Yocto Project Board Support Package Developer's Guide

Saul Wold

Intel Corporation

Richard Purdie

Linux Foundation

Permission is granted to copy, distribute and/or modify this document under the terms of the Creative Commons Attribution-Share Alike 2.0 UK: England & Wales as published by Creative Commons.

Manual Notes

  • For the latest version of the Yocto Project Board Support Package (BSP) Developer's Guide associated with this Yocto Project release (version 2.4), see the Yocto Project Board Support Package (BSP) Developer's Guide from the Yocto Project documentation page.

  • This version of the manual is version 2.4. For later releases of the Yocto Project (if they exist), go to the Yocto Project documentation page and use the drop-down "Active Releases" button and choose the Yocto Project version for which you want the manual.

  • For an in-development version of the Yocto Project Board Support Package (BSP) Developer's Guide, see http://www.yoctoproject.org/docs/latest/bsp-guide/bsp-guide.html.

Revision History
Revision 0.924 November 2010
The initial document draft released with the Yocto Project 0.9 Release.
Revision 1.06 April 2011
Released with the Yocto Project 1.0 Release.
Revision 1.0.123 May 2011
Released with the Yocto Project 1.0.1 Release.
Revision 1.16 October 2011
Released with the Yocto Project 1.1 Release.
Revision 1.2April 2012
Released with the Yocto Project 1.2 Release.
Revision 1.3October 2012
Released with the Yocto Project 1.3 Release.
Revision 1.4April 2013
Released with the Yocto Project 1.4 Release.
Revision 1.5October 2013
Released with the Yocto Project 1.5 Release.
Revision 1.5.1January 2014
Released with the Yocto Project 1.5.1 Release.
Revision 1.6April 2014
Released with the Yocto Project 1.6 Release.
Revision 1.7October 2014
Released with the Yocto Project 1.7 Release.
Revision 1.8April 2015
Released with the Yocto Project 1.8 Release.
Revision 2.0October 2015
Released with the Yocto Project 2.0 Release.
Revision 2.1April 2016
Released with the Yocto Project 2.1 Release.
Revision 2.2October 2016
Released with the Yocto Project 2.2 Release.
Revision 2.3May 2017
Released with the Yocto Project 2.3 Release.
Revision 2.4Usually October
Released with the Yocto Project 2.4 Release.

Table of Contents

1. Board Support Packages (BSP) - Developer's Guide
1.1. BSP Layers
1.2. Example Filesystem Layout
1.2.1. License Files
1.2.2. README File
1.2.3. README.sources File
1.2.4. Pre-built User Binaries
1.2.5. Layer Configuration File
1.2.6. Hardware Configuration Options
1.2.7. Miscellaneous BSP-Specific Recipe Files
1.2.8. Display Support Files
1.2.9. Linux Kernel Configuration
1.3. Developing a Board Support Package (BSP)
1.4. Requirements and Recommendations for Released BSPs
1.4.1. Released BSP Requirements
1.4.2. Released BSP Recommendations
1.5. Customizing a Recipe for a BSP
1.6. BSP Licensing Considerations
1.7. Using the Yocto Project's BSP Tools
1.7.1. Common Features
1.7.2. Creating a new BSP Layer Using the yocto-bsp Script
1.7.3. Managing Kernel Patches and Config Items with yocto-kernel

Chapter 1. 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 and manage a BSP Layer using two Yocto Project BSP Tools.

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


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


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, you might run into situations where obscure scripts 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 Yocto Project Source Repositories through a web interface at http://git.yoctoproject.org/cgit/cgit.cgi. 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. meta-raspberrypi and meta-intel). 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:

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

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

For information on the BSP development workflow, see the "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 "Working With Yocto Project Source Files" section also in the Yocto Project Development Manual.

The layer's base directory (meta-bsp_name) is the root of the BSP Layer. This root is what you add to the BBLAYERS variable in the conf/bblayers.conf file found in the Build Directory, which is established after you run one of the OpenEmbedded build environment setup scripts (i.e. oe-init-build-env and oe-init-build-env-memres). Adding the root allows the OpenEmbedded build system to recognize the BSP definition 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 \

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 BBLAYERS variable in order to build the BSP. You must also specify in the "Dependencies" section of the BSP's README file any requirements for additional layers and, preferably, any build instructions that might be contained elsewhere in the README file.

