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<chapter id='overview-yp'>
    <title>Introducing the Yocto Project</title>

    <section id='what-is-the-yocto-project'>
        <title>What is the Yocto Project?</title>

        <para>
            The Yocto Project is an open source collaboration project
            that helps developers create custom Linux-based systems that are
            designed for embedded products regardless of the product's hardware
            architecture.
            Yocto Project provides a flexible toolset and a development
            environment that allows embedded device developers across the
            world to collaborate through shared technologies, software stacks,
            configurations, and best practices used to create these tailored
            Linux images.
        </para>

        <para>
            Thousands of developers worldwide have discovered that Yocto
            Project provides advantages in both systems and applications
            development, archival and management benefits, and customizations
            used for speed, footprint, and memory utilization.
            The project is a standard when it comes to delivering hardware
            support and software stacks, allowing software configuration
            and build interchange, and build and support customizations for
            multiple hardware platforms and software stacks that can be
            maintained and scaled.
        </para>

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        <para>
            For further introductory information on the Yocto Project, you
            might be interested in this
            <ulink url='https://www.embedded.com/electronics-blogs/say-what-/4458600/Why-the-Yocto-Project-for-my-IoT-Project-'>article</ulink>
            by Drew Moseley and in this short introductory
            <ulink url='https://www.youtube.com/watch?v=utZpKM7i5Z4'>video</ulink>.
        </para>

        <para>
            The remainder of this section overviews advantages and challenges
            tied to the Yocto Project.
        </para>

        <section id='gs-features'>
            <title>Features</title>

            <para>
                The following list describes features and advantages of the
                Yocto Project:
                <itemizedlist>
                    <listitem><para>
                        <emphasis>Widely Adopted Across the Industry:</emphasis>
                        Semiconductor, operating system, software, and
                        service vendors exist whose products and services
                        adopt and support the Yocto Project.
                        For a look at the companies involved with the Yocto
                        Project, see the membership, associate, and
                        participant pages on the Yocto Project home page.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Architecture Agnostic:</emphasis>
                        Yocto Project supports Intel, ARM, MIPS, AMD, PPC
                        and other architectures.
                        Most ODMs, OSVs, and chip vendors create and supply
                        BSPs that support their hardware.
                        If you have custom silicon, you can create a BSP
                        that supports that architecture.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Images and Code Transfer Easily:</emphasis>
                        Yocto Project output can easily move between
                        architectures without moving to new development
                        environments.
                        Additionally, if you have used the Yocto Project to
                        create an image or application and you find yourself
                        not able to support it, commercial Linux vendors such
                        as Wind River, Mentor Graphics, Timesys, and ENEA could
                        take it and provide ongoing support.
                        These vendors have offerings that are built using
                        the Yocto Project.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Flexibility:</emphasis>
                        Corporations use the Yocto Project many different ways.
                        One example is to create an internal Linux distribution
                        as a code base the corporation can use across multiple
                        product groups.
                        Through customization and layering, a project group
                        can leverage the base Linux distribution to create
                        a distribution that works for their product needs.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Ideal for Constrained Embedded and IoT devices:</emphasis>
                        Unlike a full Linux distribution, you can use the
                        Yocto Project to create exactly what you need for
                        embedded devices.
                        You only add the feature support or packages that you
                        absolutely need for the device.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Comprehensive Toolchain Capabilities:</emphasis>
                        Toolchains for supported architectures satisfy most
                        use cases.
                        However, if your hardware supports features that are
                        not part of a standard toolchain, you can easily
                        customize that toolchain through specification of
                        platform-specific tuning parameters.
                        And, should you need to use a third-party toolchain,
                        mechanisms built into the Yocto Project allow for that.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Mechanism Rules Over Policy:</emphasis>
                        Focusing on mechanism rather than policy ensures that
                        you are free to set policies based on the needs of your
                        design instead of adopting decisions enforced by some
                        system software provider.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Uses a Layer Model:</emphasis>
                        The Yocto Project layer infrastructure groups related
                        functionality into separate bundles.
                        You can incrementally add these grouped functionalities
                        to your project as needed.
                        Using layers to isolate and group functionality
                        reduces project complexity and redundancy.
                        </para></listitem>
                     <listitem><para>
                        <emphasis>Supports Partial Builds:</emphasis>
                        You can build and rebuild individual packages as
                        needed.
                        Yocto Project accomplishes this through its
                        shared-state cache (sstate) scheme.
                        Being able to build and debug components individually
                        eases project development.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Releases According to a Strict Schedule:</emphasis>
                        Major releases occur on a six-month cycle predictably
                        in October and April.
                        The most recent two releases support point releases
                        to address common vulnerabilities and exposures.
                        This predictability is crucial for projects based on
                        the Yocto Project and allows development teams to
                        plan activities.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Rich Ecosystem of Individuals and Organizations:</emphasis>
                        For open source projects, the value of community is
                        very important.
                        Support forums, expertise, and active developers who
                        continue to push the Yocto Project forward are readily
                        available.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Binary Reproducibility:</emphasis>
                        The Yocto Project you to be very specific about
                        dependencies and achieves very high percentages of
                        binary reproducibility (e.g. 99.8% for
                        <filename>core-image-minimal</filename>).
                        When distributions are not specific about which
                        packages are pulled in and in what order to support
                        dependencies, other build systems can arbitrarily
                        include packages.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>License Manifest:</emphasis>
                        The Yocto Project provides a license manifest for
                        review by people that need to track the use of open
                        source licenses (e.g.legal teams).
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='gs-challenges'>
            <title>Challenges</title>

