Raspberry Pi 4 Model B - Yocto 5.0 "scarthgap" and later

[TheYoctoJester]

Board description

The Raspberry Pi 4 Model B is the probably most popular board of the Raspberry Pi family.

URL: https://www.raspberrypi.org/products/raspberry-pi-4-model-b/
Wiki: https://elinux.org/RPi_Hub

Test results

Raspberry Pi 4 is one of the official reference devices of Mender and is easy to get started with. This device is continuously tested as part of Mender testing pipelines which assures high quality of the integration.

Version notes

This tutorial uses scarthgap as the primary target, which is the current LTS release by the Yocto Project. You can find more infomation on releases here.

NOTE: before the Yocto 5.0 release “scarthgap”, meta-mender and meta-mender-community used Google Repo configuration files. Please see the Raspberry Pi 4 Model B - Yocto 4.0 "kirkstone" and earlier article for building these releases.

Supported releases for following the tutorial are:

Yocto Project	Tutorial applies	Maintenance
scarthgap (5.0)		LTS1
nanbield (4.3) and older		does not apply

1. Disabled GRUB integration for ARM systems which is default in meta-mender/meta-mender-raspberrypi. U-Boot is still primary integration method for this platform.

Please note: a failure in the “tutorial applies” column indicates that the instructions do not work without modification. Depending on the combination of release and host Linux distribution, installing other python versions or dependencies might provide a functional state.

Build Means that the Yocto Project build using this Mender integration completes without errors and outputs images.
Runtime Means that Mender has been verified to work on the board. For U-Boot-based boards, the integration checklist has been verified.

Getting started

Prerequisites

• A supported Linux distribution and dependencies installed on your workstation/laptop as described in the Yocto Development Manual
• NOTE. Instructions depend on which Yocto version you intend to use.
• kas installed and in your PATH.

Configuring the build

Setup Yocto environment

Create a directory for your mender-raspberrypi5 setup to live in and clone the

meta information.

mkdir mender-raspberrypi4 && cd mender-raspberrypi4

Clone the meta-mender-community layer:

git clone https://github.com/theyoctojester/meta-mender-community \
  -b scarthgap

Setup build environment

Change into the cloned repository and create a directory to hold the build:

cd meta-mender-community
mkdir my-raspberrypi4
cd my-raspberrypi4

Use kas to set up the build structure:

kas shell ../kas/raspberrypi4.yml

This opens a sub-shell which is initialized for the build process. You can close it using the exit command.

Configure Mender server URL (optional)

This section is not required for a successful build but images that are generated by default are only suitable for usage with the Mender client in Standalone deployments, due to lack of server configuration.

You can edit the conf/local.conf file to provide your Mender server configuration, ensuring the generated images and Mender Artifacts are connecting to the Mender server that you are using. There should already be a commented section in the generated conf/local.conf file and you can simply uncomment the relevant configuration options and assign appropriate values to them.

Build for Hosted Mender:

# To get your tenant token:
#    - log in to https://hosted.mender.io
#    - click your email at the top right and then "My organization"
#    - press the "COPY TO CLIPBOARD"
#    - assign content of clipboard to MENDER_TENANT_TOKEN
#
MENDER_SERVER_URL = "https://hosted.mender.io"
MENDER_TENANT_TOKEN = "<copy token here>"

Building the image

You can now proceed with building an image:

MACHINE=raspberrypi4 bitbake core-image-base

Replace core-image-base with your desired image target.

Using the build output

After a successful build, the images and build artifacts are:

• tmp/deploy/images/raspberrypi4/core-image-base-raspberrypi4.sdimg
• tmp/deploy/images/raspberrypi4/core-image-base-raspberrypi4.mender

The disk image (with .sdimg suffix) is used to provision the device storage for devices without Mender running already. Please proceed to the official documentation on provisioning a new device for steps to do this.

On the other hand, if you already have Mender running on your device and want to deploy a rootfs update using this build, you should use the Mender Artifact files, which have .mender suffix. You can either deploy this Artifact in managed mode with the Mender server (upload it under Releases in the server UI) or by using the Mender client standalone mode.

References

• The Mender integration layer for Raspberry Pi boards can be found in meta-mender-community.

• The official Mender documentation explains how Mender works. This is simply a board-specific complement to the official documentation.

Known issues

Boot firmware files

See Updating Raspberry Pi boot firmware files using Yocto Project and Mender.

See this thread where the limitations of the boot firmware files on Raspberry Pi are discussed.

Devicetree is not updated

To be able to support update of Linux kernel and devicetree, Mender requires these to be installed in the /boot directory for each rootfs (normally /dev/mmcblk0p2 and /dev/mmcblk0p3). On the other hand, the Raspberry Pi boot firmware requires that the DTB file is in the same partition as the boot firmware (/dev/mmcblk0p1) and the config.txt file. For now Mender will not use the DTB that is delivered with new artifacts and will continue to boot with the original DTB that was populated using the sdimg file.

Problem using ‘dtoverlay=pi3-disable-bt’

pi3-disable-bt disables the Bluetooth device and restores UART0/ttyAMA0 to GPIOs 14 and 15. It is also necessary to disable the system service that initialises the modem so it doesn’t use the UART

There is currently a known issue with above functionality, that is to enable UART0 on PIN 14 and 15.

It is actually not something that is caused by Mender specifically, but Mender requires U-Boot to be present to support robust features such as roll-back. U-Boot is typically not enabled if you do a stock Raspberry Pi and some people are often surprised that the Bluetooth UART stopped working when they integrate meta-mender.

The problem is in U-Boot which does conflicting configuration, and there is a workaround reported here and it has been reported to U-Boot but unclear when/if it will be fixed.

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[maxhochlenertarnoldn]

Thank you very much for taking the time to update the tutorial!