# BSP Development Example

This appendix provides a complete BSP example. The example assumes the following:

- No previous preparation or use of the Yocto Project.

- Use of the Crown Bay Board Support Package (BSP) as a base BSP from which to work from.

- Shell commands assume `bash`

- Example was developed on an Intel-based Core i7 platform running Ubuntu 10.04 LTS released in April of 2010.

## Getting Local Yocto Project Files and BSP Files

You need to have the Yocto Project files available on your host system. You can get files through tarball extraction or by cloning the `poky` Git repository. See the bulleted item Yocto Project Release in Getting Setup earlier in this manual for information on how to get these files.

Once you have the local `poky` Git repository set up, you have many development branches from which you can work. From inside the repository you can see the branch names and the tag names used in the Git repository using either of the following two commands:

         $ git branch -a
         $ git tag -l

For this example we are going to use the Yocto Project 1.1 Release, which maps to the `1.1` branch in the repository. These commands create a local branch named `1.1` that tracks the remote branch of the same name.

         $ cd poky
         $ git checkout -b 1.1 origin/1.1
         Switched to a new branch '1.1'

## Choosing a Base BSP

For this example, the base BSP is the Intel Atom Processor E660 with Intel Platform Controller Hub EG20T Development Kit, which is otherwise referred to as "Crown Bay." The BSP layer is `meta-crownbay`.

For information on how to choose a base BSP, see Developing a Board Support Package (BSP) earlier in this manual.

## Getting Your Base BSP

You need to have the base BSP layer on your development system. Like the local Yocto Project files, you can get the BSP layer one of two ways: download the BSP tarball and extract it, or set up a local Git repository that has the Yocto Project BSP layers. You should use the same method that you used to get the local Yocto Project files earlier. See Getting Setup earlier in this manual for information on how to get the BSP files.

This example assumes a local `meta-intel` Git repository inside the local `poky` Git repository. The `meta-intel` Git repository contains all the metadata that supports BSP creation.

Because `meta-intel` is its own Git repository, you will want to be sure you are in the appropriate branch for your work. For this example we are going to use the `1.1` branch.

         $ cd meta-intel
         $ git checkout -b 1.1 origin/1.1
         Switched to a new branch 'bernard'

## Making a Copy of the Base BSP to Create Your New BSP Layer

Now that you have the local Yocto Project files and the base BSP files you need to create a new layer for your BSP. To create your BSP layer you simply copy the `meta-crownbay` layer to a new layer.

For this example the new layer will be named `meta-mymachine`. The name must follow the BSP layer naming convention, which is `meta-<name>`. The following example assumes your working directory is `meta-intel` inside the local Yocto Project files. If you downloaded and expanded a Crown Bay tarball then you simply copy the resulting `meta-crownbay` directory structure to a location of your choice. Good practice for a Git repository, however, is to just copy the new layer alongside the existing BSP layers in the `meta-intel` Git repository:

         $ cp -a meta-crownbay/ meta-mymachine

## Making Changes to Your BSP

Right now you have two identical BSP layers with different names: `meta-crownbay` and `meta-mymachine`. You need to change your configurations so that they work for your new BSP and your particular hardware. The following sections look at each of these areas of the BSP.

### Changing the BSP Configuration

We will look first at the configurations, which are all done in the layer’s `conf` directory.

First, since in this example the new BSP will not support EMGD we will get rid of the `crownbay.conf` file and then rename the `crownbay-noemgd.conf` file to `mymachine.conf`. Much of what we do in the configuration directory is designed to help the Yocto Project build system work with the new layer and to be able to find and use the right software. The following two commands result in a single machine configuration file named `mymachine.conf`.

         $ rm meta-mymachine/conf/machine/crownbay.conf
         $ mv meta-mymachine/conf/machine/crownbay-noemgd.conf \
         meta-mymachine/conf/machine/mymachine.conf

The next step makes changes to `mymachine.conf` itself. The only changes needed for this example are changes to the comment lines. Here we simply substitute the Crown Bay name with an appropriate name.

Note that inside the `mymachine.conf` is the `PREFERRED_PROVIDER_virtual/kernel` statement. This statement identifies the kernel that the BSP is going to use. In this case the BSP is using `linux-yocto`, which is the current Linux Yocto kernel based on the Linux 3.0 release.

The next configuration file in the new BSP layer we need to edit is `layer.conf`. This file identifies build information needed for the new layer. You can see the Layer Configuration File section in the Board Support Packages (BSP) Development Guide for more information on this configuration file. Basically, we are changing the existing statements to work with our BSP.