            <para>
                The following list presents challenges you might encounter
                when developing using the Yocto Project:
                <itemizedlist>
                    <listitem><para>
                        <emphasis>Steep Learning Curve:</emphasis>
                        The Yocto Project has a steep learning curve and has
                        many different ways to accomplish similar tasks.
                        It can be difficult to choose how to proceed when
                        varying methods exist by which to accomplish a given
                        task.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Understanding What Changes You Need to Make
                        For Your Design Requires Some Research:</emphasis>
                        Beyond the simple tutorial stage, understanding what
                        changes need to be made for your particular design
                        can require a significant amount of research and
                        investigation.
                        For information that helps you transition from
                        trying out the Yocto Project to using it for your
                        project, see the "What I wish I'd Known" and
                        "Transitioning to a Custom Environment for Systems
                        Development" documents on the Yocto Project website.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Project Workflow Could Be Confusing:</emphasis>
                        The Yocto Project workflow could be confusing if you
                        used to traditional desktop and server software
                        development.
                        In a desktop development environment, mechanisms exist
                        to easily pull and install new packages, which are
                        typically pre-compiled binaries from servers accessible
                        over the Internet.
                        Using the Yocto Project, you must modify your
                        configuration and rebuild to add additional packages.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Working in a Cross-Build Environment Can
                        Feel Unfamiliar:</emphasis>
                        When developing code to run on a target, compilation,
                        execution, and testing done on the actual target
                        can be faster than running a BitBake build on a
                        development host and then deploying binaries to the
                        target for test.
                        While the Yocto Project does support development tools
                        on the target, the additional step of integrating your
                        changes back into the Yocto Project build environment
                        would be required.
                        Yocto Project supports an intermediate approach that
                        involves making changes on the development system
                        within the BitBake environment and then deploying only
                        the updated packages to the target.</para>

                        <para>The Yocto Project OpenEmbedded build system
                        produces packages in standard formats (i.e. RPM,
                        DEB, IPK, and TAR).
                        You can deploy these packages into the running system
                        on the target by using utilities on the target such
                        as <filename>rpm</filename> or
                        <filename>ipk</filename>.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Initial Build Times Can be Significant:</emphasis>
                        Long initial build times are unfortunately unavoidable
                        due to the large number of packages initially built
                        from scratch for a fully functioning Linux system.
                        Once that initial build is completed, however, the
                        shared-state (sstate) cache mechanism Yocto Project
                        uses keeps the system from rebuilding packages that
                        have not been "touched" since the last build.
                        The sstate mechanism significantly reduces times
                        for successive builds.
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>
    </section>

    <section id='the-yocto-project-layer-model'>
        <title>The Yocto Project Layer Model</title>

        <para>
            The Yocto Project's "Layer Model" is a development model for
            embedded and IoT Linux creation that distinguishes the
            Yocto Project from other simple build systems.
            The Layer Model simultaneously supports collaboration and
            customization.
            Layers are repositories that contain related sets of instructions
            that tell the OpenEmbedded build system what to do.
            You can collaborate, share, and reuse layers.
        </para>

