generic-poky/documentation/dev-manual/dev-manual-model.xml

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

<title>Common Development Models</title>

<para>
    [WRITERS NOTE: This chapter presents common development models within the Yocto Project.
    Reading this chapter will give the user a feel for the overall development process.  
    The chapter will follow the framework for the manual.  
    The team decided to present a single development model and not to try and represent all the 
    various possibilities that might exist.  
    The chapter will include an over-arching diagram that shows a simple, most-common development model.  
    The diagram will consist of boxes that represent high-level areas of the development process.  
    For example, a box for “Setting Up” will be in the model.  
    A box for “Debugging” will exist.  
    The diagram needs to account for the two use-cases we are going to showcase 
    (system development and application development)].
</para>

<para>
    Many development models exist for which you can use the Yocto Project. 
    However, for the purposes of this manual we are going to focus on two common ones:  
    System Development and User Application Development.  
    System Development covers Board Support Package (BSP) development and kernel modification.  
    User Application Development covers development of applications that you intend to run on some 
    target hardware.  
</para>

<para>
    This chapter presents an overview of the primary models.
    Supsequent appendices in the manual provide detailed explanations of the examples.
</para>

<para>
    [WRITERS NOTE:  What is undetermined at this point is how much of the entire development process 
    we include in this particular chapter.  
    In other words, do we cover debugging and emulation steps here on a case-specific basis?  
    Or, do we capture that information in the appropriate subsequent chapter by case?]
</para>

<section id='system-development-model'>
    <title>System Development</title>

    <para>
        System development involves modification or creation of an image that you want to run on 
        a specific hardware target.  
        Usually when you want to create an image that runs on embedded hardware the image does 
        not require the same amount of features that a full-fledged Linux distribution provides.  
        Thus, you can create a much smaller image that is designed to just use the hardware 
        features for your particular hardware.
    </para>

    <para>
        To help you understand how system development works in the Yocto Project, this section 
        covers two types of image development:  BSP creation and kernel modification.
    </para>

    <section id='developing-a-board-support-package-bsp-model'>
        <title>Developing a Board Support Package (BSP)</title>

        <para>
            A BSP is a package of recipes that when applied while building an image results in 
            an image you can run on a particular board.  
            Thus, the package, when compiled into the new image, supports the operation of the board.  
        </para>