Some layers function as a layer to hold other BSP layers. An example of this type of layer is the meta-intel layer, which contains a number of individual BSP sub-layers, as well as a directory named common/ full of common content across those layers. Another example is the meta-yocto-bsp layer mentioned earlier.

For more detailed information on layers, see the "Understanding and Creating Layers" section of the Yocto Project Development Manual.

1.2. Example Filesystem Layout

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.

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.

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.

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 "Released BSP Requirements" section.

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.


Below is an example of the Raspberry Pi BSP:


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

1.2.1. License Files

You can find these files in the BSP Layer at:


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.

1.2.2. README File

You can find this file in the BSP Layer at:


This file provides information on how to boot the live images that are optionally included in the binary/ directory. The README file also provides special 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.

1.2.3. README.sources File

You can find this file in the BSP Layer at:


This file provides information on where to locate the BSP source files used to build the images (if any) that reside in meta-bsp_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 Metadata used to generate the images that ship with the BSP.


If the BSP's binary directory is missing or the directory has no images, an existing README.sources file is meaningless.

1.2.4. Pre-built User Binaries

You can find these files in the BSP Layer at:


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 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 README file should be present in the BSP Layer and it will explain how to use the images with the target hardware. Additionally, the README.sources file should be present to locate the sources used to build the images and provide information on the Metadata.

1.2.5. Layer Configuration File

You can find this file in the BSP Layer at:


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" and "_bsp" with the actual name of the BSP (i.e. bsp_name from the example template).

     # We have a conf and classes directory, add to BBPATH
     BBPATH .= ":${LAYERDIR}"

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

     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 \

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

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

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

1.2.6. Hardware Configuration Options

You can find these files in the BSP Layer at:


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 MACHINE variable.

These files define things such as the kernel package to use (PREFERRED_PROVIDER 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.

Each BSP Layer requires at least one machine file. However, you can supply more than one file.

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 Source Directory. For example, the ia32-base.inc file resides in the 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/raspberrypi2.conf

1.2.7. Miscellaneous BSP-Specific Recipe Files

You can find these files in the BSP Layer at:


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:




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 Source Directory.

1.2.8. Display Support Files

You can find these files in the BSP Layer at:


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.

1.2.9. Linux Kernel Configuration

You can find these files in the BSP Layer at:


These files append machine-specific changes to the main kernel recipe you are using.

For your BSP, you typically want to use an existing Yocto Project kernel recipe found in the 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_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_name.conf file by adding PREFERRED_PROVIDER and PREFERRED_VERSION statements as follows:

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


When the preferred provider is assumed by default, the PREFERRED_PROVIDER statement does not appear in the bsp_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 "Creating the Append File" section in the Yocto Project Linux Kernel Development Manual.

1.3. Developing a Board Support Package (BSP)

This section contains the high-level procedure you can follow to create a BSP using the Yocto Project's BSP Tools. 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 "Creating a New BSP Layer Using the yocto-bsp Script" section.

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

  1. Set Up Your Host Development System to Support Development Using the Yocto Project: See the "The Linux Distribution" and the "The Build Host Packages" sections both in the Yocto Project Quick Start for build host requirements.

  2. Establish a Local Copy of the Project Files on Your System: You need this Source Directory available on your host system. Having these files on your system gives you access to the build process and to the tools you need. For information on how to set up the Source Directory, see the "Working With Yocto Project Source Files" section in the Yocto Project Development Manual.

  3. 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 build on or modify to create your BSP. For information on how to get these files, see the "Setting Up BSP Layers" section in the Yocto Project Development Manual.

  4. Create Your Own BSP Layer Using the yocto-bsp 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 yocto-bsp script. For information about that script, see the "Creating a New BSP Layer Using the yocto-bsp 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 "Understanding and Creating Layers" section in the Yocto Project Development Manual. For more information on BSP layers, see the "BSP Layers" section.


    Five BSPs exist that are part of the Yocto Project release: beaglebone (ARM), mpc8315e (PowerPC), and edgerouter (MIPS). The recipes and configurations for these five BSPs are located and dispersed within the Source Directory.

