# Board Support Packages (BSP) - Developers 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 section (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 proposed format does have elements that are specific to the Poky and OpenEmbedded build systems. It is intended that this information can be used by other systems besides Poky and OpenEmbedded and that it will be simple to extract information and convert it to other formats if required. Poky, 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.

## Example Filesystem Layout

The BSP consists of a file structure inside a base directory, meta-bsp in this example, where "bsp" is a placeholder for the machine or platform name. Examples of some files that it could contain are:

    meta-bsp/
    meta-bsp/binary/zImage
    meta-bsp/binary/poky-image-minimal.directdisk
    meta-bsp/conf/layer.conf
    meta-bsp/conf/machine/*.conf
    meta-bsp/conf/machine/include/tune-*.inc
    meta-bsp/packages/bootloader/bootloader_0.1.bb
    meta-bsp/packages/linux/linux-bsp-2.6.50/*.patch
    meta-bsp/packages/linux/linux-bsp-2.6.50/defconfig-bsp
    meta-bsp/packages/linux/linux-bsp_2.6.50.bb
    meta-bsp/packages/modem/modem-driver_0.1.bb
    meta-bsp/packages/modem/modem-daemon_0.1.bb
    meta-bsp/packages/image-creator/image-creator-native_0.1.bb
    meta-bsp/prebuilds/

The following sections detail what these files and directories could contain.

## Prebuilt User Binaries (meta-bsp/binary/*)

This optional area contains useful prebuilt kernels and userspace filesystem images appropriate to the target system. Users could use these 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 that explains how to use them with the target hardware. If prebuilt binaries are present, source code to meet licensing requirements must also be provided in some form.

## Layer Configuration (meta-bsp/conf/layer.conf)

This file identifies the structure as a Poky layer, identifies the contents of the layer and contains information about how Poky should use it. Generally, a standard boilerplate file consisting of the following works.

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

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

    BBFILE_COLLECTIONS += "bsp"
    BBFILE_PATTERN_bsp := "^${LAYERDIR}/"
    BBFILE_PRIORITY_bsp = "5"

This file simply makes bitbake aware of the recipes and conf directories and is required for recognition of the BSP by Poky.

## Hardware Configuration Options (meta-bsp/conf/machine/*.conf)

The machine files bind together all the information contained elsewhere in the BSP into a format that Poky/OpenEmbedded 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 what kernel package to use (PREFERRED_PROVIDER of virtual/kernel), what 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.

At least one machine file is required for a Poky BSP layer. However, you can supply more than one file.

## Hardware Optimization Options (meta-bsp/conf/machine/include/tune-*.inc)

These are shared hardware "tuning" definitions and are commonly used to pass specific optimization flags to the compiler. An example is tune-atom.inc:

    BASE_PACKAGE_ARCH = "core2"
    TARGET_CC_ARCH = "-m32 -march=core2 -msse3 -mtune=generic -mfpmath=sse"

This example defines a new package architecture called "core2" and uses the specified optimization flags, which are carefully chosen to give best performance on atom processors.

The tune file would be included by the machine definition and can be contained in the BSP or referenced from one of the standard core set of files included with Poky itself.

Both the base package architecuture file and the tune file are optional for a Poky BSP layer.

## Linux Kernel Configuration (meta-bsp/packages/linux/*)

These files make up the definition of a kernel to use with this hardware. In this case, it is a complete self-contained kernel with its own configuration and patches. However, kernels can be shared between many machines as well. Following is an example:

    meta-bsp/packages/linux/linux-bsp_2.6.50.bb

This example file is the core kernel recipe that details from where to get the kernel source. All standard source code locations are supported so this could be a release tarball, some git repository, or source included in the directory within the BSP itself.

The file then contains information about what patches to apply and how to configure and build them. It can reuse the main Poky kernel build class, so the definitions here can remain very simple.

    linux-bsp-2.6.50/*.patch

The above example file contains patches you can apply against the base kernel, from wherever they may have been obtained.

    meta-bsp/packages/linux/linux-bsp-2.6.50/defconfig-bsp

Finally, this last example file contains kernel configuration information.

Examples of kernel recipes are available in Poky itself. These files are optional since a kernel from Poky could be selected, although it would be unusual not to have a kernel configuration.

## Other Software (meta-bsp/packages/*)

This section describes other pieces of software that the hardware might need for best operation. This section shows examples of the kinds of things that you could encounter. The examples are standard `.bb` file recipes in the usual Poky format. You can include the source directly by referring to it in the source control system or the released tarballs of external software projects. You only need to provide these types of files if the platform requires them.

