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

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<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 chapter (or document if you are reading the BSP Developer's Guide) 
            talks about BSP Layers, defines a structure for components
            so that BSPs follow a commonly understood layout, discusses how to customize
            a recipe for a BSP, addresses BSP licensing, and provides information that
            shows you how to create and manage a 
            <link linkend='bsp-layers'>BSP Layer</link> using two Yocto Project 
            <link linkend='using-the-yocto-projects-bsp-tools'>BSP Tools</link>.
        </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 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 
                <ulink url='&YOCTO_DOCS_REF_URL;#var-BBLAYERS'><filename>BBLAYERS</filename></ulink>
                variable in the <filename>conf/bblayers.conf</filename> file found in the 
                <ulink url='&YOCTO_DOCS_DEV_URL;#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>
                Some BSPs require additional layers on
                top of the BSP's root layer in order to be functional.
                For these cases, you also need to add those layers to the
                <filename>BBLAYERS</filename> variable in order to build the BSP.  
                You must also specify in the "Dependencies" section of the BSP's
                <filename>README</filename> file any requirements for additional 
                layers and, preferably, any
                build instructions that might be contained elsewhere
                in the <filename>README</filename> file.
            </para>

            <para>
                Some layers function as a layer to hold other BSP layers.
                An example of this type of layer is the <filename>meta-intel</filename> layer.  
                The <filename>meta-intel</filename> layer contains over 10 individual BSP layers.
            </para>

            <para>
                For more detailed information on layers, see the 
                "<ulink url='&YOCTO_DOCS_DEV_URL;#understanding-and-creating-layers'>Understanding and Creating Layers</ulink>" 
                section of the Yocto Project Development Manual.
                You can also see the detailed examples in the appendices of  
                <ulink url='&YOCTO_DOCS_DEV_URL;'>The Yocto Project Development Manual</ulink>.
            </para>
        </section>


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

            <para>
                Providing a common form allows end-users to understand and become familiar 
                with the layout.  
                A common format also encourages standardization of software support of hardware.
            </para>

            <para>
                The proposed form 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>

            <para>
                Before looking at the common form for the file structure inside a BSP Layer, 
                you should be aware that some requirements do exist in order for a BSP to 
                be considered compliant with the Yocto Project.
                For that list of requirements, see the
                "<link linkend='released-bsp-requirements'>Released BSP Requirements</link>"
                section.
            </para>

            <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;/README.sources
     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-core/*
     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>
                At a minimum, the <filename>README</filename> file must
                contain a list of dependencies, such as the names of
                any other layers on which the BSP depends and the name of
                the BSP maintainer with his or her contact information.
            </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>
            </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='&YOCTO_HOME_URL;'>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='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink> variable.
            </para>

            <para>
                These files define things such as the kernel package to use
                (<ulink url='&YOCTO_DOCS_REF_URL;#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='&YOCTO_DOCS_DEV_URL;#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 
                <trademark class='registered'>Intel</trademark> Embedded
                Media and Graphics Driver (<trademark class='registered'>Intel</trademark>
                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 formfactor configuration file that is installed by the main 
                formfactor recipe 
                <filename>meta/recipes-bsp/formfactor/formfactor_0.0.bb</filename>, 
                which is found in the 
                <ulink url='&YOCTO_DOCS_DEV_URL;#yocto-project-files'>Yocto Project Files</ulink>.
            </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 
                <ulink url='&YOCTO_DOCS_DEV_URL;#yocto-project-files'>Yocto 
                Project Files</ulink> 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 BSP Layer (e.g. 
                the <filename>meta-&lt;bsp_name&gt;/recipes-kernel/linux</filename> directory).
            </para>
            <para>
                Suppose the BSP 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 <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 
                <trademark class='registered'>Intel</trademark> EMGD and the VESA graphics.
                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 and
                defines the <filename>KMACHINE</filename>.
                The file also points to some configuration fragments to use by setting the 
                <filename>KERNEL_FEATURES</filename> variable.
                The location for the configuration fragments is the kernel tree itself in the 
                <ulink url='&YOCTO_DOCS_DEV_URL;#yocto-project-build-directory'>Yocto Project Build
                Directory</ulink> under <filename>linux/meta</filename>.
                Finally, the append file points to the specific commits in the 
                <ulink url='&YOCTO_DOCS_DEV_URL;#yocto-project-files'>Yocto Project Files</ulink> 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>myconfig</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://myconfig"
                </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://myconfig \
            file://eth.cfg \
            file://gfx.cfg"
                </literallayout>
            </para>
            <para>
                The <filename>FILESEXTRAPATHS</filename> variable is in boilerplate form in the 
                previous example in order to make it easy to do that.
                This variable must be in your layer or BitBake will not find the patches or 
                configurations even if you have them in your <filename>SRC_URI</filename>.
                The <filename>FILESEXTRAPATHS</filename> variable enables the build process to
                find those configuration files.
            </para>
            <note>
                <para>
                Other methods exist to accomplish grouping and defining configuration options.
                For example, if you are working with a local clone of the kernel repository, 
                you could checkout the kernel's <filename>meta</filename> branch, make your changes, 
                and then push the changes to the local bare clone of the kernel.
                The result is that you 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='&YOCTO_DOCS_DEV_URL;#changing-the-bsp-configuration'>Changing the BSP Configuration</ulink>" 
                section in the Yocto Project Development Manual.
                For a better understanding of working with a local clone of the kernel repository
                and a local bare clone of the kernel, see the
                "<ulink url='&YOCTO_DOCS_DEV_URL;#modifying-the-kernel-source-code'>Modifying the Kernel
                Source Code</ulink>" section also 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 kernel's <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='requirements-and-recommendations-for-released-bsps'>
            <title>Requirements and Recommendations for Released BSPs</title>