    Three core Intel BSPs exist as part of 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 "Example Filesystem Layout" section. In the standard layout, you will notice a 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.

  5. 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 identify which kernel you are going to use. When you run the yocto-bsp script, you are able to interactively configure many things for the BSP (e.g. keyboard, touchscreen, and so forth).

  6. 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 you need to support your hardware.

  7. 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 or oe-init-build-env-memres) 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 "Enabling Your Layer" section in the Yocto Project Development Manual for information on how to let the build system know about your new layer.

    The entire process for building an image is overviewed in the section "Building Images" section of the Yocto Project Quick Start. You might want to reference this information.

  8. 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 BitBake User Manual.

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

1.4. Requirements and Recommendations for Released BSPs

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.

1.4.1. 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 "BSP Layers" and the "Understanding and Creating Layers" in the Yocto Project Development 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 "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, no requirement exists 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 "BSP Layers" section.

  • File System Layout: When possible, use the same directory names in your BSP layer as listed in the recipes.txt file. In particular, 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. You can find recipes.txt in the meta directory of the Source Directory, or in the OpenEmbedded Core Layer (openembedded-core) found at http://git.openembedded.org/openembedded-core/tree/meta.

    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 "OpenEmbedded Style Guide".

  • License File: You must include a license file in the meta-bsp_name 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 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_name directory. See the README 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 about the hardware the BSP targets.

    • 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.

    • 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 "Submitting a Change to the Yocto Project" section in the Yocto Project Development 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: You must include a README.sources in the meta-bsp_name directory. This file specifies exactly where you can find the sources used to generate the binary images contained in the binary directory, if present.

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

  • Machine Configuration File: You must include one or more conf/machine/bsp_name.conf files in the meta-bsp_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 are supported by the BSP. 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.


    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.

1.4.2. Released BSP Recommendations

Following are recommendations for a released BSP that conforms to the Yocto Project:

  • Bootable Images: BSP releases can contain one or more bootable images. Including bootable images allows users to easily try out the BSP on their own hardware.

    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.

    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_name directory.


    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 Source Repositories for these kernels.

1.5. 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 "Using .bbappend Files" section in the Yocto Project Development Manual.

  • 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.

  • 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 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.

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 interfaces to the init-ifupdown_1.0.bb recipe for machine "xyz" where the BSP layer also supports several other machines. Do the following:

  1. 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.

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



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

    The 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.

1.6. 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 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.

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" page from the Yocto Project website's 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.

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

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:

  1. 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 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 "Enabling Commercially Licensed Recipes" section in the Yocto Project Reference 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.

  2. Get a pre-built version of the BSP: You can get this type of BSP by visiting the "Downloads" page of the 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. 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 LICENSE_FLAGS_WHITELIST to match the encumbered recipes in the BSP.


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.

1.7. Using the Yocto Project's BSP Tools

The Yocto Project includes a couple of tools that enable you to create a BSP layer from scratch and do basic configuration and maintenance of the kernel without ever looking at a Metadata file. These tools are yocto-bsp and yocto-kernel, respectively.

The following sections describe the common location and help features as well as provide details for the yocto-bsp and yocto-kernel tools.

1.7.1. Common Features

Designed to have a command interface somewhat like Git, each tool is structured as a set of sub-commands under a top-level command. The top-level command (yocto-bsp or yocto-kernel) itself does nothing but invoke or provide help on the sub-commands it supports.

Both tools reside in the scripts/ subdirectory of the Source Directory. Consequently, to use the scripts, you must source the environment just as you would when invoking a build:

     $ source oe-init-build-env build_dir

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 help switch:

     $ yocto-bsp help

      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.

       --version    show program's version number and exit
       -h, --help   show this help message and exit
       -D, --debug  output debug information

Similarly, entering just the name of a sub-command shows the detailed usage for that sub-command:

     $ yocto-bsp create
     ERROR:root:Wrong number of arguments, exiting


      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'.


For any sub-command, you can use the word "help" option just before the sub-command to get more extensive documentation:

     $ yocto-bsp help create

         yocto-bsp create - Create a new Yocto BSP

         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.


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.


You can also use the yocto-layer tool to create a "generic" layer. For information on this tool, see the "Creating a General Layer Using the yocto-layer Script" section in the Yocto Project Development Guide.

