During the evaluation of the odds are you will face a package missing from the default image tq-image-weston. In the Yocto build system, package recipies are organized in so called Yocto layers. To find specific recipes or layers, the OpenEmbedded layer index is a good place to start looking. It lists existing layers and corresponding recipes.

Zeus Layers
Zeus Recipes

The easiest approach to add a package recipe to the image, is the usage of the IMAGE_INSTALL:append variable in conf/local.conf file which is located in the build space.

At first, open a new terminal on the development host and to move into the build directory. Continue to initialize the build environment as described in Quickstart BSP

cd ~/workspace/ci-meta-tq 
source setup-environment tqma8mxnl_build

The example below demonstrates how to add the editor nano to your build. Open conf/local.conf with an editor of your choice and insert the following lines at the end of file:

IMAGE_INSTALL:append = " nano"

You may want add multiple packages using the IMAGE_INSTALL:append variable. This can be done in one line or multiple lines, demonstrated by the following two code-examples.
Multiple packages are always separated by spaces.

IMAGE_INSTALL:append = " <recipe-name_1> <recipe-name_2>" 

IMAGE_INSTALL:append = " \
                       <recipe-name_1> \
                       <recipe-name_2> \
                       "

You have added your desired package(s) and may repeat building your image now:

bitbake tq-image-weston

Bitbake provides a script for simplyfying the process of creating new layers. It creates a template layer with the following basic structure:

├── conf
│   └── layer.conf
├── COPYING.MIT
├── README
└── recipes-example
    └── example
        └── example_0.1.bb

To add a template layer to /ci-meta-tq/sources, like meta-custom in this example, use the bitbake-layers create-layer script:

bitbake-layers create-layer <path/to/your_layer>

for example…

bitbake-layers create-layer ../sources/meta-custom

Before making changes to the new layer, it's recommended to perform the following actions:

* Initialize the new layer as git repository 
* Editing the README template 
* Check and if necessary adjust the license of the layer
* Configuring the layer priority in layer.conf 

Create a git repository for the new layer

Revision control is good practice in modern software development, therefore we recommend to initialize a git-repository for the new yocto layer.

Move into the directory of the new custom layer:

cd ~/workspace/ci-meta-tq/sources/meta-custom

Initialize the directory as git repository and make an initial commit:

git init
git add .
git commit -m "Initial Commit"

Editing README

The README file should give a brief overview of the layer.
Among other things the README should contain:

• Description of the layer content
• Dependencies to other layers e.g. meta-tq
• A description how to use the layer

The README of the meta-tq layer can be taken as an example.

Layer license

Configure layer priority

The bitbake-layers create-layer script sets a layer priority of 6 by default, which is defined in the conf/layer.conf file. In this example the layer priority is set to a value of “10” to ensure that the meta-custom example layer has the highest priority.

BBFILE_PRIORITY_meta-custom = "10"

Before the new layer can be used for the build, it must be added to the conf/bblayers.conf file in your build directory.

echo 'BBLAYERS += "${BSPDIR}/sources/meta-custom"' >> conf/bblayers.conf

As previously described, it is possible to add packages in a quick and dirty like manner by modifying the local.conf.
The more sensible approach is, to add a packages by creating *.bbappend files to expand the original image recipe. For the evaluation, the default image recipes are provided by the meta-dumpling layer.

For the tqma8mxnl module it's recommended to build a tq-image-weston. Its recipe is located in …/ci-meta-tq/sources/meta-tq/meta-dumpling/recipe-images/images/tq-image-weston.bb.

The corresponding tq-image-weston.bbappend in the custom layer has to be located in the same path as the orginal tq-image-weston.bb in the meta-dumpling layer.
The commands below demonstrate, how to create an empty tq-image-weston.bbappend file for the default image recipe tq-image-weston.bb:

cd ci-meta-tq/sources/meta-custom
mkdir -p ./recipes-images/images
cd recipes-images/images
nano tq-image-weston.bbappend

Now continue to add the following lines to the new tq-image-weston.bbappend file.
This will extend the search path and add the desired package(s). Make sure the meta-layer, from which the recipe originates, already exists in the sources directory. It also needs to be listed in bblayers.conf.

IMAGE_INSTALL:append = " <recipe-name>"

For example the nano editor will be added:

 IMAGE_INSTALL:append = " nano"

You may repeat building your image now:

bitbake tq-image-weston

The Linux kernel configuration is provided by the linux kernel sources and is located in the source tree at /arch/arm64/configs/imx_v8_defconfig.
The meta-tq layer expands the kernel configuration imx_v8_defconfig by so-called kernel configuration fragments. These fragments are located in …/ci-meta-tq/sources/meta-tq/meta-tq/recipes-kernel/linux/linux-imx-tq-5.4/tqma8.

https://www.yoctoproject.org/docs//kernel-dev/common.html#creating-configuration-fragments

Before creating the new configuration fragment, the path that holds the configuration fragments has to be recreated in meta-custom.

cd ci-meta-tq/sources/meta-custom
mkdir -p ./recipes-kernel/linux/linux-imx-tq-5.4/tqma8

