# Board Support Packages (BSP) - Developers Guide

A Board Support Package (BSP) is a collection of information which together defines how to support a particular hardware device, set of devices or hardware platform. It will include information about the hardware features present on the device, kernel configuration information along with any additional hardware drivers required and also any additional software components required in addition to a generic Linux software stack for both essential and optional platform features.

The intend of this document is to define a structure for these components so that BSPs follow a commonly understood layout allowing them to be provided in a common way that everyone understands. It also allows end users to become familiar with one common format and encourages standardisation 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/OpenEmbedded and that it will be simple to extract information and convert to other formats if required. The format descriped can be directly accepted as a layer by Poky using its standard layers mechanism but its important to recognise that 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 in use.

The BSP specification does not include a build system or other tooling, it is concerned with the hardware specific components only. At the end distribution point the BSP may be shipped combined with a build system and other tools but it is important to maintain the distinction that these are separate components which may just 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 cotains 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 will be highly hardware dependent but a README file should be present explaining 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. This file identifies the contents of the layer and how contains information about how Poky should use it. In general it will most likely be a standard boilerplate file consisting of:

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

    # We have a packages directory, add to BBFILES
    BBFILES := "${BBFILES} ${LAYERDIR}/packages/*/*.bb"

    BBFILE_COLLECTIONS += "meta-bsp"
    BBFILE_PATTERN_meta-bsp := "^${LAYERDIR}/"
    BBFILE_PRIORITY_meta-bsp = "5"

which simply makes bitbake aware of the packages and conf directories.

This file 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 it in. If the BSP supports multiple machines, multiple machine configuration files can be present. These filenames correspond to the values users set the MACHINE variable to.

These files would define things like which kernel package to use (PREFERRED_PROVIDER of virtual/kernel), which 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 but more than one may be present.

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

These are shared hardware "tuning" definitions and are commonly used to pass specific optimisation 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"

which defines a new package architecture called "core2" and uses the optimisation flags specified which are carefully chosen to give best performance on atom cpus.

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

These files 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 its a complete self contained kernel with its own configuration and patches but kernels can be shared between many machines as well. Taking some specific example files:

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

which is the core kernel recipe which firstly details where to get the kernel source from. 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. It then contains information about which patches to apply and how to configure and build it. It can reuse the main Poky kernel build class meaning the definitions here can remain very simple.

    linux-bsp-2.6.50/*.patch

which are patches which may be applied against the base kernel, wherever that may have been obtained from.

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

which is the configuration information to use to configure the kernel.

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

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

This area includes other pieces of software which the hardware may need for best operation. These are just examples of the kind of things that may be encountered. The are standard .bb file recipes in the usual Poky format so for examples, see standard Poky recipes. The source can be included directly, referred to in source control systems or release tarballs of external software projects.

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

Some kind of bootloader recipe which may be used to generate a new bootloader binary. Sometimes these are included in the final image format and needed to reflash hardware.

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

These are examples of a hardware driver and also a hardware daemon which may need to be included in images to make the hardware useful. "modem" is one example but there may be other components needed like firmware.

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

Sometimes the device will need an image in a very specific format for its update mechanism to accept and reflash with it. Recipes to build the tools needed to do this can be included with the BSP.

These files only need be provided if the platform requires them.

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

The location can contains a precompiled representation of the source code contained elsewhere in the BSP layer. It can be processed and used by Poky to provide much faster build times assuming a compatible configuration is used.

These files are optional.