poky/documentation/bsp-guide/bsp.rst

.. SPDX-License-Identifier: CC-BY-SA-2.0-UK

************************************************
Board Support Packages (BSP) - Developer's Guide
************************************************

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.

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 a BSP
Layer using the :ref:`bitbake-layers <bsp-guide/bsp:Creating a new BSP Layer Using the \`\`bitbake-layers\`\` Script>`
tool.

BSP Layers
==========

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, BSP
layers in the Yocto Project use the following well-established naming
convention::

   meta-bsp_root_name

The string "meta-" is prepended to the
machine or platform name, which is "bsp_root_name" in the above form.

.. note::

   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 ``meta-``.
   However, various scripts and tools in the Yocto Project development
   environment assume this convention.

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
:ref:`overview-manual/development-environment:yocto project source repositories`
through
a web interface at :yocto_git:`/`. If you go to that interface,
you will find a list of repositories under "Yocto Metadata Layers".

.. note::

   Layers that are no longer actively supported as part of the Yocto
   Project appear under the heading "Yocto Metadata Layer Archive."

Each repository is a BSP layer supported by the Yocto Project (e.g.
``meta-raspberrypi`` and ``meta-intel``). Each of these layers is a
repository unto itself and clicking on the layer name displays two URLs
from which you can clone the layer's repository to your local system.
Here is an example that clones the Raspberry Pi BSP layer::

   $ git clone git://git.yoctoproject.org/meta-raspberrypi

In addition to BSP layers, the ``meta-yocto-bsp`` layer is part of the
shipped ``poky`` repository. The ``meta-yocto-bsp`` layer maintains
several "reference" BSPs including the ARM-based Beaglebone, MIPS-based
EdgeRouter, and generic versions of both 32-bit and 64-bit IA machines.

For information on typical BSP development workflow, see the
:ref:`bsp-guide/bsp:developing a board support package (bsp)`
section. For more
information on how to set up a local copy of source files from a Git
repository, see the
:ref:`dev-manual/start:locating yocto project source files`
section in the Yocto Project Development Tasks Manual.

The BSP layer's base directory (``meta-bsp_root_name``) is the root
directory of that Layer. This directory is what you add to the
:term:`BBLAYERS` variable in the
``conf/bblayers.conf`` file found in your
:term:`Build Directory`, which is
established after you run the OpenEmbedded build environment setup
script (i.e. :ref:`ref-manual/structure:\`\`oe-init-build-env\`\``).
Adding the root directory allows the :term:`OpenEmbedded Build System`
to recognize the BSP
layer and from it build an image. Here is an example::

   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 \
      "

.. note::

   Ordering and :term:`BBFILE_PRIORITY` for the layers listed in ``BBLAYERS``
   matter. For example, if multiple layers define a machine configuration, the
   OpenEmbedded build system uses the last layer searched given similar layer
   priorities. The build system works from the top-down through the layers
   listed in ``BBLAYERS``.

Some BSPs require or depend on additional layers beyond the BSP's root
layer in order to be functional. In this case, you need to specify these
layers in the ``README`` "Dependencies" section of the BSP's root layer.
Additionally, if any build instructions exist for the BSP, you must add
them to the "Dependencies" section.

Some layers function as a layer to hold other BSP layers. These layers
are known as ":term:`container layers <Container Layer>`". An example of
this type of layer is OpenEmbedded's
`meta-openembedded <https://github.com/openembedded/meta-openembedded>`__
layer. The ``meta-openembedded`` layer contains many ``meta-*`` layers.
In cases like this, you need to include the names of the actual layers
you want to work with, such as::

   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 \
     .../meta-openembedded/meta-oe \
     .../meta-openembedded/meta-perl \
     .../meta-openembedded/meta-networking \
     "

and so on.

For more information on layers, see the
":ref:`dev-manual/common-tasks:understanding and creating layers`"
section of the Yocto Project Development Tasks Manual.

Preparing Your Build Host to Work With BSP Layers
=================================================

This section describes how to get your build host ready to work with BSP
layers. Once you have the host set up, you can create the layer as
described in the
":ref:`bsp-guide/bsp:creating a new bsp layer using the \`\`bitbake-layers\`\` script`"
section.

.. note::

   For structural information on BSPs, see the
   :ref:`bsp-guide/bsp:example filesystem layout` section.

#. *Set Up the Build Environment:* Be sure you are set up to use BitBake
   in a shell. See the ":ref:`dev-manual/start:preparing the build host`"
   section in the Yocto Project Development Tasks Manual for information on how
   to get a build host ready that is either a native Linux machine or a machine
   that uses CROPS.

#. *Clone the poky Repository:* You need to have a local copy of the
   Yocto Project :term:`Source Directory` (i.e. a local
   ``poky`` repository). See the
   ":ref:`dev-manual/start:cloning the \`\`poky\`\` repository`" and
   possibly the
   ":ref:`dev-manual/start:checking out by branch in poky`" or
   ":ref:`dev-manual/start:checking out by tag in poky`"
   sections
   all in the Yocto Project Development Tasks Manual for information on
   how to clone the ``poky`` repository and check out the appropriate
   branch for your work.

#. *Determine the BSP Layer You Want:* The Yocto Project supports many
   BSPs, which are maintained in their own layers or in layers designed
   to contain several BSPs. To get an idea of machine support through
   BSP layers, you can look at the `index of
   machines <&YOCTO_RELEASE_DL_URL;/machines>`__ for the release.

#. *Optionally Clone the meta-intel BSP Layer:* If your hardware is
   based on current Intel CPUs and devices, you can leverage this BSP
   layer. For details on the ``meta-intel`` BSP layer, see the layer's
   :yocto_git:`README </meta-intel/tree/README>` file.

   #. *Navigate to Your Source Directory:* Typically, you set up the
      ``meta-intel`` Git repository inside the :term:`Source Directory` (e.g.
      ``poky``). ::

         $ cd /home/you/poky

   #. *Clone the Layer:* ::

         $ git clone git://git.yoctoproject.org/meta-intel.git
         Cloning into 'meta-intel'...
         remote: Counting objects: 15585, done.
         remote: Compressing objects: 100% (5056/5056), done.
         remote: Total 15585 (delta 9123), reused 15329 (delta 8867)
         Receiving objects: 100% (15585/15585), 4.51 MiB | 3.19 MiB/s, done.
         Resolving deltas: 100% (9123/9123), done.
         Checking connectivity... done.

