path: root/documentation/bsp-guide/bsp.xml

<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

<chapter id='bsp'>

        <title>Board Support Packages (BSP) - Developer's Guide</title>

        <para>
            A Board Support Package (BSP) is a collection of information that
            defines how to support a particular hardware device, set of devices, or 
            hardware platform. 
            The BSP includes information about the hardware features 
            present on the device and kernel configuration information along with any 
            additional hardware drivers required.
            The BSP also lists any additional software 
            components required in addition to a generic Linux software stack for both 
            essential and optional platform features.
        </para>

        <para>
            This section (or document if you are reading the BSP Developer's Guide) defines
            a structure for these components
            so that BSPs follow a commonly understood layout.
            Providing a common form allows end-users to understand and become familiar 
            with the layout.  
            A common form also encourages standardization 
            of software support of hardware.
        </para>

        <note>
            The information here does not provide an example of how to create a BSP.
            For examples on how to create a BSP, see the
            "<ulink url='http://www.yoctoproject.org/docs/latest/dev-manual/dev-manual.html#dev-manual-bsp-appendix'>BSP Development Example</ulink>"
            section in The Yocto Project Development Manual.
            You can also see the 
            <ulink url='https://wiki.yoctoproject.org/wiki/Transcript:_creating_one_generic_Atom_BSP_from_another'>
            wiki page</ulink>.
        </note>

        <para>
            The proposed format does have elements that are specific to the Yocto Project and 
            OpenEmbedded build systems. 
            It is intended that this information can be 
            used by other systems besides Yocto Project and OpenEmbedded and that it will be simple
            to extract information and convert it to other formats if required.
            Yocto Project, through its standard layers mechanism, can directly accept the format 
            described as a layer.
            The BSP captures all 
            the hardware-specific details in one place in a standard format, which is 
            useful for any person wishing to use the hardware platform regardless of 
            the build system they are using.
        </para>

        <para>
            The BSP specification does not include a build system or other tools -
            it is concerned with the hardware-specific components only. 
            At the end-distribution point, you can ship the BSP combined with a build system
            and other tools. 
            However, it is important to maintain the distinction that these
            are separate components that happen to be combined in certain end products.
        </para>

        <section id='bsp-layers'>
            <title>BSP Layers</title>

            <para>
                The BSP consists of a file structure inside a base directory.
                Collectively, you can think of the base directory and the file structure 
                as a BSP Layer.
                BSP Layers use the following naming convention:
                <literallayout class='monospaced'>
     meta-&lt;bsp_name&gt;
                </literallayout>
                "bsp_name" is a placeholder for the machine or platform name.
            </para>

            <para>
                The Yocto Project organizes BSP Layers within the Yocto Metadata Layers area 
                of the Yocto Project Source Repositories at 
                <ulink url='http://git.yoctoproject.org/cgit.cgi'></ulink>.
                If you examine the source repositories, you will find many BSP Layers.
                Here are a few:
                <literallayout class='monospaced'>
     meta-baryon
     meta-fsl-ppc
     meta-intel
     meta-selinux
     meta-ti
                </literallayout>
                It is worth noting that the <filename>meta-intel</filename> BSP Layer contains 
                within itself several other BSP Layers, which makes it sort of a "super" BSP layer.
                Following is a sampling of the BSP Layers that the <filename>meta-intel</filename> 
                BSP Layer contains:
                <literallayout class='monospaced'>
     meta-cedartrail
     meta-crownbay
     meta-emenlow
     meta-fishriver
     meta-fri2
                </literallayout>
            </para>

            <para>
                The layer's base directory (<filename>meta-&lt;bsp_name&gt;</filename>) is the root 
                of the BSP Layer.
                This root is what you add to the <filename>BBLAYERS</filename>
                variable in the <filename>conf/bblayers.conf</filename> file found in the 
                <ulink url='http://www.yoctoproject.org/docs/latest/dev-manual/dev-manual.html#yocto-project-build-directory'>Yocto Project Build Directory</ulink>.
                Adding the root allows the Yocto Project build system to recognize the BSP 
                definition and from it build an image.
                Here is an example:
                <literallayout class='monospaced'>
     BBLAYERS = " \
        /usr/local/src/yocto/meta \
        /usr/local/src/yocto/meta-yocto \
        /usr/local/src/yocto/meta-&lt;bsp_name&gt; \
        "
                </literallayout>
            </para>

