You can find these files in the Yocto Project file's directory structure 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 these files in the Yocto Project file's directory structure 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.

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

You can find these files in the Yocto Project file's directory structure 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 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.

You can find this file in the Yocto Project file's directory structure 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 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 the Yocto Project build system can recognize the BSP.

You can find these files in the Yocto Project file's directory structure 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.

At least one machine file is required for a BSP layer. 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 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. To use them, you simply include them in the machine configuration file. For example, the Crown Bay BSP crownbay.conf has the following statement:

     include conf/machine/include/tune-atom.inc
                

You can find these files in the Yocto Project file's directory structure 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 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
                

You can find these files in the Yocto Project file's directory structure at:

     meta-<bsp_name>/recipes-core/*
                

This directory contains recipe files for the core. For example, in the Crown Bay BSP there is the task-core-tools.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 Yocto Project file's directory structure 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 the following files that support building a BSP that supports and does not support the Intel EMGD:

     meta-crownbay/recipes-graphics/xorg-xserver/emgd-driver-bin_1.6.bb
     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 Yocto Project file's directory structure 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 repository 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 meta-<bsp_name>/recipes-kernel/linux directory.

Suppose you use a BSP that 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 file contains the following:

     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 ?= "6b4b9acde5fb0ff66ae58fa98274bfe631501499"
     SRCREV_meta_pn-linux-yocto_crownbay ?= "5b535279e61197cb194bb2dfceb8b7a04128387c"

     SRCREV_machine_pn-linux-yocto_crownbay-noemgd ?= "6b4b9acde5fb0ff66ae58fa98274bfe631501499"
     SRCREV_meta_pn-linux-yocto_crownbay-noemgd ?= "5b535279e61197cb194bb2dfceb8b7a04128387c"
                

This append file contains statements used to support the Crown Bay BSP for both Intel EMGD and non-EMGD. 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 ?= "6b4b9acde5fb0ff66ae58fa98274bfe631501499"
     SRCREV_meta_pn-linux-yocto_crownbay ?= "5b535279e61197cb194bb2dfceb8b7a04128387c"
                

The append file defines crownbay as the compatible machine, defines the KMACHINE, points to some configuration fragments to use by setting the KERNEL_FEATURES variable, and then 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 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.