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"
[<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] >

<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 guide presents information 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>
                A BSP consists of a file structure inside a base directory.
                Collectively, you can think of the base directory, its file structure,
                and the contents as a BSP Layer.
                Although not a strict requirement, layers in the Yocto Project use the
                following well-established naming convention:
                <literallayout class='monospaced'>
     meta-<replaceable>bsp_name</replaceable>
                </literallayout>
                The string "meta-" is prepended to the machine or platform name, which is
                <replaceable>bsp_name</replaceable> in the above form.
                <note><title>Tip</title>
                    Because the BSP layer naming convention is well-established,
                    it is advisable to follow it when creating layers.
                    Technically speaking, a BSP layer name does not need to
                    start with <filename>meta-</filename>.
                    However, you might run into situations where obscure
                    scripts assume this convention.
                </note>
            </para>

            <para>
                To help understand the BSP layer concept, consider the BSPs that the
                Yocto Project supports and provides with each release.
                You can see the layers in the
                <ulink url='&YOCTO_DOCS_DEV_URL;#yocto-project-repositories'>Yocto Project Source Repositories</ulink>
                through a web interface at
                <ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi'></ulink>.
                If you go to that interface, you will find near the bottom of the list
                under "Yocto Metadata Layers" several BSP layers all of which are
                supported by the Yocto Project (e.g. <filename>meta-raspberrypi</filename> and
                <filename>meta-intel</filename>).
                Each of these layers is a repository unto itself and clicking on a
                layer reveals information that includes two links from which you can choose
                to set up a clone of the layer's repository on your local host system.
                Here is an example that clones the Raspberry Pi BSP layer:
                <literallayout class='monospaced'>
     $ git clone git://git.yoctoproject.org/meta-raspberrypi
                </literallayout>
            </para>

            <para>
                In addition to BSP layers near the bottom of that referenced
                Yocto Project Source Repository, the
                <filename>meta-yocto-bsp</filename> layer is part of the
                shipped <filename>poky</filename> repository.
                The <filename>meta-yocto-bsp</filename> layer maintains several
                BSPs such as the Beaglebone, EdgeRouter, and generic versions of
                both 32 and 64-bit IA machines.
            </para>

            <para>
                For information on the BSP development workflow, see the
                "<ulink url='&YOCTO_DOCS_DEV_URL;#developing-a-board-support-package-bsp'>Developing a Board Support Package (BSP)</ulink>"
                section in the Yocto Project Development Manual.
                For more information on how to set up a local copy of source files
                from a Git repository, see the
                "<ulink url='&YOCTO_DOCS_DEV_URL;#getting-setup'>Getting Set Up</ulink>"
                section also in the Yocto Project Development Manual.
            </para>

            <para>
                The layer's base directory
                (<filename>meta-<replaceable>bsp_name</replaceable></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;#build-directory'>Build Directory</ulink>,
                which is established after you run one of the OpenEmbedded build environment
                setup scripts (i.e.
                <ulink url='&YOCTO_DOCS_REF_URL;#structure-core-script'><filename>&OE_INIT_FILE;</filename></ulink>
                and
                <ulink url='&YOCTO_DOCS_REF_URL;#structure-memres-core-script'><filename>oe-init-build-env-memres</filename></ulink>).
                Adding the root allows the OpenEmbedded 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-poky \
       /usr/local/src/yocto/meta-yocto-bsp \
       /usr/local/src/yocto/meta-mylayer \
       "
                </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,
                which contains a number of individual BSP sub-layers, as well as a directory
                named <filename>common/</filename> full of common content across those layers.
                Another example is the <filename>meta-yocto-bsp</filename> layer mentioned
                earlier.
            </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.
            </para>
        </section>

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

            <para>
                Defining a common BSP directory structure allows end-users to understand and
                become familiar with that structure.
                A common format also encourages standardization of software support of hardware.
            </para>

            <para>
                The proposed form does have elements that are specific to the
                OpenEmbedded build system.
                It is intended that this information can be
                used by other build systems besides the OpenEmbedded build system
                and that it will be simple
                to extract information and convert it to other formats if required.
                The OpenEmbedded build system, 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-<replaceable>bsp_name</replaceable>/
     meta-<replaceable>bsp_name</replaceable>/<replaceable>bsp_license_file</replaceable>
     meta-<replaceable>bsp_name</replaceable>/README
     meta-<replaceable>bsp_name</replaceable>/README.sources
     meta-<replaceable>bsp_name</replaceable>/binary/<replaceable>bootable_images</replaceable>
     meta-<replaceable>bsp_name</replaceable>/conf/layer.conf
     meta-<replaceable>bsp_name</replaceable>/conf/machine/*.conf
     meta-<replaceable>bsp_name</replaceable>/recipes-bsp/*
     meta-<replaceable>bsp_name</replaceable>/recipes-core/*
     meta-<replaceable>bsp_name</replaceable>/recipes-graphics/*
     meta-<replaceable>bsp_name</replaceable>/recipes-kernel/linux/linux-yocto_<replaceable>kernel_rev</replaceable>.bbappend
                </literallayout>
            </para>

