%poky; ] > 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 chapter (or document if you are reading the BSP Developer's Guide) defines a structure for these components so that BSPs follow a commonly understood layout. Providing a common form allows end-users to understand and become familiar with the layout. A common form also encourages standardization of software support of hardware. The information here does not provide an example of how to create a BSP. For examples on how to create a BSP, see the "BSP Development Example" section in The Yocto Project Development Manual. You can also see the wiki page. The proposed format does have elements that are specific to the Yocto Project and OpenEmbedded build systems. It is intended that this information can be used by other systems besides Yocto Project and OpenEmbedded and that it will be simple to extract information and convert it to other formats if required. Yocto Project, through its standard layers mechanism, can directly accept the format described as a layer. The BSP captures all the hardware-specific details in one place in a standard format, which is useful for any person wishing to use the hardware platform regardless of the build system they are using. 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.

The BSP consists of a file structure inside a base directory. Collectively, you can think of the base directory and the file structure as a BSP Layer. BSP Layers use the following naming convention: meta-<bsp_name> "bsp_name" is a placeholder for the machine or platform name. 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 Yocto Project Build Directory. Adding the root allows the Yocto Project 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-yocto \ /usr/local/src/yocto/meta-<bsp_name> \ " 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 "Dependiencies" 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. For more detailed information on layers, see the "Understanding and Creating Layers" section of the Yocto Project Development Manual. You can also see the detailed examples in the appendices of The Yocto Project Development Manual.

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. meta-<bsp_name>/ meta-<bsp_name>/<bsp_license_file> meta-<bsp_name>/README meta-<bsp_name>/binary/<bootable_images> meta-<bsp_name>/conf/layer.conf meta-<bsp_name>/conf/machine/*.conf meta-<bsp_name>/recipes-bsp/* meta-<bsp_name>/recipes-graphics/* meta-<bsp_name>/recipes-kernel/linux/linux-yocto_<kernel_rev>.bbappend Below is an example of the Crown Bay BSP: meta-crownbay/COPYING.MIT meta-crownbay/README meta-crownbay/README.sources meta-crownbay/binary meta-crownbay/conf/ meta-crownbay/conf/layer.conf meta-crownbay/conf/machine/ meta-crownbay/conf/machine/crownbay.conf meta-crownbay/conf/machine/crownbay-noemgd.conf meta-crownbay/recipes-bsp/ meta-crownbay/recipes-bsp/formfactor/ meta-crownbay/recipes-bsp/formfactor/formfactor_0.0.bbappend meta-crownbay/recipes-bsp/formfactor/formfactor/ meta-crownbay/recipes-bsp/formfactor/formfactor/crownbay/ meta-crownbay/recipes-bsp/formfactor/formfactor/crownbay/machconfig meta-crownbay/recipes-bsp/formfactor/formfactor/crownbay-noemgd/ meta-crownbay/recipes-bsp/formfactor/formfactor/crownbay-noemgd/machconfig meta-crownbay/recipes-core meta-crownbay/recipes-core/tasks meta-crownbay/recipes-core/tasks/task-core-tools-profile.bbappend meta-crownbay/recipes-graphics/ meta-crownbay/recipes-graphics/xorg-xserver/ meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-config_0.1.bbappend meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-config/ meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-config/crownbay/ meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-config/crownbay/xorg.conf meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-config/crownbay-noemgd/ meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-config/crownbay-noemgd/xorg.conf meta-crownbay/recipes-kernel/ meta-crownbay/recipes-kernel/linux/ meta-crownbay/recipes-kernel/linux/linux-yocto-rt_3.0.bbappend meta-crownbay/recipes-kernel/linux/linux-yocto_2.6.37.bbappend meta-crownbay/recipes-kernel/linux/linux-yocto_3.0.bbappend The following sections describe each part of the proposed BSP format.

You can find these files in the BSP Layer at: meta-<bsp_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 Crown Bay 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.

You can find this file in the BSP Layer at: meta-<bsp_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 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.

You can find this file in the BSP Layer at: meta-<bsp_name>/README.sources This file provides information on where to locate the BSP source files. For example, information provides where to find the sources that comprise the images shipped with the BSP. Information is also included to help you find the metadata used to generate the images that ship with the BSP.

You can find these files in the BSP Layer at: meta-<bsp_name>/binary/<bootable_images> This optional area contains useful pre-built kernels and user-space filesystem images appropriate to the target system. This directory typically contains graphical (e.g. sato) and minimal live images when the BSP tarball has been created and made available in the 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. However, a README file should be present in the BSP Layer that explains how to use the kernels and images with the target hardware. If pre-built binaries are present, source code to meet licensing requirements must also exist in some form.

