# BSP Development Example

This appendix provides a complete BSP development 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. The example begins with the Crown Bay BSP as the starting point but ends by building a new 'atom-pc' BSP, which was based on the Crown Bay BSP.

- 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. The following paragraphs describe both methods. For additional information, see the bulleted item "Yocto Project Release".

As mentioned, one way to get the Yocto Project files is to use Git to clone the `poky` repository. These commands create a local copy of the Git repository. By default, the top-level directory of the repository is named `poky`:

         $ git clone git://git.yoctoproject.org/poky
         $ cd poky

Alternatively, you can start with the downloaded Poky "&DISTRO_NAME;" tarball. These commands unpack the tarball into a Yocto Project File directory structure. By default, the top-level directory of the file structure is named `&YOCTO_POKY;`:

         $ tar xfj &YOCTO_POKY_TARBALL;
         $ cd &YOCTO_POKY;

If you're using the tarball method, you can ignore all the following steps that ask you to carry out Git operations. You already have the results of those operations in the form of the &DISTRO_NAME; release tarballs. Consequently, there is nothing left to do other than extract those tarballs into the proper locations.

Once you expand the released tarball, you have a snapshot of the Git repository that represents a specific release. Fundamentally, this is different than having a local copy of the Yocto Project Git repository. Given the tarball method, changes you make are building on top of a release. With the Git repository method you have the ability to track development and keep changes in revision control. See the "Repositories, Tags, and Branches" section for more discussion around these differences.

With the local `poky` Git repository set up, you have all the development branches available to you from which you can work. Next, you need to be sure that your local repository reflects the exact release in which you are interested. From inside the repository you can see the development branches that represent areas of development that have diverged from the main (master) branch at some point, such as a branch to track a maintenance release's development. You can also see the tag names used to mark snapshots of stable releases or points in the repository. Use the following commands to list out the branches and the tags in the repository, respectively.

         $ git branch -a
         $ git tag -l

For this example, we are going to use the Yocto Project &DISTRO; Release, which is code named "&DISTRO_NAME;". To make sure we have a local area (branch in Git terms) on our machine that reflects the &DISTRO; release, we can use the following commands:

         $ cd ~/poky
         $ git fetch --tags
         $ git checkout &DISTRO_NAME;-&POKYVERSION; -b &DISTRO_NAME;
         Switched to a new branch '&DISTRO_NAME;'

The `git fetch --tags` is somewhat redundant since you just set up the repository and should have all the tags. The `fetch` command makes sure all the tags are available in your local repository. The Git `checkout` command with the `-b` option creates a local branch for you named `&DISTRO_NAME;`. Your local branch begins in the same state as the Yocto Project &DISTRO; released tarball marked with the `&DISTRO_NAME;-&POKYVERSION;` tag in the source repositories.

## 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`. The base BSP is simply the BSP we will be using as a starting point, so don't worry if you don't actually have Crown Bay hardware. The remainder of the example transforms the base BSP into a BSP that should be able to boot on generic atom-pc (netbook) hardware.

For information on how to choose a base BSP, see "Developing a Board Support Package (BSP)".

## Getting Your Base BSP

You need to have the base BSP layer on your development system. Similar to the local Yocto Project Files, you can get the BSP layer in a couple of different 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" for information on how to get the BSP files.

This example assumes the BSP layer will be located within a directory named `meta-intel` contained within the `poky` parent directory. The following steps will automatically create the `meta-intel` directory and the contained `meta-crownbay` starting point in both the Git and the tarball cases.