            <para>
                Below is an example of the Raspberry Pi BSP:

                <literallayout class='monospaced'>
     meta-raspberrypi/COPYING.MIT
     meta-raspberrypi/README
     meta-raspberrypi/classes
     meta-raspberrypi/classes/linux-raspberrypi-base.bbclass
     meta-raspberrypi/classes/sdcard_image-rpi.bbclass
     meta-raspberrypi/conf/
     meta-raspberrypi/conf/layer.conf
     meta-raspberrypi/conf/machine/
     meta-raspberrypi/conf/machine/raspberrypi.conf
     meta-raspberrypi/conf/machine/raspberrypi0.conf
     meta-raspberrypi/conf/machine/raspberrypi2.conf
     meta-raspberrypi/conf/machine/raspberrypi3.conf
     meta-raspberrypi/conf/machine/include
     meta-raspberrypi/conf/machine/include/rpi-base.inc
     meta-raspberrypi/conf/machine/include/rpi-default-providers.inc
     meta-raspberrypi/conf/machine/include/rpi-default-settings.inc
     meta-raspberrypi/conf/machine/include/rpi-default-versions.inc
     meta-raspberrypi/conf/machine/include/rpi-tune-arm1176jzf-s.inc
     meta-raspberrypi/files
     meta-raspberrypi/files/custom-licenses
     meta-raspberrypi/files/custom-licenses/Broadcom
     meta-raspberrypi/recipes-bsp
     meta-raspberrypi/recipes-bsp/bootfiles
     meta-raspberrypi/recipes-bsp/bootfiles/bcm2835-bootfiles.bb
     meta-raspberrypi/recipes-bsp/bootfiles/rpi-config_git.bb
     meta-raspberrypi/recipes-bsp/common
     meta-raspberrypi/recipes-bsp/common/firmware.inc
     meta-raspberrypi/recipes-bsp/formfactor_00.bbappend
     meta-raspberrypi/recipes-bsp/formfactor/raspberrypi/machconfig
     meta-raspberrypi/recipes-bsp/rpi-mkimage_git.bb
     meta-raspberrypi/recipes-bsp/rpi-mkimage/License
     meta-raspberrypi/recipes-bsp/rpi-mkimage/open-files-relative-to-script.patch
     meta-raspberrypi/recipes-bsp/u-boot/u-boot-rpi_git.bb
     meta-raspberrypi/recipes-core
     meta-raspberrypi/recipes-core/images
     meta-raspberrypi/recipes-core/images/rpi-basic-image.bb
     meta-raspberrypi/recipes-core/images/rpi-hwup-image.bb
     meta-raspberrypi/recipes-core/images/rpi-test-image.bb
     meta-raspberrypi/recipes-core/packagegroups
     meta-raspberrypi/recipes-core/packagegroups/packagegroup-rpi-test.bb
     meta-raspberrypi/recipes-core/psplash
     meta-raspberrypi/recipes-core/psplash/files
     meta-raspberrypi/recipes-core/psplash/psplash_git.bbappend
     meta-raspberrypi/recipes-core/psplash/files/psplash-raspberrypi-img.h
     meta-raspberrypi/recipes-devtools
     meta-raspberrypi/recipes-devtools/bcm2835
     meta-raspberrypi/recipes-devtools/bcm2835/bcm2835_1.46.bb
     meta-raspberrypi/recipes-devtools/pi-blaster
     meta-raspberrypi/recipes-devtools/pi-blaster/files
     meta-raspberrypi/recipes-devtools/pi-blaster/*.patch
     meta-raspberrypi/recipes-devtools/pi-blaster/pi-blaster.inc
     meta-raspberrypi/recipes-devtools/pi-blaster/pi-blaster_git.bb
     meta-raspberrypi/recipes-devtools/python
     meta-raspberrypi/recipes-devtools/python/python-rtimu
     meta-raspberrypi/recipes-devtools/python/python-rtimu/*.patch
     meta-raspberrypi/recipes-devtools/python/python-rtimu_git.bb
     meta-raspberrypi/recipes-devtools/python/python-sense-hat_2.1.0.bb
     meta-raspberrypi/recipes-devtools/python/rpi-gpio
     meta-raspberrypi/recipes-devtools/python/rpi-gpio/*.patch
     meta-raspberrypi/recipes-devtools/python/rpi-gpio_0.6.1.bb
     meta-raspberrypi/recipes-devtools/python/rpio
     meta-raspberrypi/recipes-devtools/python/rpio/*.patch
     meta-raspberrypi/recipes-devtools/python/rpio_0.10.0.bb
     meta-raspberrypi/recipes-devtools/wiringPi
     meta-raspberrypi/recipes-devtools/wiringPi/files
     meta-raspberrypi/recipes-devtools/wiringPi/files/*.patch
     meta-raspberrypi/recipes-devtools/wiringPi/wiringpi
     meta-raspberrypi/recipes-devtools/wiringPi/wiringpi/*.patch
     meta-raspberrypi/recipes-devtools/wiringPi/wiringpi_git.bb
     meta-raspberrypi/recipes-graphics
     meta-raspberrypi/recipes-graphics/eglinfo
     meta-raspberrypi/recipes-graphics/eglinfo/eglinfo-fb_%.bbappend
     meta-raspberrypi/recipes-graphics/eglinfo/eglinfo-x11_%.bbappend
     meta-raspberrypi/recipes-graphics/userland
     meta-raspberrypi/recipes-graphics/userland/userland
     meta-raspberrypi/recipes-graphics/userland/userland/*.patch