            <para>
                For more detailed information on layers, see the 
                "<ulink url='http://www.yoctoproject.org/docs/latest/dev-manual/dev-manual.html#usingpoky-changes-layers'>Bitbake Layers</ulink>" 
                section of the Yocto Project Development Manual.
                You can also see the detailed examples in the appendices of  
                <ulink url='http://www.yoctoproject.org/docs/latest/dev-manual/dev-manual.html'>
                The Yocto Project Development Manual</ulink>.
            </para>
        </section>


        <section id="bsp-filelayout">
            <title>Example Filesystem Layout</title>

            <para>
                Below is the common form for the file structure inside a BSP Layer.
                While you can use this basic form for the standard, realize that the actual structures
                for specific BSPs could differ. 

                <literallayout class='monospaced'>
     meta-&lt;bsp_name&gt;/                                
     meta-&lt;bsp_name&gt;/&lt;bsp_license_file&gt;
     meta-&lt;bsp_name&gt;/README
     meta-&lt;bsp_name&gt;/binary/&lt;bootable_images&gt;
     meta-&lt;bsp_name&gt;/conf/layer.conf 
     meta-&lt;bsp_name&gt;/conf/machine/*.conf
     meta-&lt;bsp_name&gt;/recipes-bsp/*
     meta-&lt;bsp_name&gt;/recipes-graphics/*            
     meta-&lt;bsp_name&gt;/recipes-kernel/linux/linux-yocto_&lt;kernel_rev&gt;.bbappend
                </literallayout>
            </para>

            <para>
                Below is an example of the Crown Bay BSP:

                <literallayout class='monospaced'>
     meta-crownbay/COPYING.MIT
     meta-crownbay/README
     meta-crownbay/README.sources
     meta-crownbay/binary
     meta-crownbay/conf/
     meta-crownbay/conf/layer.conf
     meta-crownbay/conf/machine/
     meta-crownbay/conf/machine/crownbay.conf
     meta-crownbay/conf/machine/crownbay-noemgd.conf
     meta-crownbay/recipes-bsp/
     meta-crownbay/recipes-bsp/formfactor/
     meta-crownbay/recipes-bsp/formfactor/formfactor_0.0.bbappend
     meta-crownbay/recipes-bsp/formfactor/formfactor/
     meta-crownbay/recipes-bsp/formfactor/formfactor/crownbay/
     meta-crownbay/recipes-bsp/formfactor/formfactor/crownbay/machconfig
     meta-crownbay/recipes-bsp/formfactor/formfactor/crownbay-noemgd/
     meta-crownbay/recipes-bsp/formfactor/formfactor/crownbay-noemgd/machconfig
     meta-crownbay/recipes-core
     meta-crownbay/recipes-core/tasks
     meta-crownbay/recipes-core/tasks/task-core-tools-profile.bbappend
     meta-crownbay/recipes-graphics/
     meta-crownbay/recipes-graphics/xorg-xserver/
     meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-config_0.1.bbappend
     meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-config/
     meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-config/crownbay/
     meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-config/crownbay/xorg.conf
     meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-config/crownbay-noemgd/
     meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-config/crownbay-noemgd/xorg.conf
     meta-crownbay/recipes-kernel/
     meta-crownbay/recipes-kernel/linux/
     meta-crownbay/recipes-kernel/linux/linux-yocto-rt_3.0.bbappend
     meta-crownbay/recipes-kernel/linux/linux-yocto_2.6.37.bbappend
     meta-crownbay/recipes-kernel/linux/linux-yocto_3.0.bbappend
                </literallayout>
            </para>

            <para>
                The following sections describe each part of the proposed BSP format.
            </para>

            <section id="bsp-filelayout-license">
            <title>License Files</title>

            <para>
                You can find these files in the BSP Layer at:
                <literallayout class='monospaced'>
     meta-&lt;bsp_name&gt;/&lt;bsp_license_file&gt;
                </literallayout>
            </para>

            <para>
                These optional files satisfy licensing requirements for the BSP.
                The type or types of files here can vary depending on the licensing requirements.
                For example, in the Crown Bay BSP all licensing requirements are handled with the 
                <filename>COPYING.MIT</filename> file.  
            </para>

            <para>
                Licensing files can be MIT, BSD, GPLv*, and so forth.
                These files are recommended for the BSP but are optional and totally up to the BSP developer.
            </para>
            </section>