            <para>
                Certain requirements exist for a released BSP to be considered
                compliant with the Yocto Project.
                Additionally, a single recommendation also exists. 
                This section describes the requirements and recommendation for
                released BSPs.
            </para>

            <section id='released-bsp-requirements'>
                <title>Released BSP Requirements</title>

                <para>
                    Before looking at BSP requirements, you should consider the following:
                    <itemizedlist>
                        <listitem><para>The requirements here assume the BSP layer is a well-formed, "legal"
                            layer that can be added to the Yocto Project.
                            For guidelines on creating a Yocto Project layer that meets these base requirements, see the
                            "<link linkend='bsp-layers'>BSP Layers</link>" and the 
                            "<ulink url='&YOCTO_DOCS_DEV_URL;#understanding-and-creating-layers'>Understanding
                            and Creating Layers"</ulink> in the Yocto Project Development Manual.</para></listitem>
                        <listitem><para>The requirements in this section apply regardless of how you 
                            ultimately package a BSP.
                            You should consult the packaging and distribution guidelines for your
                            specific release process. 
                            For an example of packaging and distribution requirements, see the 
                            <ulink url='https://wiki.yoctoproject.org/wiki/Third_Party_BSP_Release_Process'>Third 
                            Party BSP Release Process</ulink> wiki page.</para></listitem>
                        <listitem><para>The requirements for the BSP as it is made available to a developer
                            are completely independent of the released form of the BSP. 
                            For example, the BSP metadata can be contained within a Git repository
                            and could have a directory structure completely different from what appears
                            in the officially released BSP layer.</para></listitem>
                        <listitem><para>It is not required that specific packages or package 
                            modifications exist in the BSP layer, beyond the requirements for general 
                            compliance with the Yocto Project.
                            For example, no requirement exists dictating that a specific kernel or 
                            kernel version be used in a given BSP.</para></listitem>
                    </itemizedlist>
                </para>

