Written by Kanak Shilledar
on March 06, 2025

SWUpdate on LicheePi 4A

When working with embedded linux devices, implementing reliable OTA updates is crucial for maintaining and upgrading devices remotely. In this post, I’ll walk you through how I setup SWUpdate on the LicheePi 4A using Buildroot without using any external update managers like Hawkbit.

Little on Buildroot

Buildroot is a simple, efficient and easy-to-use tools to generate embedded linux images using corss-compilation. It helps in rapidly building custom Linux based environments for the embedded systems by compiling the Linux kernel, bootloader, root filesystem and other essential userspace packages in a streamlined manner. Buildroot is widely used for rapid prototyping because of tis lightweight approach and ability to quickly generate images. It supports numerous processor architectures such as ARM, MIPS, RISC-V, etc. Unlike the Yocto Project, which uses a layerd architecture using bitbake Layers, Buildroot follows a very simple approach where all the configurations are managed through a single Kconfig file. This makes Buildroot easier to get started with, especially for projects where customization and quick image generation are the primary goals.

While Yocto is more flexible and scalable for large production environments with complex dependency management, Buildroot is often preferred for smaller projects that require a faster and more straightforward build process.

Little on SWUpdate

SWUpdate is a lightweight and flexible software update framework designed for embedded linux devices. It provides a reliable way to deploy firmware updates. SWUpdate can handle updates via various transport methods such as HTTP, HTTPS, USB or local storage. It supports various different update strategies, including updating live partitions, fail-safe mechanisms, and digital signature verification for secure updates, although these mechanisms are not enabled by default and you can configure these by following the SWUpdate docs. From a security perspective it is highly important that you should enable encryption for your update packages.

SWUpdate uses description files to define how updates should be applied. These files, typically written in Lua or as a SWU meta-description file, specify the details such as the update contents target partitions, and post-install actions.

SWU Meta-Description File The .swu file is a CPIO archive containing the update payload and a descriptor file named sw-description. This file is a structured text file that defines the metadata, update contents and installation instructions.
Lua-Based Description File For more complex update logic, Lua scripts can be used to define update behavior dynamically. This allows for conditional updates, logging, and integration with external services.

NOTE I will be using SWU Meta-Description file for this post.

SWU Meta-Description File

This is a CPIO archive and should contain the sw-description file at the start of the archive and then the payload. If the sw-description file is missing or not in order, then the SWUpdate fails.

swu-descriptor file

Building buildroot for LicheePi 4A

The default image configuration of buildroot doesn’t contain SWUpdate package, you need to enable it from menuconfig and selecting the SWUpdate package.

NOTE

LicheePi 4A patches are not there in the upstream buildroot. So, to build the image you need to clone it from my fork.
git clone https://github.com/kanakshilledar/buildroot -b licheepi_4a_major
cd buildroot
make sipeed_licheepi_4a_defconfig
make
Don’t forget to run menuconfig and select SWUpdate package.

Once the build is complete, you can find the artefacts inside the output/images/ directory. build artefacts Flash these artefacts to the board using fastboot.

Performing SWUpdate on LicheePi 4A

To perform an OTA Update, as discussed before, we need to build the .swu file. I created a simple file named new_file.txt, which contains the string “Hello, SWUpdate!” I built the CPIO archive using the following bash script

#!/bin/bash

FILES="1-update etc etc/new_file.txt"
for i in $FILES; do echo $i; done | cpio -ov -H crc > update.swu

Next, I transferred the update.swu file via FTP, ran the swupdate client, and got the file added in the /etc directory. swupdate successful

Verifying the installation via listing the file contents new file added

References

Conclusion

SSWUpdate is a flexible tool for managing OTA updates on embedded Linux devices. In this setup, I performed a simple file update using SWUpdate on the LicheePi 4A. However, adding arbitrary files into the filesystem is not a good idea. Here, I added a file purely as a proof of concept. Please refer the SWUpdate best practies page for further details.

Thanks for reading :)

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