The file contains these statements that reference the Crown Bay BSP:

         BBFILE_COLLECTIONS += "crownbay"
         BBFILE_PATTERN_crownbay := "^${LAYERDIR}/"
         BBFILE_PRIORITY_crownbay = "6"

Simply substitute the machine string name `crownbay` with the new machine name `mymachine` to get the following:

         BBFILE_COLLECTIONS += "mymachine"
         BBFILE_PATTERN_mymachine := "^${LAYERDIR}/"
         BBFILE_PRIORITY_mymachine = "6"

### Changing the Recipes in Your BSP

Now we will take a look at the recipes in your new layer. The standard BSP structure has areas for BSP, graphics, core, and kernel recipes. When you create a BSP you use these areas for appropriate recipes and append files. Recipes take the form of `.bb` files. If you want to leverage the existing recipes the Yocto Project build system uses but change those recipes you can use `.bbappend` files. All new recipes and append files for your layer must go in the layer’s `recipes-bsp`, `recipes-kernel`, `recipes-core`, and `recipes-graphics` directories.

#### Changing `recipes-bsp`

First, let's look at `recipes-bsp`. For this example we are not adding any new BSP recipes. And, we only need to remove the formfactor we do not want and change the name of the remaining one that doesn't support EMGD. These commands take care of the `recipes-bsp` recipes:

         $ rm -rf meta-mymachine/recipes-graphics/xorg-xserver/*emgd*
         $ mv meta-mymachine/recipes-bsp/formfactor/formfactor/crownbay-noemgd/ \
         meta-mymachine/recipes-bsp/formfactor/formfactor/mymachine

#### Changing `recipes-graphics`

Now let's look at `recipes-graphics`. For this example we want to remove anything that supports EMGD and be sure to rename remaining directories appropriately. The following commands clean up the `recipes-graphics` directory:

         $ rm -rf meta-mymachine/recipes-graphics/xorg-xserver/xserver-xf86-emgd*
         $ rm -rf meta-mymachine/recipes-graphics/xorg-xserver/xserver-xf86-config/crownbay
         $ mv meta-mymachine/recipes-graphics/xorg-xserver/xserver-xf86-config/crownbay-noemgd \
            meta-mymachine/recipes-graphics/xorg-xserver/xserver-xf86-config/mymachine

At this point the `recipes-graphics` directory just has files that support Video Electronics Standards Association (VESA) graphics modes and not EMGD.

#### Changing `recipes-core`

Now let's look at changes in `recipes-core`. The file `task-core-tools.bbappend` in `recipes-core/tasks` appends the similarly named recipe located in the local Yocto Project files at `meta/recipes-core/tasks`. The "append" file in our layer right now is Crown Bay-specific and supports EMGD and non-EMGD. Here are the contents of the file:

         RRECOMMENDS_task-core-tools-profile_append_crownbay = " systemtap"
         RRECOMMENDS_task-core-tools-profile_append_crownbay-noemgd = " systemtap"

The `RRECOMMENDS` statements list packages that extend usability. The first `RRECOMMENDS` statement can be removed, while the second one can be changed to reflect `meta-mymachine`:

         RRECOMMENDS_task-core-tools-profile_append_mymachine = " systemtap"

#### Changing `recipes-kernel`

Finally, let's look at `recipes-kernel` changes. Recall that the BSP uses the `linux-yocto` kernel as determined earlier in the `mymachine.conf`. The recipe for that kernel is not located in the BSP layer but rather in the local Yocto Project files at `meta/recipes-kernel/linux` and is named `linux-yocto_3.0.bb`. The `SRCREV_machine` and `SRCREV_meta` statements point to the exact commits used by the Yocto Project development team in their source repositories that identify the right kernel for our hardware.

However, in the `meta-mymachine` layer in `recipes-kernel/linux` resides a `.bbappend` file named `linux-yocto_3.0.bbappend` that is appended to the recipe of the same name in `meta/recipes-kernel/link`. Thus, the `SRCREV` statements in the "append" file override the more general statements found in `meta`.

The `SRCREV` statements in the "append" file currently identify the kernel that supports the Crown Bay BSP with and without EMGD support. Here are the statements:

         SRCREV_machine_pn-linux-yocto_crownbay ?= \
            "372c0ab135978bd8ca3a77c88816a25c5ed8f303"
         SRCREV_meta_pn-linux-yocto_crownbay ?= \
            "d5d3c6480d61f83503ccef7fbcd765f7aca8b71b"

         SRCREV_machine_pn-linux-yocto_crownbay-noemgd ?= \
            "372c0ab135978bd8ca3a77c88816a25c5ed8f303"
         SRCREV_meta_pn-linux-yocto_crownbay-noemgd ?= \
            "d5d3c6480d61f83503ccef7fbcd765f7aca8b71b"

You will notice that there are two pairs of `SRCREV` statements. The top pair identifies the kernel that supports EMGD, which we don’t care about in this example. The bottom pair identifies the kernel that we will use: `linux-yocto`. At this point though, the unique commit strings all are still associated with Crown Bay and not `meta-mymachine`.