You can find this file in the BSP Layer at: meta-<bsp_name>/conf/layer.conf The conf/layer.conf file identifies the file structure as a Yocto Project layer, identifies the contents of the layer, and contains information about how Yocto Project should use it. Generally, a standard boilerplate file such as the following works. In the following example, you would replace "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 := "${BBPATH}:${LAYERDIR}" # We have a recipes directory, add to BBFILES BBFILES := "${BBFILES} ${LAYERDIR}/recipes/*/*.bb \ ${LAYERDIR}/recipes/*/*.bbappend" BBFILE_COLLECTIONS += "bsp" BBFILE_PATTERN_bsp := "^${LAYERDIR}/" BBFILE_PRIORITY_bsp = "6" To illustrate the string substitutions, here are the last three statements from the Crown Bay conf/layer.conf file: BBFILE_COLLECTIONS += "crownbay" BBFILE_PATTERN_crownbay := "^${LAYERDIR}/" BBFILE_PRIORITY_crownbay = "6" This file simply makes BitBake aware of the recipes and configuration directories. The file must exist so that the Yocto Project build system can recognize the BSP.

You can find these files in the BSP Layer at: meta-<bsp_name>/conf/machine/*.conf The machine files bind together all the information contained elsewhere in the BSP into a format that the Yocto Project build system can understand. If the BSP supports multiple machines, multiple machine configuration files can be present. These filenames correspond to the values to which users have set the 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. For example, in the Crown Bay BSP shown earlier in this section, the conf/machine directory contains two configuration files: crownbay.conf and crownbay-noemgd.conf. The crownbay.conf file is used for the Crown Bay BSP that supports the Intel Embedded Media and Graphics Driver (Intel EMGD), while the crownbay-noemgd.conf file is used for the Crown Bay BSP that does not support the Intel EMGD. This crownbay.conf 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 of the Yocto Project Files. Tuning files can also reside in the BSP Layer itself. For example, the ia32-base.inc file resides in the meta-intel BSP Layer in conf/machine/include. To use an include file, you simply include them in the machine configuration file. For example, the Crown Bay BSP crownbay.conf has the following statements: include conf/machine/include/tune-atom.inc include conf/machine/include/ia32-base.inc

You can find these files in the BSP Layer at: meta-<bsp_name>/recipes-bsp/* This optional directory contains miscellaneous recipe files for the BSP. Most notably would be the formfactor files. For example, in the Crown Bay BSP there is the 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 files. In the Crown Bay example, two machconfig files exist: one that supports the Intel Embedded Media and Graphics Driver (Intel EMGD) and one that does not: meta-crownbay/recipes-bsp/formfactor/formfactor/crownbay/machconfig meta-crownbay/recipes-bsp/formfactor/formfactor/crownbay-noemgd/machconfig meta-crownbay/recipes-bsp/formfactor/formfactor_0.0.bbappend 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 Yocto Project Files.

You can find these files in the BSP Layer at: meta-<bsp_name>/recipes-core/* This directory contains recipe files that are almost always necessary to build a useful, working Linux image. Thus, the term "core" is used to group these recipes. For example, in the Crown Bay BSP there is the task-core-tools-profile.bbappend file, which is an append file used to recommend that the SystemTap package be included as a package when the image is built.

You can find these files in the BSP Layer at: meta-<bsp_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. For example, the Crown Bay BSP contains two versions of the xorg.conf file. The version in crownbay builds a BSP that supports the Intel Embedded Media Graphics Driver (EMGD), while the version in crownbay-noemgd builds a BSP that supports Video Electronics Standards Association (VESA) graphics only: meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-config_0.1.bbappend meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-config/crownbay/xorg.conf meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-config/crownbay-noemgd/xorg.conf