                <para>
                    Following are the requirements for a released BSP that conforms to the 
                    Yocto Project:
                    <itemizedlist>
                        <listitem><para><emphasis>Layer Name:</emphasis>
                            The BSP must have a layer name that follows the Yocto
                            Project standards.  
                            For information on BSP layer names, see the
                            "<link linkend='bsp-layers'>BSP Layers</link>" section.
                            </para></listitem>
                        <listitem><para><emphasis>File System Layout:</emphasis>
                            When possible, use the same directory names in your 
                            BSP layer as listed in the <filename>recipes.txt</filename> file.
                            In particular, you should place recipes 
                            (<filename>.bb</filename> files) and recipe
                            modifications (<filename>.bbappend</filename> files) into  
                            <filename>recipes-*</filename> subdirectories by functional area 
                            as outlined in <filename>recipes.txt</filename>.
                            If you cannot find a category in <filename>recipes.txt</filename>
                            to fit a particular recipe, you can make up your own 
                            <filename>recipe-*</filename> subdirectory.
                            You can find <filename>recipes.txt</filename> in the
                            <filename>meta</filename> directory of the 
                            <ulink url='&YOCTO_DOCS_DEV_URL;#yocto-project-files'>Yocto 
                            Project Files</ulink>, or in the OpenEmbedded Core Layer
                            (<filename>openembedded-core</filename>) found at 
                            <ulink url='http://git.openembedded.org/openembedded-core/tree/meta'></ulink>.
                            </para>
                            <para>Within any particular <filename>recipes-*</filename> category, the layout
                            should match what is found in the OpenEmbedded Core
                            Git repository (<filename>openembedded-core</filename>)
                            or the Yocto Project Files (<filename>poky</filename>).
                            In other words, make sure you place related files in appropriately
                            related <filename>recipes-*</filename> subdirectories specific to the
                            recipe's function, or within a subdirectory containing a set of closely-related
                            recipes.  
                            The recipes themselves should follow the general guidelines
                            for recipes used in the Yocto Project found in the 
                            <ulink url='https://wiki.yoctoproject.org/wiki/Recipe_%26_Patch_Style_Guide'>Yocto
                            Recipe and Patch Style Guide</ulink>.</para></listitem>
                        <listitem><para><emphasis>License File:</emphasis>
                            You must include a license file in the 
                            <filename>meta-&lt;bsp_name&gt;</filename> directory.
                            This license covers the BSP metadata as a whole.
                            You must specify which license to use since there is no 
                            default license if one is not specified.
                            See the 
                            <ulink url='&YOCTO_GIT_URL;/cgit.cgi/meta-intel/tree/meta-fishriver/COPYING.MIT'><filename>COPYING.MIT</filename></ulink>
                            file for the Fish River BSP in the <filename>meta-fishriver</filename> BSP layer 
                            as an example.</para></listitem>
                        <listitem><para><emphasis>README File:</emphasis>
                            You must include a <filename>README</filename> file in the 
                            <filename>meta-&lt;bsp_name&gt;</filename> directory.
                            See the 
                            <ulink url='&YOCTO_GIT_URL;/cgit.cgi/meta-intel/tree/meta-fishriver/README'><filename>README</filename></ulink>
                            file for the Fish River BSP in the <filename>meta-fishriver</filename> BSP layer 
                            as an example.</para>
                            <para>At a minimum, the <filename>README</filename> file should 
                            contain the following:
                            <itemizedlist>
                                <listitem><para>A brief description about the hardware the BSP 
                                    targets.</para></listitem>
                                <listitem><para>A list of all the dependencies a 
                                    on which a BSP layer depends.
                                    These dependencies are typically a list of required layers needed 
                                    to build the BSP.
                                    However, the dependencies should also contain information regarding 
                                    any other dependencies the BSP might have.</para></listitem>
                                <listitem><para>Any required special licensing information.
                                    For example, this information includes information on 
                                    special variables needed to satisfy a EULA,
                                    or instructions on information needed to build or distribute
                                    binaries built from the BSP metadata.</para></listitem>
                                <listitem><para>The name and contact information for the 
                                    BSP layer maintainer.
                                    This is the person to whom patches and questions should
                                    be sent.</para></listitem>
                                <listitem><para>Instructions on how to build the BSP using the BSP 
                                    layer.</para></listitem>
                                <listitem><para>Instructions on how to boot the BSP build from 
                                    the BSP layer.</para></listitem>
                                <listitem><para>Instructions on how to boot the binary images 
                                    contained in the <filename>/binary</filename> directory, 
                                    if present.</para></listitem>
                                <listitem><para>Information on any known bugs or issues that users 
                                    should know about when either building or booting the BSP 
                                    binaries.</para></listitem>
                            </itemizedlist></para></listitem>
                        <listitem><para><emphasis>README.sources File:</emphasis>
                            You must include a <filename>README.sources</filename> in the 
                            <filename>meta-&lt;bsp_name&gt;</filename> directory.
                            This file specifies exactly where you can find the sources used to 
                            generate the binary images contained in the 
                            <filename>/binary</filename> directory, if present.
                            See the 
                            <ulink url='&YOCTO_GIT_URL;/cgit.cgi/meta-intel/tree/meta-fishriver/README.sources'><filename>README.sources</filename></ulink>
                            file for the Fish River BSP in the <filename>meta-fishriver</filename> BSP layer 
                            as an example.</para></listitem>
                        <listitem><para><emphasis>Layer Configuration File:</emphasis>
                            You must include a <filename>conf/layer.conf</filename> in the
                            <filename>meta-&lt;bsp_name&gt;</filename> directory.
                            This file identifies the <filename>meta-&lt;bsp_name&gt;</filename>
                            BSP layer as a layer to the build system.</para></listitem>
                        <listitem><para><emphasis>Machine Configuration File:</emphasis>
                            You must include a <filename>conf/machine/&lt;bsp_name&gt;.conf</filename>
                            in the <filename>meta-&lt;bsp_name&gt;</filename> directory.
                            This configuration file defines a machine target that can be built
                            using the BSP layer.
                            Multiple machine configuration files define variations of machine 
                            configurations that are supported by the BSP.
                            If a BSP supports more multiple machine variations, you need to 
                            adequately describe each variation in the BSP 
                            <filename>README</filename> file.
                            Do not use multiple machine configuration files to describe disparate
                            hardware. 
                            Multiple machine configuration files should describe very similar targets.
                            If you do have very different targets, you should create a separate
                            BSP.
                            <note>It is completely possible for a developer to structure the 
                            working repository as a conglomeration of unrelated BSP
                            files, and to possibly generate specifically targeted 'release' BSPs 
                            from that directory using scripts or some other mechanism.  
                            Such considerations are outside the scope of this document.</note>
                            </para></listitem>
                    </itemizedlist>
                </para>
            </section>

            <section id='released-bsp-recommendations'>
                <title>Released BSP Recommendations</title>

