
             <ulink url='&YOCTO_DOCS_ADT_URL;'>Yocto Project Application Developer's Guide</ulink>.
             For a simple example of user-space application development using the 
             <trademark class='trade'>Eclipse</trademark> IDE, see the 
             "<link linkend='application-development-workflow'>Application 
             Development Workflow</link>" section.
             </para></listitem>
         <listitem><para><emphasis>Temporary Source Code Modification:</emphasis>
             Direct modification of temporary source code is a convenient development model
             to quickly iterate and develop towards a solution.
             Once the solution has been implemented, you should of course take steps to 
             get the changes upstream and applied in the affected recipes.</para></listitem>
         <listitem><para><emphasis>Image Development using Hob:</emphasis>
             You can use the <ulink url='&YOCTO_HOME_URL;/projects/hob'>Hob</ulink> to build 
             custom operating system images within the build environment.
             Hob provides an efficient interface to the OpenEmbedded build system.</para></listitem>
         <listitem><para><emphasis>Using a Development Shell:</emphasis>
             You can use a <filename>devshell</filename> to efficiently debug commands or simply 
             edit packages.
             Working inside a development shell is a quick way to set up the OpenEmbedded build 
             environment to work on parts of a project.</para></listitem>
     </itemizedlist>
</para>

<section id='system-development-model'>
    <title>System Development Workflow</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 number of features that a full-fledged Linux distribution provides.
        Thus, you can create a much smaller image that is designed to use only the 
        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 or 
        configuration.
    </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 during a build, results in 
            an image that you can run on a particular board.  
            Thus, the package when compiled into the new image, supports the operation of the board.  
        </para>

        <note>
            For a brief list of terms used when describing the development process in the Yocto Project, 
            see the "<link linkend='yocto-project-terms'>Yocto Project Terms</link>" section.
        </note>

        <para>
            The remainder of this section presents the basic steps used to create a BSP 
            based on an existing BSP that ships with the Yocto Project.
            You can reference the "<link linkend='dev-manual-bsp-appendix'>BSP Development Example</link>"
            appendix for a detailed example that uses the Crown Bay BSP as a base BSP from which to start.
        </para>

        <para>
            The following illustration and list summarize the BSP creation general workflow.
        </para>

        <para>
            <imagedata fileref="figures/bsp-dev-flow.png" width="6in" depth="7in" align="center" scalefit="1" />
        </para>

        <para>
            <orderedlist>
                <listitem><para><emphasis>Set up your host development system to support 
                    development using the Yocto Project</emphasis>:  See the
                    "<ulink url='&YOCTO_DOCS_QS_URL;#the-linux-distro'>The Linux Distributions</ulink>" 
                    and the 
                    "<ulink url='&YOCTO_DOCS_QS_URL;#packages'>The Packages</ulink>" sections both
                    in the Yocto Project Quick Start for requirements.</para></listitem>
                <listitem><para><emphasis>Establish a local copy of the project files on your 
                    system</emphasis>:  You need this <link linkend='source-directory'>source 
                    directory</link> available on your host system. 
                    Having these files on your system gives you access to the build
                    process and to the tools you need.
                    For information on how to set up the source directory, see the
                    "<link linkend='getting-setup'>Getting Setup</link>" section.</para></listitem>
                <listitem><para><emphasis>Establish a local copy of the base BSP files</emphasis>:  Having    
                    the BSP files on your system gives you access to the build
                    process and to the tools you need for creating a BSP.
                    For information on how to get these files, see the
                    "<link linkend='getting-setup'>Getting Setup</link>" section.</para></listitem>    
                <listitem><para><emphasis>Choose a BSP that is supported by the Yocto Project 
                    as your base BSP</emphasis>:  
                    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, leveraging off an existing BSP
                    gives you some structure with which to start.</para>
                    <para>At this point you need to understand your target hardware well enough to determine which 
                    existing BSP it most closely matches.  
                    Things to consider are your hardware’s on-board features, such as CPU type and graphics support.  
                    You should look at the README files for supported BSPs to get an idea of which one 
                    you could use.  
                    A generic <trademark class='registered'>Intel</trademark> 
                    <trademark class='trade'>Atom</trademark>-based BSP to consider is the 
                    Crown Bay that does not support the <trademark class='registered'>Intel</trademark> 
                    Embedded Media Graphics Driver (EMGD).  
                    The remainder of this example uses that base BSP.</para>
                    <para>To see the supported BSPs, go to the 
                    <ulink url='&YOCTO_HOME_URL;/download'>Downloads</ulink> page on the Yocto Project
                    website and click on “BSP Downloads.”</para></listitem>
                <listitem><para><emphasis>Create your own BSP layer</emphasis>:  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.   
                    </para>
                    <para>
                    Another example that illustrates a layer is an application.  
                    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 OpenEmbedded build 
                    system knows about.
                    For more information on layers, see the 
                    "<link linkend='understanding-and-creating-layers'>Understanding and Creating Layers</link>"
                    section.
                    For more information on BSP layers, see the
                    "<ulink url='&YOCTO_DOCS_BSP_URL;#bsp-layers'>BSP Layers</ulink>" section in the 
                    Yocto Project Board Support Package (BSP) Developer's Guide.</para>
                    <note>Four BSPs exist 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 the <link linkend='source-directory'>source directory</link>.
                    On the other hand, BSP layers for Cedar Trail, Chief River, Crown Bay, 
                    Crystal Forest, Emenlow, Fish River, Fish River 2, Jasper Forest, N450, 
                    Romley, sys940x, Sugar Bay, and tlk exist in their own separate layers 
                    within the larger <filename>meta-intel</filename> layer.</note>
                    <para>When you set up a layer for a new BSP, you should follow a standard layout.  
                    This layout is described in the section
                    "<ulink url='&YOCTO_DOCS_BSP_URL;#bsp-filelayout'>Example Filesystem Layout</ulink>"
                    section of the Board Support Package (BSP) Development Guide.  
                    In the standard layout, you will notice a suggested structure for recipes and  
                    configuration information.  
                    You can see the standard layout for the Crown Bay BSP in this example by examining the 
                    directory structure of the <filename>meta-crownbay</filename> layer inside the 
                    source directory.</para></listitem>
                <listitem><para><emphasis>Make configuration changes to your new BSP 
                    layer</emphasis>:  The standard BSP layer structure organizes the files you need 
                    to edit in <filename>conf</filename> and several <filename>recipes-*</filename>
                    directories within the BSP layer.
                    Configuration changes identify where your new layer is on the local system
                    and identify which kernel you are going to use.
                    </para></listitem>
                <listitem><para><emphasis>Make recipe changes to your new BSP layer</emphasis>:  Recipe 
                    changes include altering recipes (<filename>.bb</filename> files), removing 
                    recipes you don't use, and adding new recipes that you need to support your hardware.
                    </para></listitem>
                <listitem><para><emphasis>Prepare for the build</emphasis>:  Once you have made all the 
                    changes to your BSP layer, there remains a few things 
                    you need to do for the OpenEmbedded 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 section
                    "<ulink url='&YOCTO_DOCS_QS_URL;#building-image'>Building an Image</ulink>" section 
                    of the Yocto Project Quick Start.    
                    You might want to reference this information.</para></listitem>
                <listitem><para><emphasis>Build the image</emphasis>:  The OpenEmbedded build system 
                    uses the BitBake tool to build images based on the type of image you want to create.  
                    You can find more information about BitBake in the user manual, which is found in the 
                    <filename>bitbake/doc/manual</filename> directory of the 
                    <link linkend='source-directory'>Source Directory</link>.</para>
                    <para>The build process supports several types of images to satisfy different needs.  
                    See the 
                    "<ulink url='&YOCTO_DOCS_REF_URL;#ref-images'>Images</ulink>" chapter 
                    in the Yocto Project Reference Manual for information on 
                    supported images.</para></listitem>
            </orderedlist>
        </para>

        <para>
            You can view a video presentation on "Building Custom Embedded Images with Yocto"
            at <ulink url='http://free-electrons.com/blog/elc-2011-videos'>Free Electrons</ulink>.  
            You can also find supplemental information in  
            <ulink url='&YOCTO_DOCS_BSP_URL;'>
            The Board Support Package (BSP) Development Guide</ulink>.
            Finally, there is wiki page write up of the example also located 
            <ulink url='&YOCTO_WIKI_URL;/wiki/Transcript:_creating_one_generic_Atom_BSP_from_another'>
            here</ulink> that you might find helpful.
       </para>
    </section>

    <section id='modifying-the-kernel'>
        <title><anchor id='kernel-spot' />Modifying the Kernel</title>

        <para>
            Kernel modification involves changing the Yocto Project kernel, which could involve changing
            configuration options as well as adding new kernel recipes.  
            Configuration changes can be added in the form of configuration fragments, while recipe
            modification comes through the kernel's <filename>recipes-kernel</filename> area
            in a kernel layer you create.
        </para>

        <para>
            The remainder of this section presents a high-level overview of the Yocto Project
            kernel architecture and the steps to modify the kernel.
            For a complete discussion of the kernel, see the
            <ulink url='&YOCTO_DOCS_KERNEL_URL;'>Yocto Project Kernel Architecture and Use Manual</ulink>.
            You can reference the appendix 
            "<link linkend='dev-manual-kernel-appendix'>Kernel Modification Example</link>"
            for a detailed example that changes the configuration of a kernel.
        </para>

        <section id='kernel-overview'>
            <title>Kernel Overview</title>

            <para>
                Traditionally, when one thinks of a patched kernel, they think of a base kernel
                source tree and a fixed structure that contains kernel patches.
                The Yocto Project, however, employs mechanisms, that in a sense, result in a kernel source
                generator.
                By the end of this section, this analogy will become clearer.
            </para>

            <para>
                You can find a web interface to the Yocto Project kernel source repositories at
                <ulink url='&YOCTO_GIT_URL;'></ulink>.
                If you look at the interface, you will see to the left a grouping of 
                Git repositories titled "Yocto Linux Kernel."  
                Within this group, you will find several kernels supported by 
                the Yocto Project:
                <itemizedlist>
                    <listitem><para><emphasis><filename>linux-yocto-2.6.34</filename></emphasis> - The 
                    stable Yocto Project kernel that is based on the Linux 2.6.34 released kernel.</para></listitem>
                    <listitem><para><emphasis><filename>linux-yocto-2.6.37</filename></emphasis> - The
                    stable Yocto Project kernel that is based on the Linux 2.6.37 released kernel.</para></listitem>
                    <listitem><para><emphasis><filename>linux-yocto-3.0</filename></emphasis> - The stable
                    Yocto Project kernel that is based on the Linux 3.0 released kernel.</para></listitem>
                    <listitem><para><emphasis><filename>linux-yocto-3.0-1.1.x</filename></emphasis> - The 
                    stable Yocto Project kernel to use with the Yocto Project Release 1.1.x. This kernel 
                    is based on the Linux 3.0 released kernel.</para></listitem>
                    <listitem><para><emphasis><filename>linux-yocto-3.2</filename></emphasis> - The 
                    stable Yocto Project kernel to use with the Yocto Project Release 1.2. This kernel 
                    is based on the Linux 3.2 released kernel.</para></listitem>
                    <listitem><para><emphasis><filename>linux-yocto-3.4</filename></emphasis> - The 
                    stable Yocto Project kernel to use with the Yocto Project Release 1.3. This kernel 
                    is based on the Linux 3.4 released kernel.</para></listitem>
                    <listitem><para><emphasis><filename>linux-yocto-dev</filename></emphasis> - A development
                    kernel based on the latest upstream release candidate available.</para></listitem>
                </itemizedlist>
            </para>

