How to compile the device tree with the Distribution Package

1. Introduction↑

This article is intended for Yocto experts, or people who have some practical experience of the Yocto environmment.

This section describes the steps needed to create and configure a demo layer using DeviceTree files from the STM32CubeMX tool, and to add and configure a machine similar to those already supported by the OpenSTLinux Distribution Package (in particular the machine delivered inside the existing STM32MP BSP layer 'addons').

Reminder: this addon-layer is deployed under the following path in the delivery : <path of OpenSTLinux distribution delivery>/layers/meta-st/meta-st-stm32mp-addons/

2. Creating a new open embedded layer for your demo↑

You first need to create a new layer. See the latest How to create a new open embedded layer

After creation, you have under <path of OpenSTLinux distribution delivery>/layers/meta-st/:

$ tree meta-my-demo-layer
meta-my-demo-layer
├── conf
│   └── layer.conf
├── COPYING.MIT
├── README
└── recipes-example
    └── example
        └── example.bb

3 directories, 4 files

2.1. Update layer.conf file↑

Open the layer.conf file and add the lines below for the licenses, demo layer path, and dependency with the STM32MP BSP layer 'addons' :

EULA_FILE_ST_stm32mpmydemo = "${LAYERDIR}/conf/eula/${MACHINE}"
EULA_FILE_ST_MD5SUM_stm32mpmydemo = "8b505090fb679839cefbcc784afe8ce9"

#Inform bitbake for adding another location to search for licenses
LICENSE_PATH += "${LAYERDIR}/files/licenses"

# Set a variable to get the STM32MP MX BSP location
STM32MP_MY_DEMO_BASE = "${LAYERDIR}"

# This should only be incremented on significant changes that may
# cause compatibility issues with other layers
LAYERVERSION_meta-my-demo-layer = "1"

LAYERDEPENDS_meta-my-demo-layer = "stm-st-stm32mp-mx"

# OpenEmbedded compatibility information
# This should only be incremented on significant changes that will
# cause compatibility issues with other layers
LAYERVERSION_meta-my-demo-layer = "1"
LAYERSERIES_COMPAT_meta-my-demo-layer = "dunfell"

Information

LAYERSERIES_COMPAT must be aligned with the version of OpenEmbedded used.
Please refer to https://wiki.yoctoproject.org/wiki/Releases

2.2. Create the machine for your demo↑

Copy the machine delivered inside the existing STM32MP BSP layer 'addons' into your demo layer

$ cp <path of OpenSTLinux distribution delivery>/layers/meta-st/meta-st-stm32mp-addons/conf/machine/stm32mp1-mx.conf <path of OpenSTLinux distribution delivery>/layers/meta-st/meta-my-demo-layer/conf/machine/stm32mp1-demo.conf

Open stm32mp1-demo.conf and update the line below

#@NEEDED_BSPLAYERS: layers/meta-openembedded/meta-oe layers/meta-openembedded/meta-python layers/meta-st/meta-st-stm32mp-addons

Replace STM32MP_MX_BASE by STM32MP_MY_DEMO_BASE

Add these lines after the series of includes:

# Define specific common machine name
MACHINEOVERRIDES .= ":stm32mpmydemo"

Uncomment variables to configure your own Boot Mode Choice, Boot Device Choice, Board Type Choice, DeviceTree files and path

2.3. Associate EULA with the new demo machine↑

Copy the eula folder delivered inside the existing STM32MP BSP layer 'addons' into your demo layer

$ cp -rf <path of OpenSTLinux distribution delivery>/layers/meta-st/meta-st-stm32mp-addons/conf/eula/ <path of OpenSTLinux distribution delivery>/layers/meta-st/meta-my-demo-layer/conf/.

Then replace the existing symbolic link with the machine used for your demo:

$ rm stm32mp1-mx
$ ln -s ST_EULA_SLA stm32mp1-demo

2.4. Move DeviceTree files and project coming from STM32CubeMX tool↑

The principle is that the user generates devicetree files for the targeted demo from the STM32CubeMX tool.

Warning

Most of the time, generated devicetree files - mainly user sections - must be reworked by the end user for compilation and functional purposes. Each demo is delivered with an application note that describe changes applied on STM32CubeMX devicetree files

.

These files are then moved into the “mx” folder created into your demo layer : <path of OpenSTLinux distribution delivery>/layers/meta-st/meta-my-demo-layer/mx/

Sub-folders are created and populated with the generated devicetree files:

mx/${CUBEMX_PROJECT}/kernel
mx/${CUBEMX_PROJECT}/u-boot
mx/${CUBEMX_PROJECT}/tf-a
mx/${CUBEMX_PROJECT}/optee-os

With CUBEMX_PROJECT that is equal to the value defined inside the machine used for the demo.

2.5. Update the README file↑

Please update the README file with the information needed for building and executing the demo.

2.6. Clean up useless content↑

You can delete the content of the recipes-example folder created by the create-layer command.

After making all of the updates, your demo layer should be similar to:

$ tree meta-my-demo-layer
meta-my-demo-layer
├── conf
│   └── eula
│       └── ST_EULA_SLA
│       └── stm32mp1-demo -> ST_EULA_SLA
│       └──  ...
│   └── layer.conf
│   └── machine
│       └── stm32mp1-demo.conf
├── COPYING.MIT
├── mx
│   └── STM32MP157C-EV1
│        └── my-demo
│            └── DeviceTree
│                └── my-demo
│                    └── kernel
│                        └── stm32mp157c-my-demo.dts
│                    └── tf-a
│                        └── stm32mp157c-my-demo.dts
│                        └── stm32mp15-mx.h
│                    └── u-boot
│                        └── stm32mp157c-my-demo.dts
│                        └── stm32mp157c-my-demo-u-boot.dtsi
│                        └── stm32mp15-mx.h
│                    └── optee-os
│                        └── stm32mp157c-my-demo.dts
└── README

3. Adding specific recipes and content necessary for your demo↑

Examples of further add-on components:

Recipes for installing distro-specific configuration files
Any image recipes specific to user distribution
A psplash append file for a branded splash screen
Any other append files to make custom changes

Some other added components (*bb) are more specific: images, system services, and so on (a non-exhaustive list is shown below):

Recipes-core for psplash screen, systemd services
Recipes-samples for example images

...