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

<title>Getting Started with the Yocto Project</title>

<para>
    This chapter introduces the Yocto Project and gives you an idea of what you need to get started.  
    You can find enough information to set up your development host and build or use images for 
    hardware supported by the Yocto Project by reading  
    <ulink url='&YOCTO_DOCS_QS_URL;'>
    The Yocto Project Quick Start</ulink>.
</para>

<para>
    The remainder of this chapter summarizes what is in the Yocto Project Quick Start and provides 
    some higher-level concepts you might want to consider.
</para>

<section id='introducing-the-yocto-project'>
    <title>Introducing the Yocto Project</title>

    <para>
        The Yocto Project is an open-source collaboration project focused on embedded Linux development.  
        The project currently provides a build system, which is 
        referred to as the OpenEmbedded build system in the Yocto Project documentation.
        The Yocto Project provides various ancillary tools suitable for the embedded developer  
        and also features the Sato reference User Interface, which is optimized for 
        stylus driven, low-resolution screens.
    </para>

    <para>
        You can use the OpenEmbedded build system, which uses 
        <ulink url='&BITBAKE_DOCS_URL;'>BitBake</ulink>, to develop complete Linux 
        images and associated user-space applications for architectures based on ARM, MIPS, PowerPC, 
        x86 and x86-64.  
        While the Yocto Project does not provide a strict testing framework,
        it does provide or generate for you artifacts that let you perform target-level and 
        emulated testing and debugging.  
        Additionally, if you are an <trademark class='trade'>Eclipse</trademark>
        IDE user, you can install an Eclipse Yocto Plug-in to allow you to 
        develop within that familiar environment.
    </para>
</section>