            <para>
                The kernels are maintained using the Git revision control system
                that structures them using the familiar "tree", "branch", and "leaf" scheme.
                Branches represent diversions from general code to more specific code, while leaves
                represent the end-points for a complete and unique kernel whose source files 
                when gathered from the root of the tree to the leaf accumulate to create the files
                necessary for a specific piece of hardware and its features.
                The following figure displays this concept:
            <para>
                <imagedata fileref="figures/kernel-overview-1.png" 
                    width="6in" depth="6in" align="center" scale="100" />
            </para> 

            <para>
                Within the figure, the "Kernel.org Branch Point" represents the point in the tree
                where a supported base kernel is modified from the Linux kernel.
                For example, this could be the branch point for the <filename>linux-yocto-3.0</filename>
                kernel.
                Thus, everything further to the right in the structure is based on the 
                <filename>linux-yocto-3.0</filename> kernel.
                Branch points to right in the figure represent where the 
                <filename>linux-yocto-3.0</filename> kernel is modified for specific hardware 
                or types of kernels, such as real-time kernels.
                Each leaf thus represents the end-point for a kernel designed to run on a specific
                targeted device.
            </para>

            <para>
                The overall result is a Git-maintained repository from which all the supported
                kernel types can be derived for all the supported devices.
                A big advantage to this scheme is the sharing of common features by keeping them in 
                "larger" branches within the tree.  
                This practice eliminates redundant storage of similar features shared among kernels.
            </para>

            <note>
                Keep in mind the figure does not take into account all the supported Yocto
                Project kernel types, but rather shows a single generic kernel just for conceptual purposes.
                Also keep in mind that this structure represents the Yocto Project source repositories 
                that are either pulled from during the build or established on the host development system
                prior to the build by either cloning a particular kernel's Git repository or by 
                downloading and unpacking a tarball.
            </note>

            <para>
                Storage of all the available kernel source code is one thing, while representing the 
                code on your host development system is another.  
                Conceptually, you can think of the kernel source repositories as all the 
                source files necessary for all the supported kernels. 
                As a developer, you are just interested in the source files for the kernel on 
                on which you are working.
                And, furthermore, you need them available on your host system.
            </para>

            <para>
                You make kernel source code available on your host development system by using 
                Git to create a bare clone of the Yocto Project kernel Git repository 
                in which you are interested.
                Then, you use Git again to clone a copy of that bare clone.  
                This copy represents the directory structure on your host system that is particular
                to the kernel you want.  
                These are the files you actually modify to change the kernel.
                See the <link linkend='local-kernel-files'>Yocto Project Kernel</link> item earlier
                in this manual for an example of how to set up the kernel source directory
                structure on your host system.
            </para>

            <para>
                This next figure illustrates how the kernel source files might be arranged on 
                your host system.
            </para>

            <para>
                <imagedata fileref="figures/kernel-overview-3-denzil.png" 
                    width="6in" depth="4in" align="center" scale="100" />
            </para> 

            <para>
                In the previous figure, the file structure on the left represents the bare clone 
                set up to track the Yocto Project kernel Git repository. 
                The structure on the right represents the copy of the bare clone. 
                When you make modifcations to the kernel source code, this is the area in which 
                you work.
                Once you make corrections, you must use Git to push the committed changes to the 
                bare clone.
                The example in <xref linkend='modifying-the-kernel-source-code'>
                Modifying the Kernel Source Code</xref> provides a detailed example.
            </para>

            <para>
                What happens during the build?  
                When you build the kernel on your development system all files needed for the build
                are taken from the source repositories pointed to by the 
                <filename>SRC_URI</filename> variable and gathered in a temporary work area
                where they are subsequently used to create the unique kernel.
                Thus, in a sense, the process constructs a local source tree specific to your 
                kernel to generate the new kernel image - a source generator if you will.
            </para>
                The following figure shows the temporary file structure
                created on your host system when the build occurs. 
                This build directory contains all the source files used during the build.
            </para>

            <para>
                <imagedata fileref="figures/kernel-overview-2.png" 
                    width="6in" depth="5in" align="center" scale="100" />
            </para> 

            <para>
                Again, for a complete discussion of the Yocto Project kernel's architecture and its 
                branching strategy, see the
                <ulink url='&YOCTO_DOCS_KERNEL_URL;'>Yocto Project Kernel Architecture and Use Manual</ulink>.
                You can also reference the
                "<link linkend='modifying-the-kernel-source-code'>Modifying the Kernel Source Code</link>"
                section for a detailed example that modifies the kernel.
            </para>
        </section> 

        <section id='kernel-modification-workflow'>
            <title>Kernel Modification Workflow</title>

            <para>
                This illustration and the following list summarizes the kernel modification general workflow.
            </para>

            <para>
                <imagedata fileref="figures/kernel-dev-flow.png" 
                    width="6in" depth="7.5in" align="center" scalefit="1" />
            </para> 

            <para>
                <orderedlist>
                    <listitem><para><emphasis>Set up your host development system to support 
                        development using the Yocto Project</emphasis>:  See  
                        "<ulink url='&YOCTO_DOCS_QS_URL;#the-linux-distro'>The Linux Distributions</ulink>" and  
                        "<ulink url='&YOCTO_DOCS_QS_URL;#packages'>The Packages</ulink>" sections both
                        in the Yocto Project Quick Start for requirements.</para></listitem>
                    <listitem><para><emphasis>Establish a local copy of project files on your 
                        system</emphasis>:  Having the <link linkend='source-directory'>source
                        directory</link> on your system gives you access to the build process and tools 
                        you need.
                        For information on how to get these files, see the bulleted item
                        "<link linkend='local-yp-release'>Yocto Project Release</link>" earlier in this manual.
                        </para></listitem>
                    <listitem><para><emphasis>Set up a local copy of the <filename>poky-extras</filename> Git 
                        repository</emphasis>:  This local repository is the area for your configuration 
                        fragments, new kernel recipes, and the kernel <filename>.bbappend</filename>
                        file used during the build. 
                        It is good practice to set this repository up inside your local 
                        source directory.
                        For information on how to get these files, see the bulleted item
                        "<link linkend='poky-extras-repo'>The <filename>poky-extras</filename> Git Repository</link>"
                        earlier in this manual.
                        <note>While it is certainly possible to modify the kernel without involving
                            a local Git repository, the suggested workflow for kernel modification
                            using the Yocto Project does use a Git repository.</note></para></listitem>
                    <listitem><para><emphasis>Establish a local copy of the Yocto Project kernel files on your 
                        system</emphasis>:  In order to make modifications to the kernel you need two things:
                        a bare clone of the Yocto Project kernel you are modifying and  
                        a copy of that bare clone. 
                        The bare clone is required by the build process and is the area to which you 
                        push your kernel source changes (pulling does not work with bare clones). 
                        The copy of the bare clone is a local Git repository that contains all the kernel's 
                        source files. 
                        You make your changes to the files in this copy of the bare clone.
                        For information on how to set these two items up, see the bulleted item
                        "<link linkend='local-kernel-files'>Yocto Project Kernel</link>" 
                        earlier in this manual.</para></listitem>
                    <listitem><para><emphasis>Make changes to the kernel source code if 
                        applicable</emphasis>:  Modifying the kernel does not always mean directly
                        changing source files. 
                        However, if you have to do this, you make the changes in the local 
                        Git repository you set up to hold the source files (i.e. the copy of the 
                        bare clone).
                        Once the changes are made, you need to use Git commands to commit the changes
                        and then push them to the bare clone.</para></listitem>                      
                    <listitem><para><emphasis>Make kernel configuration changes
                        if applicable</emphasis>:  
                        If your situation calls for changing the kernel's configuration, you can 
                        use <filename>menuconfig</filename>
                        to enable and disable kernel configurations.  
                        Using <filename>menuconfig</filename> allows you to interactively develop and test the 
                        configuration changes you are making to the kernel.
                        When saved, changes using <filename>menuconfig</filename> update the kernel's
                        <filename>.config</filename>.
                        Try to resist the temptation of directly editing the <filename>.config</filename> 
                        file found in the 
                        <link linkend='build-directory'>build directory</link> at 
                        <filename>tmp/sysroots/&lt;machine-name&gt;/kernel</filename>.
                        Doing so, can produce unexpected results when the OpenEmbedded build system 
                        regenerates the configuration file.</para>
                        <para>Once you are satisfied with the configuration changes made using 
                        <filename>menuconfig</filename>, you can directly examine the 
                        <filename>.config</filename> file against a saved original and gather those
                        changes into a config fragment to be referenced from within the kernel's   
                        <filename>.bbappend</filename> file.</para></listitem>                      
                    <listitem><para><emphasis>Add or extend kernel recipes if applicable</emphasis>:  
                        The standard 
                        layer structure organizes recipe files inside the 
                        <filename>meta-kernel-dev</filename> layer that is within the local
                        <filename>poky-extras</filename> Git repository.
                        If you need to add new kernel recipes, you add them within this layer. 
                        Also within this area, you will find the <filename>.bbappend</filename> 
                        file that appends information to the kernel's recipe file used during the 
                        build.
                        </para></listitem>
                    <listitem><para><emphasis>Prepare for the build</emphasis>:  Once you have made all the 
                        changes to your kernel (configurations, source code changes, recipe additions, 
                        or recipe changes), there remains a few things 
                        you need to do in order for the build system to create your image.  
                        If you have not done so, you need to get the build environment ready by sourcing 
                        the environment setup script described earlier.
                        You also need to be sure two key configuration files 
                        (<filename>local.conf</filename> and <filename>bblayers.conf</filename>)
                        are configured appropriately.</para>
                        <para>The entire process for building an image is overviewed in the 
                        "<ulink url='&YOCTO_DOCS_QS_URL;#building-image'>Building an Image</ulink>" 
                        section of the Yocto Project Quick Start.    
                        You might want to reference this information.
                        Also, you should look at the detailed examples found in the appendices at 
                        at the end of this manual.</para></listitem>
                    <listitem><para><emphasis>Build the image</emphasis>:  The OpenEmbedded 
                        build system uses the BitBake 
                        tool to build images based on the type of image you want to create.  
                        You can find more information on BitBake in the user manual, which is found in the
                        <filename>bitbake/doc/manual</filename> directory of the 
                        <link linkend='source-directory'>Source Directory</link>.</para>
                        <para>The build process supports several types of images to satisfy different needs.  
                        See the "<ulink url='&YOCTO_DOCS_REF_URL;#ref-images'>Images</ulink>" chapter in 
                        the Yocto Project Reference Manual for information on supported images.</para></listitem>
                    <listitem><para><emphasis>Make your configuration changes available
                        in the kernel layer</emphasis>:  Up to this point, all the configuration changes to the 
                        kernel have been done and tested iteratively.  
                        Once they are tested and ready to go, you can move them into the kernel layer, 
                        which allows you to distribute the layer.</para></listitem>
                    <listitem><para><emphasis>If applicable, share your in-tree changes</emphasis>:  
                        If the changes you made
                        are suited for all Yocto Project kernel users, you might want to send them on 
                        for inclusion into the upstream kernel's Git repository. 
                        If the changes are accepted, the Yocto Project Maintainer pulls them into 
                        the master branch of the kernel tree. 
                        Doing so makes them available to everyone using the kernel.</para></listitem> 
                </orderedlist>
            </para>
        </section>
    </section>
</section>

