Raspberry Pi 4 Model B + Raspbian

Board description

The speed and performance of the new Raspberry Pi 4 is a step up from earlier models. For the first time, we’ve built a complete desktop experience. Whether you’re editing documents, browsing the web with a bunch of tabs open, juggling spreadsheets or drafting a presentation, you’ll find the experience smooth and very recognisable — but on a smaller, more energy-efficient and much more cost-effective machine.

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

Test results

The Raspbian releases in the table below have been tested by the Mender community. Please update it if you have tested this integration on other Raspbian releases:

Rasbian Build Runtime
Raspbian Buster 2019-06-20 :test_works: :test_works: 1

1. This integration is based on the mender-convert/next branch which has not yet been released.

Build Means that the image generation completes without errors and outputs images.
Runtime Means that Mender has been verified to work on the board.

Getting started

Prerequisites

  • A Linux-based laptop/workstation (Ubuntu has been verified to work)
  • You need to install Docker Engine to use this tutorial

Build Docker image for mender-convert

Open a terminal and clone the mender-convert repository, e.g.

git clone -b next https://github.com/mendersoftware/mender-convert.git

Enter your mender-convert environment:

cd mender-convert

There is a utility script which can be used to generate the appropriate docker image to run mender-convert:

./docker-build

This will create a container image you can use to run mender-convert.

Download the latest stable Raspberry Pi raw disk image

Download the raw Raspberry Pi disk image into a subdirectory input:

mkdir -p input
cd input
wget https://downloads.raspberrypi.org/raspbian_lite/images/raspbian_lite-2019-06-24/2019-06-20-raspbian-buster-lite.zip

Extract the raw Raspberry Pi disk image:

unzip 2019-06-20-raspbian-buster-lite.zip && cd ..

Convert the Raspberry Pi disk image to support Mender

With the raw disk image and the container configured above, we can convert the image.

You can get your Mender Professional tenant token at the My organization page in Mender Professional.

Configure the Mender client for hosted Mender server:

./scripts/bootstrap-rootfs-overlay-hosted-server.sh \
    --output-dir ${PWD}/rootfs_overlay_demo \
    --tenant-token "Paste token from Mender Professional"

There are additional scripts in the scripts/ directory to configure with a local demo server, or production server.

Run mender-convert inside the container by running:

MENDER_ARTIFACT_NAME=release-1 ./docker-mender-convert \
    --disk-image input/2019-06-20-raspbian-buster-lite.img \
    --config configs/raspberrypi4_config \
    --overlay ${PWD}/rootfs_overlay_demo

Conversion will take 10-15 minutes, depending on your storage and resources available.

NOTE!

You will need an SD card with an capacity of at least 8GB when using the default arguments. The SD card layout will be the following using the default arguments:

Part Type Purpose Size Configure size
mmcblk0p1 vfat Store the bootloader 44MB MENDER_BOOT_PART_SIZE_MB
mmcblk0p2 ext4 Store the root file system and kernel (active) 3908MB MENDER_STORAGE_TOTAL_SIZE_MB 1
mmcblk0p3 ext4 Store the root file system and kernel (inactive) 3908MB MENDER_STORAGE_TOTAL_SIZE_MB 1
mmcblk0p4 ext4 Store persistent data, preserved during Mender updates. 128MB MENDER_DATA_PART_SIZE_MB 2

1. The rootfs partition size is calculated using the following formula:

 (storage-total-size-mb - data-part-size-mb - boot-part-size) / 2

2. You rarely need to adjust the data part size using MENDER_DATA_PART_SIZE_MB as this will expanded on first boot to occupy the remaining free blocks of the SD card.

You can read more about the partition layout required for Mender here

Use the output images

After a successful conversion, the images and artifacts are:

  • deploy/raspberrypi-release-1.sdimg.gz
  • deploy/raspberrypi-release-1.ext4
  • deploy/raspberrypi-release-1.mender

The disk image (with .sdimg.gz suffix) is used to provision the device storage for devices without Mender running already. You can write write the sdimg.gz image to an SD card using the following command:

zcat deploy/raspberrypi-release-1.sdimg.gz | sudo dd of=<path to device> bs=4M && sudo sync

Be careful! If you point to the wrong <path to device> when executing the above command, you risk overwriting your workstation’s local or connected storage devices.

On the other hand, if you already have Mender running on your device and want to deploy a rootfs update from this conversion, you should use the Mender Artifact files, which have .mender suffix. You can either deploy this Artifact in managed mode with the Mender server as described in Deploy to physical devices or by using the Mender client only in Standalone deployments.

Boot from the SD card and connect to your Mender server

Ensure your device has Internet connectivity (e.g. through Ethernet cable with DHCP support).

After provisioning a SD card with the converted disk image (.sdimg) above, boot your device from it.

After about 10 minutes, you should see your device Pending authorization under the Devices tab in your Mender server.
Authorize your device to join your Mender server.

You can now deploy software updates to your Raspberry Pi using the Mender server!

An improved workflow to generate Artifacts

The workflow of using an emulated device works for testing purposes, but it might
have some limitations as we are emulating and not logged in to a real device or user.

When working with real deployments the recommended workflow is to have
one golden device, that has not been converted to support Mender.
On this device you carry out all the modifications you need, and then
use the resulting SD card to create Mender Artifact files, in summary:

  • flash vanilla Rasbian to the SD card
  • boot the SD card, log in and make any modifications needed
  • copy the SD card into an image on your workstation (e.g. using dd)
  • run mender-convert with the --disk-image option to generate a Mender Artifact (like above)
  • upload the Artifact to your Mender server
  • deploy it to your devices

Note that your golden device or SD card is not running Mender and is not modified during deployments. It is simply the “source” for generating the Artifacts that you deploy to the devices in the field.

References

  • The documentation on Building a Mender Debian image contains more information about using Mender with the Debian family of distributions.

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

Known issues

raspi-config does not work as expected on a converted image

The raspi-config tool is a small utility that is commonly used on Raspbian to configure various aspects of the Raspberry Pi hardware and trying to use this tool on a converted image will not work (by design).

Specifically it relates to fact that we change the mount point of the boot partition, which on a stock image is mounted at /boot, but on a converted image it is mounted at /uboot. The raspi-config tool will try to perform lookups of files in /boot, and this is typically what will fail when trying to run this tool on a converted image.

The recommend approach is to use the raspi-config utility on the “Golden Image” as described in the “An improved workflow to generate Artifacts” section above, and not try to modify the converted image as this should be viewed as a static configuration that you can share across your device fleet.

Boot firmware files

Raspberry Pi boards have a set of boot firmware files that are located on the vfat boot part, and a selection of these files are:

bootcode.bin  fixup.dat     fixup_cd.dat  fixup_db.dat
fixup_x.dat   start.elf     start_cd.elf  start_db.elf
start_x.elf

Occasionally there will be changes to the Raspberry Pi software stack that requires that these files are updated. One example would be a change in the Linux kernel that relies on functional changes in the boot firmware and in this case you need to update the boot firmware together with the Linux kernel to get a functional device.

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

Because of this limitation certain upgrade paths using Mender might not work out-of-the box, e.g one known that will not work is:

  • Raspbian Stretch 2019-04-08 -> Raspbian Buster 2019-06-20

To support this update path you must update the boot firmware files at the same time you are updating to Raspbian Buster 2019-06-20. You can utilize state-scripts for this.

Note that it is unsafe to do update the boot firmware files because there is no way you can update these files atomically and it is not possible to roll-back in case you install something that does not boot, which might render your device unusable without physical intervention.

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/mmcbl0p1 ) 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 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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