                <para>
                    Following are recommendations for a released BSP that conforms to the 
                    Yocto Project:
                    <itemizedlist>
                        <listitem><para><emphasis>Bootable Images:</emphasis>
                            BSP releases 
                            can contain one or more bootable images.
                            Including bootable images allows users to easily try out the BSP
                            on their own hardware.</para>
                            <para>In some cases, it might not be convenient to include a 
                            bootable image. 
                            In this case, you might want to make two versions of the 
                            BSP available: one that contains binary images, and one
                            that does not.
                            The version that does not contain bootable images avoids 
                            unnecessary download times for users not interested in the images.
                            </para>
                            <para>If you need to distribute a BSP and include bootable images or build kernel and
                            filesystems meant to allow users to boot the BSP for evaluation
                            purposes, you should put the images and artifacts within a 
                            <filename>binary/</filename> subdirectory located in the 
                            <filename>meta-&lt;bsp_name&gt;</filename> directory.
                            <note>If you do include a bootable image as part of the BSP and the image
                            was built by software covered by the GPL or other open source licenses,
                            it is your responsibility to understand
                            and meet all licensing requirements, which could include distribution
                            of source files.</note></para></listitem>
                        <listitem><para><emphasis>Use a Yocto Linux Kernel:</emphasis>
                            Kernel recipes in the BSP should be based on a Yocto Linux kernel. 
                            Basing your recipes on these kernels reduces the costs for maintaining 
                            the BSP and increases its scalability.
                            See the <filename>Yocto Linux Kernel</filename> category in the 
                            <ulink url='&YOCTO_GIT_URL;/cgit.cgi'><filename>Yocto Source Repositories</filename></ulink>
                            for these kernels.</para></listitem>
                    </itemizedlist>
                </para>
            </section>
        </section>

        <section id='customizing-a-recipe-for-a-bsp'>
            <title>Customizing a Recipe for a BSP</title>

            <para>
               If you plan on customizing a recipe for a particular BSP, you need to do the
               following:
               <itemizedlist>
                   <listitem><para>Include within the BSP layer a <filename>.bbappend</filename>
                       file for the modified recipe.</para></listitem>
                   <listitem><para>Place the BSP-specific file in the BSP's recipe
                       <filename>.bbappend</filename> file path under a directory named
                       after the machine.</para></listitem>
               </itemizedlist>
           </para>

           <para>
               To better understand this, consider an example that customizes a recipe by adding 
               a BSP-specific configuration file named <filename>interfaces</filename> to the 
               <filename>netbase_4.47.bb</filename> recipe for machine "xyz".
               Do the following:
               <orderedlist>
                   <listitem><para>Edit the <filename>netbase_4.47.bbappend</filename> file so that it 
                       contains the following:
                       <literallayout class='monospaced'>
     FILESEXTRAPATHS_prepend := "${THISDIR}/files:"
     PRINC := "${@int(PRINC) + 2}"
                       </literallayout></para></listitem>
                   <listitem><para>Create and place the new <filename>interfaces</filename> 
                       configuration file in the BSP's layer here:
                       <literallayout class='monospaced'>
     meta-xyz/recipes-core/netbase/files/xyz/interfaces
                       </literallayout></para></listitem>
               </orderedlist>
            </para>
        </section>

        <section id='bsp-licensing-considerations'>
            <title>BSP Licensing Considerations</title>

            <para>
                In some cases, a BSP contains separately licensed Intellectual Property (IP)
                for a component or components.
                For these cases, you are required to accept the terms of a commercial or other 
                type of license that requires some kind of explicit End User License Agreement (EULA).  
                Once the license is accepted, the Yocto Project build system can then build and 
                include the corresponding component in the final BSP image.
                If the BSP is available as a pre-built image, you can download the image after
                agreeing to the license or EULA.
            </para>

            <para>
                You could find that some separately licensed components that are essential 
                for normal operation of the system might not have an unencumbered (or free)
                substitute.
                Without these essential components, the system would be non-functional.
                Then again, you might find that other licensed components that are simply 
                'good-to-have' or purely elective do have an unencumbered, free replacement 
                component that you can use rather than agreeing to the separately licensed component.
                Even for components essential to the system, you might find an unencumbered component 
                that is not identical but will work as a less-capable version of the 
                licensed version in the BSP recipe.
            </para>

            <para>
                For cases where you can substitute a free component and still
                maintain the system's functionality, the Yocto Project website's
                <ulink url='&YOCTO_HOME_URL;/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 your
                simplest and most preferred options.  
                Use of these substitutions of course assumes the resulting functionality meets
                system requirements.
            </para>

            <para>
                If however, a non-encumbered version is unavailable or
                it provides unsuitable functionality or quality, you can use an encumbered
                version.
            </para>