            <section id="bsp-filelayout-readme">
            <title>README File</title>
            <para>
                You can find this file in the BSP Layer at:
                <literallayout class='monospaced'>
     meta-&lt;bsp_name&gt;/README
                </literallayout>
            </para>

            <para>
                This file provides information on how to boot the live images that are optionally 
                included in the <filename>/binary</filename> directory.
                The <filename>README</filename> file also provides special information needed for 
                building the image.
            </para>

            <para>
                Technically speaking a <filename>README</filename> file is optional but it is highly 
                recommended that every BSP has one.
            </para>
            </section>

            <section id="bsp-filelayout-readme-sources">
            <title>README.sources File</title>
            <para>
                You can find this file in the BSP Layer at:
                <literallayout class='monospaced'>
     meta-&lt;bsp_name&gt;/README.sources
                </literallayout>
            </para>

            <para>
                This file provides information on where to locate the BSP source files.
                For example, information provides where to find the sources that comprise
                the images shipped with the BSP.
                Information is also included to help you find the metadata used to generate the images
                that ship with the BSP.
            </para>

            <para>
                Technically speaking a <filename>README.sources</filename> file is optional but it is highly 
                recommended that every BSP has one.
            </para>
            </section>

            <section id="bsp-filelayout-binary">
            <title>Pre-built User Binaries</title>
            <para>
                You can find these files in the BSP Layer at:
                <literallayout class='monospaced'>
     meta-&lt;bsp_name&gt;/binary/&lt;bootable_images&gt;
                </literallayout>
            </para>

            <para>
                This optional area contains useful pre-built kernels and user-space filesystem 
                images appropriate to the target system.
                This directory typically contains graphical (e.g. sato) and minimal live images 
                when the BSP tarball has been created and made available in the 
                <ulink url='http://www.yoctoproject.org'>Yocto Project</ulink> website. 
                You can use these kernels and images to get a system running and quickly get started 
                on development tasks.
            </para>

            <para> 
                The exact types of binaries present are highly hardware-dependent.
                However, a README file should be present in the BSP Layer that explains how to use 
                the kernels and images with the target hardware. 
                If pre-built binaries are present, source code to meet licensing requirements must also 
                exist in some form.
            </para>
            </section>

            <section id='bsp-filelayout-layer'>
            <title>Layer Configuration File</title>
            <para>
                You can find this file in the BSP Layer at:
                <literallayout class='monospaced'>
     meta-&lt;bsp_name&gt;/conf/layer.conf
                </literallayout>
            </para>

            <para>
                The <filename>conf/layer.conf</filename> file identifies the file structure as a Yocto 
                Project layer, identifies the  
                contents of the layer, and contains information about how Yocto Project should use it. 
                Generally, a standard boilerplate file such as the following works.
                In the following example, you would replace "<filename>bsp</filename>" and 
                "<filename>_bsp</filename>" with the actual name
                of the BSP (i.e. <filename>&lt;bsp_name&gt;</filename> from the example template).
            </para>

            <para>
               <literallayout class='monospaced'>
     # We have a conf and classes directory, add to BBPATH
     BBPATH := "${BBPATH}:${LAYERDIR}"

     # We have a recipes directory, add to BBFILES
     BBFILES := "${BBFILES} ${LAYERDIR}/recipes/*/*.bb \ 
                 ${LAYERDIR}/recipes/*/*.bbappend"

     BBFILE_COLLECTIONS += "bsp"
     BBFILE_PATTERN_bsp := "^${LAYERDIR}/"
     BBFILE_PRIORITY_bsp = "6"
                </literallayout>
            </para>

            <para>
                To illustrate the string substitutions, here are the last three statements from the Crown 
                Bay <filename>conf/layer.conf</filename> file:
               <literallayout class='monospaced'>
     BBFILE_COLLECTIONS += "crownbay"
     BBFILE_PATTERN_crownbay := "^${LAYERDIR}/"
     BBFILE_PRIORITY_crownbay = "6"
                </literallayout>
            </para>

            <para>
                This file simply makes BitBake aware of the recipes and configuration directories.
                The file must exist so that the Yocto Project build system can recognize the BSP.
            </para>
            </section>

            <section id="bsp-filelayout-machine">
            <title>Hardware Configuration Options</title>
            <para>
                You can find these files in the BSP Layer at:
                <literallayout class='monospaced'>
     meta-&lt;bsp_name&gt;/conf/machine/*.conf
                </literallayout>
            </para>