Continue to navigate back to the build directory. To begin creating a new configuration fragment, enter the Linux kernel menuconfig with the the following command:

bitbake -c menuconfig virtual/kernel

Select/deselect the required/desired kernel options, then save and exit the menuconfig. The new configuration fragment can now be created by:

bitbake -c diffconfig virtual/kernel 

After applying the diffconfig command, the path of the new config fragment is printed to the shell. This should look like so:

Config fragment has been dumped into:
/home/embedded/workspace/Zeus-tqma8mxnl/ci-meta-tq/tqma8mxnl_build/tmp/work/

Move the configuration fragment to the example layer meta-custom. Here it is good practice, to give the fragment a unique name with reference to the options it activates/deactivates.
For this example, it will simply be named example.cfg:

mv ~/workspace/Zeus-tqma8mxnl/ci-meta-tq/tqma8mxnl_build/tmp/work/ ~/workspace/Zeus-tqma8mxnl/ci-meta-tq/sources/meta-custom/recipes-kernel/linux/linux-imx-tq-5.4/tqma8/example.cfg

The next step is to create a .bbappend file for the kernel recipe located in recipes-kernel/linux/

FILESEXTRAPATHS:prepend := "${THISDIR}/${PN}:"
SRC_URI_mx8 += "file://example.cfg"

The FILESEXTRAPATHS:prepend variable extends the search path of BitBake to include a directory named after the package that is being processed.
In this case, the package name (PN) is “linux-imx-tq-5.4”. The PN describes the package name under the current directory THISDIR.

Finally the Linux kernel has to be cleaned and the image rebuilt:

bitbake -c cleansstate virtual/kernel 

bitbake tq-image-weston

The Linux kernel source is provided as a git repository and available in the following path after building tq-image-weston with the Quickstart BSP

~/workspace/Zeus-tqma8mxnl/ci-meta-tq/tqma8mxnl_build/tmp/work-shared/tqma8mxnl-1gb-mba8mx/kernel-source

Open a new terminal and navigate to the kernel sources used for the build

cd ~/workspace/ci-meta-tq/tqma8xx_build/tmp/work-shared/tqma8mxnl-1gb-mba8mx/kernel-source

Make your changes in the source code, e.g. in the device tree file arch/arm64/boot/dts/freescale/imx8mn-mba8mx.dtsi

nano arch/arm64/boot/dts/freescale/imx8mn-mba8mx.dtsi

Check the status of the repository with git status command

git log 

Take the latest commit from the output and execute git diff <latest commit> to see all changes.

Redirect the output to a patch file in the example layer …/ci-meta-tq/sources/meta-custom/recipes-kernel/example.patch.

Add patch to the build

Now expand the SRC_URI_mx8 variable in the Linux kernel recipe by the .patch file created before.
For this purpose, the .bbappend file from the Customize linux kernel configuration section can be reused.
If the file wasn't created yet, do so now.

You created the file just now -> add this:

FILESEXTRAPATHS:prepend := "${THISDIR}/${PN}:"
SRC_URI_mx8 += "\
    file://example.patch \
    "

You created the file before, following this guide -> add only the example.patch to the ''SRC_URI'' variable:

FILESEXTRAPATHS:prepend := "${THISDIR}/${PN}:"
SRC_URI_mx8 += "\
    file://example.cfg \
    file://example.patch \
    "

Now, finally the kernel has to be cleaned and rebuilt:

bitbake -c cleansstate virtual/kernel 

bitbake tq-image-weston

The best way to develope using your own mainboard, is to create a new repository with kernel sources.

Follow the first five steps from the Quickstart BSP guide and navigate to the build directory.
Now clone the kernel sources to a local git repository:

mkdir -p ../local_repos/
https://github.com/tq-systems/linux-tqmaxx.git
cd ../local_repos/linux-tqmaxx
git reset --hard
git clean -fdx
git checkout  

Make your own branch in the git repository

git checkout -b custom-branch

Make your changes in the source code and make a commit:

e.g. nano arch/arm64/boot/dts/freescale/imx8mn-mba8mx.dtsi
edit and save
git commit -a -m "my changes"

Save the commit ID, you can print them using one of the following commands:

To list all of the commits:
git log 
Get the latest commit id:
git rev-parse HEAD

Create a new yocto layer by following the steps previously described.

Navigate into the new layer and recreate the path structure of meta-tq.

cd ci-meta-tq/sources/meta-custom
mkdir -p ./recipes-kernel/linux/linux-imx-tq-5.4/tqma8

Now create the .bbappend file for the kernel recipe located in meta-custom/recipes-kernel/linux/

SRC_URI_remove_mx8 = "${TQ_GIT_BASEURL}/linux-tqmaxx.git;protocol=${TQ_GIT_PROTOCOL};branch=${SRCBRANCH}"
SRC_URI_append_mx8 = "git://${BSPDIR}/local_repos/linux-tqmaxx;protocol=file;branch=${SRCBRANCH}"
SRCBRANCH = "custom-branch"
SRCREV = "Your commit ID of the changes"

Finally rebuild your kernel using the following command:

bitbake -c build virtual/kernel

You may repeat building your image now

bitbake tq-image-weston