The following file is a bootloader recipe that can be used to generate a new bootloader binary. Sometimes these files are included in the final image format and are needed to re-flash hardware.

    meta-bsp/packages/bootloader/bootloader_0.1.bb

These next two files are examples of a hardware driver and a hardware daemon that might need to be included in images to make the hardware useful. Although the example uses "modem" there may be other components needed, such as firmware.

    meta-bsp/packages/modem/modem-driver_0.1.bb
    meta-bsp/packages/modem/modem-daemon_0.1.bb

Sometimes the device needs an image in a very specific format so that the update mechanism can accept and re-flash it. Recipes to build the tools needed to do this can be included with the BSP. Following is an example.

    meta-bsp/packages/image-creator/image-creator-native_0.1.bb

## Append BSP-Specific Information to Existing Recipes

Suppose you have a recipe such as 'pointercal' that requires machine-specific information. At the same time, you have your new BSP code nicely partitioned into a layer through which you would also like to specify any machine-specific information associated with your new machine. Before the `.bbappend` extension was introduced, you would have to copy the whole pointercal recipe and files into your layer and then add the single file for your machine.

With the `.bbappend` extension, however, your work becomes much easier. This extension allows you to easily merge BSP-specific information with the original recipe. Whenever bitbake finds any `.bbappend` files they will be included after bitbake loads the associated `.bb` but before any finalize or anonymous methods run. This allows the BSP layer to do whatever it might want to do to customize the original recipe.

If your recipe needs to reference extra files it can use the FILESEXTRAPATH variable to specify their location. The example below shows extra files contained in a folder called ${PN} (the package name).

    FILESEXTRAPATHS := "${THISDIR}/${PN}"

This technique allows the BSP to add machine-specific configuration files to the layer directory, which will be picked up by bitbake. For an example see `meta-emenlow/packages/formfactor`.

## Prebuild Data (meta-bsp/prebuilds/*)

This location can contain precompiled representations of the source code contained elsewhere in the BSP layer. Assuming a compatible configuration is used, Poky can process and use these optional precompiled representations to provide much faster build times.

## BSP 'Click-Through' Licensing Procedure

This section describes how click-through licensing is expected to work. Currently, this functionality is not yet implemented.

In some cases, a BSP contains separately licensed IP (Intellectual Property) for a component that imposes upon the user a requirement to accept the terms of a 'click-through' license. Once the license is accepted the Poky build system can then build and include the corresponding component in the final BSP image. Some affected components might be essential to the normal functioning of the system and have no 'free' replacement (i.e. the resulting system would be non-functional without them). On the other hand, other components might be simply 'good-to-have' or purely elective, or if essential nonetheless have a 'free' (possibly less-capable) version that could be used as a in the BSP recipe.

For cases where you can substitute something and still maintain functionality, the Poky website will make available a 'de-featured' BSP completely free of the encumbered IP. In that case you can use the substitution directly and without any further licensing requirements. If present, this fully 'de-featured' BSP will be named meta-bsp (i.e. the normal default naming convention). If available, this is the simplest the most preferred option. This, of course, assumes the resulting functionality meets requirements.

If however, a non-encumbered version is unavailable or the 'free' version would provide unsuitable functionality or quality, an encumbered version can be used. Encumbered versions of a BSP are given names of the form meta-bsp-nonfree.

Several methods exist within the Poky build system to satisfy the licensing requirements for an encumbered BSP. The following list describes them in preferential order:

1. Get a license key (or keys) for the encumbered BSP by visiting https://pokylinux.org/bsp-keys.html and give the name of the BSP and your e-mail address in the web form.

       		  [screenshot of dialog box]

   After agreeing to any applicable license terms, the BSP key(s) will be immediately sent to the address you gave and you can use them by specifying BSPKEY_<keydomain> environment variables when building the image:

       		  $ BSPKEY_<keydomain>=<key> bitbake poky-image-sato

   These steps allow the encumbered image to be built with no change at all to the normal build process.

   Equivalently and probably more conveniently, a line for each key can instead be put into the user's `local.conf` file.

   The <keydomain> component of the BSPKEY_<keydomain> is required because there might be multiple licenses in effect for a give BSP. In such cases, a given <keydomain> corresponds to a particular license. In order for an encumbered BSP that encompasses multiple key domains to be built successfully, a <keydomain> entry for each applicable license must be present in `local.conf` or supplied on the command-line.

2. Do nothing - build as you normally would. When a license is needed the build will stop and prompt you with instructions. Follow the license prompts that originate from the encumbered BSP. These prompts usually take the form of instructions needed to manually fetch the encumbered package(s) and md5 sums into the required directory (e.g. the poky/build/downloads) Once the manual package fetch has been completed, restart the build to continue where it left off. During the build the prompt will not appear again since you have satisfied the requirement.

3. Get a full-featured BSP recipe rather than a key, by visiting https://pokylinux.org/bsps.html. Accepting the license agreement(s) presented will subsequently allow you to download a tarball containing a full-featured BSP that is legally cleared for your use by the just-given license agreement(s). This method will also allow the encumbered image to be built with no change at all to the normal build process.

Note that the third method is also the only option available when downloading pre-compiled images generated from non-free BSPs. Those images are likewise available at https://pokylinux.org/bsps.html.