If you're using the Git method, you could do the following to create the starting layout after you have made sure you are in the `poky` directory created in the previous steps:

         $ git clone git://git.yoctoproject.org/meta-intel.git
         $ cd meta-intel

Alternatively, you can start with the downloaded Crown Bay tarball. You can download the &DISTRO_NAME; version of the BSP tarball from the Download page of the Yocto Project website. Here is the specific link for the tarball needed for this example: . Again, be sure that you are already in the `poky` directory as described previously before installing the tarball:

         $ tar xfj crownbay-noemgd-&DISTRO_NAME;-&POKYVERSION;.tar.bz2
         $ cd meta-intel

The `meta-intel` directory contains all the metadata that supports BSP creation. If you're using the Git method, the following step will switch to the &DISTRO_NAME; metadata. If you're using the tarball method, you already have the correct metadata and can skip to the next step. 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 `&DISTRO_NAME;` branch.

         $ git checkout -b &DISTRO_NAME; origin/&DISTRO_NAME;
         Branch &DISTRO_NAME; set up to track remote branch &DISTRO_NAME; from origin.
         Switched to a new branch '&DISTRO_NAME;'

## 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 should follow the BSP layer naming convention, which is `meta-<name>`. The following assumes your working directory is `meta-intel` inside the local Yocto Project files. To start your new layer, just copy the new layer alongside the existing BSP layers in the `meta-intel` directory:

         $ 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

Next, we need to make changes to the `mymachine.conf` itself. The only changes we want to make for this example are to the comment lines. Changing comments, of course, is never strictly necessary, but it's alway good form to make them reflect reality as much as possible.

Here, simply substitute the Crown Bay name with an appropriate name for the BSP (`mymachine` in this case) and change the description to something that describes your hardware.

Note that inside the `mymachine.conf` is the `PREFERRED_VERSION_linux-yocto` 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 3.2 release.

The next configuration file in the new BSP layer we need to edit is `meta-mymachine/conf/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"

         LAYERDEPENDS_crownbay = "intel"

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"

         LAYERDEPENDS_mymachine = "intel"

### 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, while append files take the form of `.bbappend` 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-bsp/formfactor/formfactor/crownbay
         $ 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-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_3.2.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. In other words, the `SRCREV` values are simply Git commit IDs that identify which commit on each of the kernel branches (machine and meta) will be checked out and used to build the kernel.

However, in the `meta-mymachine` layer in `recipes-kernel/linux` resides a `.bbappend` file named `linux-yocto_3.2.bbappend` that appends information to the recipe of the same name in `meta/recipes-kernel/linux`. 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:

The commit ID strings used in this manual might not match the actual commit ID strings found in the `linux-yocto_3.2.bbappend` file. For the example, this difference does not matter.

         SRCREV_machine_pn-linux-yocto_crownbay ?= \
            "211fc7f4d10ec2b82b424286aabbaff9254b7cbd"
         SRCREV_meta_pn-linux-yocto_crownbay ?= \
            "514847185c78c07f52e02750fbe0a03ca3a31d8f"

         SRCREV_machine_pn-linux-yocto_crownbay-noemgd ?= \
            "211fc7f4d10ec2b82b424286aabbaff9254b7cbd"
         SRCREV_meta_pn-linux-yocto_crownbay-noemgd ?= \
            "514847185c78c07f52e02750fbe0a03ca3a31d8f"

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_3.2.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. In this case, because we're working with the &DISTRO_NAME; branch of everything, we need to use the `SRCREV` values for the atom-pc branch that are associated with the &DISTRO_NAME; release. To find those values, we need to find the `SRCREV` values that &DISTRO_NAME; uses for the atom-pc branch, which we find in the `poky/meta-yocto/recipes-kernel/linux/linux-yocto_3.2.bbappend` file.

The machine `SRCREV` we want is in the `SRCREV_machine_atom-pc` variable. The meta `SRCREV` isn't specified in this file, so it must be specified in the base kernel recipe in the `poky/meta/recipes-kernel/linux/linux-yocto_3.2.bb` file, in the `SRCREV_meta` variable found there. Here are the final `SRCREV` statements:

         SRCREV_machine_pn-linux-yocto_mymachine ?= \
            "f29531a41df15d74be5ad47d958e4117ca9e489e"
         SRCREV_meta_pn-linux-yocto_mymachine ?= \
            "b14a08f5c7b469a5077c10942f4e1aec171faa9d"

In this example, we're using the `SRCREV` values we found already captured in the &DISTRO_NAME; release because we're creating a BSP based on &DISTRO_NAME;. If, instead, we had based our BSP on the master branches, we would want to use the most recent `SRCREV` values taken directly from the kernel repo. We will not be doing that for this example. However, if you do base a future BSP on master and 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-3.2` kernel at .