You can find these files in the BSP Layer at: meta-<bsp_name>/recipes-kernel/linux/linux-yocto_*.bbappend These files append your specific changes to the kernel you are using. For your BSP, you typically want to use an existing Yocto Project kernel found in the Yocto Project Files at meta/recipes-kernel/linux. You can append your specific changes to the kernel recipe by using a similarly named append file, which is located in the BSP Layer (e.g. the meta-<bsp_name>/recipes-kernel/linux directory). Suppose the BSP uses the linux-yocto_3.0.bb kernel, which is the preferred kernel to use for developing a new BSP using the Yocto Project. In other words, you have selected the kernel in your <bsp_name>.conf file by adding the following statements: PREFERRED_PROVIDER_virtual/kernel ?= "linux-yocto" PREFERRED_VERSION_linux-yocto = "3.0%" You would use the linux-yocto_3.0.bbappend file to append specific BSP settings to the kernel, thus configuring the kernel for your particular BSP. As an example, look at the existing Crown Bay BSP. The append file used is: meta-crownbay/recipes-kernel/linux/linux-yocto_3.0.bbappend The following listing shows the file. Be aware that the actual commit ID strings in this example listing might be different than the actual strings in the file from the meta-intel Git source repository. FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:" COMPATIBLE_MACHINE_crownbay = "crownbay" KMACHINE_crownbay = "yocto/standard/crownbay" KERNEL_FEATURES_append_crownbay += " cfg/smp.scc" COMPATIBLE_MACHINE_crownbay-noemgd = "crownbay-noemgd" KMACHINE_crownbay-noemgd = "yocto/standard/crownbay" KERNEL_FEATURES_append_crownbay-noemgd += " cfg/smp.scc" SRCREV_machine_pn-linux-yocto_crownbay ?= "63c65842a3a74e4bd3128004ac29b5639f16433f" SRCREV_meta_pn-linux-yocto_crownbay ?= "59314a3523e360796419d76d78c6f7d8c5ef2593" SRCREV_machine_pn-linux-yocto_crownbay-noemgd ?= "63c65842a3a74e4bd3128004ac29b5639f16433f" SRCREV_meta_pn-linux-yocto_crownbay-noemgd ?= "59314a3523e360796419d76d78c6f7d8c5ef2593" This append file contains statements used to support the Crown Bay BSP for both Intel EMGD and the VESA graphics. The build process, in this case, recognizes and uses only the statements that apply to the defined machine name - crownbay in this case. So, the applicable statements in the linux-yocto_3.0.bbappend file are follows: FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:" COMPATIBLE_MACHINE_crownbay = "crownbay" KMACHINE_crownbay = "yocto/standard/crownbay" KERNEL_FEATURES_append_crownbay += " cfg/smp.scc" SRCREV_machine_pn-linux-yocto_crownbay ?= "63c65842a3a74e4bd3128004ac29b5639f16433f" SRCREV_meta_pn-linux-yocto_crownbay ?= "59314a3523e360796419d76d78c6f7d8c5ef2593" The append file defines crownbay as the compatible machine and defines the KMACHINE. The file also points to some configuration fragments to use by setting the KERNEL_FEATURES variable. The location for the configuration fragments is the kernel tree itself in the Yocto Project Build Directory under linux/meta. Finally, the append file points to the specific commits in the Yocto Project Files Git repository and the meta Git repository branches to identify the exact kernel needed to build the Crown Bay BSP. One thing missing in this particular BSP, which you will typically need when developing a BSP, is the kernel configuration file (.config) for your BSP. When developing a BSP, you probably have a kernel configuration file or a set of kernel configuration files that, when taken together, define the kernel configuration for your BSP. You can accomplish this definition by putting the configurations in a file or a set of files inside a directory located at the same level as your append file and having the same name as the kernel. With all these conditions met simply reference those files in a SRC_URI statement in the append file. For example, suppose you had a set of configuration options in a file called myconfig. If you put that file inside a directory named /linux-yocto and then added a SRC_URI statement such as the following to the append file, those configuration options will be picked up and applied when the kernel is built. SRC_URI += "file://myconfig" As mentioned earlier, you can group related configurations into multiple files and name them all in the SRC_URI statement as well. For example, you could group separate configurations specifically for Ethernet and graphics into their own files and add those by using a SRC_URI statement like the following in your append file: SRC_URI += "file://myconfig \ file://eth.cfg \ file://gfx.cfg" The FILESEXTRAPATHS variable is in boilerplate form in the previous example in order to make it easy to do that. This variable must be in your layer or BitBake will not find the patches or configurations even if you have them in your SRC_URI. The FILESEXTRAPATHS variable enables the build process to find those configuration files. Other methods exist to accomplish grouping and defining configuration options. For example, if you are working with a local clone of the kernel repository, you could checkout the kernel's meta branch, make your changes, and then push the changes to the local bare clone of the kernel. The result is that you directly add configuration options to the Yocto kernel meta branch for your BSP. The configuration options will likely end up in that location anyway if the BSP gets added to the Yocto Project. For an example showing how to change the BSP configuration, see the "Changing the BSP Configuration" section in the Yocto Project Development Manual. For a better understanding of working with a local clone of the kernel repository and a local bare clone of the kernel, see the "Modifying the Kernel Source Code" section also in the Yocto Project Development Manual. In general, however, the Yocto Project maintainers take care of moving the SRC_URI-specified configuration options to the kernel's meta branch. Not only is it easier for BSP developers to not have to worry about putting those configurations in the branch, but having the maintainers do it allows them to apply 'global' knowledge about the kinds of common configuration options multiple BSPs in the tree are typically using. This allows for promotion of common configurations into common features.

In some cases, a BSP contains separately licensed Intellectual Property (IP) for a component or components. For these cases, you are required to accept the terms of a commercial or other type of license that requires some kind of explicit End User License Agreement (EULA). Once the license is accepted, the Yocto Project build system can then build and include the corresponding component in the final BSP image. If the BSP is available as a pre-built image, you can download the image after agreeing to the license or EULA. 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 Yocto Project website's BSP Download Page 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 Yocto Project 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 Yocto Project 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 whitelisted 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 visiting the Yocto Project website's Download page and clicking on "BSP Downloads". You can download BSP tarballs that contain proprietary components after agreeing to the licensing requirements of each of the individually encumbered packages as part of the download process. Obtaining the BSP this way allows you to access an encumbered image immediately after agreeing to the click-through license agreements presented by the website. Note that if you want to build the image yourself using the recipes contained within the BSP tarball, you will still need to create an appropriate 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.