        <para>
            Layers can contain changes to previous instructions or settings
            at any time.
            This powerful override capability is what allows you to customize
            previously supplied collaborative or community layers to suit your
            product requirements.
        </para>

        <para>
            You use different layers to logically separate information in your
            build.
            As an example, you could have BSP, GUI, distro configuration,
            middleware, or application layers.
            Putting your entire build into one layer limits and complicates
            future customization and reuse.
            Isolating information into layers, on the other hand, helps
            simplify future customizations and reuse.
            You might find it tempting to keep everything in one layer when
            working on a single project.
            However, the more modular your Metadata, the easier
            it is to cope with future changes.
            <note><title>Notes</title>
                <itemizedlist>
                    <listitem><para>
                        Use Board Support Package (BSP) layers from silicon
                        vendors when possible.
                        </para></listitem>
                    <listitem><para>
                        Familiarize yourself with the
                        <ulink url='https://caffelli-staging.yoctoproject.org/software-overview/layers/'>Yocto Project curated layer index</ulink>
                        or the
                        <ulink url='http://layers.openembedded.org/layerindex/branch/master/layers/'>OpenEmbedded layer index</ulink>.
                        The latter contains more layers but they are less
                        universally validated.
                        </para></listitem>
                    <listitem><para>
                        Layers support the inclusion of technologies, hardware
                        components, and software components.
                        The Yocto Project Compatible designation provides a
                        minimum level of standardization that contributes to a
                        strong ecosystem.
                        "YP Compatible" is applied to appropriate products and
                        software components such as BSPs, other OE-compatible
                        layers, and related open-source projects, allowing the
                        producer to use Yocto Project badges and branding
                        assets.
                        </para></listitem>
                </itemizedlist>
            </note>
        </para>

        <para>
            To illustrate how layers are used to keep things modular, consider
            machine customizations.
            These types of customizations typically reside in a special layer,
            rather than a general layer, called a BSP Layer.
            Furthermore, the machine customizations should be isolated from
            recipes and Metadata that support a new GUI environment,
            for example.
            This situation gives you a couple of layers: one for the machine
            configurations, and one for the GUI environment.
            It is important to understand, however, that the BSP layer can
            still make machine-specific additions to recipes within the GUI
            environment layer without polluting the GUI layer itself
            with those machine-specific changes.
            You can accomplish this through a recipe that is a BitBake append
            (<filename>.bbappend</filename>) file, which is described later
            in this section.
            <note>
                For general information on BSP layer structure, see the
                <ulink url='&YOCTO_DOCS_BSP_URL;#bsp'>Board Support Packages (BSP) - Developer's Guide</ulink>.
            </note>
        </para>

        <para>
            The
            <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>
            contains both general layers and BSP layers right out of the box.
            You can easily identify layers that ship with a Yocto Project
            release in the Source Directory by their names.
            Layers typically have names that begin with the string
            <filename>meta-</filename>.
            <note>
                It is not a requirement that a layer name begin with the
                prefix <filename>meta-</filename>, but it is a commonly
                accepted standard in the Yocto Project community.
            </note>
            For example, if you were to examine the
            <ulink url='https://git.yoctoproject.org/cgit/cgit.cgi/poky/tree/'>tree view</ulink>
            of the <filename>poky</filename> repository, you will see several
            layers: <filename>meta</filename>,
            <filename>meta-skeleton</filename>,
            <filename>meta-selftest</filename>,
            <filename>meta-poky</filename>, and
            <filename>meta-yocto-bsp</filename>.
            Each of these repositories represents a distinct layer.
        </para>

        <para>
            For procedures on how to create layers, see the
            "<ulink url='&YOCTO_DOCS_DEV_URL;#understanding-and-creating-layers'>Understanding and Creating Layers</ulink>"
            section in the Yocto Project Development Tasks Manual.
        </para>
    </section>

    <section id='components-and-tools'>
        <title>Components and Tools</title>

    </section>

    <section id='the-development-environment'>
        <title>The Development Environment</title>

    </section>

    <section id='reference-embedded-distribution'>
        <title>Reference Embedded Distribution (Poky)</title>

    </section>

    <section id='the-yocto-project-workflow'>
        <title>The Yocto Project Workflow</title>

    </section>


    <section id='some-basic-terms'>
        <title>Some Basic Terms</title>

    </section>

</chapter>
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