            <para> 
                A couple different methods exist within the Yocto
                Project build system to satisfy the licensing
                requirements for an encumbered BSP.  
                The following list describes them in order of preference:
	        <orderedlist>
                    <listitem><para><emphasis>Use the <filename>LICENSE_FLAGS</filename> variable
                        to define the Yocto Project recipes that have commercial or other types of
                        specially-licensed packages:</emphasis>  
                        For each of those recipes, you can 
                        specify a matching license string in a
                        <filename>local.conf</filename> variable named 
                        <filename>LICENSE_FLAGS_WHITELIST</filename>.
                        Specifying the matching license string signifies that you agree to the license.
                        Thus, the build system can build the corresponding recipe and include 
                        the component in the image.
                        See the 
                        "<ulink url='&YOCTO_DOCS_REF_URL;#enabling-commercially-licensed-recipes'>Enabling 
                        Commercially Licensed Recipes</ulink>" section in the Yocto Project Reference
                        Manual for details on how to use these variables.</para>
                        <para>If you build as you normally would, without
		        specifying any recipes in the
		        <filename>LICENSE_FLAGS_WHITELIST</filename>, the build stops and
		        provides you with the list of recipes that you have
		        tried to include in the image that need entries in
		        the <filename>LICENSE_FLAGS_WHITELIST</filename>.  
		        Once you enter the appropriate license flags into the whitelist,
		        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>
                        <para>Once the appropriate license flags are on the white list
		        in the <filename>LICENSE_FLAGS_WHITELIST</filename> variable, you 
		        can build the encumbered image with no change at all
		        to the normal build process.</para></listitem> 
                    <listitem><para><emphasis>Get a pre-built version of the BSP:</emphasis>
                        You can get this type of BSP by visiting the Yocto Project website's
                        <ulink url='&YOCTO_HOME_URL;/download'>Download</ulink>
                        page and clicking on "BSP Downloads".
                        You can download BSP tarballs that contain proprietary components
                        after agreeing to the licensing
                        requirements of each of the individually encumbered
                        packages as part of the download process.  
                        Obtaining the BSP this way allows you to access an encumbered
                        image immediately after agreeing to the
                        click-through license agreements presented by the
                        website.  
                        Note that if you want to build the image
                        yourself using the recipes contained within the BSP
                        tarball, you will still need to create an
                        appropriate <filename>LICENSE_FLAGS_WHITELIST</filename> to match the
                        encumbered recipes in the BSP.</para></listitem>
	        </orderedlist>
            </para>

            <note>
                Pre-compiled images are bundled with
                a time-limited kernel that runs for a
                predetermined amount of time (10 days) before it forces
                the system to reboot.  
                This limitation is meant to discourage direct redistribution
                of the image.
                You must eventually rebuild the image if you want to remove this restriction.
            </note> 
        </section>

        <section id='using-the-yocto-projects-bsp-tools'>
            <title>Using the Yocto Project's BSP Tools</title>

            <para>
                The Yocto Project includes a couple of tools that enable
                you to create a <link linkend='bsp-layers'>BSP layer</link> 
                from scratch and do basic configuration and maintenance 
                of the kernel without ever looking at a Yocto Project metadata file.
                These tools are <filename>yocto-bsp</filename> and <filename>yocto-kernel</filename>,
                respectively. 
	    </para>

            <para>
                The following sections describe the common location and help features as well 
                as details for the <filename>yocto-bsp</filename> and <filename>yocto-kernel</filename> 
                tools.
            </para>

            <section id='common-features'>
                <title>Common Features</title>

                <para>
                    Designed to have a  command interface somewhat like 
                    <ulink url='&YOCTO_DOCS_DEV_URL;#git'>Git</ulink>, each
                    tool is structured as a set of sub-commands under a
                    top-level command.
                    The top-level command (<filename>yocto-bsp</filename>
                    or <filename>yocto-kernel</filename>) itself does
                    nothing but invoke or provide help on the sub-commands
                    it supports.
                </para>

                <para>
                    Both tools reside in the <filename>scripts/</filename> subdirectory 
                    of the <ulink url='&YOCTO_DOCS_DEV_URL;#yocto-project-files'>Yocto Project 
                    Files</ulink>.
                    Consequently, to use the scripts, you must <filename>source</filename> the 
                    environment just as you would when invoking a build:
                    <literallayout class='monospaced'>
     $ source oe-init-build-env [build_dir]
                    </literallayout>
                </para>

                <para>
                    The most immediately useful function is to get help on both tools.
                    The built-in help system makes it easy to drill down at
                    any time and view the syntax required for any specific command.
                    Simply enter the name of the command, or the command along with 
                    <filename>help</filename> to display a list of the available sub-commands. 
                    Here is an example:
                    <literallayout class='monospaced'>
     $ yocto-bsp
     $ yocto-bsp help

     Usage:

     Create a customized Yocto BSP layer.

     usage: yocto-bsp [--version] [--help] COMMAND [ARGS]

     The most commonly used 'yocto-bsp' commands are:
     create            Create a new Yocto BSP
     list              List available values for options and BSP properties

     See 'yocto-bsp help COMMAND' for more information on a specific command.


