The early years and the tight relation to µOS++

The history of the xPack project was deeply intertwined with the history of µOS++, as it was initially intended to automate building and running multi-platform unit tests for µOS++. Later it was also used to build the binary xPacks, which further validated the concept.

To avoid redundancy, the full story is not replicated here, so please read the history of µOS++ before continuing; the brief list of the important events is:

  • eCos CDL was the inspiration for a component based design (early 2000s)
  • in 2013, the GNU ARM Eclipse plug-ins (later rebranded as the Eclipse Embedded CDT) was the first attempt to find a solution that avoids generating make files by hand, but this prevented building and running unit tests in a scriptable environment
  • in 2013, the experimental XCDL (eXtended Components Definition Language) project, inspired by eCos CDL, implemented in Python, validated the concept
  • in 2014, the CMSIS Packs solution was evaluated, and an Eclipse plug-in was created to manage them, but the solution was later found to have too many design issues, and was abandoned
  • in 2015, the yotta solution was considered, and the first XCDL packs based on yotta were tested; for various reasons, yotta was later abandoned by Arm
  • in 2017, the first release of xpm was available, as a complementary solution to npm, and packages managed by it were named xPacks; xpm complements npm as the industry standard package manager for JavaScript packages, and uses the same as the hugely popular public package repository
  • in 2019, xpm was extended to also support installing binary packages, and a new class of tools was created as xPack 3rd Party Development Tools
  • in 2022, xpm was used to build the binary packages; this proved that the technology is standalone, with the newer versions of the tools being built with existing xPacks
  • in 2023, with most of the tools in place, a first C/C++ project (@micro-os-plus/utils-lists) was fully tested via xpm, validating again the whole concept

The xPack project goals

The project came to life as a practical need to find a replacement for the Eclipse CDT managed build, with the additional requirement to be able to run unit tests in a scriptable environment.

By trial and error, the main aspects that need to be addressed by such a solution were identified as:

  • the build (defining which files enter the build, the compiler/linker options, etc)
  • the project configuration (e.g. managing the values of the #define in a consistent way)
  • the tools (toolchains, debuggers, emulators, etc)

The XCDL experimental version

The first experimental solution was XCDL, which was used in the µOS++ Second Edition; basically some of the eCos CDL functionality was implemented in Python.

The result looked like this:

The implementation was quite easy, and worked pretty well.

However several issues were identified:

  • using configuration files written in a programming language was convenient, but it had a major drawback: since parsing Python is not trivial, it prevented the configuration being edited with a GUI tool (similar to the Eclipse settings pages); in other words, the configuration files must be in a structured format, otherwise editing them by a machine is problematic
  • although the µOS++ SE was more or less modular, the project was basically a mono-repo, and writing unit tests for each module was difficult
  • running unit tests with several toolchains, not to mention with different versions of the same toolchain, proved extremely difficult, and doing this on multiple platforms (macOS, windows, linux) was even more difficult

The lessons learned from this experiment were:

  • if a configuration needs to be edited by a machine, it must be written in a structured format, JSON being the favourite
  • if each module is expected to be tested, it is better to use multiple small repositories, each with its CI tests
  • if the project is split into multiple packages, a tool to automate installing/managing the dependencies is a great addition
  • toolchains and other tools need to be standalone & relocatable, to allow multiple versions to be installed in different folders on the same machine; managing these multiple tools can also be automated with a tool

Binary xPacks

The first binary tools prepared were arm-none-eabi-gcc, openocd, qemu and windows-build-tools; they were also used in Eclipse project; initially they were installed manually, and Eclipse was able to identify them in certain fixed location.


While searching for a solution to automate installing different source packages, a solution that looked pretty close to the needs was npm, so most of the concepts were adopted, and the tool was extended to handle the C/C++ linear dependencies; this is how xpm was created.

Later xpm was extended to automate installing the toolchains and other binary archives.

As of now, there are toolchains for Arm, AArch64, RISC-V and native (GCC & clang), that run on Windows, Linux, macOS; it is probably fair to say that the tools part of the project is covered properly, and fully automated.

Build system generators

As for the build and configuration tools in the project, things are work in progress.

For the build, the first idea was to rewrite the initial Python code in JavaScript, but later a step by step approach was considered.

In the first step the existing build system generators were used, like CMake and meson, with several advantages:

  • they allow to add tests to the µOS++ projects immediately, without having to wait for any special/future tools
  • they are a good chance to get a lot of experience on how to organise projects with such tools
  • they provide the users a direct way to integrate the µOS++ source code libraries into their existing projects built with CMake/meson.

To manage the multi-platform, multi-architecture, multi-version, multi-etc tests, a tool to manage multiple build configurations was needed, and since each configuration needs its own tools, with different versions, it became clear that the build configurations must be managed by the same tool, so xpm was extended to handle multiple build configurations; later, xPack actions were added, to automate running sequences of commands, like cmake or meson, to build and run the tests.

Future plans

At the moment of writing this (mid 2023), the project is pretty advanced, but it is not yet complete.

Soon all the µOS++ projects will be updated to use the multiple build configurations automated by xpm, and so have everything fully tested in µOS++.

With the experience from this step, the next step is to finalise the specs for the xPack Project Builder that will perform the builds and manage the project configurations.

The tool will probably be called xpmake, and will use json files, with a content similar to this one:

As it can be seen, this file defines the include folders, the source files, and some preprocessor definitions that might be enabled while building the project.

This file, together with all other similar files from the packages that are part of the project, will provide the input data for a tree of components, that can be rendered in a graphical tool like VS Code, thus allowing to configure a project in a way similar, possibly even more advanced, than the Eclipse CDT settings, since the hierarchical components reflect the logical structure of the application, and allow to automatically manage dependencies between components, and between configuration options.

Additions to the VS Code xPack extension are planned, to edit the tree of xPack CDL components, and run the builds directly, without CMake/meson; this will be a true xPack enabled tool, and will be an alternate solution to Eclipse Embedded CDT.

But the use of this tool should be optional, the whole functionality should also be available from a terminal and a plain text editor.


As it can be seen, the xPack project originated from the need to automate the workflow for existing open source projects, especially the execution of multiple tests for embedded projects, which often poses more challenges than developing the projects themselves.

To be continued…