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

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

        <para>
            Here are the basic steps involved in creating a BSP:
            <orderedlist>
                <listitem><para><emphasis>Set up your host development system to support 
                    development using the Yocto Project</emphasis>:  See  
                    <ulink url='http://www.yoctoproject.org/docs/1.1/yocto-project-qs/yocto-project-qs.html#the-linux-distro'>
                    The Linux Distributions</ulink> section and  
                    <ulink url='http://www.yoctoproject.org/docs/1.1/yocto-project-qs/yocto-project-qs.html#packages'>
                    The Packages</ulink> section both
                    in the Yocto Project Quick Start for requirements.
                    You will also need a release of Yocto Project installed on the host.</para></listitem>
                <listitem><para><emphasis>Establish a local copy of the Yocto Project files on your 
                    system</emphasis>:  You need to have the Yocto Project files available on your host system. 
                    Having the Yocto Project files on your system gives you access to the build
                    process and tools you need.
                    For information on how to get these files, see the
                    <xref linkend='getting-setup'>Getting Setup</xref> section in this manual.</para></listitem>
                <listitem><para><emphasis>Choose a Yocto Project-supported BSP 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, it gives you some structure with which to start.</para>
                    <para>At this point you need to understand your target hardware well enough to determine which 
                    existing BSP it most closely matches.  
                    Things to consider are your hardware’s on-board features such as CPU type and graphics support.  
                    You should look at the README files for supported BSPs to get an idea of which one 
                    you could use.  
                    A generic Atom-based BSP to consider is the Crown Bay that does not support
                    the Intel® Embedded Media Graphics Driver (EMGD).  
                    The remainder of this example uses that base BSP.</para>
                    <para>To see the supported BSPs, go to the Yocto Project
                    <ulink url='http://www.yoctoproject.org/download'>download page</ulink> and click 
                    on “BSP Downloads.”</para></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 tools you need.
                    For information on how to get these files, see 
                    <xref linkend='getting-setup'>Getting Setup</xref> earlier in this manual.</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.   
                    Consider an application as another example that illustrates a layer.  
                    Suppose you are creating an application that has library or other dependencies in 
                    order for it to compile and run.  
                    The layer, in this case, would be where all the recipes that define those dependencies 
                    are kept.  The key point for a layer is that it is an isolated area that contains 
                    all the relevant information for the project that the Yocto Project build 
                    system knows about.</para>
                    <note>The Yocto Project supports four BSPs that are part of the 
                   Yocto Project release: <filename>atom-pc</filename>, <filename>beagleboard</filename>,
                   <filename>mpc8315e</filename>, and <filename>routerstationpro</filename>.  
                    The recipes and configurations for these four BSPs are located and dispersed 
                    within local Yocto Project files.
                    Consequently, they are not totally isolated in the spirit of layers unless you think 
                    of <filename>meta-yocto</filename> as a layer itself.  
                    On the other hand, BSP layers for Crown Bay, Emenlow, Jasper Forest, 
                    N450, and Sugar Bay are isolated.</note>
                    <para>When you set up a layer for a new BSP you should follow a standard layout.  
                    This layout is described in the
                   <ulink url='http://www.yoctoproject.org/docs/1.1/bsp-guide/bsp-guide.html#bsp-filelayout'>
                    Example Filesystem Layout</ulink> section of the Board Support Package (BSP) Development
                    Guide.  
                    In the standard layout you will notice a suggested structure for recipes and  
                    configuration information.  
                    You can see the standard layout for the Crown Bay BSP in this example by examining the 
                    directory structure of the <filename>meta-crownbay</filename> layer inside the 
                    local Yocto Project files.</para></listitem>
                <listitem><para><emphasis>Make configuration and recipe 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> within the 
                   BSP layer.</para>
                    <para>Configuration changes identify where your new layer is on the local system
                    and identify which kernel you are going to use.
                    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 Yocto Project build system in order for it to create your image.  
                    You need to get the build environment ready by sourcing an environment setup script 
                    and you need to be sure two key configuration files are configured appropriately.</para>
                    <para>The entire process for building an image is overviewed in the 
                    <ulink url='http://www.yoctoproject.org/docs/1.1/yocto-project-qs/yocto-project-qs.html#building-image'>
                    Building an Image</ulink> section of the Yocto Project Quick Start.    
                    You might want to reference this information.</para></listitem>
                <listitem><para><emphasis>Build the image</emphasis>:  The Yocto Project uses the BitBake 
                    tool to build images based on the type of image 
                    you want to create.  
                    You can find more information on BitBake 
                    <ulink url='http://bitbake.berlios.de/manual/'>here</ulink>.</para>
                    <para>The build process supports several types of images to satisfy different needs.  
                    When you issue the BitBake command you provide a “top-level” recipe that essentially 
                    starts the process off of building the type of image you want.</para>
                    <para>[WRITER'S NOTE: Consider moving this to the Poky Reference Manual.]</para>
                    <para>You can find these recipes in the <filename>meta/recipes-core/images</filename> and 
                    <filename>meta/recipes-sato/images</filename> directories of your local Yocto Project 
                    file structure (Git repository or extracted release tarball).  
                    Although the recipe names are somewhat explanatory, here is a list that describes them:
                    <itemizedlist>
                        <listitem><para><emphasis>Base</emphasis> – A foundational basic image without support 
                            for X that can be reasonably used for customization.</para></listitem>
                        <listitem><para><emphasis>Core</emphasis> – A foundational basic image with support for 
                            X that can be reasonably used for customization.</para></listitem>
                        <listitem><para><emphasis>Direct Disk</emphasis> – An image that you can copy directory to 
                            the disk of the target device.</para></listitem>
                        <listitem><para><emphasis>Live</emphasis> – An image you can run from a USB device or from 
                            a CD without having to first install something.</para></listitem>
                        <listitem><para><emphasis>Minimal</emphasis> – A small image without a GUI.  
                            This image is not much more than a kernel with a shell.</para></listitem>
                        <listitem><para><emphasis>Minimal Development</emphasis> – A Minimal image suitable for 
                            development work.</para></listitem>
                        <listitem><para><emphasis>Minimal Direct Disk</emphasis> – A Minimal Direct 
                            Disk image.</para></listitem>
                        <listitem><para><emphasis>Minimal RAM-based Initial Root Filesystem</emphasis> – 
                            A minimal image 
                           that has the <filename>initramfs</filename> as part of the kernel, which allows the 
                            system to find the first “init” program more efficiently.</para></listitem>
                        <listitem><para><emphasis>Minimal Live</emphasis> – A Minimal Live image.</para></listitem>
                       <listitem><para><emphasis>Minimal MTD Utilities</emphasis> – A minimal image that has support 
                            for the MTD utilities, which let the user interact with the MTD subsystem in 
                            the kernel to perform operations on flash devices.</para></listitem>
                        <listitem><para><emphasis>Sato</emphasis> – An image with Sato support, a mobile environment 
                            and visual style that works well with mobile devices.</para></listitem>
                        <listitem><para><emphasis>Sato Development</emphasis> – A Sato image suitable for 
                            development work.</para></listitem>
                        <listitem><para><emphasis>Sato Direct Disk</emphasis> – A Sato Direct 
                            Disk image.</para></listitem>
                        <listitem><para><emphasis>Sato Live</emphasis> – A Sato Live image.</para></listitem>
                        <listitem><para><emphasis>Sato SDK</emphasis> – A Sato image that includes the Yocto Project 
                            toolchain and development libraries.</para></listitem>
                        <listitem><para><emphasis>Sato SDK Direct Disk</emphasis> – A Sato SDK Direct 
                            Disk image.</para></listitem>
                        <listitem><para><emphasis>Sato SDK Live</emphasis> – A Sato SDK Live 
                           image.</para></listitem>
                    </itemizedlist>
                </para></listitem>
            </orderedlist>
        </para>

        <para>
            You can view a video presentation of the BSP creation process 
            <ulink url='http://free-electrons.com/blog/elc-2011-videos'>here</ulink>.  
            You can also find supplemental information in the 
            <ulink url='http://yoctoproject.org/docs/1.1/bsp-guide/bsp-guide.html'>
            Board Support Package (BSP) Development Guide</ulink>.
            Finally, there is wiki page write up of the example located 
            <ulink url='https://wiki.yoctoproject.org/wiki/Transcript:_creating_one_generic_Atom_BSP_from_another'>
            here</ulink> you might find helpful.
       </para>
    </section>

    <section id='place-holder-section-kernel-development-model'>
        <title>Place-Holder Section For Kernel Development Model</title>

        <para>
            Text needed here.
        </para>
    </section>
</section>

<section id='place-holder-section-two'>
    <title>Place-Holder Section For Application Development</title>

    <para>
        Text needed here.
    </para>
</section>

</chapter>
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