     meta-raspberrypi/recipes-graphics/userland/userland_git.bb
     meta-raspberrypi/recipes-graphics/vc-graphics
     meta-raspberrypi/recipes-graphics/vc-graphics/files
     meta-raspberrypi/recipes-graphics/vc-graphics/files/egl.pc
     meta-raspberrypi/recipes-graphics/vc-graphics/files/vchiq.sh
     meta-raspberrypi/recipes-graphics/vc-graphics/vc-graphics-hardfp.bb
     meta-raspberrypi/recipes-graphics/vc-graphics/vc-graphics.bb
     meta-raspberrypi/recipes-graphics/vc-graphics/vc-graphics.inc
     meta-raspberrypi/recipes-graphics/wayland
     meta-raspberrypi/recipes-graphics/wayland/weston_%.bbappend
     meta-raspberrypi/recipes-graphics/weston
     meta-raspberrypi/recipes-graphics/weston/weston_%.bbappend
     meta-raspberrypi/recipes-graphics/xorg-xserver
     meta-raspberrypi/recipes-graphics/xorg-xserver/xserver-xf86-config
     meta-raspberrypi/recipes-graphics/xorg-xserver/xserver-xf86-config/rpi
     meta-raspberrypi/recipes-graphics/xorg-xserver/xserver-xf86-config/rpi/xorg.conf
     meta-raspberrypi/recipes-graphics/xorg-xserver/xserver-xf86-config/rpi/xorg.conf.d
     meta-raspberrypi/recipes-graphics/xorg-xserver/xserver-xf86-config/rpi/xorg.conf.d/10-evdev.conf
     meta-raspberrypi/recipes-graphics/xorg-xserver/xserver-xf86-config/rpi/xorg.conf.d/99-pitft.conf
     meta-raspberrypi/recipes-graphics/xorg-xserver/xserver-xf86-config_0.1.bbappend
     meta-raspberrypi/recipes-kernel
     meta-raspberrypi/recipes-kernel/linux-firmware
     meta-raspberrypi/recipes-kernel/linux-firmware/linux-firmware
     meta-raspberrypi/recipes-kernel/linux-firmware/linux-firmware/LICENSE.broadcom_brcm80211
     meta-raspberrypi/recipes-kernel/linux-firmware/linux-firmware/brcmfmac43430-sdio.bin
     meta-raspberrypi/recipes-kernel/linux-firmware/linux-firmware/brcmfmac43430-sdio.txt
     meta-raspberrypi/recipes-kernel/linux-firmware/linux-firmware_git.bbappend
     meta-raspberrypi/recipes-kernel/linux
     meta-raspberrypi/recipes-kernel/linux/linux-raspberrypi-3.14
     meta-raspberrypi/recipes-kernel/linux/linux-raspberrypi-3.14/*.patch
     meta-raspberrypi/recipes-kernel/linux/linux-raspberrypi-3.18
     meta-raspberrypi/recipes-kernel/linux/linux-raspberrypi-3.18/*.patch
     meta-raspberrypi/recipes-kernel/linux/linux-raspberrypi-4.1
     meta-raspberrypi/recipes-kernel/linux/linux-raspberrypi-4.1/*.patch
     meta-raspberrypi/recipes-kernel/linux/linux-raspberrypi.inc
     meta-raspberrypi/recipes-kernel/linux/linux-raspberrypi
     meta-raspberrypi/recipes-kernel/linux/linux-raspberrypi/defconfig
     meta-raspberrypi/recipes-kernel/linux/linux-raspberrypi_3.14.bb
     meta-raspberrypi/recipes-kernel/linux/linux-raspberrypi_3.18.bb
     meta-raspberrypi/recipes-kernel/linux/linux-raspberrypi_4.1.bb
     meta-raspberrypi/recipes-kernel/linux/linux-raspberrypi_4.4.bb
     meta-raspberrypi/recipes-kernel/linux/linux.inc
     meta-raspberrypi/recipes-multimedia
     meta-raspberrypi/recipes-multimedia/gstreamer
     meta-raspberrypi/recipes-multimedia/gstreamer/gstreamer1.0-omx
     meta-raspberrypi/recipes-multimedia/gstreamer/gstreamer1.0-omx/*.patch
     meta-raspberrypi/recipes-multimedia/gstreamer/gstreamer1.0-omx_%.bbappend
     meta-raspberrypi/recipes-multimedia/gstreamer/gstreamer1.0-plugins-bad_%.bbappend
     meta-raspberrypi/recipes-multimedia/omxplayer
     meta-raspberrypi/recipes-multimedia/omxplayer/omxplayer
     meta-raspberrypi/recipes-multimedia/omxplayer/omxplayer/*.patch
     meta-raspberrypi/recipes-multimedia/omxplayer/omxplayer_git.bb
     meta-raspberrypi/scripts
     meta-raspberrypi/scripts/lib
     meta-raspberrypi/scripts/lib/image
     meta-raspberrypi/scripts/lib/image/canned-wks
     meta-raspberrypi/scripts/lib/image/canned-wks/sdimage-raspberrypi.wks
                </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-<replaceable>bsp_name</replaceable>/<replaceable>bsp_license_file</replaceable>
                </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 Raspberry Pi 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-<replaceable>bsp_name</replaceable>/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-<replaceable>bsp_name</replaceable>/README.sources
                </literallayout>
            </para>

