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

...

Board support package

Board support package