            <para>
                The machine files bind together all the information contained elsewhere
                in the BSP into a format that the Yocto Project build system can understand. 
                If the BSP supports multiple machines, multiple machine configuration files
                can be present. 
                These filenames correspond to the values to which users have set the 
                <ulink url='http://www.yoctoproject.org/docs/latest/poky-ref-manual/poky-ref-manual.html#var-MACHINE'><filename>MACHINE</filename></ulink> variable.
            </para>

            <para>
                These files define things such as the kernel package to use
                (<ulink url='http://www.yoctoproject.org/docs/latest/poky-ref-manual/poky-ref-manual.html#var-PREFERRED_PROVIDER'><filename>PREFERRED_PROVIDER</filename></ulink>
                of virtual/kernel), the hardware drivers to
                include in different types of images, any special software components
                that are needed, any bootloader information, and also any special image
                format requirements.
            </para>

            <para>
                Each BSP Layer requires at least one machine file.
                However, you can supply more than one file.
                For example, in the Crown Bay BSP shown earlier in this section, the 
                <filename>conf/machine</filename> directory contains two configuration files:
                <filename>crownbay.conf</filename> and <filename>crownbay-noemgd.conf</filename>.
                The <filename>crownbay.conf</filename> file is used for the Crown Bay BSP
                that supports the <trademark class='registered'>Intel</trademark> Embedded
                Media and Graphics Driver (<trademark class='registered'>Intel</trademark>
                EMGD), while the <filename>crownbay-noemgd.conf</filename> file is used for the 
                Crown Bay BSP that does not support the <trademark class='registered'>Intel</trademark>
                EMGD.
            </para>

            <para>
                This <filename>crownbay.conf</filename> file could also include
                a hardware "tuning" file that is commonly used to
                define the package architecture and specify 
                optimization flags, which are carefully chosen to give best
                performance on a given processor.
            </para>

            <para>
                Tuning files are found in the <filename>meta/conf/machine/include</filename>
                directory of the 
                <ulink url='http://www.yoctoproject.org/docs/latest/dev-manual/dev-manual.html#yocto-project-files'>Yocto Project Files</ulink>.
                Tuning files can also reside in the BSP Layer itself.  
                For example, the <filename>ia32-base.inc</filename> file resides in the 
                <filename>meta-intel</filename> BSP Layer in <filename>conf/machine/include</filename>.
            </para>

            <para>
                To use an include file, you simply include them in the machine configuration file. 
                For example, the Crown Bay BSP <filename>crownbay.conf</filename> has the 
                following statements:
                <literallayout class='monospaced'>
     include conf/machine/include/tune-atom.inc
     include conf/machine/include/ia32-base.inc
                </literallayout>
            </para>
            </section>

            <section id='bsp-filelayout-misc-recipes'>
            <title>Miscellaneous Recipe Files</title>
            <para>
                You can find these files in the BSP Layer at:
                <literallayout class='monospaced'>
     meta-&lt;bsp_name&gt;/recipes-bsp/*
                </literallayout> 
            </para>

            <para>
                This optional directory contains miscellaneous recipe files for the BSP.
                Most notably would be the formfactor files.
                For example, in the Crown Bay BSP there is the 
                <filename>formfactor_0.0.bbappend</filename> file, which is an append file used 
                to augment the recipe that starts the build.  
                Furthermore, there are machine-specific settings used during the build that are
                defined by the <filename>machconfig</filename> files.
                In the Crown Bay example, two <filename>machconfig</filename> files exist:
                one that supports the Intel EMGD and one that does not:
                <literallayout class='monospaced'>
     meta-crownbay/recipes-bsp/formfactor/formfactor/crownbay/machconfig
     meta-crownbay/recipes-bsp/formfactor/formfactor/crownbay-noemgd/machconfig
     meta-crownbay/recipes-bsp/formfactor/formfactor_0.0.bbappend
                </literallayout>
            </para>

            <note><para>
                If a BSP does not have a formfactor entry, defaults are established according to
                the configuration script.
            </para></note>
            </section>

            <section id='bsp-filelayout-core-recipes'>
            <title>Core Recipe Files</title>
            <para>
                You can find these files in the BSP Layer at:
                <literallayout class='monospaced'>
     meta-&lt;bsp_name&gt;/recipes-core/*
                </literallayout> 
            </para>