            <para>
                This file provides information on where to locate the BSP
                source files used to build the images (if any) that reside in
                <filename>meta-<replaceable>bsp_name</replaceable>/binary</filename>.
                Images in the <filename>binary</filename> would be images
                released with the BSP.
                The information in the <filename>README.sources</filename>
                file also helps you find the
                <ulink url='&YOCTO_DOCS_DEV_URL;#metadata'>Metadata</ulink>
                used to generate the images that ship with the BSP.
                <note>
                    If the BSP's <filename>binary</filename> directory is
                    missing or the directory has no images, an existing
                    <filename>README.sources</filename> file is
                    meaningless.
                </note>
            </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-<replaceable>bsp_name</replaceable>/binary/<replaceable>bootable_images</replaceable>
                </literallayout>
            </para>

            <para>
                This optional area contains useful pre-built kernels and
                user-space filesystem images released with the BSP that are
                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.
                The <filename>README</filename> file should be present in the
                BSP Layer and it will explain how to use the images with the
                target hardware.
                Additionally, the <filename>README.sources</filename> file
                should be present to locate the sources used to build the
                images and provide information on the Metadata.
            </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-<replaceable>bsp_name</replaceable>/conf/layer.conf
                </literallayout>
            </para>

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

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

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

     BBFILE_COLLECTIONS += "<replaceable>bsp</replaceable>"
     BBFILE_PATTERN_<replaceable>bsp</replaceable> = "^${LAYERDIR}/"
     BBFILE_PRIORITY_<replaceable>bsp</replaceable> = "6"

     LAYERDEPENDS_<replaceable>bsp</replaceable> = "intel"
                </literallayout>
            </para>

            <para>
                To illustrate the string substitutions, here are the corresponding statements
                from the Raspberry Pi <filename>conf/layer.conf</filename> file:
               <literallayout class='monospaced'>
     # We have a conf and classes directory, append to BBPATH
     BBPATH .= ":${LAYERDIR}"

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

     BBFILE_COLLECTIONS += "raspberrypi"
     BBFILE_PATTERN_raspberrypi := "^${LAYERDIR}/"
     BBFILE_PRIORITY_raspberrypi = "9"