   #. *Check Out the Proper Branch:* The branch you check out for
      ``meta-intel`` must match the same branch you are using for the
      Yocto Project release (e.g. ``&DISTRO_NAME_NO_CAP;``)::

         $ cd meta-intel
         $ git checkout -b &DISTRO_NAME_NO_CAP; remotes/origin/&DISTRO_NAME_NO_CAP;
         Branch &DISTRO_NAME_NO_CAP; set up to track remote branch
         &DISTRO_NAME_NO_CAP; from origin.
         Switched to a new branch '&DISTRO_NAME_NO_CAP;'

      .. note::

         To see the available branch names in a cloned repository, use the ``git
         branch -al`` command. See the
         ":ref:`dev-manual/start:checking out by branch in poky`"
         section in the Yocto Project Development Tasks Manual for more
         information.

#. *Optionally Set Up an Alternative BSP Layer:* If your hardware can be
   more closely leveraged to an existing BSP not within the
   ``meta-intel`` BSP layer, you can clone that BSP layer.

   The process is identical to the process used for the ``meta-intel``
   layer except for the layer's name. For example, if you determine that
   your hardware most closely matches the ``meta-raspberrypi``, clone
   that layer::

      $ git clone git://git.yoctoproject.org/meta-raspberrypi
      Cloning into 'meta-raspberrypi'...
      remote: Counting objects: 4743, done.
      remote: Compressing objects: 100% (2185/2185), done.
      remote: Total 4743 (delta 2447), reused 4496 (delta 2258)
      Receiving objects: 100% (4743/4743), 1.18 MiB | 0 bytes/s, done.
      Resolving deltas: 100% (2447/2447), done.
      Checking connectivity... done.

#. *Initialize the Build Environment:* While in the root directory of
   the Source Directory (i.e. ``poky``), run the
   :ref:`ref-manual/structure:\`\`oe-init-build-env\`\`` environment
   setup script to define the OpenEmbedded build environment on your
   build host. ::

      $ source oe-init-build-env

   Among other things, the script creates the :term:`Build Directory`, which is
   ``build`` in this case and is located in the :term:`Source Directory`.  After
   the script runs, your current working directory is set to the ``build``
   directory.

Example Filesystem Layout
=========================

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

The proposed form described in this section does have elements that are
specific to the OpenEmbedded build system. It is intended that
developers can use this structure with other build systems besides the
OpenEmbedded build system. It is also intended that it will be simple
to extract information and convert it to other formats if required. The
OpenEmbedded build system, through its standard :ref:`layers mechanism
<overview-manual/yp-intro:the yocto project layer model>`, can
directly accept the format described as a layer. The BSP layer captures
all the hardware-specific details in one place using a standard format,
which is useful for any person wishing to use the hardware platform
regardless of the build system they are using.

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

Before looking at the recommended form for the directory structure
inside a BSP layer, you should be aware that there are some requirements
in order for a BSP layer to be considered compliant with the Yocto
Project. For that list of requirements, see the
":ref:`bsp-guide/bsp:released bsp requirements`" section.

Below is the typical directory structure for a BSP layer. While this
basic form represents the standard, realize that the actual layout for
individual BSPs could differ. ::

   meta-bsp_root_name/
   meta-bsp_root_name/bsp_license_file
   meta-bsp_root_name/README
   meta-bsp_root_name/README.sources
   meta-bsp_root_name/binary/bootable_images
   meta-bsp_root_name/conf/layer.conf
   meta-bsp_root_name/conf/machine/*.conf
   meta-bsp_root_name/recipes-bsp/*
   meta-bsp_root_name/recipes-core/*
   meta-bsp_root_name/recipes-graphics/*
   meta-bsp_root_name/recipes-kernel/linux/linux-yocto_kernel_rev.bbappend

Below is an example of the Raspberry Pi BSP layer that is available from
the :yocto_git:`Source Repositories <>`:

.. code-block:: none

   meta-raspberrypi/COPYING.MIT
   meta-raspberrypi/README.md
   meta-raspberrypi/classes
   meta-raspberrypi/classes/sdcard_image-rpi.bbclass
   meta-raspberrypi/conf/
   meta-raspberrypi/conf/layer.conf
   meta-raspberrypi/conf/machine/
   meta-raspberrypi/conf/machine/raspberrypi-cm.conf
   meta-raspberrypi/conf/machine/raspberrypi-cm3.conf
   meta-raspberrypi/conf/machine/raspberrypi.conf
   meta-raspberrypi/conf/machine/raspberrypi0-wifi.conf
   meta-raspberrypi/conf/machine/raspberrypi0.conf
   meta-raspberrypi/conf/machine/raspberrypi2.conf
   meta-raspberrypi/conf/machine/raspberrypi3-64.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/tune-arm1176jzf-s.inc
   meta-raspberrypi/docs
   meta-raspberrypi/docs/Makefile
   meta-raspberrypi/docs/conf.py
   meta-raspberrypi/docs/contributing.md
   meta-raspberrypi/docs/extra-apps.md
   meta-raspberrypi/docs/extra-build-config.md
   meta-raspberrypi/docs/index.rst
   meta-raspberrypi/docs/layer-contents.md
   meta-raspberrypi/docs/readme.md
   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
   meta-raspberrypi/recipes-bsp/formfactor/formfactor
   meta-raspberrypi/recipes-bsp/formfactor/formfactor/raspberrypi
   meta-raspberrypi/recipes-bsp/formfactor/formfactor/raspberrypi/machconfig
   meta-raspberrypi/recipes-bsp/formfactor/formfactor_0.0.bbappend
   meta-raspberrypi/recipes-bsp/rpi-u-boot-src
   meta-raspberrypi/recipes-bsp/rpi-u-boot-src/files
   meta-raspberrypi/recipes-bsp/rpi-u-boot-src/files/boot.cmd.in
   meta-raspberrypi/recipes-bsp/rpi-u-boot-src/rpi-u-boot-scr.bb
   meta-raspberrypi/recipes-bsp/u-boot
   meta-raspberrypi/recipes-bsp/u-boot/u-boot
   meta-raspberrypi/recipes-bsp/u-boot/u-boot/*.patch
   meta-raspberrypi/recipes-bsp/u-boot/u-boot_%.bbappend
   meta-raspberrypi/recipes-connectivity
   meta-raspberrypi/recipes-connectivity/bluez5
   meta-raspberrypi/recipes-connectivity/bluez5/bluez5
   meta-raspberrypi/recipes-connectivity/bluez5/bluez5/*.patch
   meta-raspberrypi/recipes-connectivity/bluez5/bluez5/BCM43430A1.hcd
   meta-raspberrypi/recipes-connectivity/bluez5/bluez5brcm43438.service
   meta-raspberrypi/recipes-connectivity/bluez5/bluez5_%.bbappend
   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/files/psplash-raspberrypi-img.h
   meta-raspberrypi/recipes-core/psplash/psplash_git.bbappend
   meta-raspberrypi/recipes-core/udev
   meta-raspberrypi/recipes-core/udev/udev-rules-rpi
   meta-raspberrypi/recipes-core/udev/udev-rules-rpi/99-com.rules
   meta-raspberrypi/recipes-core/udev/udev-rules-rpi.bb
   meta-raspberrypi/recipes-devtools
   meta-raspberrypi/recipes-devtools/bcm2835
   meta-raspberrypi/recipes-devtools/bcm2835/bcm2835_1.52.bb
   meta-raspberrypi/recipes-devtools/pi-blaster
   meta-raspberrypi/recipes-devtools/pi-blaster/files
   meta-raspberrypi/recipes-devtools/pi-blaster/files/*.patch
   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_2.2.0.bb
   meta-raspberrypi/recipes-devtools/python/rpi-gpio
   meta-raspberrypi/recipes-devtools/python/rpi-gpio/*.patch
   meta-raspberrypi/recipes-devtools/python/rpi-gpio_0.6.3.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_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/mesa
   meta-raspberrypi/recipes-graphics/mesa/mesa-gl_%.bbappend
   meta-raspberrypi/recipes-graphics/mesa/mesa_%.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/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/98-pitft.conf
   meta-raspberrypi/recipes-graphics/xorg-xserver/xserver-xf86-config/rpi/xorg.conf.d/99-calibration.conf
   meta-raspberrypi/recipes-graphics/xorg-xserver/xserver-xf86-config_0.1.bbappend
   meta-raspberrypi/recipes-graphics/xorg-xserver/xserver-xorg_%.bbappend
   meta-raspberrypi/recipes-kernel
   meta-raspberrypi/recipes-kernel/linux-firmware
   meta-raspberrypi/recipes-kernel/linux-firmware/files
   meta-raspberrypi/recipes-kernel/linux-firmware/files/brcmfmac43430-sdio.bin
   meta-raspberrypi/recipes-kernel/linux-firmware/files/brcfmac43430-sdio.txt
   meta-raspberrypi/recipes-kernel/linux-firmware/linux-firmware_%.bbappend
   meta-raspberrypi/recipes-kernel/linux
   meta-raspberrypi/recipes-kernel/linux/linux-raspberrypi-dev.bb
   meta-raspberrypi/recipes-kernel/linux/linux-raspberrypi.inc
   meta-raspberrypi/recipes-kernel/linux/linux-raspberrypi_4.14.bb
   meta-raspberrypi/recipes-kernel/linux/linux-raspberrypi_4.9.bb
   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/gstreamer/gstreamer1.0-omx-1.12
   meta-raspberrypi/recipes-multimedia/gstreamer/gstreamer1.0-omx-1.12/*.patch
   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/recipes-multimedia/x264
   meta-raspberrypi/recipes-multimedia/x264/x264_git.bbappend
   meta-raspberrypi/wic meta-raspberrypi/wic/sdimage-raspberrypi.wks

The following sections describe each part of the proposed BSP format.

License Files
-------------

You can find these files in the BSP Layer at::

   meta-bsp_root_name/bsp_license_file

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 ``COPYING.MIT`` file.

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. For information on how to maintain license compliance, see
the ":ref:`dev-manual/common-tasks:maintaining open source license compliance during your product's lifecycle`"
section in the Yocto Project Development Tasks Manual.

README File
-----------

You can find this file in the BSP Layer at::

   meta-bsp_root_name/README

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

At a minimum, the ``README`` 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.

README.sources File
-------------------

You can find this file in the BSP Layer at::

   meta-bsp_root_name/README.sources

This file provides information on where to locate the BSP source files
used to build the images (if any) that reside in
``meta-bsp_root_name/binary``. Images in the ``binary`` would be images
released with the BSP. The information in the ``README.sources`` file
also helps you find the :term:`Metadata`
used to generate the images that ship with the BSP.

.. note::

   If the BSP's ``binary`` directory is missing or the directory has no images, an
   existing ``README.sources`` file is meaningless and usually does not exist.

Pre-built User Binaries
-----------------------

You can find these files in the BSP Layer at::

   meta-bsp_root_name/binary/bootable_images

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 :yocto_home:`Yocto Project <>` website. You can
use these kernels and images to get a system running and quickly get
started on development tasks.

The exact types of binaries present are highly hardware-dependent. The
:ref:`README <bsp-guide/bsp:readme file>` file should be present in the
BSP Layer and it explains how to use the images with the target
hardware. Additionally, the
:ref:`README.sources <bsp-guide/bsp:readme.sources file>` file should be
present to locate the sources used to build the images and provide
information on the Metadata.

Layer Configuration File
------------------------

You can find this file in the BSP Layer at::

   meta-bsp_root_name/conf/layer.conf

The ``conf/layer.conf`` 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
"bsp" with the actual name of the BSP (i.e. "bsp_root_name" from the example
template). ::

   # We have a conf and classes directory, add 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 += "bsp"
   BBFILE_PATTERN_bsp = "^${LAYERDIR}/"
   BBFILE_PRIORITY_bsp = "6"
   LAYERDEPENDS_bsp = "intel"

To illustrate the string substitutions, here are the corresponding
statements from the Raspberry Pi ``conf/layer.conf`` file::

   # 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"
   .
   .
   .

This file simply makes :term:`BitBake` aware of the recipes and configuration
directories. The file must exist so that the OpenEmbedded build system can
recognize the BSP.

Hardware Configuration Options
------------------------------

You can find these files in the BSP Layer at::

   meta-bsp_root_name/conf/machine/*.conf

The machine files bind together all the information contained elsewhere
in the BSP into a format that the build system can understand. Each BSP
Layer requires at least one machine file. If the BSP supports multiple
machines, multiple machine configuration files can exist. These
filenames correspond to the values to which users have set the
:term:`MACHINE` variable.

These files define things such as the kernel package to use
(:term:`PREFERRED_PROVIDER` of
:ref:`virtual/kernel <dev-manual/common-tasks:using virtual providers>`),
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.

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.