            <para>
                This directory contains recipe files that are almost always necessary to build a 
                useful, working Linux image.
                Thus, the term "core" is used to group these recipes.
                For example, in the Crown Bay BSP there is the 
                <filename>task-core-tools-profile.bbappend</filename> file, which is an append file used 
                to recommend that the 
                <ulink url='http://sourceware.org/systemtap/wiki'>SystemTap</ulink>
                package be included as a package when the image is built.
            </para>
            </section>

            <section id='bsp-filelayout-recipes-graphics'>
            <title>Display Support Files</title>
            <para>
                You can find these files in the BSP Layer at:
                <literallayout class='monospaced'>
     meta-&lt;bsp_name&gt;/recipes-graphics/*            
                </literallayout>
            </para>

            <para>
                This optional directory contains recipes for the BSP if it has 
                special requirements for graphics support.
                All files that are needed for the BSP to support a display are kept here. 
                For example, the Crown Bay BSP contains two versions of the 
                <filename>xorg.conf</filename> file.
                The version in <filename>crownbay</filename> builds a BSP that supports the 
                <trademark class='registered'>Intel</trademark> Embedded Media Graphics Driver (EMGD),
                while the version in <filename>crownbay-noemgd</filename> builds 
                a BSP that supports Video Electronics Standards Association (VESA) graphics only:
                <literallayout class='monospaced'>
     meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-config_0.1.bbappend
     meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-config/crownbay/xorg.conf
     meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-config/crownbay-noemgd/xorg.conf
                </literallayout>
            </para>
            </section>

            <section id='bsp-filelayout-kernel'>
            <title>Linux Kernel Configuration</title>
            <para>
                You can find these files in the BSP Layer at:
                <literallayout class='monospaced'>
     meta-&lt;bsp_name&gt;/recipes-kernel/linux/linux-yocto_*.bbappend
                </literallayout>
            </para>

            <para>
                These files append your specific changes to the kernel you are using.
            </para>
            <para>
                For your BSP, you typically want to use an existing Yocto Project kernel found in the 
                Yocto Project repository at <filename>meta/recipes-kernel/linux</filename>.
                You can append your specific changes to the kernel recipe by using a
                similarly named append file, which is located in the 
                <filename>meta-&lt;bsp_name&gt;/recipes-kernel/linux</filename> 
                directory.
            </para>
            <para>
                Suppose you use a BSP that uses the <filename>linux-yocto_3.0.bb</filename> kernel, 
                which is the preferred kernel to use for developing a new BSP using the Yocto Project.
                In other words, you have selected the kernel in your 
                <filename>&lt;bsp_name&gt;.conf</filename> file by adding the following statements:
                <literallayout class='monospaced'>
     PREFERRED_PROVIDER_virtual/kernel ?= "linux-yocto"
     PREFERRED_VERSION_linux-yocto = "3.0%"
                </literallayout>
                You would use the <filename>linux-yocto_3.0.bbappend</filename> file to append 
                specific BSP settings to the kernel, thus configuring the kernel for your particular BSP.
            </para>
            <para>
                As an example, look at the existing Crown Bay BSP.
                The append file used is:
                <literallayout class='monospaced'>
     meta-crownbay/recipes-kernel/linux/linux-yocto_3.0.bbappend
                </literallayout>
                The following listing shows the file.
                Be aware that the actual commit ID strings in this example listing might be different
                than the actual strings in the file from the Yocto Project <filename>meta-intel</filename>
                Git source repository.
                <literallayout class='monospaced'>
     FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"

     COMPATIBLE_MACHINE_crownbay = "crownbay"
     KMACHINE_crownbay  = "yocto/standard/crownbay"
     KERNEL_FEATURES_append_crownbay += " cfg/smp.scc"

     COMPATIBLE_MACHINE_crownbay-noemgd = "crownbay-noemgd"
     KMACHINE_crownbay-noemgd  = "yocto/standard/crownbay"
     KERNEL_FEATURES_append_crownbay-noemgd += " cfg/smp.scc"

     SRCREV_machine_pn-linux-yocto_crownbay ?= "63c65842a3a74e4bd3128004ac29b5639f16433f"
     SRCREV_meta_pn-linux-yocto_crownbay ?= "59314a3523e360796419d76d78c6f7d8c5ef2593"