     # Additional license directories.
     LICENSE_PATH += "${LAYERDIR}/files/custom-licenses"
                </literallayout>
            </para>

            <para>
                This file simply makes
                <ulink url='&YOCTO_DOCS_DEV_URL;#bitbake-term'>BitBake</ulink>
                aware of the recipes and configuration directories.
                The file must exist so that the OpenEmbedded 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-<replaceable>bsp_name</replaceable>/conf/machine/*.conf
                </literallayout>
            </para>

            <para>
                The machine files bind together all the information contained elsewhere
                in the BSP into a format that the 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.
            </para>

            <para>
                This configuration 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 within the
                <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink>.
                For example, the <filename>ia32-base.inc</filename> file resides in the
                <filename>meta/conf/machine/include</filename> directory.
            </para>

            <para>
                To use an include file, you simply include them in the
                machine configuration file.
                For example, the Raspberry Pi BSP
                <filename>raspberrypi3.conf</filename> contains the
                following statement:
                <literallayout class='monospaced'>
     include conf/machine/raspberrypi2.conf
                </literallayout>
            </para>
            </section>

            <section id='bsp-filelayout-misc-recipes'>
            <title>Miscellaneous BSP-Specific Recipe Files</title>
            <para>
                You can find these files in the BSP Layer at:
                <literallayout class='monospaced'>
     meta-<replaceable>bsp_name</replaceable>/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 Raspberry Pi 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> file further down in the
                directory.
                Here is the <filename>machconfig</filename>
                file for the Raspberry Pi BSP:
                <literallayout class='monospaced'>
     HAVE_TOUCHSCREEN=0
     HAVE_KEYBOARD=1

     DISPLAY_CAN_ROTATE=0
     DISPLAY_ORIENTATION=0
     DISPLAY_DPI=133
                </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;#source-directory'>Source Directory</ulink>.
            </para></note>
            </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-<replaceable>bsp_name</replaceable>/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.
            </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-<replaceable>bsp_name</replaceable>/recipes-kernel/linux/linux-yocto*.bbappend
                </literallayout>
            </para>

            <para>
                These files append your specific changes to the main kernel recipe you are using.
            </para>
            <para>
                For your BSP, you typically want to use an existing Yocto Project kernel recipe found in the
                <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</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-<replaceable>bsp_name</replaceable>/recipes-kernel/linux</filename> directory).
            </para>
            <para>
                Suppose you are using the <filename>linux-yocto_4.4.bb</filename> recipe to build
                the kernel.
                In other words, you have selected the kernel in your
                <replaceable>bsp_name</replaceable><filename>.conf</filename> file by adding these types
                of statements:
                <literallayout class='monospaced'>
     PREFERRED_PROVIDER_virtual/kernel ?= "linux-yocto"
     PREFERRED_VERSION_linux-yocto ?= "4.4%"
                </literallayout>
                <note>
                    When the preferred provider is assumed by default, the
                    <filename>PREFERRED_PROVIDER</filename> statement does not appear in the
                    <replaceable>bsp_name</replaceable><filename>.conf</filename> file.
                </note>
                You would use the <filename>linux-yocto_4.4.bbappend</filename>
                file to append specific BSP settings to the kernel, thus
                configuring the kernel for your particular BSP.
            </para>

            <para>
                As an example, consider the following append file
                used by the BSPs in <filename>meta-yocto-bsp</filename>:
                <literallayout class='monospaced'>
     meta-yocto-bsp/recipes-kernel/linux/linux-yocto_4.4.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-yocto-bsp</filename>
                layer upstream.
                <literallayout class='monospaced'>
     KBRANCH_genericx86  = "standard/base"
     KBRANCH_genericx86-64  = "standard/base"

     KMACHINE_genericx86 ?= "common-pc"
     KMACHINE_genericx86-64 ?= "common-pc-64"
     KBRANCH_edgerouter = "standard/edgerouter"
     KBRANCH_beaglebone = "standard/beaglebone"
     KBRANCH_mpc8315e-rdb = "standard/fsl-mpc8315e-rdb"

     SRCREV_machine_genericx86    ?= "ff4c4ef15b51f45b9106d71bf1f62fe7c02e63c2"
     SRCREV_machine_genericx86-64 ?= "ff4c4ef15b51f45b9106d71bf1f62fe7c02e63c2"
     SRCREV_machine_edgerouter ?= "ff4c4ef15b51f45b9106d71bf1f62fe7c02e63c2"
     SRCREV_machine_beaglebone ?= "ff4c4ef15b51f45b9106d71bf1f62fe7c02e63c2"
     SRCREV_machine_mpc8315e-rdb ?= "df00877ef9387b38b9601c82db57de2a1b23ce53"