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 `standard/default/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_3.2.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_3.2.bbappend` file are `COMPATIBLE_MACHINE`, `KMACHINE`, and `KBRANCH` 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`. Because we are using the `atom-pc` branch for this new BSP, we can also find the exact branch we need for the `KMACHINE` and `KBRANCH` variables in our new BSP from the value we find in the `poky/meta-yocto/recipes-kernel/linux/linux-yocto_3.2.bbappend` file we looked at in a previous step. In this case, the values we want are in the `KMACHINE_atom-pc` variable and the `KBRANCH_atom-pc` variables in that file. Here is the final `linux-yocto_3.2.bbappend` file after all the edits:

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

         COMPATIBLE_MACHINE_mymachine = "mymachine"
         KMACHINE_mymachine  = "atom-pc"
         KBRANCH_mymachine  = "standard/default/common-pc/atom-pc"

         SRCREV_machine_pn-linux-yocto_mymachine ?= \
            "f29531a41df15d74be5ad47d958e4117ca9e489e"
         SRCREV_meta_pn-linux-yocto_mymachine ?= \
            "b14a08f5c7b469a5077c10942f4e1aec171faa9d"

### 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-mymachine` 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 `yocto-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 your development system supports multiple cores. For development systems that support multiple cores, a good rule of thumb is to set both the `BB_NUMBER_THREADS` and `PARALLEL_MAKE` variables to twice the number of cores your system supports.

3. Update the `bblayers.conf` file so that it includes both the path to your new BSP layer and the path to the `meta-intel` layer. In this example, you need to include both these paths as part of the `BBLAYERS` variable:

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

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

## Building and Booting 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

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.

Finally, once you have an image, you can try booting it from a device (e.g. a USB device). To prepare a bootable USB device, insert a USB flash drive into your build system and copy the `.hddimg` file, located in the `poky/build/tmp/deploy/images` directory after a successful build to the flash drive. Assuming the USB flash drive takes device `/dev/sdf`, use `dd` to copy the live image to it. For example:

         # dd if=core-image-sato-mymachine-20111101223904.hddimg of=/dev/sdf
         # sync
         # eject /dev/sdf

You should now have a bootable USB flash device.

Insert the device into a bootable USB socket on the target, and power it on. The system should boot to the Sato graphical desktop. Because this new image is not in any way tailored to the system you're booting it on, which is assumed to be some sort of atom-pc (netbook) system for this example, it might not be completely functional though it should at least boot to a text prompt. Specifically, it might fail to boot into graphics without some tweaking. If this ends up being the case, a possible next step would be to replace the `mymachine.conf` contents with the contents of `atom-pc.conf` and replace `xorg.conf` with `atom-pc xorg.conf` in `meta-yocto` and see if it fares any better. In any case, following the previous steps will give you a buildable image that will probably boot on most systems. Getting things working like you want them to for your hardware will normally require some amount of experimentation with configuration settings.

For reference, the sato image produced by the previous steps for &DISTRO_NAME; should look like the following in terms of size. If your sato image is much different from this, you probably made a mistake in one of the above steps:

         260538368 2012-04-27 01:44 core-image-sato-mymachine-20120427025051.hddimg

The previous instructions are also present in the README that was copied from meta-crownbay, which should also be updated to reflect the specifics of your new BSP. That file and the `README.hardware` file in the top-level `poky` directory also provides some suggestions for things to try if booting fails and produces strange error messages.