     SRCREV_machine_pn-linux-yocto_crownbay-noemgd ?= "63c65842a3a74e4bd3128004ac29b5639f16433f"
     SRCREV_meta_pn-linux-yocto_crownbay-noemgd ?= "59314a3523e360796419d76d78c6f7d8c5ef2593"
                </literallayout>
                This append file contains statements used to support the Crown Bay BSP for both
                Intel EMGD and non-EMGD.
                The build process, in this case, recognizes and uses only the statements that 
                apply to the defined machine name - <filename>crownbay</filename> in this case.
                So, the applicable statements in the <filename>linux-yocto_3.0.bbappend</filename> 
                file are follows:
                <literallayout class='monospaced'>
     FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"

     COMPATIBLE_MACHINE_crownbay = "crownbay"
     KMACHINE_crownbay  = "yocto/standard/crownbay"
     KERNEL_FEATURES_append_crownbay += " cfg/smp.scc"

     SRCREV_machine_pn-linux-yocto_crownbay ?= "63c65842a3a74e4bd3128004ac29b5639f16433f"
     SRCREV_meta_pn-linux-yocto_crownbay ?= "59314a3523e360796419d76d78c6f7d8c5ef2593"
                </literallayout>
                The append file defines <filename>crownbay</filename> as the compatible machine,
                defines the <filename>KMACHINE</filename>, points to some configuration fragments
                to use by setting the <filename>KERNEL_FEATURES</filename> variable, and then points
                to the specific commits in the Yocto Project files Git repository and the 
                <filename>meta</filename> Git repository branches to identify the exact kernel needed 
                to build the Crown Bay BSP.
            </para>
            <para>
                One thing missing in this particular BSP, which you will typically need when 
                developing a BSP, is the kernel configuration file (<filename>.config</filename>) for your BSP.
                When developing a BSP, you probably have a kernel configuration file or a set of kernel
                configuration files that, when taken together, define the kernel configuration for your BSP.
                You can accomplish this definition by putting the configurations in a file or a set of files 
                inside a directory located at the same level as your append file and having the same name 
                as the kernel.
                With all these conditions met simply reference those files in a 
                <filename>SRC_URI</filename> statement in the append file.
            </para>
            <para>
                For example, suppose you had a set of configuration options in a file called 
                <filename>defconfig</filename>.  
                If you put that file inside a directory named 
                <filename>/linux-yocto</filename> and then added 
                a <filename>SRC_URI</filename> statement such as the following to the append file, 
                those configuration
                options will be picked up and applied when the kernel is built.
                <literallayout class='monospaced'>
     SRC_URI += "file://defconfig"
                </literallayout>
            </para>
            <para>
                As mentioned earlier, you can group related configurations into multiple files and 
                name them all in the <filename>SRC_URI</filename> statement as well.
                For example, you could group separate configurations specifically for Ethernet and graphics
                into their own files and add those by using a <filename>SRC_URI</filename> statement like the 
                following in your append file:
                <literallayout class='monospaced'>
     SRC_URI += "file://defconfig \
            file://eth.cfg \
            file://gfx.cfg"
                </literallayout>
            </para>
            <para>
                The <filename>FILESEXTRAPATHS</filename> variable is in boilerplate form here 
                in order to make it easy to do that.
                It basically allows those configuration files to be found by the build process.
            </para>
            <note>
                <para>
                Other methods exist to accomplish grouping and defining configuration options.
                For example, you could directly add configuration options to the Yocto kernel 
                <filename>meta</filename> branch for your BSP.
                The configuration options will likely end up in that location anyway if the BSP gets 
                added to the Yocto Project. 
                For an example showing how to change the BSP configuration, see the
                "<ulink url='http://www.yoctoproject.org/docs/latest/dev-manual/dev-manual.html#changing-the-bsp-configuration'>Changing the BSP Configuration</ulink>" section 
                in the Yocto Project Development Manual.</para>
                <para>
                In general, however, the Yocto Project maintainers take care of moving the 
                <filename>SRC_URI</filename>-specified 
                configuration options to the <filename>meta</filename> branch.
                Not only is it easier for BSP developers to not have to worry about putting those 
                configurations in the branch, but having the maintainers do it allows them to apply 
                'global' knowledge about the kinds of common configuration options multiple BSPs in 
                the tree are typically using.  
                This allows for promotion of common configurations into common features.</para>
            </note>
            </section>
        </section>

        <section id='bsp-click-through-licensing'>
            <title>BSP 'Click-Through' Licensing Procedure</title>

            <note> This section describes how
		click-through licensing is expected to work.
                Currently, this functionality is not yet implemented.
            </note>