<section id='application-development-workflow'>
    <title>Application Development Workflow</title>

    <para>
        Application development involves creating an application that you want 
        to run on your target hardware, which is running a kernel image created using the 
        OpenEmbedded build system.
        The Yocto Project provides an Application Development Toolkit (ADT) and 
        stand-alone cross-development toolchains that 
        facilitate quick development and integration of your application into its run-time environment. 
        Using the ADT and toolchains, you can compile and link your application. 
        You can then deploy your application to the actual hardware or to the QEMU emulator for testing.
        If you are familiar with the popular Eclipse IDE, you can use an Eclipse Yocto Plug-in to 
        allow you to develop, deploy, and test your application all from within Eclipse.
    </para>

    <para>
        While we strongly suggest using the ADT to develop your application, this option might not 
        be best for you.  
        If this is the case, you can still use pieces of the Yocto Project for your development process. 
        However, because the process can vary greatly, this manual does not provide detail on the process.
    </para>

    <section id='workflow-using-the-adt-and-eclipse'>
        <title>Workflow Using the ADT and <trademark class='trade'>Eclipse</trademark></title>

        <para>
            To help you understand how application development works using the ADT, this section 
            provides an overview of the general development process and a detailed example of the process 
            as it is used from within the Eclipse IDE.
        </para>

        <para>
            The following illustration and list summarize the application development general workflow.
        </para>

        <para>
            <imagedata fileref="figures/app-dev-flow.png" 
                width="7in" depth="8in" align="center" scale="100" />
        </para> 

        <para>
            <orderedlist>
                <listitem><para><emphasis>Prepare the Host System for the Yocto Project</emphasis>:  
                    See  
                    "<ulink url='&YOCTO_DOCS_QS_URL;#the-linux-distro'>The Linux Distributions</ulink>" and  
                    "<ulink url='&YOCTO_DOCS_QS_URL;#packages'>The Packages</ulink>" sections both
                    in the Yocto Project Quick Start for requirements.</para></listitem>
                <listitem><para><emphasis>Secure the Yocto Project Kernel Target Image</emphasis>:  
                    You must have a target kernel image that has been built using the OpenEmbeded
                    build system.</para>
                    <para>Depending on whether the Yocto Project has a pre-built image that matches your target
                    architecture and where you are going to run the image while you develop your application
                    (QEMU or real hardware), the area from which you get the image differs.
                        <itemizedlist>
                            <listitem><para>Download the image from  
                                <ulink url='&YOCTO_MACHINES_DL_URL;'>  
                                <filename>machines</filename></ulink> if your target architecture is supported
                                and you are going to develop and test your application on actual hardware. 
                                </para></listitem>
                            <listitem><para>Download the image from the 
                                <ulink url='&YOCTO_QEMU_DL_URL;'>  
                                <filename>machines/qemu</filename></ulink> if your target architecture is supported
                                and you are going to develop and test your application using the QEMU 
                                emulator.</para></listitem>
                            <listitem><para>Build your image if you cannot find a pre-built image that matches
                                your target architecture.
                                If your target architecture is similar to a supported architecture, you can 
                                modify the kernel image before you build it.
                                See the 
                                "<link linkend='kernel-modification-workflow'>Kernel Modification Workflow</link>"
                                section earlier in this manual for information on how to create a modified 
                                Yocto Project kernel.</para></listitem>
                        </itemizedlist></para>
                    <para>For information on pre-built kernel image naming schemes for images 
                    that can run on the QEMU emulator, see the
                    "<ulink url='&YOCTO_DOCS_QS_URL;#downloading-the-pre-built-linux-kernel'>Downloading the Pre-Built Linux Kernel</ulink>"
                    section in the Yocto Project Quick Start.</para></listitem>
                <listitem><para><emphasis>Install the ADT</emphasis>:  
                    The ADT provides a target-specific cross-development toolchain, the root filesystem,
                    the QEMU emulator, and other tools that can help you develop your application.
                    While it is possible to get these pieces separately, the ADT Installer provides an 
                    easy method.
                    You can get these pieces by running an ADT installer script, which is configurable.
                    For information on how to install the ADT, see the
                    "<ulink url='&YOCTO_DOCS_ADT_URL;#using-the-adt-installer'>Using the ADT Installer</ulink>"
                    section 
                    in the Yocto Project Application Developer's Guide.</para></listitem>
                <listitem><para><emphasis>If Applicable, Secure the Target Root Filesystem</emphasis>:  
                    If you choose not to install the ADT using the ADT Installer,
                    you need to find and download the 
                    appropriate root filesystems.
                    You can find these tarballs in the same areas used for the kernel images.
                    Depending on the type of image you are running, the root filesystem you need differs. 
                    For example, if you are developing an application that runs on an image that 
                    supports Sato, you need to get root filesystem that supports Sato.
                    </para></listitem>
                <listitem><para><emphasis>Create and Build your Application</emphasis>:  
                    At this point, you need to have source files for your application.
                    Once you have the files, you can use the Eclipse IDE to import them and build the 
                    project. 
                    If you are not using Eclipse, you need to use the cross-development tools you have 
                    installed to create the image.</para></listitem>                      
                <listitem><para><emphasis>Deploy the Image with the Application</emphasis>:  
                    If you are using the Eclipse IDE, you can deploy your image to the hardware or to 
                    QEMU through the project's preferences.  
                    If you are not using the Eclipse IDE, then you need to deploy the application using 
                    other methods to the hardware.
                    Or, if you are using QEMU, you need to use that tool and load your image in for testing. 
                    </para></listitem>                      
                <listitem><para><emphasis>Test and Debug the Application</emphasis>:  
                    Once your application is deployed, you need to test it.
                    Within the Eclipse IDE, you can use the debubbing environment along with the 
                    set of user-space tools installed along with the ADT to debug your application. 
                    Of course, the same user-space tools are available separately if you choose
                    not to use the Eclipse IDE.</para></listitem>
           </orderedlist>
        </para>
    </section>

    <section id='adt-eclipse'>
        <title>Working Within Eclipse</title>

        <para>
            The Eclipse IDE is a popular development environment and it fully supports 
            development using the Yocto Project.
            <note>This release of the Yocto Project supports both the Juno and Indigo versions
                of the Eclipse IDE.
                Thus, the following information provides setup information for both versions.
            </note>
        </para>

        <para>  
            When you install and configure the Eclipse Yocto Project Plug-in into 
            the Eclipse IDE, you maximize your Yocto Project experience.  
            Installing and configuring the Plug-in results in an environment that 
            has extensions specifically designed to let you more easily develop software.  
            These extensions allow for cross-compilation, deployment, and execution of 
            your output into a QEMU emulation session.  
            You can also perform cross-debugging and profiling.  
            The environment also supports a suite of tools that allows you to perform 
            remote profiling, tracing, collection of power data, collection of 
            latency data, and collection of performance data.
        </para>

        <para>
            This section describes how to install and configure the Eclipse IDE 
            Yocto Plug-in and how to use it to develop your application.
        </para>

        <section id='setting-up-the-eclipse-ide'>
            <title>Setting Up the Eclipse IDE</title>

            <para>
                To develop within the Eclipse IDE, you need to do the following:
                <orderedlist>
                    <listitem><para>Install the optimal version of the Eclipse IDE.</para></listitem>
                    <listitem><para>Configure the Eclipse IDE.</para></listitem>
                    <listitem><para>Install the Eclipse Yocto Plug-in.</para></listitem>
                    <listitem><para>Configure the Eclipse Yocto Plug-in.</para></listitem>
                </orderedlist>
                <note>
                    Do not install Eclipse from your distribution's package repository.
                    Be sure to install Eclipse from the official Eclipse download site as directed
                    in the next section.
                </note>
            </para>

            <section id='installing-eclipse-ide'>
                <title>Installing the Eclipse IDE</title>

                <para>
                    It is recommended that you have the Juno 4.2 version of the 
                    Eclipse IDE installed on your development system.  
                    However, if you currently have the Indigo 3.7.2 version installed and you do 
                    not want to upgrade the IDE, you can configure Indigo to work with the 
                    Yocto Project.
                    See the
                    "<link linkend='configuring-the-eclipse-ide-indigo'>Configuring the Eclipse IDE (Indigo)</link>"
                    section.
                </para>

                <para>
                    If you don’t have the Juno 4.2 Eclipse IDE installed, you can find the tarball at 
                    <ulink url='&ECLIPSE_MAIN_URL;'></ulink>.  
                    From that site, choose the Eclipse Classic version particular to your development
                    host.  
                    This version contains the Eclipse Platform, the Java Development 
                    Tools (JDT), and the Plug-in Development Environment.
                </para>

                <para>
                    Once you have downloaded the tarball, extract it into a clean 
                    directory.
                    For example, the following commands unpack and install the Eclipse IDE
                    tarball found in the <filename>Downloads</filename> area 
                    into a clean directory using the default name <filename>eclipse</filename>:
                    <literallayout class='monospaced'>
     $ cd ~
     $ tar -xzvf ~/Downloads/eclipse-SDK-4.2-linux-gtk-x86_64.tar.gz
                    </literallayout>
                </para>

                <para>
                    If you have the Indigo 3.7.2 Eclipse IDE already installed and you want to use that
                    version, one issue exists that you need to be aware of regarding the Java 
                    Virtual machine’s garbage collection (GC) process.  
                    The GC process does not clean up the permanent generation 
                    space (PermGen).  
                    This space stores metadata descriptions of classes.  
                    The default value is set too small and it could trigger an 
                    out-of-memory error such as the following:
                    <literallayout class='monospaced'>
     Java.lang.OutOfMemoryError: PermGen space
                    </literallayout>
                </para>

                <para>
                    This error causes the application to hang.
                </para>

                <para>
                    To fix this issue, you can use the <filename>--vmargs</filename>
                    option when you start the Indigo 3.7.2 Eclipse IDE 
                    to increase the size of the permanent generation space:
                    <literallayout class='monospaced'>
     eclipse --vmargs --XX:PermSize=256M
                    </literallayout>
                </para>
            </section>

            <section id='configuring-the-eclipse-ide-juno'>
                <title>Configuring the Eclipse IDE (Juno)</title>

                <para>
                    This section presents the steps needed to configure the Juno 4.2 Eclipse IDE.
                    If you are using Indigo 3.7.2, see the 
                    "<link linkend='configuring-the-eclipse-ide-indigo'>Configuring the Eclipse IDE (Indigo)</link>".
                </para>