     Options:
     --version    show program's version number and exit
     -h, --help   show this help message and exit
     -D, --debug  output debug information
                    </literallayout>
                </para>

                <para>
                    Similarly, entering just the name of a sub-command shows the detailed usage 
                    for that sub-command:
                    <literallayout class='monospaced'>
     $ yocto-bsp create

     Usage:

     Create a new Yocto BSP
     usage: yocto-bsp create &lt;bsp-name&gt; &lt;karch&gt; [-o &lt;DIRNAME&gt; | --outdir &lt;DIRNAME&gt;]
             [-i &lt;JSON PROPERTY FILE&gt; | --infile &lt;JSON PROPERTY_FILE&gt;]

                 This command creates a Yocto BSP based on the specified parameters.
                 The new BSP will be a new Yocto BSP layer contained by default within
                 the top-level directory specified as 'meta-bsp-name'.  The -o option
                 can be used to place the BSP layer in a directory with a different
                 name and location.

                 ...
                    </literallayout>
                </para>

                <para>
                    For any sub-command, you can also use the word 'help' just before the 
                    sub-command to get more extensive documentation:
                    <literallayout class='monospaced'>
     $ yocto-bsp help create

     NAME
     yocto-bsp create - Create a new Yocto BSP

     SYNOPSIS
     yocto-bsp create &lt;bsp-name&gt; &lt;karch&gt; [-o &lt;DIRNAME&gt; | --outdir &lt;DIRNAME&gt;]
             [-i &lt;JSON PROPERTY FILE&gt; | --infile &lt;JSON PROPERTY_FILE&gt;]

     DESCRIPTION
     This command creates a Yocto BSP based on the specified
     parameters.  The new BSP will be a new Yocto BSP layer contained
     by default within the top-level directory specified as
     'meta-bsp-name'.  The -o option can be used to place the BSP layer
     in a directory with a different name and location.
			    
     The value of the 'karch' parameter determines the set of files
     that will be generated for the BSP, along with the specific set of
     'properties' that will be used to fill out the BSP-specific
     portions of the BSP.
			    
     ...
			    
     NOTE: Once created, you should add your new layer to your
     bblayers.conf file in order for it to be subsequently seen and
     modified by the yocto-kernel tool.
			    
     NOTE for x86- and x86_64-based BSPs: The generated BSP assumes the
     presence of the of the meta-intel layer, so you should also have a
     meta-intel layer present and added to your bblayers.conf as well.
                    </literallayout>
                </para>

                <para>
                    Now that you know where these two commands reside and how to access information 
                    on them, you should find it relatively straightforward to discover the commands 
                    necessary to create a BSP and perform basic kernel maintenance on that BSP using
                    the tools.
                    The next sections provide a concrete starting point to expand on a few points that 
                    might not be immediately obvious or that could use further explanation.
                </para>
            </section>


            <section id='creating-a-new-bsp-layer-using-the-yocto-bsp-script'>
                <title>Creating a new BSP Layer Using the yocto-bsp Script</title>

                <para>
                    The <filename>yocto-bsp</filename> script creates a new 
                    <link linkend='bsp-layers'>BSP layer</link> for any architecture supported 
                    by the Yocto Project, as well as QEMU versions of the same.
                    The default mode of the script's operation is to prompt you for information needed 
                    to generate the BSP layer.
                    For the current set of BSPs, the script prompts you for various important
                    parameters such as:
                    <itemizedlist>
                        <listitem><para>which kernel to use</para></listitem>
                        <listitem><para>which branch of that kernel to use (or re-use)</para></listitem>
                        <listitem><para>whether or not to use X, and if so, which drivers to use</para></listitem>
                        <listitem><para>whether to turn on SMP</para></listitem>
                        <listitem><para>whether the BSP has a keyboard</para></listitem>
                        <listitem><para>whether the BSP has a touchscreen</para></listitem>
                        <listitem><para>any remaining configurable items associated with the BSP</para></listitem>
                    </itemizedlist>
                </para>

                <para>
                    You use the <filename>yocto-bsp create</filename> sub-command to create 
                    a new BSP layer. 
                    This command requires you to specify a particular architecture on which to 
                    base the BSP.
                    Assuming you have sourced the environment, you can use the 
                    <filename>yocto-bsp list karch</filename> sub-command to list the
                    architectures available for BSP creation as follows:
                    <literallayout class='monospaced'>
     $ yocto-bsp list karch
     Architectures available:
         arm
         powerpc
         i386
         mips
         x86_64
         qemu
                    </literallayout>
                </para>

                <para>
                    The remainder of this section presents an example that uses  
                    <filename>myarm</filename> as the machine name and <filename>qemu</filename>
                    as the machine architecture.
                    Of the available architectures, <filename>qemu</filename> is the only architecture
                    that causes the script to prompt you further for an actual architecture.
                    In every other way, this architecture is representative of how creating a BSP for
                    a 'real' machine would work.
                    The reason the example uses this architecture is because it is an emulated architecture
                    and can easily be followed without requiring actual hardware.
                </para>

                <para>
                    As the <filename>yocto-bsp create</filename> command runs, default values for 
                    the prompts appear in brackets.
                    Pressing enter without supplying anything on the command line or pressing enter
                    and providing an invalid response causes the script to accept the default value.
                </para>