To fix this situation in `linux-yocto_3.0.bbappend` we delete the two `SRCREV` statements that support EMGD (the top pair). We also change the remaining pair to specify `mymachine` and insert the commit identifiers to identify the kernel in which we are interested, which will be based on the `atom-pc-standard` kernel. Here are the final `SRCREV` statements:

         SRCREV_machine_pn-linux-yocto_mymachine ?= \
            "fce17f046d3756045e4dfb49221d1cf60fcae329"
         SRCREV_meta_pn-linux-yocto_mymachine ?= \
            "84f1a422d7e21fbc23a687035bdf9d42471f19e0"

If you are familiar with Git repositories you probably won’t have trouble locating the exact commit strings in the Yocto Project source repositories you need to change the `SRCREV` statements. You can find all the `machine` and `meta` branch points (commits) for the `linux-yocto-3.0` kernel here [WRITER's NOTE: Need new link to the 3.0 source repo area when it is available].

If you need a little more assistance after going to the link then do the following:

1. Expand the list of branches by clicking `[…]`

2. Click on the `yocto/standard/common-pc/atom-pc` branch

3. Click on the commit column header to view the top commit

4. Copy the commit string for use in the `linux-yocto_3.0.bbappend` file

For the `SRCREV` statement that points to the `meta` branch use the same procedure except expand the `meta` branch in step 2 above.

Also in the `linux-yocto_3.0.bbappend` file are `COMPATIBLE_MACHINE`, `KMACHINE`, and `KERNEL_FEATURES` statements. Two sets of these exist: one set supports EMGD and one set does not. Because we are not interested in supporting EMGD those three can be deleted. The remaining three must be changed so that `mymachine` replaces `crownbay-noemgd` and `crownbay`. Here is the final `linux-yocto_3.0.bbappend` file after all the edits:

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

         COMPATIBLE_MACHINE_mymachine = "mymachine"
         KMACHINE_mymachine  = "yocto/standard/mymachine"
         KERNEL_FEATURES_append_mymachine += " cfg/smp.scc"

         SRCREV_machine_pn-linux-yocto_mymachine ?= \
            "fce17f046d3756045e4dfb49221d1cf60fcae329"
         SRCREV_meta_pn-linux-yocto_mymachine ?= \
            "84f1a422d7e21fbc23a687035bdf9d42471f19e0"

### BSP Recipe Change Summary

In summary, the edits to the layer’s recipe files result in removal of any files and statements that do not support your targeted hardware in addition to the inclusion of any new recipes you might need. In this example, it was simply a matter of ridding the new layer `meta-machine` of any code that supported the EMGD features and making sure we were identifying the kernel that supports our example, which is the `atom-pc-standard` kernel. We did not introduce any new recipes to the layer.

Finally, it is also important to update the layer’s `README` file so that the information in it reflects your BSP.

## Preparing for the Build

To get ready to build your image that uses the new layer you need to do the following:

1. Get the environment ready for the build by sourcing the environment script. The environment script is in the top-level of the local Yocto Project files directory structure. The script has the string `init-build-env` in the file’s name. For this example, the following command gets the build environment ready:

            $ source oe-init-build-env yocto-build

   When you source the script a build directory is created in the current working directory. In our example we were in the `poky` directory. Thus, entering the previous command created the `yocto-build` directory. If you do not provide a name for the build directory it defaults to `build`. The `yocot-build` directory contains a `conf` directory that has two configuration files you will need to check: `bblayers.conf` and `local.conf`.

2. Check and edit the resulting `local.conf` file. This file minimally identifies the machine for which to build the image by configuring the `MACHINE` variable. For this example you must set the variable to mymachine as follows:

            MACHINE ??= “mymachine”

   You should also be sure any other variables in which you are interested are set. Some variables to consider are `BB_NUMBER_THREADS` and `PARALLEL_MAKE`, both of which can greatly reduce your build time if you are using a multi-threaded development system (e.g. values of `8` and `j 6`, respectively are optimal for a development machine that has four available cores).

3. Update the `bblayers.conf` file so that it includes the path to your new BSP layer. In this example you need to include the pathname to `meta-mymachine`. For this example the `BBLAYERS` variable in the file would need to include the following path:

            $HOME/poky/meta-intel/meta-mymachine

The appendix Reference: Variables Glossary in the Yocto Project Reference Manual has more information on configuration variables.

## Building the Image

To build the image for our `meta-mymachine` BSP enter the following command from the same shell from which you ran the setup script. You should run the `bitbake` command without any intervening shell commands. For example, moving your working directory around could cause problems. Here is the command for this example:

         $ bitbake –k core-image-sato-live

This command specifies an image that has Sato support and that can be run from a USB device or from a CD without having to first install anything. The build process takes significant time and includes thousands of tasks, which are reported at the console. If the build results in any type of error you should check for misspellings in the files you changed or problems with your host development environment such as missing packages.