                <para>
                    Before installing and configuring the Eclipse Yocto Plug-in, you need to configure
                    the Juno 4.2 Eclipse IDE.  
                    Follow these general steps:
                    <orderedlist>
                        <listitem><para>Start the Eclipse IDE.</para></listitem>
                        <listitem><para>Make sure you are in your Workbench and select 
                            "Install New Software" from the "Help" pull-down menu.
                            </para></listitem>
                        <listitem><para>Select <filename>Juno - &ECLIPSE_JUNO_URL;</filename>
                            from the "Work with:" pull-down menu.</para></listitem>
                        <listitem><para>Expand the box next to "Linux Tools" and select the 
                            "LTTng - Linux Tracing Toolkit" boxes.</para></listitem>
                        <listitem><para>Expand the box next to "Mobile and Device Development" and select the 
                            following boxes:
                            <itemizedlist>
                                <listitem><para><filename>C/C++ Remote Launch</filename></para></listitem>
                                <listitem><para><filename>Remote System Explorer End-user Runtime</filename></para></listitem>
                                <listitem><para><filename>Remote System Explorer User Actions</filename></para></listitem>
                                <listitem><para><filename>Target Management Terminal</filename></para></listitem>
                                <listitem><para><filename>TCF Remote System Explorer add-in</filename></para></listitem>
                                <listitem><para><filename>TCF Target Explorer</filename></para></listitem>
                            </itemizedlist></para></listitem>
                        <listitem><para>Expand the box next to <filename>Programming Languages</filename>
                            and select the <filename>Autotools Support for CDT</filename>
                            and <filename>C/C++ Development Tools</filename> boxes.</para></listitem>
                        <listitem><para>Complete the installation and restart the Eclipse IDE.</para></listitem>
                    </orderedlist>
                </para>
            </section>

            <section id='configuring-the-eclipse-ide-indigo'>
                <title>Configuring the Eclipse IDE (Indigo)</title>

                <para>
                    This section presents the steps needed to configure the Indigo 3.7.2 Eclipse IDE.
                    If you are using Juno 4.2, see the 
                    "<link linkend='configuring-the-eclipse-ide-juno'>Configuring the Eclipse IDE (Juno)</link>".
                </para>

                <para>
                    Before installing and configuring the Eclipse Yocto Plug-in, you need to configure
                    the Indigo 3.7.2 Eclipse IDE.  
                    Follow these general steps:
                    <orderedlist>
                        <listitem><para>Start the Eclipse IDE.</para></listitem>
                        <listitem><para>Make sure you are in your Workbench and select 
                            "Install New Software" from the "Help" pull-down menu.
                            </para></listitem>
                        <listitem><para>Select <filename>indigo - &ECLIPSE_INDIGO_URL;</filename>
                            from the "Work with:" pull-down menu.</para></listitem>
                        <listitem><para>Expand the box next to <filename>Programming Languages</filename>
                            and select the <filename>Autotools Support for CDT (incubation)</filename>
                            and <filename>C/C++ Development Tools</filename> boxes.</para></listitem>
                        <listitem><para>Expand the box next to "Linux Tools" and select the 
                            "LTTng - Linux Tracing Toolkit(incubation)" boxes.</para></listitem>
                        <listitem><para>Complete the installation and restart the Eclipse IDE.</para></listitem>
                        <listitem><para>After the Eclipse IDE restarts and from the Workbench, select 
                            "Install New Software" from the "Help" pull-down menu.</para></listitem>
                        <listitem><para>Click the 
                            "Available Software Sites" link.</para></listitem>
                        <listitem><para>Check the box next to 
                            <filename>&ECLIPSE_UPDATES_URL;</filename>
                            and click "OK".</para></listitem>
                        <listitem><para>Select <filename>&ECLIPSE_UPDATES_URL;</filename>
                            from the "Work with:" pull-down menu.</para></listitem>
                        <listitem><para>Check the box next to <filename>TM and RSE Main Features</filename>.
                            </para></listitem>
                        <listitem><para>Expand the box next to <filename>TM and RSE Optional Add-ons</filename>
                            and select every item except <filename>RSE Unit Tests</filename> and 
                            <filename>RSE WinCE Services (incubation)</filename>.</para></listitem>
                        <listitem><para>Complete the installation and restart the Eclipse IDE.</para></listitem>
                        <listitem><para>If necessary, select 
                            "Install New Software" from the "Help" pull-down menu so you can click the 
                            "Available Software Sites" link again.</para></listitem>
                        <listitem><para>After clicking "Available Software Sites", check the box next to 
                            <filename>http://download.eclipse.org/tools/cdt/releases/indigo</filename>
                           and click "OK".</para></listitem>
                        <listitem><para>Select <filename>&ECLIPSE_INDIGO_CDT_URL;</filename>
                            from the "Work with:" pull-down menu.</para></listitem>
                        <listitem><para>Check the box next to <filename>CDT Main Features</filename>.
                            </para></listitem>
                        <listitem><para>Expand the box next to <filename>CDT Optional Features</filename>
                            and select <filename>C/C++ Remote Launch</filename> and 
                            <filename>Target Communication Framework (incubation)</filename>.</para></listitem>
                        <listitem><para>Complete the installation and restart the Eclipse IDE.</para></listitem>
                    </orderedlist>
                </para>
            </section>

            <section id='installing-the-eclipse-yocto-plug-in'>
                <title>Installing or Accessing the Eclipse Yocto Plug-in</title>

                <para>
                    You can install the Eclipse Yocto Plug-in into the Eclipse IDE
                    one of two ways:  use the Yocto Project's Eclipse Update site to install the pre-built plug-in,
                    or build and install the plug-in from the latest source code.
                    If you don't want to permanently install the plug-in but just want to try it out
                    within the Eclipse environment, you can import the plug-in project from the 
                    Yocto Project source repositories.
                </para>

                <section id='new-software'>
                    <title>Installing the Pre-built Plug-in from the Yocto Project Eclipse Update Site</title>

                    <para>
                        To install the Eclipse Yocto Plug-in from the update site, 
                        follow these steps:
                        <orderedlist>
                            <listitem><para>Start up the Eclipse IDE.</para></listitem>
                            <listitem><para>In Eclipse, select "Install New Software" from the "Help" menu.</para></listitem>
                            <listitem><para>Click "Add..." in the "Work with:" area.</para></listitem>
                           <listitem><para>Enter 
                                <filename>&ECLIPSE_DL_PLUGIN_URL;</filename> 
                                in the URL field and provide a meaningful name in the "Name" field.</para></listitem>
                            <listitem><para>Click "OK" to have the entry added to the "Work with:" 
                                drop-down list.</para></listitem>
                            <listitem><para>Select the entry for the plug-in from the "Work with:" drop-down 
                                list.</para></listitem>
                            <listitem><para>Check the box next to <filename>Development tools and SDKs for Yocto Linux</filename>.
                                </para></listitem>
                            <listitem><para>Complete the remaining software installation steps and 
                                then restart the Eclipse IDE to finish the installation of the plug-in.
                                </para></listitem>
                        </orderedlist>
                    </para>
                </section>

               <section id='zip-file-method'>
                   <title>Installing the Plug-in Using the Latest Source Code</title>
         
                   <para>
                        To install the Eclipse Yocto Plug-in from the latest source code, follow these steps:
                        <orderedlist>
                            <listitem><para>Open a shell and create a Git repository with:
                                <literallayout class='monospaced'>
     $ git clone git://git.yoctoproject.org/eclipse-poky yocto-eclipse
                                </literallayout>
                                For this example, the repository is named     
                                <filename>~/yocto-eclipse</filename>.</para></listitem>
                            <listitem><para>Be sure you are in the right branch for your Git repository.
                                For this release set the branch to <filename>1.3_beta</filename>:
                                <literallayout class='monospaced'>
     $ git checkout -b 1.3_beta origin/1.3_beta
                                </literallayout></para></listitem>
                            <listitem><para>Locate the <filename>build.sh</filename> script in the 
                                Git repository you created in the previous step.
                                The script is located in the <filename>scripts</filename>.</para></listitem>
                            <listitem><para>Be sure to set and export the <filename>ECLIPSE_HOME</filename> environment
                                variable to the top-level directory in which you installed your version of Eclipse.
                                For example, if your Eclipse directory is <filename>$HOME/eclipse</filename>, 
                                use the following:
                                <literallayout class='monospaced'>
     $ export ECLIPSE_HOME=$HOME/eclipse
                                </literallayout></para></listitem>
                            <listitem><para>Be sure you have the right branch in the Poky Git repository
                                checked out.
                                For example, the following commands checkout the <filename>1.3_beta</filename>
                                branch in the local Poky Git repository:
                                <literallayout class='monospaced'>
     $ cd ~/poky
     $ git checkout -b 1.3_beta origin/1.3_beta
                                </literallayout></para></listitem>
                            <listitem><para>Move back to your Yocto Eclipse directory and 
                                run the <filename>build.sh</filename> script.  
                                Provide the name of the Git branch along with the Yocto Project release you are 
                                using.
                                Here is an example that uses the <filename>1.3_beta</filename> branches:
                                <literallayout class='monospaced'>
     $ scripts/build.sh 1.3_beta 1.3_beta 
                                </literallayout>
                                After running the script, the file
                                <filename>org.yocto.sdk-&lt;release&gt;-&lt;date&gt;-archive.zip</filename>
                                is in the current directory.</para></listitem>
                            <listitem><para>If necessary, start the Eclipse IDE and be sure you are in the 
                                Workbench.</para></listitem>
                            <listitem><para>Select "Install New Software" from the "Help" pull-down menu.
                                </para></listitem>
                            <listitem><para>Click "Add".</para></listitem>
                            <listitem><para>Provide anything you want in the "Name" field.</para></listitem>
                            <listitem><para>Click "Archive" and browse to the ZIP file you built 
                                in step four.  
                                This ZIP file should not be "unzipped", and must be the 
                                <filename>*archive.zip</filename> file created by running the 
                                <filename>build.sh</filename> script.</para></listitem>
                            <listitem><para>Click through the "Okay" buttons.</para></listitem>
                            <listitem><para>Check the box next to the new entry in the installation window and complete
                        the installation.</para></listitem>
                            <listitem><para>Restart the Eclipse IDE if necessary.</para></listitem>
                        </orderedlist>
                    </para>

                    <para>
                        At this point you should be able to configure the Eclipse Yocto Plug-in as described in the
                        "<link linkend='configuring-the-eclipse-yocto-plug-in'>Configuring the Eclipse Yocto Plug-in</link>"
                        section.</para>
                </section>            

                <section id='yocto-project-source'>
                    <title>Importing the Plug-in Project into the Eclipse Environment</title>

                    <para>
                        Importing the Eclipse Yocto Plug-in project from the Yocto Project source repositories
                        is useful when you want to try out the latest plug-in from the tip of plug-in's 
                        development tree.
                        It is important to understand when you import the plug-in you are not installing 
                        it into the Eclipse application.
                        Rather, you are importing the project and just using it.
                        To import the plug-in project, follow these steps:
                        <orderedlist>
                            <listitem><para>Open a shell and create a Git repository with:
                                <literallayout class='monospaced'>
     $ git clone git://git.yoctoproject.org/eclipse-poky yocto-eclipse
                                </literallayout>
                                For this example, the repository is named 
                                <filename>~/yocto-eclipse</filename>.</para></listitem>
                            <listitem><para>In Eclipse, select "Import" from the "File" menu.</para></listitem>
                            <listitem><para>Expand the "General" box and select "existing projects into workspace"
                                and then click "Next".</para></listitem>
                            <listitem><para>Select the root directory and browse to 
                                <filename>~/yocto-eclipse/plugins</filename>.</para></listitem>
                            <listitem><para>Three plug-ins exist: "org.yocto.bc.ui", "org.yocto.sdk.ide", and
                                "org.yocto.sdk.remotetools". 
                                Select and import all of them.</para></listitem>
                        </orderedlist>
                    </para>