<section id='getting-setup'>
    <title>Getting Set Up</title>

    <para>
        Here is what you need to get set up to use the Yocto Project:
        <itemizedlist>
            <listitem><para><emphasis>Host System:</emphasis>  You should have a reasonably current 
                Linux-based host system.
                You will have the best results with a recent release of Fedora, 
                OpenSUSE, Ubuntu, or CentOS as these releases are frequently tested against the Yocto Project
                and officially supported.  
                You should also have about 100 gigabytes of free disk space for building images.
                </para></listitem>
            <listitem><para><emphasis>Packages:</emphasis>  The OpenEmbedded build system
                requires certain packages exist on your development system (e.g. Python 2.6 or 2.7).  
                See "<ulink url='&YOCTO_DOCS_QS_URL;#packages'>The Packages</ulink>" 
                section in the Yocto Project Quick Start for the exact package
                requirements and the installation commands to install them 
                for the supported distributions.</para></listitem>
            <listitem id='local-yp-release'><para><emphasis>Yocto Project Release:</emphasis>  
                You need a release of the Yocto Project.  
                You set up a with local <link linkend='source-directory'>source directory</link>
                one of two ways depending on whether you 
                are going to contribute back into the Yocto Project or not.
                <note>
                    Regardless of the method you use, this manual refers to the resulting local
                    hierarchical set of files as the "source directory."
                </note>
                <itemizedlist>
                    <listitem><para><emphasis>Tarball Extraction:</emphasis>  If you are not going to contribute 
                        back into the Yocto Project, you can simply download a Yocto Project release you want 
                        from the website’s <ulink url='&YOCTO_HOME_URL;/download'>download page</ulink>.
                        Once you have the tarball, just extract it into a directory of your choice.</para>
                        <para>For example, the following command extracts the Yocto Project &DISTRO; 
                        release tarball 
                        into the current working directory and sets up the local source directory
                        with a top-level folder named <filename>&YOCTO_POKY;</filename>:
                        <literallayout class='monospaced'>
     $ tar xfj &YOCTO_POKY_TARBALL;
                        </literallayout></para>
                        <para>This method does not produce a local Git repository. 
                        Instead, you simply end up with a snapshot of the release.</para></listitem>
                    <listitem><para><emphasis>Git Repository Method:</emphasis>  If you are going to be contributing
                        back into the Yocto Project or you simply want to keep up
                        with the latest developments, you should use Git commands to set up a local
                        Git repository of the upstream <filename>poky</filename> source repository.
                        Doing so creates a repository with a complete history of changes and allows 
                        you to easily submit your changes upstream to the project.
                        Because you cloned the repository, you have access to all the Yocto Project development
                        branches and tag names used in the upstream repository.</para>
                        <para>The following transcript shows how to clone the <filename>poky</filename>  
                        Git repository into the current working directory.
                        <note>You can view the Yocto Project Source Repositories at
                        <ulink url='&YOCTO_GIT_URL;/cgit.cgi'></ulink></note>  
                        The command creates the local repository in a directory named <filename>poky</filename>.
                        For information on Git used within the Yocto Project, see the
                        "<link linkend='git'>Git</link>" section.
                        <literallayout class='monospaced'>
     $ git clone git://git.yoctoproject.org/poky
     Initialized empty Git repository in /home/scottrif/poky/.git/
     remote: Counting objects: 141863, done.
     remote: Compressing objects: 100% (38624/38624), done.
     remote: Total 141863 (delta 99661), reused 141816 (delta 99614)
     Receiving objects: 100% (141863/141863), 76.64 MiB | 126 KiB/s, done.
     Resolving deltas: 100% (99661/99661), done.
                        </literallayout></para>
                        <para>For another example of how to set up your own local Git repositories, see this
                        <ulink url='&YOCTO_WIKI_URL;/wiki/Transcript:_from_git_checkout_to_meta-intel_BSP'>
                        wiki page</ulink>, which describes how to create both <filename>poky</filename>
                        and <filename>meta-intel</filename> Git repositories.</para></listitem>
                </itemizedlist></para></listitem>
            <listitem id='local-kernel-files'><para><emphasis>Yocto Project Kernel:</emphasis>  
                If you are going to be making modifications to a supported Yocto Project kernel, you 
                need to establish local copies of the source.
                You can find Git repositories of supported Yocto Project Kernels organized under
                "Yocto Project Linux Kernel" in the Yocto Project Source Repositories at
                <ulink url='&YOCTO_GIT_URL;/cgit.cgi'></ulink>.</para>
                <para>This setup involves creating a bare clone of the Yocto Project kernel and then 
                copying that cloned repository.
                You can create the bare clone and the copy of the bare clone anywhere you like.
                For simplicity, it is recommended that you create these structures outside of the 
                source directory (usually <filename>poky</filename>).</para>
                <para>As an example, the following transcript shows how to create the bare clone
                of the <filename>linux-yocto-3.2</filename> kernel and then create a copy of 
                that clone.
                <note>When you have a local Yocto Project kernel Git repository, you can 
                reference that repository rather than the upstream Git repository as 
                part of the <filename>clone</filename> command.
                Doing so can speed up the process.</note></para>
                <para>In the following example, the bare clone is named 
                <filename>linux-yocto-3.2.git</filename>, while the 
                copy is named <filename>my-linux-yocto-3.2-work</filename>: 
                <literallayout class='monospaced'>
     $ git clone --bare git://git.yoctoproject.org/linux-yocto-3.2 linux-yocto-3.2.git
     Initialized empty Git repository in /home/scottrif/linux-yocto-3.2.git/
     remote: Counting objects: 2468027, done.
     remote: Compressing objects: 100% (392255/392255), done.
     remote: Total 2468027 (delta 2071693), reused 2448773 (delta 2052498)
     Receiving objects: 100% (2468027/2468027), 530.46 MiB | 129 KiB/s, done.
     Resolving deltas: 100% (2071693/2071693), done.
                </literallayout></para>
                <para>Now create a clone of the bare clone just created:
                <literallayout class='monospaced'>
     $ git clone linux-yocto-3.2.git my-linux-yocto-3.2-work
     Initialized empty Git repository in /home/scottrif/my-linux-yocto-3.2-work/.git/
     Checking out files: 100% (37619/37619), done.
                </literallayout></para></listitem>
            <listitem id='poky-extras-repo'><para><emphasis>
                The <filename>poky-extras</filename> Git Repository</emphasis>:
                The <filename>poky-extras</filename> Git repository contains metadata needed 
                only if you are modifying and building the kernel image.
                In particular, it contains the kernel BitBake append (<filename>.bbappend</filename>)
                files that you 
                edit to point to your locally modified kernel source files and to build the kernel
                image. 
                Pointing to these local files is much more efficient than requiring a download of the 
                kernel's source files from upstream each time you make changes to the kernel.</para>
                <para>You can find the <filename>poky-extras</filename> Git Repository in the 
                "Yocto Metadata Layers" area of the Yocto Project Source Repositories at 
                <ulink url='&YOCTO_GIT_URL;/cgit.cgi'></ulink>.
                It is good practice to create this Git repository inside the source directory.</para>
                <para>Following is an example that creates the <filename>poky-extras</filename> Git 
                repository inside the source directory, which is named <filename>poky</filename> 
                in this case:
                <literallayout class='monospaced'>
     $ git clone git://git.yoctoproject.org/poky-extras poky-extras
     Initialized empty Git repository in /home/scottrif/poky/poky-extras/.git/
     remote: Counting objects: 618, done.
     remote: Compressing objects: 100% (558/558), done.
     remote: Total 618 (delta 192), reused 307 (delta 39)
     Receiving objects: 100% (618/618), 526.26 KiB | 111 KiB/s, done.
     Resolving deltas: 100% (192/192), done.
                </literallayout></para></listitem>
           <listitem><para id='supported-board-support-packages-(bsps)'><emphasis>Supported Board 
                Support Packages (BSPs):</emphasis>  
                The Yocto Project provides a layer called <filename>meta-intel</filename> and 
                it is maintained in its own separate Git repository.
                The <filename>meta-intel</filename> layer contains many supported 
                <ulink url='&YOCTO_DOCS_BSP_URL;#bsp-layers'>BSP Layers</ulink>.</para>
                <para>Similar considerations exist for setting up the <filename>meta-intel</filename>
                layer.  
                You can get set up for BSP development one of two ways: tarball extraction or
                with a local Git repository.
                It is a good idea to use the same method that you used to set up the source directory.
                Regardless of the method you use, the Yocto Project uses the following BSP layer 
                naming scheme:
                <literallayout class='monospaced'> 
     meta-&lt;BSP_name&gt; 
                </literallayout>
                where &lt;BSP_name&gt; is the recognized BSP name.
                Here are some examples:
                <literallayout class='monospaced'>
     meta-crownbay
     meta-emenlow
     meta-n450
                </literallayout>
                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 for more
                information on BSP Layers.
                <itemizedlist>
                    <listitem><para><emphasis>Tarball Extraction:</emphasis>  You can download any released 
                        BSP tarball from the same 
                        <ulink url='&YOCTO_HOME_URL;/download'>download site</ulink> used 
                        to get the Yocto Project release.  
                        Once you have the tarball, just extract it into a directory of your choice.
                        Again, this method just produces a snapshot of the BSP layer in the form
                        of a hierarchical directory structure.</para></listitem>
                    <listitem><para><emphasis>Git Repository Method:</emphasis>  If you are working 
                        with a local Git repository for your source directory, you should also use this method 
                        to set up the <filename>meta-intel</filename> Git repository.
                        You can locate the <filename>meta-intel</filename> Git repository in the 
                        "Yocto Metadata Layers" area of the Yocto Project Source Repositories at
                        <ulink url='&YOCTO_GIT_URL;/cgit.cgi'></ulink>.</para>
                        <para>Typically, you set up the <filename>meta-intel</filename> Git repository inside
                        the source directory.
                        For example, the following transcript shows the steps to clone the 
                        <filename>meta-intel</filename>
                        Git repository inside the local <filename>poky</filename> Git repository.
                        <literallayout class='monospaced'>
     $ git clone git://git.yoctoproject.org/meta-intel.git
     Initialized empty Git repository in /home/scottrif/poky/meta-intel/.git/
     remote: Counting objects: 3380, done.
     remote: Compressing objects: 100% (2750/2750), done.
     remote: Total 3380 (delta 1689), reused 227 (delta 113)
     Receiving objects: 100% (3380/3380), 1.77 MiB | 128 KiB/s, done.
     Resolving deltas: 100% (1689/1689), done.
                        </literallayout></para>
                        <para>The same  
                        <ulink url='&YOCTO_WIKI_URL;/wiki/Transcript:_from_git_checkout_to_meta-intel_BSP'>
                        wiki page</ulink> referenced earlier covers how to 
                        set up the <filename>meta-intel</filename> Git repository.</para></listitem>
                </itemizedlist></para></listitem>
            <listitem><para><emphasis>Eclipse Yocto Plug-in:</emphasis>  If you are developing 
                applications using the Eclipse Integrated Development Environment (IDE),
                you will need this plug-in.  
                See the 
                "<link linkend='setting-up-the-eclipse-ide'>Setting up the Eclipse IDE</link>"
                section for more information.</para></listitem>
        </itemizedlist>
    </para>
</section>