Tuning files are found in the ``meta/conf/machine/include`` directory
within the :term:`Source Directory`.
For example, many ``tune-*`` files (e.g. ``tune-arm1136jf-s.inc``,
``tune-1586-nlp.inc``, and so forth) reside in the
``poky/meta/conf/machine/include`` directory.

To use an include file, you simply include them in the machine
configuration file. For example, the Raspberry Pi BSP
``raspberrypi3.conf`` contains the following statement::

   include conf/machine/include/rpi-base.inc

Miscellaneous BSP-Specific Recipe Files
---------------------------------------

You can find these files in the BSP Layer at::

   meta-bsp_root_name/recipes-bsp/*

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 ``formfactor_0.0.bbappend`` 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 ``machconfig`` file further down in the
directory. Here is the ``machconfig`` file for the Raspberry Pi BSP::

   HAVE_TOUCHSCREEN=0
   HAVE_KEYBOARD=1

   DISPLAY_CAN_ROTATE=0
   DISPLAY_ORIENTATION=0
   DISPLAY_DPI=133

.. note::

   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
   ``meta/recipes-bsp/formfactor/formfactor_0.0.bb``, which is found in
   the :term:`Source Directory`.

Display Support Files
---------------------

You can find these files in the BSP Layer at::

   meta-bsp_root_name/recipes-graphics/*

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.

Linux Kernel Configuration
--------------------------

You can find these files in the BSP Layer at::

   meta-bsp_root_name/recipes-kernel/linux/linux*.bbappend
   meta-bsp_root_name/recipes-kernel/linux/*.bb

Append files (``*.bbappend``) modify the main kernel recipe being used
to build the image. The ``*.bb`` files would be a developer-supplied
kernel recipe. This area of the BSP hierarchy can contain both these
types of files although, in practice, it is likely that you would have
one or the other.

For your BSP, you typically want to use an existing Yocto Project kernel
recipe found in the :term:`Source Directory`
at
``meta/recipes-kernel/linux``. 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
``meta-bsp_root_name/recipes-kernel/linux`` directory).

Suppose you are using the ``linux-yocto_4.4.bb`` recipe to build the
kernel. In other words, you have selected the kernel in your
``"bsp_root_name".conf`` file by adding
:term:`PREFERRED_PROVIDER` and :term:`PREFERRED_VERSION`
statements as follows::

   PREFERRED_PROVIDER_virtual/kernel ?= "linux-yocto"
   PREFERRED_VERSION_linux-yocto ?= "4.4%"

.. note::

   When the preferred provider is assumed by default, the ``PREFERRED_PROVIDER``
   statement does not appear in the ``"bsp_root_name".conf`` file.

You would use the ``linux-yocto_4.4.bbappend`` file to append specific
BSP settings to the kernel, thus configuring the kernel for your
particular BSP.

You can find more information on what your append file should contain in
the ":ref:`kernel-dev/common:creating the append file`" section
in the Yocto Project Linux Kernel Development Manual.

An alternate scenario is when you create your own kernel recipe for the
BSP. A good example of this is the Raspberry Pi BSP. If you examine the
``recipes-kernel/linux`` directory you see the following::

   linux-raspberrypi-dev.bb
   linux-raspberrypi.inc
   linux-raspberrypi_4.14.bb
   linux-raspberrypi_4.9.bb

The directory contains three kernel recipes and a common include file.

Developing a Board Support Package (BSP)
========================================

This section describes the high-level procedure you can follow to create
a BSP. Although not required for BSP creation, the ``meta-intel``
repository, which contains many BSPs supported by the Yocto Project, is
part of the example.

For an example that shows how to create a new layer using the tools, see
the ":ref:`bsp-guide/bsp:creating a new bsp layer using the \`\`bitbake-layers\`\` script`"
section.

The following illustration and list summarize the BSP creation general
workflow.

.. image:: figures/bsp-dev-flow.png
   :align: center

#. *Set up Your Host Development System to Support Development Using the
   Yocto Project*: See the ":ref:`dev-manual/start:preparing the build host`"
   section in the Yocto Project Development Tasks Manual for options on how to
   get a system ready to use the Yocto Project.

#. *Establish the meta-intel Repository on Your System:* Having
   local copies of these supported BSP layers on your system gives you
   access to layers you might be able to leverage when creating your
   BSP. For information on how to get these files, see the
   ":ref:`bsp-guide/bsp:preparing your build host to work with bsp layers`"
   section.

#. *Create Your Own BSP Layer Using the bitbake-layers Script:*
   Layers are ideal for isolating and storing work for a given piece of
   hardware. A layer is really just a location or area in which you
   place the recipes and configurations for your BSP. In fact, a BSP is,
   in itself, a special type of layer. The simplest way to create a new
   BSP layer that is compliant with the Yocto Project is to use the
   ``bitbake-layers`` script. For information about that script, see the
   ":ref:`bsp-guide/bsp:creating a new bsp layer using the \`\`bitbake-layers\`\` script`"
   section.

   Another example that illustrates a layer is an application. Suppose
   you are creating an application that has library or other
   dependencies in order for it to compile and run. The layer, in this
   case, would be where all the recipes that define those dependencies
   are kept. The key point for a layer is that it is an isolated area
   that contains all the relevant information for the project that the
   OpenEmbedded build system knows about. For more information on
   layers, see the ":ref:`overview-manual/yp-intro:the yocto project layer model`"
   section in the Yocto Project Overview and Concepts Manual. You can also
   reference the ":ref:`dev-manual/common-tasks:understanding and creating layers`"
   section in the Yocto Project Development Tasks Manual. For more
   information on BSP layers, see the ":ref:`bsp-guide/bsp:bsp layers`"
   section.

   .. note::

      -  There are four hardware reference BSPs in the Yocto
         Project release, located in the ``poky/meta-yocto-bsp``
         BSP layer:

         -  Texas Instruments Beaglebone (``beaglebone-yocto``)

         -  Ubiquiti Networks EdgeRouter Lite (``edgerouter``)

         -  Two general IA platforms (``genericx86`` and ``genericx86-64``)

      -  There are three core Intel BSPs in the Yocto Project
         release, in the ``meta-intel`` layer:

         -  ``intel-core2-32``, which is a BSP optimized for the Core2
            family of CPUs as well as all CPUs prior to the Silvermont
            core.

         -  ``intel-corei7-64``, which is a BSP optimized for Nehalem
            and later Core and Xeon CPUs as well as Silvermont and later
            Atom CPUs, such as the Baytrail SoCs.