     COMPATIBLE_MACHINE_genericx86 = "genericx86"
     COMPATIBLE_MACHINE_genericx86-64 = "genericx86-64"
     COMPATIBLE_MACHINE_edgerouter = "edgerouter"
     COMPATIBLE_MACHINE_beaglebone = "beaglebone"
     COMPATIBLE_MACHINE_mpc8315e-rdb = "mpc8315e-rdb"

     LINUX_VERSION_genericx86 = "4.4.3"
     LINUX_VERSION_genericx86-64 = "4.4.3"
                </literallayout>
                This append file contains statements used to support
                several BSPs that ship with the Yocto Project.
                The file defines machines using the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-COMPATIBLE_MACHINE'><filename>COMPATIBLE_MACHINE</filename></ulink>
                variable and uses the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-KMACHINE'><filename>KMACHINE</filename></ulink>
                variable to ensure the machine name used by the OpenEmbedded
                build system maps to the machine name used by the Linux Yocto
                kernel.
                The file also uses the optional
                <ulink url='&YOCTO_DOCS_REF_URL;#var-KBRANCH'><filename>KBRANCH</filename></ulink>
                variable to ensure the build process uses the
                appropriate kernel branch.
            </para>

            <para>
                Although this particular example does not use it, the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-KERNEL_FEATURES'><filename>KERNEL_FEATURES</filename></ulink>
                variable could be used to enable features specific to
                the kernel.
                The append file points to specific commits in the
                <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink>
                Git repository and the <filename>meta</filename> Git repository
                branches to identify the exact kernel needed to build the
                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 kernel's append file and having the same
                name as the kernel's main recipe file.
                With all these conditions met, simply reference those files in the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
                statement in the append file.
            </para>

            <para>
                For example, suppose you had some configuration options
                in a file called <filename>network_configs.cfg</filename>.
                You can place that file inside a directory named
                <filename>linux-yocto</filename> and then add
                a <filename>SRC_URI</filename> statement such as the
                following to the append file.
                When the OpenEmbedded build system builds the kernel, the
                configuration options are picked up and applied.
                <literallayout class='monospaced'>
     SRC_URI += "file://network_configs.cfg"
                </literallayout>
            </para>

            <para>
                To group related configurations into multiple files, you
                perform a similar procedure.
                Here is an example that groups separate configurations
                specifically for Ethernet and graphics into their own
                files and adds the configurations by using a
                <filename>SRC_URI</filename> statement like the following
                in your append file:
                <literallayout class='monospaced'>
     SRC_URI += "file://myconfig.cfg \
                 file://eth.cfg \
                 file://gfx.cfg"
                </literallayout>
            </para>