                    <para>
                        The left navigation pane in the Eclipse application shows the default projects. 
                        Right-click on one of these projects and run it as an Eclipse application.
                        This brings up a second instance of Eclipse IDE that has the Yocto Plug-in.
                    </para>
                </section>
            </section>

            <section id='configuring-the-eclipse-yocto-plug-in'>
                <title>Configuring the Eclipse Yocto Plug-in</title>

                <para>
                    Configuring the Eclipse Yocto Plug-in involves setting the Cross 
                    Compiler options and the Target options.  
                    The configurations you choose become the default settings for all projects.  
                    You do have opportunities to change them later when 
                    you configure the project (see the following section).  
                </para>

                <para>
                    To start, you need to do the following from within the Eclipse IDE:
                    <itemizedlist>
                        <listitem><para>Choose <filename>Windows -&gt; Preferences</filename> to display 
                            the <filename>Preferences</filename> Dialog</para></listitem>
                        <listitem><para>Click <filename>Yocto Project ADT</filename></para></listitem>
                    </itemizedlist>
                </para>

                <section id='configuring-the-cross-compiler-options'>
                    <title>Configuring the Cross-Compiler Options</title>

                    <para>
                        To configure the Cross Compiler Options, you must select the type of toolchain,
                        point to the toolchain, specify the sysroot location, and select the target architecture.
                        <itemizedlist>
                            <listitem><para><emphasis>Selecting the Toolchain Type:</emphasis>
                                Choose between <filename>Standalone pre-built toolchain</filename>
                                and <filename>Build system derived toolchain</filename> for Cross 
                                Compiler Options.
                                    <itemizedlist>
                                        <listitem><para><emphasis>
                                            <filename>Standalone Pre-built Toolchain:</filename></emphasis> 
                                            Select this mode when you are using a stand-alone cross-toolchain.
                                            For example, suppose you are an application developer and do not 
                                            need to build a target image.
                                            Instead, you just want to use an architecture-specific toolchain on an 
                                            existing kernel and target root filesystem.
                                            </para></listitem>
                                       <listitem><para><emphasis>
                                            <filename>Build System Derived Toolchain:</filename></emphasis> 
                                            Select this mode if the cross-toolchain has been installed and built 
                                            as part of the build directory.  
                                            When you select <filename>Build system derived toolchain</filename>,
                                            you are using the toolchain bundled 
                                            inside the build directory.
                                            </para></listitem>
                                    </itemizedlist>
                                </para></listitem>
                            <listitem><para><emphasis>Point to the Toolchain:</emphasis>
                                If you are using a stand-alone pre-built toolchain, you should be pointing to the
                                <filename>&YOCTO_ADTPATH_DIR;</filename> directory.
                                This is the location for toolchains installed by the ADT Installer or by hand.
                                Sections "<ulink url='&YOCTO_DOCS_ADT_URL;#configuring-and-running-the-adt-installer-script'>Configuring 
                                and Running the ADT Installer Script</ulink>" and 
                                "<ulink url='&YOCTO_DOCS_ADT_URL;#using-an-existing-toolchain-tarball'>Using a Cross-Toolchain Tarball</ulink>" 
                                in the Yocto Project Application Developer's Guide 
                                describe two ways to install a stand-alone cross-toolchain in the 
                                <filename>/opt/poky</filename> directory.
                                <note>It is possible to install a stand-alone cross-toolchain in a directory
                                other than <filename>/opt/poky</filename>.
                                However, doing so is discouraged.</note></para>
                                <para>If you are using a system-derived toolchain, the path you provide 
                                for the <filename>Toolchain Root Location</filename>
                                field is the build directory.
                                See the "<ulink url='&YOCTO_DOCS_ADT_URL;#using-the-toolchain-from-within-the-build-tree'>Using 
                                BitBake and the build directory</ulink>" section in the Yocto Project Application
                                Developer's Guide for information on how to install the toolchain into the build 
directory.</para></listitem> 
                            <listitem><para><emphasis>Specify the Sysroot Location:</emphasis>
                                This location is where the root filesystem for the target hardware resides. 
                                If you used the ADT Installer, then the location is 
                                <filename>/opt/poky/&lt;release&gt;</filename>.
                                Additionally, when you use the ADT Installer, the same location is used for 
                                the QEMU user-space tools and the NFS boot process.</para>
                                <para>If you used either of the other two methods to install the toolchain, then the 
                                location of the sysroot filesystem depends on where you separately
                                extracted and intalled the filesystem.</para>
                                <para>For information on how to install the toolchain and on how to extract 
                                and install the sysroot filesystem, see the
                                "<ulink url='&YOCTO_DOCS_ADT_URL;#installing-the-adt'>Installing the ADT and Toolchains</ulink>" section.
                                </para></listitem>
                            <listitem><para><emphasis>Select the Target Architecture:</emphasis>
                                The target architecture is the type of hardware you are 
                                going to use or emulate.
                                Use the pull-down <filename>Target Architecture</filename> menu to make
                                your selection.
                                The pull-down menu should have the supported architectures.  
                                If the architecture you need is not listed in the menu, you 
                                will need to build the image.
                                See the "<ulink url='&YOCTO_DOCS_QS_URL;#building-image'>Building an Image</ulink>" section 
                                of the Yocto Project Quick Start for more information.</para></listitem>
                        </itemizedlist>
                    </para>
                </section>

                <section id='configuring-the-target-options'>
                    <title>Configuring the Target Options</title>

                    <para>
                        You can choose to emulate hardware using the QEMU emulator, or you 
                        can choose to run your image on actual hardware.
                        <itemizedlist>
                            <listitem><para><emphasis><filename>QEMU:</filename></emphasis> Select this option if 
                                you will be using the QEMU emulator.  
                                If you are using the emulator, you also need to locate the kernel 
                                and specify any custom options.</para>
                                <para>If you selected <filename>Build system derived toolchain</filename>, 
                                the target kernel you built will be located in the 
                                build directory in <filename>tmp/deploy/images</filename> directory.   
                                If you selected <filename>Standalone pre-built toolchain</filename>, the 
                                pre-built image you downloaded is located 
                                in the directory you specified when you downloaded the image.</para>
                                <para>Most custom options are for advanced QEMU users to further 
                                customize their QEMU instance.  
                                These options are specified between paired angled brackets.  
                                Some options must be specified outside the brackets.
                               In particular, the options <filename>serial</filename>, 
                                <filename>nographic</filename>, and <filename>kvm</filename> must all 
                                be outside the brackets.  
                                Use the <filename>man qemu</filename> command to get help on all the options
                                and their use.  
                                The following is an example:
                               <literallayout class='monospaced'>
    serial ‘&lt;-m 256 -full-screen&gt;’
                                </literallayout></para>
                                <para>
                                Regardless of the mode, Sysroot is already defined as part of the 
                                Cross Compiler Options configuration in the 
                                <filename>Sysroot Location:</filename> field.</para></listitem>
                            <listitem><para><emphasis><filename>External HW:</filename></emphasis> Select this option 
                                if you will be using actual hardware.</para></listitem>
                        </itemizedlist>
                    </para>

                    <para>
                        Click the <filename>OK</filename> button to save your plug-in configurations.
                    </para>
                </section>
            </section>
        </section>

        <section id='creating-the-project'>
            <title>Creating the Project</title>

            <para>
                You can create two types of projects:  Autotools-based, or Makefile-based.  
                This section describes how to create Autotools-based projects from within 
                the Eclipse IDE.  
                For information on creating Makefile-based projects in a terminal window, see the section
                "<ulink url='&YOCTO_DOCS_ADT_URL;#using-the-command-line'>Using the Command Line</ulink>"
                in the Yocto Project Application Developer's Guide.
            </para>

            <para>
                To create a project based on a Yocto template and then display the source code, 
                follow these steps:
                <orderedlist>
                    <listitem><para>Select <filename>File -&gt; New -&gt; Project</filename>.</para></listitem>
                    <listitem><para>Double click <filename>CC++</filename>.</para></listitem>
                    <listitem><para>Double click <filename>C Project</filename> to create the project.</para></listitem>
                    <listitem><para>Expand <filename>Yocto Project ADT Project</filename>.</para></listitem>
                    <listitem><para>Select <filename>Hello World ANSI C Autotools Project</filename>.  
                        This is an Autotools-based project based on a Yocto template.</para></listitem>
                    <listitem><para>Put a name in the <filename>Project name:</filename> field.
                        Do not use hyphens as part of the name.</para></listitem>
                    <listitem><para>Click <filename>Next</filename>.</para></listitem>
                    <listitem><para>Add information in the <filename>Author</filename> and
                        <filename>Copyright notice</filename> fields.</para></listitem>
                    <listitem><para>Be sure the <filename>License</filename> field is correct.</para></listitem>
                    <listitem><para>Click <filename>Finish</filename>.</para></listitem>
                    <listitem><para>If the "open perspective" prompt appears, click "Yes" so that you 
                        in the C/C++ perspective.</para></listitem>
                    <listitem><para>The left-hand navigation pane shows your project.
                        You can display your source by double clicking the project's source file.
                        </para></listitem>
                </orderedlist>
            </para>
        </section>

        <section id='configuring-the-cross-toolchains'>
            <title>Configuring the Cross-Toolchains</title>

            <para>
                The earlier section, "<link linkend='configuring-the-eclipse-yocto-plug-in'>Configuring 
                the Eclipse Yocto Plug-in</link>", sets up the default project 
                configurations.  
                You can override these settings for a given project by following these steps:
                <orderedlist>
                    <listitem><para>Select <filename>Project -&gt; Change Yocto Project Settings</filename>:  
                        This selection brings up the <filename>Yocot Project Settings</filename> Dialog
                        and allows you to make changes specific to an individual project.  
                        </para>
                        <para>By default, the Cross Compiler Options and Target Options for a project
                        are inherited from settings you provide using the <filename>Preferences</filename>
                        Dialog as described earlier 
                        in the "<link linkend='configuring-the-eclipse-yocto-plug-in'>Configuring the Eclipse 
                        Yocto Plug-in</link>" section.
                        The <filename>Yocto Project Settings</filename>
                        Dialog allows you to override those default settings
                        for a given project.</para></listitem>
                    <listitem><para>Make your configurations for the project and click "OK".
                        If you are runing the Juno version of Eclipse, you can skip down to the next
                        section where you build the project. 
                        If you are not working with Juno, you need to reconfigure the project as 
                        described in the next step.</para></listitem>
                    <listitem><para>Select <filename>Project -&gt; Reconfigure Project</filename>:   
                        This selection reconfigures the project by running
                       <filename>autogen.sh</filename> in the workspace for your project.  
                        The script also runs <filename>libtoolize</filename>, <filename>aclocal</filename>,
                        <filename>autoconf</filename>, <filename>autoheader</filename>, 
                        <filename>automake --a</filename>, and 
                        <filename>./configure</filename>.
                        Click on the <filename>Console</filename> tab beneath your source code to 
                        see the results of reconfiguring your project.</para></listitem>
                </orderedlist>
            </para>
        </section>