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.

1.7.2. Creating a new BSP Layer Using the yocto-bsp Script

The yocto-bsp script creates a new BSP layer for any architecture supported by the Yocto Project, as well as QEMU versions of the same. The default mode of the script's operation is to prompt you for information needed to generate the BSP layer.

For the current set of BSPs, the script prompts you for various important parameters such as:

  • The kernel to use

  • The branch of that kernel to use (or re-use)

  • Whether or not to use X, and if so, which drivers to use

  • Whether to turn on SMP

  • Whether the BSP has a keyboard

  • Whether the BSP has a touchscreen

  • Remaining configurable items associated with the BSP

You use the yocto-bsp create sub-command to create a new BSP layer. This command requires you to specify a particular kernel architecture (karch) on which to base the BSP. Assuming you have sourced the environment, you can use the yocto-bsp list karch sub-command to list the architectures available for BSP creation as follows:

     $ yocto-bsp list karch
     Architectures available:

The remainder of this section presents an example that uses myarm as the machine name and qemu as the machine architecture. Of the available architectures, qemu 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.

As the yocto-bsp create 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 meta-myarm BSP layer is created in the current working directory. This example assumes you have sourced the oe-init-build-env setup script.

Following is the complete example:

     $ yocto-bsp create myarm qemu
     Checking basic git connectivity...

     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)
     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
     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

Take a closer look at the example now:

  1. For the QEMU architecture, the script first prompts you for which emulated architecture to use. In the example, we use the ARM architecture.

  2. 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.

  3. Next, the script asks whether you would like to have a new branch created especially for your BSP in the local Linux Yocto Kernel Git repository . If not, then the script re-uses an existing branch.

    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.

  4. 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 #1 at the prompt, which selects the ARM-versatile branch.

  5. The remainder of the prompts are routine. Defaults are accepted for each.

  6. By default, the script creates the new BSP Layer in the current working directory of the Source Directory, (i.e. poky/build).

Once the BSP Layer is created, you must add it to your bblayers.conf file. 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-myarm \

Adding the layer to this file allows the build system to build the BSP and the yocto-kernel tool to be able to find the layer and other Metadata it needs on which to operate.

1.7.3. Managing Kernel Patches and Config Items with yocto-kernel

Assuming you have created a BSP Layer using yocto-bsp and you added it to your BBLAYERS variable in the bblayers.conf file, you can now use the yocto-kernel script to add patches and configuration items to the BSP's kernel.

The yocto-kernel script allows you to add, remove, and list patches and kernel config settings to a BSP's kernel .bbappend 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 yocto-kernel built-in help as follows:

     $ yocto-kernel --help

      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.

       --version    show program's version number and exit
       -h, --help   show this help message and exit
       -D, --debug  output debug information

The yocto-kernel patch add sub-command allows you to add a patch to a BSP. The following example adds two patches to the myarm BSP:

     $ yocto-kernel patch add myarm ~/test.patch
     Added patches:

     $ yocto-kernel patch add myarm ~/yocto-testmod.patch
     Added patches:


Although the previous example adds patches one at a time, it is possible to add multiple patches at the same time.

You can verify patches have been added by using the yocto-kernel patch list sub-command. Here is an example:

     $ yocto-kernel patch list myarm
     The current set of machine-specific patches for myarm is:
       1) test.patch
       2) yocto-testmod.patch

You can also use the yocto-kernel script to remove a patch using the yocto-kernel patch rm sub-command. Here is an example:

     $ yocto-kernel patch rm myarm
     Specify the patches to remove:
       1) test.patch
       2) yocto-testmod.patch
     Removed patches:

Again, using the yocto-kernel patch list sub-command, you can verify that the patch was in fact removed:

     $ yocto-kernel patch list myarm
     The current set of machine-specific patches for myarm is:
       1) yocto-testmod.patch

In a completely similar way, you can use the yocto-kernel config add 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 myarm BSP:

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

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


Although the previous example adds config items one at a time, it is possible to add multiple config items at the same time.

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:

     $ 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

Finally, you can remove one or more config items using the yocto-kernel config rm sub-command in a manner completely analogous to yocto-kernel patch rm.