            <para>
                Another variable you can use in your kernel recipe append
                file is the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESEXTRAPATHS'><filename>FILESEXTRAPATHS</filename></ulink>
                variable.
                When you use this statement, you are extending the locations
                used by the OpenEmbedded system to look for files and
                patches as the recipe is processed.
            </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
                    <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.
                </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, recommendations also exist.
                This section describes the requirements and recommendations 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 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
                            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 conform 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>recipes-*</filename> subdirectory.
                            You can find <filename>recipes.txt</filename> in the
                            <filename>meta</filename> directory of the
                            <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</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 Source Directory (<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='http://openembedded.org/wiki/Styleguide'>OpenEmbedded Style Guide</ulink>".
                            </para></listitem>
                        <listitem><para><emphasis>License File:</emphasis>
                            You must include a license file in the
                            <filename>meta-<replaceable>bsp_name</replaceable></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-raspberrypi/tree/COPYING.MIT'><filename>COPYING.MIT</filename></ulink>
                            file for the Raspberry Pi BSP in the
                            <filename>meta-raspberrypi</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-<replaceable>bsp_name</replaceable></filename> directory.
                            See the
                            <ulink url='&YOCTO_GIT_URL;/cgit.cgi/meta-raspberrypi/tree/README'><filename>README</filename></ulink>
                            file for the Raspberry Pi BSP in the <filename>meta-raspberrypi</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
                                    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.
                                    For information on how to find the right person, see the
                                    "<ulink url='&YOCTO_DOCS_DEV_URL;#how-to-submit-a-change'>How to Submit a Change</ulink>"
                                    section in the Yocto Project Development Manual.
                                    </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-<replaceable>bsp_name</replaceable></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.
                            </para></listitem>
                        <listitem><para><emphasis>Layer Configuration File:</emphasis>
                            You must include a <filename>conf/layer.conf</filename> in the
                            <filename>meta-<replaceable>bsp_name</replaceable></filename> directory.
                            This file identifies the <filename>meta-<replaceable>bsp_name</replaceable></filename>
                            BSP layer as a layer to the build system.</para></listitem>
                        <listitem><para><emphasis>Machine Configuration File:</emphasis>
                            You must include one or more
                            <filename>conf/machine/<replaceable>bsp_name</replaceable>.conf</filename>
                            files in the <filename>meta-<replaceable>bsp_name</replaceable></filename> directory.
                            These configuration files define machine targets 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 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.
                            If you do have very different targets, you should create separate
                            BSP layers for each target.
                            <note>It is completely possible for a developer to structure the
                            working repository as a conglomeration of unrelated BSP
                            files, and to possibly generate BSPs targeted for release
                            from that directory using scripts or some other mechanism
                            (e.g. <filename>meta-yocto-bsp</filename> layer).
                            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-<replaceable>bsp_name</replaceable></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'>Source Repositories</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>Create a <filename>.bbappend</filename>
                       file for the modified recipe.
                       For information on using append files, see the
                       "<ulink url='&YOCTO_DOCS_DEV_URL;#using-bbappend-files'>Using .bbappend Files</ulink>"
                       section in the Yocto Project Development Manual.
                       </para></listitem>
                   <listitem><para>
                       Ensure your directory structure in the BSP layer
                       that supports your machine is such that it can be found
                       by the build system.
                       See the example later in this section for more information.
                       </para></listitem>
                   <listitem><para>
                       Put the append file in a directory whose name matches
                       the machine's name and is located in an appropriate
                       sub-directory inside the BSP layer (i.e.
                       <filename>recipes-bsp</filename>, <filename>recipes-graphics</filename>,
                       <filename>recipes-core</filename>, and so forth).
                       </para></listitem>
                   <listitem><para>Place the BSP-specific files in the proper directory
                       inside the BSP layer.
                       How expansive the layer is affects where you must place these files.
                       For example, if your layer supports several different machine types,
                       you need to be sure your layer's directory structure includes hierarchy
                       that separates the files out according to machine.
                       If your layer does not support multiple machines, the layer would not
                       have that additional hierarchy and the files would obviously not be
                       able to reside in a machine-specific directory.
                       </para></listitem>
               </itemizedlist>
           </para>

           <para>
               Following is a specific example to help you better understand the process.
               Consider an example that customizes a recipe by adding
               a BSP-specific configuration file named <filename>interfaces</filename> to the
               <filename>init-ifupdown_1.0.bb</filename> recipe for machine "xyz" where the
               BSP layer also supports several other machines.
               Do the following:
               <orderedlist>
                   <listitem><para>Edit the <filename>init-ifupdown_1.0.bbappend</filename> file so that it
                       contains the following:
                       <literallayout class='monospaced'>
     FILESEXTRAPATHS_prepend := "${THISDIR}/files:"
                       </literallayout>
                       The append file needs to be in the
                       <filename>meta-xyz/recipes-core/init-ifupdown</filename> directory.
                       </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/init-ifupdown/files/xyz-machine-one/interfaces
                       </literallayout>
                       <note>
                           If the <filename>meta-xyz</filename> layer did not support
                           multiple machines, you would place the
                           <filename>interfaces</filename> configuration file in the
                           layer here:
                           <literallayout class='monospaced'>
     meta-xyz/recipes-core/init-ifupdown/files/interfaces
                           </literallayout>
                       </note>
                       The
                       <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESEXTRAPATHS'><filename>FILESEXTRAPATHS</filename></ulink>
                       variable in the append files extends the search path
                       the build system uses to find files during the build.
                       Consequently, for this example you need to have the
                       <filename>files</filename> directory in the same location
                       as your append file.</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 OpenEmbedded 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 "Downloads" page from the
                <ulink url='&YOCTO_HOME_URL;'>Yocto Project website's</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 OpenEmbedded 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
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-LICENSE_FLAGS'><filename>LICENSE_FLAGS</filename></ulink>
                        variable to define the 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
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-LICENSE_FLAGS_WHITELIST'><filename>LICENSE_FLAGS_WHITELIST</filename></ulink>.
                        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
                        "Downloads" page of the
                        <ulink url='&YOCTO_HOME_URL;'>Yocto Project website</ulink>.
                        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 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 provide 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;#source-directory'>Source Directory</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 <replaceable>build_dir</replaceable>
                    </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 with the <filename>help</filename>
                    switch:
                    <literallayout class='monospaced'>
     $ yocto-bsp help
     Usage:

      Create a customized Yocto BSP layer.

