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|
<!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_REF_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_REF_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_REF_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 machine-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 machine-specific changes to the kernel recipe
by using a similarly named append file, which is located in
the BSP Layer for your target device (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
<ulink url='&YOCTO_DOCS_REF_URL;#var-PREFERRED_PROVIDER'><filename>PREFERRED_PROVIDER</filename></ulink>
and
<ulink url='&YOCTO_DOCS_REF_URL;#var-PREFERRED_VERSION'><filename>PREFERRED_VERSION</filename></ulink>
statements as follows:
<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>
You can find more information on what your append file
should contain in the
"<ulink url='&YOCTO_DOCS_KERNEL_URL;#creating-the-append-file'>Creating the Append File</ulink>"
section in the Yocto Project Linux Kernel Development
Manual.
</para>
</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 <bsp-name> <karch> [-o <DIRNAME> | --outdir <DIRNAME>]
[-i <JSON PROPERTY FILE> | --infile <JSON PROPERTY_FILE>]
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 <bsp-name> <karch> [-o <DIRNAME> | --outdir <DIRNAME>]
[-i <JSON PROPERTY FILE> | --infile <JSON PROPERTY_FILE>]
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>
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