                <para>
                    Following is the complete example:
                    <literallayout class='monospaced'>
     $ yocto-bsp create myarm qemu
     Which qemu architecture would you like to use? [default: x86]
             1) common 32-bit x86
             2) common 64-bit x86
             3) common 32-bit ARM
             4) common 32-bit PowerPC
             5) common 32-bit MIPS
     3
     Would you like to use the default (3.2) kernel? (Y/n)
     Do you need a new machine branch for this BSP (the alternative is to re-use an existing branch)? [Y/n]
     Getting branches from remote repo git://git.yoctoproject.org/linux-yocto-3.2...
     Please choose a machine branch to base this BSP on => [default: standard/default/common-pc]
             1) base
             2) standard/base
             3) standard/default/arm-versatile-926ejs
             4) standard/default/base
             5) standard/default/beagleboard
             6) standard/default/cedartrailbsp (copy).xml
             7) standard/default/common-pc-64/base
             8) standard/default/common-pc-64/jasperforest
             9) standard/default/common-pc-64/romley
             10) standard/default/common-pc-64/sugarbay
             11) standard/default/common-pc/atom-pc
             12) standard/default/common-pc/base
             13) standard/default/crownbay
             14) standard/default/emenlow
             15) standard/default/fishriver
             16) standard/default/fri2
             17) standard/default/fsl-mpc8315e-rdb
             18) standard/default/mti-malta32-be
             19) standard/default/mti-malta32-le
             20) standard/default/preempt-rt
             21) standard/default/qemu-ppc32
             22) standard/default/routerstationpro
             23) standard/preempt-rt/base
             24) standard/preempt-rt/qemu-ppc32
             25) standard/preempt-rt/routerstationpro
             26) standard/tiny
     3
     Do you need SMP support? (Y/n)
     Does your BSP have a touchscreen? (y/N)
     Does your BSP have a keyboard? (Y/n)
     New qemu BSP created in meta-myarm
                    </literallayout>
                    Let's take a closer look at the example now:
                    <orderedlist>
                        <listitem><para>For the <filename>qemu</filename> architecture, 
                            the script first prompts you for which emulated architecture to use.
                            In the example, we use the <filename>arm</filename> architecture.
                            </para></listitem>
                        <listitem><para>The script then prompts you for the kernel.
                            The default kernel is 3.2 and is acceptable.  
                            So, the example accepts the default.
                            If you enter 'n', the script prompts you to further enter the kernel
                            you do want to use (e.g. 3.0, 3.2_preempt-rt, etc.).</para></listitem>
                        <listitem><para>Next, the script asks whether you would like to have a new 
                            branch created especially for your BSP in the local 
                            <ulink url='&YOCTO_DOCS_DEV_URL;#local-kernel-files'>Linux Yocto Kernel</ulink> 
                            Git repository .
                            If not, then the script re-uses an existing branch.</para>
                            <para>In this example, the default (or 'yes') is accepted.
                            Thus, a new branch is created for the BSP rather than using a common, shared
                            branch.
                            The new branch is the branch committed to for any patches you might later add. 
                            The reason a new branch is the default is that typically
                            new BSPs do require BSP-specific patches.
                            The tool thus assumes that most of time a new branch is required.
                            <note>In the current implementation, creation or re-use of a branch does 
                            not actually matter.
                            The reason is because the generated BSPs assume that patches and 
                            configurations live in recipe-space, which is something that can be done 
                            with or without a dedicated branch.  
                            Generated BSPs, however, are different.
                            This difference becomes significant once the tool's 'publish' functionality 
                            is implemented.</note></para></listitem>
                        <listitem><para>Regardless of which choice is made in the previous step, 
                            you are now given the opportunity to select a particular machine branch on
                            which to base your new BSP-specific machine branch on 
                            (or to re-use if you had elected to not create a new branch).  
                            Because this example is generating an <filename>arm</filename> BSP, the example 
                            uses <filename>#3</filename> at the prompt, which selects the arm-versatile branch.
                            </para></listitem>
                        <listitem><para>The remainder of the prompts are routine. 
                            Defaults are accepted for each.</para></listitem>
                        <listitem><para>By default, the script creates the new BSP Layer in the 
                            <ulink url='&YOCTO_DOCS_DEV_URL;#yocto-project-build-directory'>Yocto Project
                            Build Directory</ulink>.</para></listitem>
                    </orderedlist> 
                </para>

                <para>
                    Once the BSP Layer is created, you must add it to your 
                    <filename>bblayers.conf</filename> file.
                    Here is an example:
                    <literallayout class='monospaced'>
     BBLAYERS = " \
        /usr/local/src/yocto/meta \
        /usr/local/src/yocto/meta-yocto \
        /usr/local/src/yocto/meta-myarm \
        "
                    </literallayout> 
                    Adding the layer to this file allows the build system to build the BSP and 
                    the <filename>yocto-kernel</filename> tool to be able to find the layer and 
                    other metadata it needs on which to operate.
                </para> 
            </section>