         -  ``intel-quark``, which is a BSP optimized for the Intel
            Galileo gen1 & gen2 development boards.

   When you set up a layer for a new BSP, you should follow a standard
   layout. This layout is described in the ":ref:`bsp-guide/bsp:example filesystem layout`"
   section. In the standard layout, notice
   the suggested structure for recipes and configuration information.
   You can see the standard layout for a BSP by examining any supported
   BSP found in the ``meta-intel`` layer inside the Source Directory.

#. *Make Configuration Changes to Your New BSP Layer:* The standard BSP
   layer structure organizes the files you need to edit in ``conf`` and
   several ``recipes-*`` directories within the BSP layer. Configuration
   changes identify where your new layer is on the local system and
   identifies the kernel you are going to use. When you run the
   ``bitbake-layers`` script, you are able to interactively configure
   many things for the BSP (e.g. keyboard, touchscreen, and so forth).

#. *Make Recipe Changes to Your New BSP Layer:* Recipe changes include
   altering recipes (``*.bb`` files), removing recipes you do not use,
   and adding new recipes or append files (``.bbappend``) that support
   your hardware.

#. *Prepare for the Build:* Once you have made all the changes to your
   BSP layer, there remains a few things you need to do for the
   OpenEmbedded build system in order for it to create your image. You
   need to get the build environment ready by sourcing an environment
   setup script (i.e. ``oe-init-build-env``) and you need to be sure two
   key configuration files are configured appropriately: the
   ``conf/local.conf`` and the ``conf/bblayers.conf`` file. You must
   make the OpenEmbedded build system aware of your new layer. See the
   ":ref:`dev-manual/common-tasks:enabling your layer`"
   section in the Yocto Project Development Tasks Manual for information
   on how to let the build system know about your new layer.

#. *Build the Image:* The OpenEmbedded build system uses the BitBake
   tool to build images based on the type of image you want to create.
   You can find more information about BitBake in the
   :doc:`BitBake User Manual <bitbake:index>`.

   The build process supports several types of images to satisfy
   different needs. See the
   ":ref:`ref-manual/images:Images`" chapter in the Yocto
   Project Reference Manual for information on supported images.

Requirements and Recommendations for Released BSPs
==================================================

This section describes requirements and recommendations for a released
BSP to be considered compliant with the Yocto Project.

Released BSP Requirements
-------------------------

Before looking at BSP requirements, you should consider the following:

-  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
   ":ref:`bsp-guide/bsp:bsp layers`" section in this manual and the
   ":ref:`dev-manual/common-tasks:understanding and creating layers`"
   section in the Yocto Project Development Tasks Manual.

-  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 ":yocto_wiki:`Third Party BSP Release
   Process </Third_Party_BSP_Release_Process>`"
   wiki page.

-  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.

-  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, there is no requirement
   dictating that a specific kernel or kernel version be used in a given
   BSP.

Following are the requirements for a released BSP that conform to the
Yocto Project:

-  *Layer Name:* The BSP must have a layer name that follows the Yocto
   Project standards. For information on BSP layer names, see the
   ":ref:`bsp-guide/bsp:bsp layers`" section.

-  *File System Layout:* When possible, use the same directory names in
   your BSP layer as listed in the ``recipes.txt`` file, which is found
   in ``poky/meta`` directory of the :term:`Source Directory`
   or in the OpenEmbedded-Core Layer (``openembedded-core``) at
   https://git.openembedded.org/openembedded-core/tree/meta.

   You should place recipes (``*.bb`` files) and recipe modifications
   (``*.bbappend`` files) into ``recipes-*`` subdirectories by
   functional area as outlined in ``recipes.txt``. If you cannot find a
   category in ``recipes.txt`` to fit a particular recipe, you can make
   up your own ``recipes-*`` subdirectory.

   Within any particular ``recipes-*`` category, the layout should match
   what is found in the OpenEmbedded-Core Git repository
   (``openembedded-core``) or the Source Directory (``poky``). In other
   words, make sure you place related files in appropriately-related
   ``recipes-*`` 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 ":oe_wiki:`OpenEmbedded
   Style Guide </Styleguide>`".

-  *License File:* You must include a license file in the
   ``meta-bsp_root_name`` directory. This license covers the BSP
   Metadata as a whole. You must specify which license to use since no
   default license exists. See the
   :yocto_git:`COPYING.MIT </meta-raspberrypi/tree/COPYING.MIT>`
   file for the Raspberry Pi BSP in the ``meta-raspberrypi`` BSP layer
   as an example.

-  *README File:* You must include a ``README`` file in the
   ``meta-bsp_root_name`` directory. See the
   :yocto_git:`README.md </meta-raspberrypi/tree/README.md>`
   file for the Raspberry Pi BSP in the ``meta-raspberrypi`` BSP layer
   as an example.

   At a minimum, the ``README`` file should contain the following:

   -  A brief description of the target hardware.

   -  A list of all the dependencies of the BSP. 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.

   -  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.

   -  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
      ":ref:`dev-manual/common-tasks:submitting a change to the yocto project`"
      section in the Yocto Project Development Tasks Manual.

   -  Instructions on how to build the BSP using the BSP layer.

   -  Instructions on how to boot the BSP build from the BSP layer.

   -  Instructions on how to boot the binary images contained in the
      ``binary`` directory, if present.

   -  Information on any known bugs or issues that users should know
      about when either building or booting the BSP binaries.

-  *README.sources File:* If your BSP contains binary images in the
   ``binary`` directory, you must include a ``README.sources`` file in
   the ``meta-bsp_root_name`` directory. This file specifies exactly
   where you can find the sources used to generate the binary images.

-  *Layer Configuration File:* You must include a ``conf/layer.conf``
   file in the ``meta-bsp_root_name`` directory. This file identifies
   the ``meta-bsp_root_name`` BSP layer as a layer to the build
   system.

-  *Machine Configuration File:* You must include one or more
   ``conf/machine/bsp_root_name.conf`` files in the
   ``meta-bsp_root_name`` 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 the BSP supports. If a BSP supports multiple
   machine variations, you need to adequately describe each variation in
   the BSP ``README`` 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.  ``meta-yocto-bsp`` layer). Such considerations
      are outside the scope of this document.

Released BSP Recommendations
----------------------------

Following are recommendations for released BSPs that conform to the
Yocto Project:

-  *Bootable Images:* Released BSPs can contain one or more bootable
   images. Including bootable images allows users to easily try out the
   BSP using their own hardware.