        <section id='building-the-project'>
            <title>Building the Project</title>

            <para>
                To build the project in Juno, right click on the project in the navigator pane and select
                <filename>Build Project</filename>.
                If you are not running Juno, select <filename>Project -&gt; Build Project</filename>.  
                The console should update and you can note the cross-compiler you are using.
            </para>
        </section>

        <section id='starting-qemu-in-user-space-nfs-mode'>
            <title>Starting QEMU in User Space NFS Mode</title>

            <para>
                To start the QEMU emulator from within Eclipse, follow these steps:
                <orderedlist>
                    <listitem><para>Expose the <filename>Run -&gt; External Tools</filename> menu.
                        Your image should appear as a selectable menu item.
                        </para></listitem>
                    <listitem><para>Select your image from the menu to launch the 
                        emulator in a new window.</para></listitem>
                    <listitem><para>If needed, enter your host root password in the shell window at the prompt.  
                        This sets up a <filename>Tap 0</filename> connection needed for running in user-space 
                        NFS mode.</para></listitem>
                    <listitem><para>Wait for QEMU to launch.</para></listitem>
                    <listitem><para>Once QEMU launches, you can begin operating within that 
                        environment.
                        For example, you could determine the IP Address 
                       for the user-space NFS by using the <filename>ifconfig</filename> command.
                        </para></listitem>
                </orderedlist>
            </para>
        </section>

        <section id='deploying-and-debugging-the-application'>
            <title>Deploying and Debugging the Application</title>

            <para>
                Once the QEMU emulator is running the image, using the Eclipse IDE 
                you can deploy your application and use the emulator to perform debugging.  
                Follow these steps to deploy the application.
                <orderedlist>
                    <listitem><para>Select <filename>Run -&gt; Debug Configurations...</filename></para></listitem>
                    <listitem><para>In the left area, expand <filename>C/C++Remote Application</filename>.</para></listitem>
                    <listitem><para>Locate your project and select it to bring up a new 
                        tabbed view in the <filename>Debug Configurations</filename> Dialog.</para></listitem>
                    <listitem><para>Enter the absolute path into which you want to deploy 
                        the application.  
                        Use the <filename>Remote Absolute File Path for C/C++Application:</filename> field.  
                        For example, enter <filename>/usr/bin/&lt;programname&gt;</filename>.</para></listitem>
                    <listitem><para>Click on the <filename>Debugger</filename> tab to see the cross-tool debugger 
                        you are using.</para></listitem>
                    <listitem><para>Click on the <filename>Main</filename> tab.</para></listitem>
                    <listitem><para>Create a new connection to the QEMU instance 
                        by clicking on <filename>new</filename>.</para></listitem>
                    <listitem><para>Select <filename>TCF</filename>, which means Target Communication 
                        Framework.</para></listitem>
                    <listitem><para>Click <filename>Next</filename>.</para></listitem>
                    <listitem><para>Clear out the <filename>host name</filename> field and enter the IP Address 
                        determined earlier.</para></listitem>
                    <listitem><para>Click <filename>Finish</filename> to close the 
                        <filename>New Connections</filename> Dialog.</para></listitem>
                    <listitem><para>Use the drop-down menu now in the <filename>Connection</filename> field and pick 
                        the IP Address you entered.</para></listitem>
                    <listitem><para>Click <filename>Run</filename> to bring up a login screen 
                        and login.</para></listitem>
                    <listitem><para>Accept the debug perspective.</para></listitem>
                </orderedlist>
            </para>
        </section>

        <section id='running-user-space-tools'>
            <title>Running User-Space Tools</title>

            <para>
                As mentioned earlier in the manual, several tools exist that enhance 
                your development experience.  
                These tools are aids in developing and debugging applications and images.  
                You can run these user-space tools from within the Eclipse IDE through the 
                <filename>YoctoTools</filename> menu.
            </para>

            <para>
                Once you pick a tool, you need to configure it for the remote target. 
                Every tool needs to have the connection configured. 
                You must select an existing TCF-based RSE connection to the remote target. 
                If one does not exist, click <filename>New</filename> to create one.
            </para>

            <para>
                Here are some specifics about the remote tools:
                <itemizedlist>
                    <listitem><para><emphasis><filename>OProfile</filename>:</emphasis>  Selecting this tool causes 
                        the <filename>oprofile-server</filename> on the remote target to launch on 
                        the local host machine.  
                        The <filename>oprofile-viewer</filename> must be installed on the local host machine and the 
                        <filename>oprofile-server</filename> must be installed on the remote target, 
                        respectively, in order to use.
                        You must compile and install the <filename>oprofile-viewer</filename> from the source code 
                        on your local host machine.
                        Furthermore, in order to convert the target's sample format data into a form that the 
                        host can use, you must have <filename>oprofile</filename> version 0.9.4 or 
                        greater installed on the host.</para>
                        <para>You can locate both the viewer and server from 
                        <ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi/oprofileui/'></ulink>.
                        <note>The <filename>oprofile-server</filename> is installed by default on 
                        the <filename>core-image-sato-sdk</filename> image.</note></para></listitem>
                    <listitem><para><emphasis><filename>Lttng-ust</filename>:</emphasis> Selecting this tool runs
                        <filename>usttrace</filename> on the remote target, transfers the output data back 
                        to the local host machine, and uses the <filename>lttng</filename> Eclipse plug-in to 
                        graphically display the output. 
                        For information on how to use <filename>lttng</filename> to trace an application, see
                        <ulink url='http://lttng.org/files/ust/manual/ust.html'></ulink>.</para>
                        <para>For <filename>Application</filename>, you must supply the absolute path name of the 
                        application to be traced by user mode <filename>lttng</filename>.  
                        For example, typing <filename>/path/to/foo</filename> triggers 
                        <filename>usttrace /path/to/foo</filename> on the remote target to trace the 
                        program <filename>/path/to/foo</filename>.</para>
                        <para><filename>Argument</filename> is passed to <filename>usttrace</filename>
                        running on the remote target.</para>
                        <para>Before you use the <filename>lttng-ust</filename> tool, you need to setup 
                        the <filename>lttng</filename> Eclipse plug-in and create a <filename>lttng</filename>
                        project.
                        Do the following:
                        <orderedlist>
                            <listitem><para>Follow these 
                                <ulink url='http://wiki.eclipse.org/Linux_Tools_Project/LTTng#Downloading_and_installing_the_LTTng_parser_library'>instructions</ulink>
                                to download and install the <filename>lttng</filename> parser library.
                                </para></listitem>
                            <listitem><para>Select <filename>Window -> Open Perspective -> Other</filename>
                                and then select <filename>LTTng</filename>.</para></listitem>
                            <listitem><para>Click <filename>OK</filename> to change the Eclipse perspective 
                                into the <filename>LTTng</filename> perspective.</para></listitem>
                            <listitem><para>Create a new <filename>LTTng</filename> project by selecting 
                                <filename>File -> New -> Project</filename>.</para></listitem>
                            <listitem><para>Choose <filename>LTTng -> LTTng Project</filename>.</para></listitem>
                            <listitem><para>Click <filename>YoctoTools -> lttng-ust</filename> to start user mode 
                                <filename>lttng</filename> on the remote target.</para></listitem>
                        </orderedlist></para>
                        <para>After the output data has been transferred from the remote target back to the local
                        host machine, new traces will be imported into the selected <filename>LTTng</filename> project.
                        Then you can go to the <filename>LTTng</filename> project, right click the imported 
                        trace, and set the trace type as the <filename>LTTng</filename> kernel trace.
                        Finally, right click the imported trace and select <filename>Open</filename>
                        to display the data graphically.</para></listitem>
                    <listitem><para><emphasis><filename>PowerTOP</filename>:</emphasis> Selecting this tool runs 
                        <filename>powertop</filename> on the remote target machine and displays the results in a 
                        new view called <filename>powertop</filename>.</para>
                        <para><filename>Time to gather data(sec):</filename> is the time passed in seconds before data 
                        is gathered from the remote target for analysis.</para>
                        <para><filename>show pids in wakeups list:</filename> corresponds to the 
                        <filename>-p</filename> argument 
                        passed to <filename>powertop</filename>.</para></listitem>
                        <listitem><para><emphasis><filename>LatencyTOP and Perf</filename>:</emphasis>  
                        <filename>latencytop</filename> identifies system latency, while 
                        <filename>perf</filename> monitors the system's 
                        performance counter registers. 
                        Selecting either of these tools causes an RSE terminal view to appear 
                        from which you can run the tools. 
                        Both tools refresh the entire screen to display results while they run.</para></listitem>
                </itemizedlist>
            </para>
        </section> 

        <section id='customizing-an-image-using-a-bitbake-commander-project-and-hob'>
            <title>Customizing an Image Using a BitBake Commander Project and Hob</title>

            <para>
                Within Eclipse, you can create a Yocto BitBake Commander project, 
                edit the metadata, and then use the 
                <ulink url='&YOCTO_HOME_URL;/projects/hob'>Hob</ulink> to build a customized 
                image all within one IDE.
            </para>

            <section id='creating-the-yocto-bitbake-commander-project'>
                <title>Creating the Yocto BitBake Commander Project</title>

                <para>
                    To create a Yocto BitBake Commander project, follow these steps:
                    <orderedlist>
                        <listitem><para>Select <filename>Window -> Open Perspective -> Other</filename>
                            and then choose <filename>Bitbake Commander</filename>.</para></listitem>
                        <listitem><para>Click <filename>OK</filename> to change the Eclipse perspective into the 
                            Bitbake Commander perspective.</para></listitem>
                        <listitem><para>Select <filename>File -> New -> Project</filename> to create a new Yocto 
                            Bitbake Commander project.</para></listitem>
                        <listitem><para>Choose <filename>Yocto Project Bitbake Commander -> New Yocto Project</filename>
                            and click <filename>Next</filename>.</para></listitem>
                        <listitem><para>Enter the Project Name and choose the Project Location. 
                            The Yocto project's metadata files will be put under the directory 
                            <filename>&lt;project_location&gt;/&lt;project_name&gt;</filename>. 
                            If that directory does not exist, you need to check 
                            the "Clone from Yocto Git Repository" box, which would execute a 
                            <filename>git clone</filename> command to get the project's metadata files.
                            </para></listitem>
                        <listitem><para>Select <filename>Finish</filename> to create the project.</para></listitem>
                    </orderedlist>
                </para>
            </section>

            <section id='editing-the-metadata-files'>
                <title>Editing the Metadata Files</title>

                <para>
                    After you create the Yocto Bitbake Commander project, you can modify the metadata files
                    by opening them in the project.
                    When editing recipe files (<filename>.bb</filename> files), you can view BitBake
                    variable values and information by hovering the mouse pointer over the variable name and 
                    waiting a few seconds.
                </para>