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

      Current '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
     ERROR:root:Wrong number of arguments, exiting

     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.

      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.  The possible values for the 'karch' parameter can be
      listed via 'yocto-bsp list karch'.

      ...
                    </literallayout>
                </para>

                <para>
                    For any sub-command, you can use the word "help" option 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> &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.

         ...
                    </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.
                    <note>
                        You can also use the <filename>yocto-layer</filename> tool to create
                        a "generic" layer.
                        For information on this tool, see the
                        "<ulink url='&YOCTO_DOCS_DEV_URL;#creating-a-general-layer-using-the-yocto-layer-script'>Creating a General Layer Using the yocto-layer Script</ulink>"
                        section in the Yocto Project Development Guide.
                    </note>
                </para>

                <para>
                    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.
                </para>

                <para>
                    For the current set of BSPs, the script prompts you for various important
                    parameters such as:
                    <itemizedlist>
                        <listitem><para>The kernel to use</para></listitem>
                        <listitem><para>The 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>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 kernel architecture
                    (<filename>karch</filename>) 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:
         powerpc
         x86_64
         i386
         arm
         qemu
         mips
         mips64
                    </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
                    an actual 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
                    with an invalid response causes the script to accept the default value.
                    Once the script completes, the new <filename>meta-myarm</filename> BSP layer
                    is created in the current working directory.
                    This example assumes you have sourced the
                    <ulink url='&YOCTO_DOCS_REF_URL;#structure-core-script'><filename>&OE_INIT_FILE;</filename></ulink>
                    setup script.
                </para>

                <para>
                    Following is the complete example:
                    <literallayout class='monospaced'>
     $ yocto-bsp create myarm qemu
     Checking basic git connectivity...
     Done.

     Which qemu architecture would you like to use? [default: i386]
	     1) i386    (32-bit)
	     2) x86_64  (64-bit)
	     3) ARM     (32-bit)
	     4) PowerPC (32-bit)
	     5) MIPS    (32-bit)
	     6) MIPS64  (64-bit)
     3
     Would you like to use the default (4.8) kernel? (y/n) [default: y]
     Do you need a new machine branch for this BSP (the alternative is to re-use an existing branch)? [y/n] [default: y]
     Getting branches from remote repo git://git.yoctoproject.org/linux-yocto-4.8.git...
     Please choose a machine branch to base this BSP on: [default: standard/base]
	     1) standard/arm-versatile-926ejs
	     2) standard/base
	     3) standard/beaglebone
	     4) standard/edgerouter
	     5) standard/fsl-mpc8315e-rdb
	     6) standard/mti-malta32
	     7) standard/mti-malta64
	     8) standard/qemuarm64
	     9) standard/qemuppc
     1
     Would you like SMP support? (y/n) [default: y]
     Does your BSP have a touchscreen? (y/n) [default: n]
     Does your BSP have a keyboard? (y/n) [default: y]

     New qemu BSP created in meta-myarm
                    </literallayout>
                    Take a closer look at the example now:
                    <orderedlist>
                        <listitem><para>For the QEMU architecture,
                            the script first prompts you for which emulated architecture to use.
                            In the example, we use the ARM architecture.
                            </para></listitem>
                        <listitem><para>The script then prompts you for the kernel.
                            The default 4.8 kernel 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.</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.
                            </para></listitem>
                        <listitem><para>Regardless of which choice you make 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
                            (or to re-use if you had elected to not create a new branch).
                            Because this example is generating an ARM-based BSP, the example
                            uses <filename>#1</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
                            current working directory of the
                            <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink>,
                            (i.e. <filename>poky/build</filename>).
                            </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-poky \
        /usr/local/src/yocto/meta-yocto-bsp \
        /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 <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 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 --help
     Usage:

      Modify and list Yocto BSP kernel config items and patches.

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

      Current '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
        feature list      List the features used by a BSP
        feature add       Have a BSP use a feature
        feature rm        Have a BSP stop using a feature
        features list     List the features available to BSPs
        feature describe  Describe a particular feature
        feature create    Create a new BSP-local feature
        feature destroy   Remove a BSP-local feature

      See 'yocto-kernel 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>
                    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 item:
       CONFIG_MISC_DEVICES=y

     $ yocto-kernel config add myarm CONFIG_YOCTO_TESTMOD=y
     Added item:
       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>