   In some cases, it might not be convenient to include a bootable
   image. If so, 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.

   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
   ``binary/`` subdirectory located in the ``meta-bsp_root_name``
   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.

-  *Use a Yocto Linux Kernel:* 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 ``Yocto Linux Kernel`` category in the
   :yocto_git:`Source Repositories <>` for these kernels.

Customizing a Recipe for a BSP
==============================

If you plan on customizing a recipe for a particular BSP, you need to do
the following:

-  Create a ``*.bbappend`` file for the modified recipe. For information on using
   append files, see the ":ref:`dev-manual/common-tasks:using
   .bbappend files in your layer`" section in the Yocto Project Development
   Tasks Manual.

-  Ensure your directory structure in the BSP layer that supports your
   machine is such that the OpenEmbedded build system can find it. See
   the example later in this section for more information.

-  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. ``recipes-bsp``, ``recipes-graphics``, ``recipes-core``,
   and so forth).

-  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 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.

Following is a specific example to help you better understand the
process. This example customizes a recipe by adding a
BSP-specific configuration file named ``interfaces`` to the
``init-ifupdown_1.0.bb`` recipe for machine "xyz" where the BSP layer
also supports several other machines:

#. Edit the ``init-ifupdown_1.0.bbappend`` file so that it contains the
   following::

      FILESEXTRAPATHS_prepend := "${THISDIR}/files:"

   The append file needs to be in the ``meta-xyz/recipes-core/init-ifupdown``
   directory.

#. Create and place the new ``interfaces`` configuration file in the
   BSP's layer here::

      meta-xyz/recipes-core/init-ifupdown/files/xyz-machine-one/interfaces

   .. note::

      If the ``meta-xyz`` layer did not support multiple machines, you would place
      the interfaces configuration file in the layer here::

         meta-xyz/recipes-core/init-ifupdown/files/interfaces

   The :term:`FILESEXTRAPATHS` 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 ``files`` directory in the same location as
   your append file.

BSP Licensing Considerations
============================

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 you accept
the license, 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.

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.

For cases where you can substitute a free component and still maintain
the system's functionality, the "DOWNLOADS" selection from the
"SOFTWARE" tab on the :yocto_home:`Yocto Project Website <>` 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 their respective encumbered BSPs. If available, these
substitutions are your simplest and most preferred options. Obviously,
use of these substitutions assumes the resulting functionality meets
system requirements.

.. note::

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

There are two different methods within the OpenEmbedded build system to
satisfy the licensing requirements for an encumbered BSP. The following
list describes them in order of preference:

#. *Use the LICENSE_FLAGS Variable to Define the Recipes that Have Commercial or
   Other Types of Specially-Licensed Packages:* For each of those recipes, you can
   specify a matching license string in a ``local.conf`` variable named
   :term:`LICENSE_FLAGS_WHITELIST`.
   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
   ":ref:`dev-manual/common-tasks:enabling commercially licensed recipes`"
   section in the Yocto Project Development Tasks Manual for details on
   how to use these variables.

   If you build as you normally would, without specifying any recipes in
   the ``LICENSE_FLAGS_WHITELIST``, 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 ``LICENSE_FLAGS_WHITELIST``. 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.

   Once the appropriate license flags are on the white list in the
   ``LICENSE_FLAGS_WHITELIST`` variable, you can build the encumbered
   image with no change at all to the normal build process.

#. *Get a Pre-Built Version of the BSP:* You can get this type of BSP by
   selecting the "DOWNLOADS" item from the "SOFTWARE" tab on the
   :yocto_home:`Yocto Project website <>`. 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. If you
   want to build the image yourself using the recipes contained within
   the BSP tarball, you will still need to create an appropriate
   ``LICENSE_FLAGS_WHITELIST`` to match the encumbered recipes in the
   BSP.

.. 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.

Creating a new BSP Layer Using the ``bitbake-layers`` Script
============================================================

The ``bitbake-layers create-layer`` script automates creating a BSP
layer. What makes a layer a "BSP layer" is the presence of at least one
machine configuration file. Additionally, a BSP layer usually has a
kernel recipe or an append file that leverages off an existing kernel
recipe. The primary requirement, however, is the machine configuration.

Use these steps to create a BSP layer:

-  *Create a General Layer:* Use the ``bitbake-layers`` script with the
   ``create-layer`` subcommand to create a new general layer. For
   instructions on how to create a general layer using the
   ``bitbake-layers`` script, see the
   ":ref:`dev-manual/common-tasks:creating a general layer using the \`\`bitbake-layers\`\` script`"
   section in the Yocto Project Development Tasks Manual.

-  *Create a Layer Configuration File:* Every layer needs a layer
   configuration file. This configuration file establishes locations for
   the layer's recipes, priorities for the layer, and so forth. You can
   find examples of ``layer.conf`` files in the Yocto Project
   :yocto_git:`Source Repositories <>`. To get examples of what you need
   in your configuration file, locate a layer (e.g. "meta-ti") and
   examine the
   :yocto_git:`local.conf </meta-ti/tree/conf/layer.conf>`
   file.

-  *Create a Machine Configuration File:* Create a
   ``conf/machine/bsp_root_name.conf`` file. See
   :yocto_git:`meta-yocto-bsp/conf/machine </poky/tree/meta-yocto-bsp/conf/machine>`
   for sample ``bsp_root_name.conf`` files. There are other samples such as
   :yocto_git:`meta-ti </meta-ti/tree/conf/machine>`
   and
   :yocto_git:`meta-freescale </meta-freescale/tree/conf/machine>`
   from other vendors that have more specific machine and tuning
   examples.

-  *Create a Kernel Recipe:* Create a kernel recipe in
   ``recipes-kernel/linux`` by either using a kernel append file or a
   new custom kernel recipe file (e.g. ``yocto-linux_4.12.bb``). The BSP
   layers mentioned in the previous step also contain different kernel
   examples. See the ":ref:`kernel-dev/common:modifying an existing recipe`"
   section in the Yocto Project Linux Kernel Development Manual for
   information on how to create a custom kernel.

The remainder of this section provides a description of the Yocto
Project reference BSP for Beaglebone, which resides in the
:yocto_git:`meta-yocto-bsp </poky/tree/meta-yocto-bsp>`
layer.