                <para>
                    To edit the metadata, follow these steps:
                    <orderedlist>
                        <listitem><para>Select your Yocto Bitbake Commander project.</para></listitem>
                        <listitem><para>Select <filename>File -> New -> Yocto BitBake Commander -> BitBake Recipe</filename>
                            to open a new recipe wizard.</para></listitem>
                        <listitem><para>Point to your source by filling in the "SRC_URL" field.
                            For example, you can add a recipe to your 
                            <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>source directory</ulink>
                            by defining "SRC_URL" as follows:
                            <literallayout class='monospaced'>
     ftp://ftp.gnu.org/gnu/m4/m4-1.4.9.tar.gz
                            </literallayout></para></listitem>
                        <listitem><para>Click "Populate" to calculate the archive md5, sha256, 
                            license checksum values and to auto-generate the recipe filename.</para></listitem>
                        <listitem><para>Fill in the "Description" field.</para></listitem>
                        <listitem><para>Be sure values for all required fields exist.</para></listitem>
                        <listitem><para>Click <filename>Finish</filename>.</para></listitem>
                    </orderedlist>
                </para>
            </section>

            <section id='buiding-and-customizing-the-image'>
                <title>Building and Customizing the Image</title>

                <para>
                    To build and customize the image in Eclipse, follow these steps:
                    <orderedlist>
                        <listitem><para>Select your Yocto Bitbake Commander project.</para></listitem>
                        <listitem><para>Select <filename>Project -> Launch HOB</filename>.</para></listitem>
                        <listitem><para>Enter the build directory where you want to put your final images.</para></listitem>
                        <listitem><para>Click <filename>OK</filename> to launch Hob.</para></listitem>
                        <listitem><para>Use Hob to customize and build your own images. 
                            For information on Hob, see the 
                            <ulink url='&YOCTO_HOME_URL;/projects/hob'>Hob Project Page</ulink> on the 
                            Yocto Project website.</para></listitem>
                    </orderedlist>
                </para>
            </section>
        </section>
    </section>

    <section id='workflow-using-stand-alone-cross-development-toolchains'>
        <title>Workflow Using Stand-alone Cross-development Toolchains</title>

        <para>
            If you want to develop an application without prior installation of the ADT, you 
            still can employ the cross-development toolchain, the QEMU emulator, and a number of supported
            target image files.  
            You just need to follow these general steps:
            <orderedlist>
                <listitem><para><emphasis>Install the cross-development toolchain for your target hardware:</emphasis> 
                    For information on how to install the toolchain, see the
                    "<ulink url='&YOCTO_DOCS_ADT_URL;#using-an-existing-toolchain-tarball'>Using a Cross-Toolchain Tarball</ulink>" 
                    section
                    in the Yocto Project Application Developer's Guide.</para></listitem>
                <listitem><para><emphasis>Download the Target Image:</emphasis>  The Yocto Project supports
                    several target architectures and has many pre-built kernel images and root filesystem 
                    images.</para>
                    <para>If you are going to develop your application on hardware, go to the 
                    <ulink url='&YOCTO_MACHINES_DL_URL;'><filename>machines</filename></ulink> 
                    download area and choose a target machine area
                    from which to download the kernel image and root filesystem.
                    This download area could have several files in it that support development using   
                    actual hardware. 
                    For example, the area might contain <filename>.hddimg</filename> files that combine the 
                    kernel image with the filesystem, boot loaders, etc.
                    Be sure to get the files you need for your particular development process.</para>
                    <para>If you are going to develop your application and then run and test it using the QEMU
                    emulator, go to the 
                    <ulink url='&YOCTO_QEMU_DL_URL;'><filename>machines/qemu</filename></ulink> 
                    download area.
                    From this area, go down into the directory for your target architecture
                    (e.g. <filename>qemux86_64</filename> for an 
                    <trademark class='registered'>Intel</trademark>-based 64-bit architecture).
                    Download kernel, root filesystem, and any other files you need for your process.
                    <note>In order to use the root filesystem in QEMU, you need to extract it.
                    See the 
                    "<ulink url='&YOCTO_DOCS_ADT_URL;#extracting-the-root-filesystem'>Extracting the Root Filesystem</ulink>" 
                    section for information on how to extract the root filesystem.</note></para></listitem>
                <listitem><para><emphasis>Develop and Test your Application:</emphasis>  At this point, 
                    you have the tools to develop your application.  
                    If you need to separately install and use the QEMU emulator, you can go to 
                    <ulink url='http://www.qemu.org'>QEMU Home Page</ulink> to download and learn about the 
                    emulator.</para></listitem>
            </orderedlist>
        </para>
    </section>
</section>

<section id="modifying-temporary-source-code">
    <title>Modifying Temporary Source Code</title>

    <para>
        You might
        find it helpful during development to modify the temporary source code used by recipes
        to build packages.
        For example, suppose you are developing a patch and you need to experiment a bit
        to figure out your solution.
        After you have initially built the package, you can iteratively tweak the 
        source code, which is located in the 
        <link linkend='build-directory'>build directory</link>, and then 
        you can force a re-compile and quickly test your altered code.
        Once you settle on a solution, you can then preserve your changes in the form of 
        patches.
        You can accomplish these steps all within either a 
        <ulink url='http://savannah.nongnu.org/projects/quilt'>Quilt</ulink> or 
        <link linkend='git'>Git</link> workflow.
    </para>

    <section id='finding-the-temporary-source-code'>
        <title>Finding the Temporary Source Code</title>

        <para>
            During a build, the unpacked temporary source code used by recipes 
            to build packages is available in the build directory as 
            defined by the 
            <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-S'>S</ulink></filename> variable.
            Below is the default value for the <filename>S</filename> variable as defined in the 
            <filename>meta/conf/bitbake.conf</filename> configuration file in the 
            <link linkend='source-directory'>source directory</link>:
            <literallayout class='monospaced'>
     S = ${WORKDIR}/${BP}
            </literallayout>
            You should be aware that many recipes override the <filename>S</filename> variable.
            For example, recipes that fetch their source from Git usually set 
            <filename>S</filename> to <filename>${WORKDIR}/git</filename>.
            <note>
                <filename>BP</filename> represents the "Base Package", which is the base package
                name and the package version:
                <literallayout class='monospaced'>
     BP = ${BPN}-${PV}
                </literallayout>
            </note> 
        </para>

        <para>
            The path to the work directory for the recipe 
            (<ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink>) depends
            on the package name and the architecture of the target device.
            For example, here is the work directory for packages whose targets are not device-dependent:
            <literallayout class='monospaced'>
     ${TMPDIR}/work/${PACKAGE_ARCH}-poky-${TARGET_OS}/${PN}-${PV}-${PR}
            </literallayout>
            Let's look at an example without variables.
            Assuming a top-level source directory named <filename>poky</filename>
            and a default build directory of <filename>poky/build</filename>, 
            the following is the work directory for the <filename>acl</filename> package:
            <literallayout class='monospaced'>
     ~/poky/build/tmp/work/i586-poky-linux/acl-2.2.51-r3
            </literallayout>
        </para>

        <para>
            If your package is dependent on the target device, the work directory varies slightly:
            <literallayout class='monospaced'>
     ${TMPDIR}/work/${MACHINE}-poky-${TARGET_OS}/${PN}-${PV}-${PR}
            </literallayout>
            Again, assuming top-level source directory named <filename>poky</filename>
            and a default build directory of <filename>poky/build</filename>, the 
            following is the work directory for the <filename>acl</filename> package that is being 
            built for a MIPS-based device:
            <literallayout class='monospaced'>
     ~/poky/build/tmp/work/mips-poky-linux/acl-2.2.51-r2
            </literallayout>
        </para>

        <note>
            To better understand how the OpenEmbedded build system resolves directories during the 
            build process, see the glossary entries for the
            <ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink>,
            <ulink url='&YOCTO_DOCS_REF_URL;#var-TMPDIR'><filename>TMPDIR</filename></ulink>,
            <ulink url='&YOCTO_DOCS_REF_URL;#var-TOPDIR'><filename>TOPDIR</filename></ulink>,
            <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_ARCH'><filename>PACKAGE_ARCH</filename></ulink>,
            <ulink url='&YOCTO_DOCS_REF_URL;#var-TARGET_OS'><filename>TARGET_OS</filename></ulink>,
            <ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink>,
            <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>,
            and
            <ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink>
            variables in the Yocto Project Reference Manual.
        </note>

        <para>
            Now that you know where to locate the directory that has the temporary source code, you can use a 
            Quilt or Git workflow to make your edits, test the changes, and preserve the 
            changes in the form of patches.
        </para>
    </section>

    <section id="using-a-quilt-workflow">
        <title>Using a Quilt Workflow</title>
            
        <para>
            <ulink url='http://savannah.nongnu.org/projects/quilt'>Quilt</ulink>
            is a powerful tool that allows you to capture source code changes without having 
            a clean source tree.
            This section outlines the typical workflow you can use to modify temporary source code, 
            test changes, and then preserve the changes in the form of a patch all using Quilt.
        </para>

        <para>
            Follow these general steps:
            <orderedlist>
                <listitem><para><emphasis>Find the Source Code:</emphasis>
                    The temporary source code used by the OpenEmbedded build system is kept in the 
                    build directory.  
                    See the 
                    "<link linkend='finding-the-temporary-source-code'>Finding the Temporary Source Code</link>"
                    section to learn how to locate the directory that has the temporary source code for a 
                    particular package.</para></listitem>
                <listitem><para><emphasis>Change Your Working Directory:</emphasis>
                    You need to be in the directory that has the temporary source code.
                    That directory is defined by the 
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-S'>S</ulink>
                    variable.</para></listitem>
                <listitem><para><emphasis>Create a New Patch:</emphasis>
                    Before modifying source code, you need to create a new patch.
                    To create a new patch file, use <filename>quilt new</filename> as below:
                    <literallayout class='monospaced'>
     $ quilt new my_changes.patch
                    </literallayout></para></listitem>
                <listitem><para><emphasis>Notify Quilt and Add Files:</emphasis>
                    After creating the patch, you need to notify Quilt about the files you will 
                    be changing.
                    Add the files you will be modifying into the patch you just created:
                    <literallayout class='monospaced'>
     $ quilt add file1.c file2.c file3.c
                    </literallayout></para></listitem>
                <listitem><para><emphasis>Edit the Files:</emphasis>
                    Make the changes to the temporary source code.</para></listitem>
                <listitem><para><emphasis>Test Your Changes:</emphasis>
                    Once you have modified the source code, the easiest way to test your changes 
                    is by calling the <filename>compile</filename> task as shown in the following example:
                    <literallayout class='monospaced'>
     $ bitbake -c compile -f &lt;name_of_package&gt;
                    </literallayout>
                    The <filename>-f</filename> or <filename>--force</filename>
                    option forces re-execution of the specified task.
                    If you find problems with your code, you can just keep editing and 
                    re-testing iteratively until things work as expected.
                    <note>All the modifications you make to the temporary source code
                    disappear once you <filename>-c clean</filename> or 
                    <filename>-c cleanall</filename> with BitBake for the package.
                    Modifications will also disappear if you use the <filename>rm_work</filename>
                    feature as described in the
                    "<ulink url='&YOCTO_DOCS_QS_URL;#building-image'>Building an Image</ulink>" 
                    section of the Yocto Project Quick Start.
                    </note></para></listitem>
                <listitem><para><emphasis>Generate the Patch:</emphasis>
                    Once your changes work as expected, you need to use Quilt to generate the final patch that 
                    contains all your modifications.
                    <literallayout class='monospaced'>
     $ quilt refresh
                    </literallayout>
                    At this point the <filename>my_changes.patch</filename> file has all your edits made 
                    to the <filename>file1.c</filename>, <filename>file2.c</filename>, and 
                    <filename>file3.c</filename> files.</para>
                    <para>You can find the resulting patch file in the <filename>patches/</filename> 
                    subdirectory of the source (<filename>S</filename>) directory.</para></listitem>
                <listitem><para><emphasis>Copy the Patch File:</emphasis> 
                    For simplicity, copy the patch file into a directory named <filename>files</filename>,
                    which you can create in the same directory as the recipe.
                    Placing the patch here guarantees that the OpenEmbedded build system will find
                    the patch.
                    Next, add the patch into the  
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'>SRC_URI</ulink></filename> 
                    of the recipe.  
                    Here is an example:
                    <literallayout class='monospaced'>
     SRC_URI += "file://my_changes.patch"
                    </literallayout></para></listitem>
                <listitem><para><emphasis>Increment the Package Revision Number:</emphasis>
                    Finally, don't forget to 'bump' the 
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PR'>PR</ulink></filename>
                    value in the same recipe since the resulting packages have changed.</para></listitem>
            </orderedlist>
        </para>     </section>