<section id='building-images'>
    <title>Building Images</title>

    <para>
        The build process creates an entire Linux distribution, including the toolchain, from source.  
        For more information on this topic, see the 
        "<ulink url='&YOCTO_DOCS_QS_URL;#building-image'>Building an Image</ulink>"
        section in the Yocto Project Quick Start.
    </para>

    <para>
        The build process is as follows:
        <orderedlist>
            <listitem><para>Make sure you have set up the source directory described in the 
                previous section.</para></listitem>
            <listitem><para>Initialize the build environment by sourcing a build environment 
                script.</para></listitem>
            <listitem><para>Optionally ensure the <filename>conf/local.conf</filename> configuration file,
                which is found in the 
                <link linkend='build-directory'>build directory</link>, 
                is set up how you want it.  
                This file defines many aspects of the build environment including 
                the target machine architecture through the 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'>MACHINE</ulink></filename> variable, 
                the development machine's processor use through the 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BB_NUMBER_THREADS'>BB_NUMBER_THREADS</ulink></filename> and 
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PARALLEL_MAKE'>PARALLEL_MAKE</ulink></filename> variables, and
                a centralized tarball download directory through the  
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-DL_DIR'>DL_DIR</ulink></filename> variable.</para></listitem>
            <listitem><para>Build the image using the <filename>bitbake</filename> command.
                If you want information on BitBake, see the user manual at
                <ulink url='&OE_DOCS_URL;/bitbake/html'></ulink>.</para></listitem>
            <listitem><para>Run the image either on the actual hardware or using the QEMU 
                emulator.</para></listitem>
        </orderedlist>
    </para>
</section>