            <section id='managing-kernel-patches-and-config-items-with-yocto-kernel'>
                <title>Managing Kernel Patches and Config Items with yocto-kernel</title>

                <para>
                    Assuming you have created a Yocto Project 
                    <link linkend='bsp-layers'>BSP Layer</link> using
                    <link linkend='creating-a-new-bsp-layer-using-the-yocto-bsp-script'>
                    <filename>yocto-bsp</filename></link> and you added it to your
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-BBLAYERS'><filename>BBLAYERS</filename></ulink>
                    variable in the <filename>bblayers.conf</filename> file, you can now use
                    the <filename>yocto-kernel</filename> script to add patches and configuration
                    items to the BSP's kernel.
                </para>

                <para>
                    The <filename>yocto-kernel</filename> script allows you to add, remove, and list patches
                    and kernel config settings to a Yocto Project BSP's kernel 
                    <filename>.bbappend</filename> file.
                    All you need to do is use the appropriate sub-command.
                    Recall that the easiest way to see exactly what sub-commands are available
                    is to use the <filename>yocto-kernel</filename> built-in help as follows:
                    <literallayout class='monospaced'>
     $ yocto-kernel
     Usage:

     Modify and list Yocto BSP kernel config items and patches.

     usage: yocto-kernel [--version] [--help] COMMAND [ARGS]

     The most commonly used 'yocto-kernel' commands are:
     config list       List the modifiable set of bare kernel config options for a BSP
     config add        Add or modify bare kernel config options for a BSP 
     config rm         Remove bare kernel config options from a BSP
     patch list        List the patches associated with a BSP
     patch add         Patch the Yocto kernel for a BSP
     patch rm          Remove patches from a BSP

     See 'yocto-kernel help COMMAND' for more information on a specific command.
                    </literallayout>
                </para>

                <para>
                    The <filename>yocto-kernel patch add</filename> sub-command allows you to add a 
                    patch to a BSP.  
                    The following example adds two patches to the <filename>myarm</filename> BSP:
                    <literallayout class='monospaced'>
     $ yocto-kernel patch add myarm ~/test.patch
     Added patches:
             test.patch

     $ yocto-kernel patch add myarm ~/yocto-testmod.patch
     Added patches:
             yocto-testmod.patch
                    </literallayout>
                    <note>Although the previous example adds patches one at a time, it is possible
                    to add multiple patches at the same time.</note>
                </para>

                <para>
                    You can verify patches have been added by using the 
                    <filename>yocto-kernel patch list</filename> sub-command.
                    Here is an example:
                    <literallayout class='monospaced'>
     $ yocto-kernel patch list myarm
     The current set of machine-specific patches for myarm is:
             1) test.patch
             2) yocto-testmod.patch
                    </literallayout>
                </para>

                <para>
                    You can also use the <filename>yocto-kernel</filename> script to
                    remove a patch using the <filename>yocto-kernel patch rm</filename> sub-command.
                    Here is an example:
                    <literallayout class='monospaced'>
     $ yocto-kernel patch rm myarm
     Specify the patches to remove:
             1) test.patch
             2) yocto-testmod.patch
     1
     Removed patches:
             test.patch
                    </literallayout>
                </para>

                <para>
                    Again, using the <filename>yocto-kernel patch list</filename> sub-command,
                    you can verify that the patch was in fact removed:
                    <literallayout class='monospaced'>
     $ yocto-kernel patch list myarm
     The current set of machine-specific patches for myarm is:
             1) yocto-testmod.patch
                    </literallayout>
                </para>

                <para>
                    In a completely similar way, you can use the <filename>yocto-kernel config add</filename>
                    sub-command to add one or more kernel config item settings to a BSP.
                    The following commands add a couple of config items to the 
                    <filename>myarm</filename> BSP:
                    <literallayout class='monospaced'>
     $ yocto-kernel config add myarm CONFIG_MISC_DEVICES=y
     Added items:
             CONFIG_MISC_DEVICES=y

     $ yocto-kernel config add myarm KCONFIG_YOCTO_TESTMOD=y
     Added items:
             CONFIG_YOCTO_TESTMOD=y
                    </literallayout>
                    <note>Although the previous example adds config items one at a time, it is possible
                    to add multiple config items at the same time.</note>
                </para>

                <para>
                    You can list the config items now associated with the BSP.
                    Doing so shows you the config items you added as well as others associated
                    with the BSP:
                    <literallayout class='monospaced'>
     $ yocto-kernel config list myarm
     The current set of machine-specific kernel config items for myarm is:
             1) CONFIG_MISC_DEVICES=y
             2) CONFIG_YOCTO_TESTMOD=y
                    </literallayout>
                </para>

                <para>
                    Finally, you can remove one or more config items using the 
                    <filename>yocto-kernel config rm</filename> sub-command in a manner
                    completely analogous to <filename>yocto-kernel patch rm</filename>.
                </para>
            </section>
        </section>
</chapter>