BSP Layer Configuration Example
-------------------------------

The layer's ``conf`` directory contains the ``layer.conf`` configuration
file. In this example, the ``conf/layer.conf`` is the following::

   # We have a conf and classes directory, add 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 += "yoctobsp"
   BBFILE_PATTERN_yoctobsp = "^${LAYERDIR}/"
   BBFILE_PRIORITY_yoctobsp = "5"
   LAYERVERSION_yoctobsp = "4"
   LAYERSERIES_COMPAT_yoctobsp = "&DISTRO_NAME_NO_CAP;"

The variables used in this file configure the layer. A good way to learn about layer
configuration files is to examine various files for BSP from the
:yocto_git:`Source Repositories <>`.

For a detailed description of this particular layer configuration file,
see ":ref:`step 3 <dev-manual/common-tasks:creating your own layer>`"
in the discussion that describes how to create layers in the Yocto
Project Development Tasks Manual.

BSP Machine Configuration Example
---------------------------------

As mentioned earlier in this section, the existence of a machine
configuration file is what makes a layer a BSP layer as compared to a
general or kernel layer.

There are one or more machine configuration files in the
``bsp_layer/conf/machine/`` directory of the layer::

   bsp_layer/conf/machine/machine1\.conf
   bsp_layer/conf/machine/machine2\.conf
   bsp_layer/conf/machine/machine3\.conf
   ... more ...

For example, the machine configuration file for the `BeagleBone and
BeagleBone Black development boards <https://beagleboard.org/bone>`__ is
located in the layer ``poky/meta-yocto-bsp/conf/machine`` and is named
``beaglebone-yocto.conf``::

   #@TYPE: Machine
   #@NAME: Beaglebone-yocto machine
   #@DESCRIPTION: Reference machine configuration for http://beagleboard.org/bone and http://beagleboard.org/black boards

   PREFERRED_PROVIDER_virtual/xserver ?= "xserver-xorg"
   XSERVER ?= "xserver-xorg \
               xf86-video-modesetting \
              "

   MACHINE_EXTRA_RRECOMMENDS = "kernel-modules kernel-devicetree"

   EXTRA_IMAGEDEPENDS += "u-boot"

   DEFAULTTUNE ?= "cortexa8hf-neon"
   include conf/machine/include/tune-cortexa8.inc

   IMAGE_FSTYPES += "tar.bz2 jffs2 wic wic.bmap"
   EXTRA_IMAGECMD_jffs2 = "-lnp "
   WKS_FILE ?= "beaglebone-yocto.wks"
   IMAGE_INSTALL_append = " kernel-devicetree kernel-image-zimage"
   do_image_wic[depends] += "mtools-native:do_populate_sysroot dosfstools-native:do_populate_sysroot"

   SERIAL_CONSOLES ?= "115200;ttyS0 115200;ttyO0"
   SERIAL_CONSOLES_CHECK = "${SERIAL_CONSOLES}"

   PREFERRED_PROVIDER_virtual/kernel ?= "linux-yocto"
   PREFERRED_VERSION_linux-yocto ?= "5.0%"

   KERNEL_IMAGETYPE = "zImage"
   KERNEL_DEVICETREE = "am335x-bone.dtb am335x-boneblack.dtb am335x-bonegreen.dtb"
   KERNEL_EXTRA_ARGS += "LOADADDR=${UBOOT_ENTRYPOINT}"

   SPL_BINARY = "MLO"
   UBOOT_SUFFIX = "img"
   UBOOT_MACHINE = "am335x_evm_defconfig"
   UBOOT_ENTRYPOINT = "0x80008000"
   UBOOT_LOADADDRESS = "0x80008000"

   MACHINE_FEATURES = "usbgadget usbhost vfat alsa"

   IMAGE_BOOT_FILES ?= "u-boot.${UBOOT_SUFFIX} MLO zImage am335x-bone.dtb am335x-boneblack.dtb am335x-bonegreen.dtb"

The variables used to configure the machine define machine-specific properties; for
example, machine-dependent packages, machine tunings, the type of kernel
to build, and U-Boot configurations.

The following list provides some explanation for the statements found in
the example reference machine configuration file for the BeagleBone
development boards. Realize that much more can be defined as part of a
machine's configuration file. In general, you can learn about related
variables that this example does not have by locating the variables in
the ":ref:`ref-manual/variables:variables glossary`" in the Yocto
Project Reference Manual.

-  :term:`PREFERRED_PROVIDER_virtual/xserver <PREFERRED_PROVIDER>`:
   The recipe that provides "virtual/xserver" when more than one
   provider is found. In this case, the recipe that provides
   "virtual/xserver" is "xserver-xorg", available in
   ``poky/meta/recipes-graphics/xorg-xserver``.

-  :term:`XSERVER`: The packages that
   should be installed to provide an X server and drivers for the
   machine. In this example, the "xserver-xorg" and
   "xf86-video-modesetting" are installed.

-  :term:`MACHINE_EXTRA_RRECOMMENDS`:
   A list of machine-dependent packages not essential for booting the
   image. Thus, the build does not fail if the packages do not exist.
   However, the packages are required for a fully-featured image.

   .. tip::

      There are many ``MACHINE*`` variables that help you configure a particular piece
      of hardware.

-  :term:`EXTRA_IMAGEDEPENDS`:
   Recipes to build that do not provide packages for installing into the
   root filesystem but building the image depends on the recipes.
   Sometimes a recipe is required to build the final image but is not
   needed in the root filesystem. In this case, the U-Boot recipe must
   be built for the image.

-  :term:`DEFAULTTUNE`: Machines
   use tunings to optimize machine, CPU, and application performance.
   These features, which are collectively known as "tuning features",
   are set in the :term:`OpenEmbedded-Core (OE-Core)` layer (e.g.
   ``poky/meta/conf/machine/include``). In this example, the default
   tuning file is ``cortexa8hf-neon``.

   .. note::

      The include statement that pulls in the
      ``conf/machine/include/tune-cortexa8.inc`` file provides many tuning
      possibilities.

-  :term:`IMAGE_FSTYPES`: The
   formats the OpenEmbedded build system uses during the build when
   creating the root filesystem. In this example, four types of images
   are supported.

-  :term:`EXTRA_IMAGECMD`:
   Specifies additional options for image creation commands. In this
   example, the "-lnp " option is used when creating the
   `JFFS2 <https://en.wikipedia.org/wiki/JFFS2>`__ image.

-  :term:`WKS_FILE`: The location of
   the :ref:`Wic kickstart <ref-manual/kickstart:openembedded kickstart (\`\`.wks\`\`) reference>` file used
   by the OpenEmbedded build system to create a partitioned image
   (image.wic).