            <para>
	      In some cases, a BSP contains separately licensed IP
	      (Intellectual Property) for a component that imposes
	      upon the user a requirement to accept the terms of a
	      'click-through' license.  
              Once the license is accepted the
	      Yocto Project build system can then build and include the
	      corresponding component in the final BSP image.  
              Some affected components might be essential to the normal
	      functioning of the system and have no 'free' replacement
	      (i.e. the resulting system would be non-functional
	      without them).
              On the other hand, other components might be simply
	      'good-to-have' or purely elective, or if essential
	      nonetheless have a 'free' (possibly less-capable)
	      version that could be used as a in the BSP recipe.
            </para>

            <para>
	      For cases where you can substitute something and still maintain functionality, 
              the Yocto Project website's  
              <ulink url='http://www.yoctoproject.org/download/all?keys=&amp;download_type=1&amp;download_version='>BSP Download Page</ulink> 
              makes available 'de-featured' BSPs that are completely free of any IP encumbrances.
              For these cases you can use the substitution directly and without any further licensing
              requirements.  
              If present, these fully 'de-featured' BSPs are named appropriately different 
              as compared to the names of the respective encumbered BSPs.
              If available, these substitutions are the simplest and most preferred options.
              This, of course, assumes the resulting functionality meets requirements.
            </para>

            <para>
	      If however, a non-encumbered version is unavailable or the 'free' version 
              would provide unsuitable functionality or quality, you can use 
              an encumbered version.  
            </para>

            <para>  
              Several methods exist within the Yocto Project build system to satisfy the licensing
	      requirements for an encumbered BSP.
              The following list describes them in preferential order:
            </para>

	    <orderedlist>
            <listitem>

		<para>
		  Get a license key (or keys) for the encumbered BSP by visiting 
                  a website and providing the name of the BSP and your email address
                  through a web form.
                </para>
 
		<para>
		  After agreeing to any applicable license terms, the
		  BSP key(s) will be immediately sent to the address
		  you gave and you can use them by specifying BSPKEY_&lt;keydomain&gt;
		  environment variables when building the image:
		</para>

		<literallayout class='monospaced'>
     $ BSPKEY_&lt;keydomain&gt;=&lt;key&gt; bitbake core-image-sato
		</literallayout>

		<para>
		  These steps allow the encumbered image to be built
		  with no change at all to the normal build process.
		</para>

		<para>
		  Equivalently and probably more conveniently, a line
		  for each key can instead be put into the user's
		  <filename>local.conf</filename> file found in the Yocto Project file's
                  build directory.
		</para>

		<para>
		  The &lt;keydomain&gt; component of the
		  BSPKEY_&lt;keydomain&gt; is required because there
		  might be multiple licenses in effect for a given BSP.
                  In such cases, a given &lt;keydomain&gt; corresponds to
		  a particular license.  In order for an encumbered
		  BSP that encompasses multiple key domains to be built
		  successfully, a &lt;keydomain&gt; entry for each
		  applicable license must be present in <filename>local.conf</filename> or
		  supplied on the command-line.
		</para>
              </listitem> 
              <listitem>
		<para>
		  Do nothing - build as you normally would.
                  When a license is needed the build will stop and prompt you with instructions.
                  Follow the license prompts that originate from the
		  encumbered BSP.  
                  These prompts usually take the form of instructions
		  needed to manually fetch the encumbered package(s)
		  and md5 sums into the required directory 
                  (e.g. the <filename>yocto/build/downloads</filename>).
                  Once the manual package fetch has been
		  completed, restart the build to continue where
		  it left off.
                  During the build the prompt will not appear again since you have satisfied the 
                  requirement.
		</para>
              </listitem>
              <listitem>
		<para>
		  Get a full-featured BSP recipe rather than a key.
                  You can do this by visiting the Yocto Project website's
                  <ulink url='http://www.yoctoproject.org/download'>Download</ulink> page and 
                  clicking on "BSP Downloads".
		  BSP tarballs that have proprietary information can be downloaded after agreeing 
                  to licensing requirements as part of the download process. 
                  Obtaining the code this way allows you to build an encumbered image with 
                  no changes at all as compared to the normal build. 
                </para>
              </listitem>
	    </orderedlist>
	    <para>
	      Note that the third method is also the only option available
	      when downloading pre-compiled images generated from non-free BSPs.  
              Those images are likewise available at from the Yocto Project website.
            </para> 
        </section>

</chapter>