<section id='using-pre-built-binaries-and-qemu'>
    <title>Using Pre-Built Binaries and QEMU</title>

    <para>
        Another option you have to get started is to use pre-built binaries. 
        The Yocto Project provides many types of binaries with each release. 
        See the <ulink url='&YOCTO_DOCS_REF_URL;#ref-images'>Images</ulink>
        chapter in the Yocto Project Reference Manual
        for descriptions of the types of binaries that ship with a Yocto Project
        release.
    </para>

    <para>
        Using a pre-built binary is ideal for developing software applications to run on your 
        target hardware.  
        To do this, you need to be able to access the appropriate cross-toolchain tarball for 
        the architecture on which you are developing.  
        If you are using an SDK type image, the image ships with the complete toolchain native to 
        the architecture. 
        If you are not using an SDK type image, you need to separately download and 
        install the stand-alone Yocto Project cross-toolchain tarball.
    </para>

    <para>
        Regardless of the type of image you are using, you need to download the pre-built kernel 
        that you will boot in the QEMU emulator and then download and extract the target root 
        filesystem for your target machine’s architecture.
        You can get architecture-specific binaries and filesystem from
        <ulink url='&YOCTO_MACHINES_DL_URL;'>machines</ulink>.
        You can get stand-alone toolchains from
        <ulink url='&YOCTO_TOOLCHAIN_DL_URL;'>toolchains</ulink>.
        Once you have all your files, you set up the environment to emulate the hardware 
        by sourcing an environment setup script. 
        Finally, you start the QEMU emulator.
        You can find details on all these steps in the 
        "<ulink url='&YOCTO_DOCS_QS_URL;#using-pre-built'>Using Pre-Built Binaries and QEMU</ulink>"
        section of the Yocto Project Quick Start. 
    </para>

    <para> 
        Using QEMU to emulate your hardware can result in speed issues
        depending on the target and host architecture mix.
        For example, using the <filename>qemux86</filename> image in the emulator 
        on an Intel-based 32-bit (x86) host machine is fast because the target and 
        host architectures match.
        On the other hand, using the <filename>qemuarm</filename> image on the same Intel-based
        host can be slower.
        But, you still achieve faithful emulation of ARM-specific issues. 
    </para>

    <para>
        To speed things up, the QEMU images support using <filename>distcc</filename>
        to call a cross-compiler outside the emulated system. 
        If you used <filename>runqemu</filename> to start QEMU, and the
        <filename>distccd</filename> application is present on the host system, any 
        BitBake cross-compiling toolchain available from the build system is automatically
        used from within QEMU simply by calling <filename>distcc</filename>.
        You can accomplish this by defining the cross-compiler variable 
        (e.g. <filename>export CC="distcc"</filename>).
        Alternatively, if you are using a suitable SDK image or the appropriate
        stand-alone toolchain is present in <filename>/opt/poky</filename>,
        the toolchain is also automatically used.
    </para>

    <note>
        Several mechanisms exist that let you connect to the system running on the 
        QEMU emulator:
        <itemizedlist>
            <listitem><para>QEMU provides a framebuffer interface that makes standard 
                consoles available.</para></listitem>
            <listitem><para>Generally, headless embedded devices have a serial port.
                If so, you can configure the operating system of the running image
                to use that port to run a console. 
                The connection uses standard IP networking.</para></listitem>
            <listitem><para>SSH servers exist in some QEMU images.
                The <filename>core-image-sato</filename> QEMU image has a Dropbear secure 
                shell (ssh) server that runs with the root password disabled.
                The <filename>core-image-basic</filename> and <filename>core-image-lsb</filename> QEMU images 
                have OpenSSH instead of Dropbear.
                Including these SSH servers allow you to use standard <filename>ssh</filename> and 
                <filename>scp</filename> commands.
                The <filename>core-image-minimal</filename> QEMU image, however, contains no ssh 
                server.</para></listitem>
            <listitem><para>You can use a provided, user-space NFS server to boot the QEMU session 
                using a local copy of the root filesystem on the host.
                In order to make this connection, you must extract a root filesystem tarball by using the 
                <filename>runqemu-extract-sdk</filename> command.
                After running the command, you must then point the <filename>runqemu</filename>
                script to the extracted directory instead of a root filesystem image file.</para></listitem>
        </itemizedlist>
    </note>
</section>
</chapter>
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