-  :term:`IMAGE_INSTALL`:
   Specifies packages to install into an image through the
   :ref:`image <ref-classes-image>` class. Recipes
   use the ``IMAGE_INSTALL`` variable.

-  ``do_image_wic[depends]``: A task that is constructed during the
   build. In this example, the task depends on specific tools in order
   to create the sysroot when building a Wic image.

-  :term:`SERIAL_CONSOLES`:
   Defines a serial console (TTY) to enable using getty. In this case,
   the baud rate is "115200" and the device name is "ttyO0".

-  :term:`PREFERRED_PROVIDER_virtual/kernel <PREFERRED_PROVIDER>`:
   Specifies the recipe that provides "virtual/kernel" when more than
   one provider is found. In this case, the recipe that provides
   "virtual/kernel" is "linux-yocto", which exists in the layer's
   ``recipes-kernel/linux`` directory.

-  :term:`PREFERRED_VERSION_linux-yocto <PREFERRED_VERSION>`:
   Defines the version of the recipe used to build the kernel, which is
   "5.0" in this case.

-  :term:`KERNEL_IMAGETYPE`:
   The type of kernel to build for the device. In this case, the
   OpenEmbedded build system creates a "zImage" image type.

-  :term:`KERNEL_DEVICETREE`:
   The names of the generated Linux kernel device trees (i.e. the
   ``*.dtb``) files. All the device trees for the various BeagleBone
   devices are included.

-  :term:`KERNEL_EXTRA_ARGS`:
   Additional ``make`` command-line arguments the OpenEmbedded build
   system passes on when compiling the kernel. In this example,
   ``LOADADDR=${UBOOT_ENTRYPOINT}`` is passed as a command-line argument.

-  :term:`SPL_BINARY`: Defines the
   Secondary Program Loader (SPL) binary type. In this case, the SPL
   binary is set to "MLO", which stands for Multimedia card LOader.

   The BeagleBone development board requires an SPL to boot and that SPL
   file type must be MLO. Consequently, the machine configuration needs
   to define ``SPL_BINARY`` as ``MLO``.

   .. note::

      For more information on how the SPL variables are used, see the
      :yocto_git:`u-boot.inc </poky/tree/meta/recipes-bsp/u-boot/u-boot.inc>`
      include file.

-  :term:`UBOOT_* <UBOOT_ENTRYPOINT>`: Defines
   various U-Boot configurations needed to build a U-Boot image. In this
   example, a U-Boot image is required to boot the BeagleBone device.
   See the following variables for more information:

   -  :term:`UBOOT_SUFFIX`:
      Points to the generated U-Boot extension.

   -  :term:`UBOOT_MACHINE`:
      Specifies the value passed on the make command line when building
      a U-Boot image.

   -  :term:`UBOOT_ENTRYPOINT`:
      Specifies the entry point for the U-Boot image.

   -  :term:`UBOOT_LOADADDRESS`:
      Specifies the load address for the U-Boot image.

-  :term:`MACHINE_FEATURES`:
   Specifies the list of hardware features the BeagleBone device is
   capable of supporting. In this case, the device supports "usbgadget
   usbhost vfat alsa".

-  :term:`IMAGE_BOOT_FILES`:
   Files installed into the device's boot partition when preparing the
   image using the Wic tool with the ``bootimg-partition`` or
   ``bootimg-efi`` source plugin.

BSP Kernel Recipe Example
-------------------------

The kernel recipe used to build the kernel image for the BeagleBone
device was established in the machine configuration::

   PREFERRED_PROVIDER_virtual/kernel ?= "linux-yocto"
   PREFERRED_VERSION_linux-yocto ?= "5.0%"

The ``meta-yocto-bsp/recipes-kernel/linux`` directory in the layer contains
metadata used to build the kernel. In this case, a kernel append file
(i.e. ``linux-yocto_5.0.bbappend``) is used to override an established
kernel recipe (i.e. ``linux-yocto_5.0.bb``), which is located in
:yocto_git:`/poky/tree/meta/recipes-kernel/linux`.

Following is the contents of the append file::

   KBRANCH_genericx86 = "v5.0/standard/base"
   KBRANCH_genericx86-64 = "v5.0/standard/base"
   KBRANCH_edgerouter = "v5.0/standard/edgerouter"
   KBRANCH_beaglebone-yocto = "v5.0/standard/beaglebone"

   KMACHINE_genericx86 ?= "common-pc"
   KMACHINE_genericx86-64 ?= "common-pc-64"
   KMACHINE_beaglebone-yocto ?= "beaglebone"

   SRCREV_machine_genericx86 ?= "3df4aae6074e94e794e27fe7f17451d9353cdf3d"
   SRCREV_machine_genericx86-64 ?= "3df4aae6074e94e794e27fe7f17451d9353cdf3d"
   SRCREV_machine_edgerouter ?= "3df4aae6074e94e794e27fe7f17451d9353cdf3d"
   SRCREV_machine_beaglebone-yocto ?= "3df4aae6074e94e794e27fe7f17451d9353cdf3d"

   COMPATIBLE_MACHINE_genericx86 = "genericx86"
   COMPATIBLE_MACHINE_genericx86-64 = "genericx86-64"
   COMPATIBLE_MACHINE_edgerouter = "edgerouter"
   COMPATIBLE_MACHINE_beaglebone-yocto = "beaglebone-yocto"

   LINUX_VERSION_genericx86 = "5.0.3"
   LINUX_VERSION_genericx86-64 = "5.0.3"
   LINUX_VERSION_edgerouter = "5.0.3"
   LINUX_VERSION_beaglebone-yocto = "5.0.3"

This particular append file works for all the machines that are
part of the ``meta-yocto-bsp`` layer. The relevant statements are
appended with the "beaglebone-yocto" string. The OpenEmbedded build
system uses these statements to override similar statements in the
kernel recipe:

-  :term:`KBRANCH`: Identifies the
   kernel branch that is validated, patched, and configured during the
   build.

-  :term:`KMACHINE`: Identifies the
   machine name as known by the kernel, which is sometimes a different
   name than what is known by the OpenEmbedded build system.

-  :term:`SRCREV`: Identifies the
   revision of the source code used to build the image.

-  :term:`COMPATIBLE_MACHINE`:
   A regular expression that resolves to one or more target machines
   with which the recipe is compatible.

-  :term:`LINUX_VERSION`: The
   Linux version from kernel.org used by the OpenEmbedded build system
   to build the kernel image.