    <section id='using-a-git-workflow'>
        <title>Using a Git Workflow</title>
        <para>
            Git is an even more powerful tool that allows you to capture source code changes without having 
            a clean source tree.
            This section outlines the typical workflow you can use to modify temporary source code, 
            test changes, and then preserve the changes in the form of a patch all using Git.
            For general information on Git as it is used in the Yocto Project, see the 
            "<link linkend='git'>Git</link>" section.
        </para>

        <note>
            This workflow uses Git only for its ability to manage local changes to the source code 
            and produce patches independent of any version control system used with the Yocto Project.
        </note>

        <para>
            Follow these general steps:
            <orderedlist>
                <listitem><para><emphasis>Find the Source Code:</emphasis>
                    The temporary source code used by the OpenEmbedded build system is kept in the 
                    build directory.  
                    See the 
                    "<link linkend='finding-the-temporary-source-code'>Finding the Temporary Source Code</link>"
                    section to learn how to locate the directory that has the temporary source code for a 
                    particular package.</para></listitem>
                <listitem><para><emphasis>Change Your Working Directory:</emphasis>
                    You need to be in the directory that has the temporary source code.
                    That directory is defined by the 
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-S'>S</ulink>
                    variable.</para></listitem>
                <listitem><para><emphasis>Initialize a Git Repository:</emphasis>
                    Use the <filename>git init</filename> command to initialize a new local repository
                    that is based on the work directory:
                    <literallayout class='monospaced'>
     $ git init
                    </literallayout></para></listitem>
                <listitem><para><emphasis>Stage all the files:</emphasis>
                    Use the <filename>git add *</filename> command to stage all the files in the source
                    code directory so that they can be committed:
                    <literallayout class='monospaced'>
     $ git add *
                    </literallayout></para></listitem>
                <listitem><para><emphasis>Commit the Source Files:</emphasis>
                    Use the <filename>git commit</filename> command to initially commit all the files in 
                    the work directory:
                    <literallayout class='monospaced'>
     $ git commit
                    </literallayout>
                    At this point, your Git repository is aware of all the source code files.
                    Any edits you now make to files will be tracked by Git.</para></listitem>
                <listitem><para><emphasis>Edit the Files:</emphasis>
                    Make the changes to the temporary source code.</para></listitem>
                <listitem><para><emphasis>Test Your Changes:</emphasis>
                    Once you have modified the source code, the easiest way to test your changes 
                    is by calling the <filename>compile</filename> task as shown in the following example:
                    <literallayout class='monospaced'>
     $ bitbake -c compile -f &lt;name_of_package&gt;
                    </literallayout>
                    The <filename>-f</filename> or <filename>--force</filename>
                    option forces re-execution of the specified task.
                    If you find problems with your code, you can just keep editing and 
                    re-testing iteratively until things work as expected.
                    <note>All the modifications you make to the temporary source code
                    disappear once you <filename>-c clean</filename> or 
                    <filename>-c cleanall</filename> with BitBake for the package.
                    Modifications will also disappear if you use the <filename>rm_work</filename>
                    feature as described in the
                    "<ulink url='&YOCTO_DOCS_QS_URL;#building-image'>Building an Image</ulink>" 
                    section of the Yocto Project Quick Start.
                    </note></para></listitem>
                <listitem><para><emphasis>See the List of Files You Changed:</emphasis>
                    Use the <filename>git status</filename> command to see what files you have actually edited. 
                    The ability to have Git track the files you have changed is an advantage that this
                    workflow has over the Quilt workflow.
                    Here is the Git command to list your changed files:
                    <literallayout class='monospaced'>
     $ git status
                    </literallayout></para></listitem>
                <listitem><para><emphasis>Stage the Modified Files:</emphasis>
                    Use the <filename>git add</filename> command to stage the changed files so they
                    can be committed as follows:
                    <literallayout class='monospaced'>
     $ git add file1.c file2.c file3.c
                    </literallayout></para></listitem>
                <listitem><para><emphasis>Commit the Staged Files and View Your Changes:</emphasis>
                    Use the <filename>git commit</filename> command to commit the changes to the 
                    local repository.  
                    Once you have committed the files, you can use the <filename>git log</filename>
                    command to see your changes:
                    <literallayout class='monospaced'>
     $ git commit
     $ git log
                    </literallayout></para></listitem>
                <listitem><para><emphasis>Generate the Patch:</emphasis>
                    Once the changes are committed, use the <filename>git format-patch</filename>
                    command to generate a patch file:
                    <literallayout class='monospaced'>
     $ git format-patch HEAD~1
                    </literallayout>
                    The <filename>HEAD~1</filename> part of the command causes Git to generate the 
                    patch file for the most recent commit.</para>
                    <para>At this point, the patch file has all your edits made 
                    to the <filename>file1.c</filename>, <filename>file2.c</filename>, and 
                    <filename>file3.c</filename> files.
                    You can find the resulting patch file in the current directory.
                    The patch file ends with <filename>.patch</filename>.</para></listitem>
                <listitem><para><emphasis>Copy the Patch File:</emphasis> 
                    For simplicity, copy the patch file into a directory named <filename>files</filename>,
                    which you can create in the same directory as the recipe.
                    Placing the patch here guarantees that the OpenEmbedded build system will find
                    the patch.
                    Next, add the patch into the  
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'>SRC_URI</ulink></filename> 
                    of the recipe.  
                    Here is an example:
                    <literallayout class='monospaced'>
     SRC_URI += "file://my_changes.patch"
                    </literallayout></para></listitem>
                <listitem><para><emphasis>Increment the Package Revision Number:</emphasis>
                    Finally, don't forget to 'bump' the 
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PR'>PR</ulink></filename>
                    value in the same recipe since the resulting packages have changed.</para></listitem>
            </orderedlist>
        </para>
    </section>
</section>

<section id='image-development-using-hob'>
    <title>Image Development Using Hob</title>

    <para>
        The <ulink url='&YOCTO_HOME_URL;/projects/hob'>Hob</ulink> is a graphical user interface for the 
        OpenEmbedded build system, which is based on BitBake.
        You can use the Hob to build custom operating system images within the Yocto Project build environment.
        Hob simply provides a friendly interface over the build system used during system development.
        In other words, building images with the Hob lets you take care of common build tasks more easily.
    </para>

    <para>
        For a better understanding of Hob, see the project page at
        <ulink url='&YOCTO_HOME_URL;/projects/hob'></ulink> on the Yocto Project website.
        The page has a short introductory training video on Hob.
        The following lists some features of Hob:
        <itemizedlist>
            <listitem><para>You can setup and run Hob using these commands:
            <literallayout class='monospaced'>
     $ source oe-init-build-env
     $ hob
            </literallayout></para></listitem>
            <listitem><para>You can set the 
                <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
                for which you are building the image.</para></listitem>
            <listitem><para>You can modify various policy settings such as the package format used to build with, 
                the parrallelism BitBake uses, whether or not to build an external toolchain, and which host 
                to build against.</para></listitem>
            <listitem><para>You can manage 
                <link linkend='understanding-and-creating-layers'>layers</link>.</para></listitem>
            <listitem><para>You can select a base image and then add extra packages for your custom build.
                </para></listitem>
            <listitem><para>You can launch and monitor the build from within Hob.</para></listitem>
        </itemizedlist>
    </para>
</section>

<section id="platdev-appdev-devshell">
    <title>Using a Development Shell</title>

    <para>
        When debugging certain commands or even when just editing packages, 
        <filename>devshell</filename> can be a useful tool.
        When you invoke <filename>devshell</filename>, source files are 
        extracted into your working directory and patches are applied. 
        Then, a new terminal is opened and you are placed in the working directory.
        In the new terminal, all the OpenEmbedded build-related environment variables are 
        still defined so you can use commands such as <filename>configure</filename> and 
        <filename>make</filename>. 
        The commands execute just as if the OpenEmbedded build system were executing them. 
        Consequently, working this way can be helpful when debugging a build or preparing 
        software to be used with the OpenEmbedded build system.
    </para>

    <para>
        Following is an example that uses <filename>devshell</filename> on a target named
        <filename>matchbox-desktop</filename>:
        <literallayout class='monospaced'>
     $ bitbake matchbox-desktop -c devshell
        </literallayout>
    </para>

    <para>
        This command opens a terminal with a shell prompt within the OpenEmbedded build environment. 
        The default shell is xterm.
        The following occurs:
        <itemizedlist>
            <listitem><para>The <filename>PATH</filename> variable includes the 
                cross-toolchain.</para></listitem>
            <listitem><para>The <filename>pkgconfig</filename> variables find the correct 
                <filename>.pc</filename> files.</para></listitem>
                <listitem><para>The <filename>configure</filename> command finds the 
                Yocto Project site files as well as any other necessary files.</para></listitem>
        </itemizedlist>
        Within this environment, you can run <filename>configure</filename>
        or <filename>compile</filename> commands as if they were being run by 
        the OpenEmbedded build system itself.
        As noted earlier, the working directory also automatically changes to the 
        source directory (<ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink>).
    </para>

    <para> 
        When you are finished, you just exit the shell or close the terminal window.
    </para>

    <para>
        Because an external shell is launched rather than opening directly into the 
        original terminal window, it allows easier interaction with BitBake's multiple
        threads as well as accomodates a future client/server split.
    </para>

    <note>
        <para>
            It is worth remembering that when using <filename>devshell</filename>
            you need to use the full compiler name such as <filename>arm-poky-linux-gnueabi-gcc</filename> 
            instead of just using <filename>gcc</filename>.
            The same applies to other applications such as <filename>binutils</filename>, 
            <filename>libtool</filename> and so forth.
            BitBake sets up environment variables such as <filename>CC</filename>
            to assist applications, such as <filename>make</filename> to find the correct tools.
        </para>
        
        <para>
            It is also worth noting that <filename>devshell</filename> still works over
            X11 forwarding and similar situations
        </para>
    </note>
</section>

</chapter>
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