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 crownbay 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.

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.

Technically speaking a README is optional but it is highly recommended that every BSP has one.

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 file structure 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 be provided in some form.

meta-<bsp_name>/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 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 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 configuration directories. This file must exist so that Poky can recognize the BSP.

meta-<bsp_name>/conf/machine/*.conf
            

The machine files bind together all the information contained elsewhere in the BSP into a format that Poky 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.

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

This directory could also contain shared hardware "tuning" definitions that 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 architecture file and the tune file are optional for a Poky BSP layer.

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 crownbay BSP there is a machconfig file and a formfactor_0.0.bbappend file:

meta-crownbay/recipes-bsp/formfactor/formfactor/crownbay/machconfig
meta-crownbay/recipes-bsp/formfactor/formfactor_0.0.bbappend
                

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, in the crownbay BSP several display support files exist:

meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-config/crownbay/xcorg.conf
meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-config_0.1.bbappend
meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-emgd-bin/.gitignore
meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-emgd-bin_1.7.99.2.bb
meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-emgd/crosscompile.patch
meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-emgd/fix_open_max_preprocessor_error.patch
meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-emgd/macro_tweak.patch
meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-emgd/nodolt.patch
meta-crownbay/recipes-graphics/xorg-xserver/xserver-xf86-emgd_1.7.99.2.bb
                

meta-<bsp_name>/recipes-kernel/linux/linux-yocto_git.bbappend
            

This file appends your specific changes to the kernel you are using.

For your BSP you typically want to use an existing Poky kernel found in the Poky repository at meta/recipes-kernel/kernel. You can append your specific changes to the kernel recipe by using an append file, which is located in the meta-<bsp_name>/recipes-kernel/linux directory.

Suppose you use a BSP that uses the linux-yocto_git.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 statement:

PREFERRED_PROVIDER_virtual/kernel ?= "linux-yocto"
                

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

Now take a look at the existing "crownbay" BSP. The append file used is:

meta-crownbay/recipes-kernel/linux/linux-yocto_git.bbappend
                

The file contains the following:

FILESEXTRAPATHS := "${THISDIR}/${PN}"
COMPATIBLE_MACHINE_crownbay = "crownbay"
KMACHINE_crownbay = "yocto/standard/crownbay"
                

This append file adds "crownbay" as a compatible machine, and additionally sets a Yocto Kernel-specific variable that identifies the name of the BSP branch to use in the GIT repository to find configuration information.

One thing missing in this particular BSP, which you will typically need when developing a BSP, is the kernel configuration (.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 defconfig. 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://defconfig"
                

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://defconfig \
            file://eth.cfg \
            file://gfx.cfg"
                

The FILESEXTRAPATHS variable is in boilerplate form here in order to make it easy to do that. It basically allows those configuration files to be found by the build process.