Docker or Development Container are great for isolation. And they work very well with things outside which are TCP/IP based. But most debug probes are USB only. Docker container don’t work well with USB. In Remote Debugging with DevContainer and VS Code, I showed how to use USB based debug probes. I demonstrated using them with an IP connection. In this article I show how Windows USB devices can be used from a container, with the help of usbipd.
The Rust programming language is making its way into different areas: Rust gets added to the Linux Kernel. I see an increasing interest for using Rust in embedded projects. And Rust is used for embedded tools. I noticed this with the latest LinkServer v25.09 release: there is a new tool included in the package, rblhost.
rblhost on crates.io
The release note just mentioned:
- Switched to using rapid blhost (rblhost) utility.
This triggered my interest, and actually that utility is implemented in Rust :-).
Today’s projects and systems get more and more complex. Many systems include multiple MCUs, connected with a field bus or network, for example CAN. For example there can be up to 70 CAN nodes in modern cars. Such larger and connected systems are a challenge for debugging.
Traditional hardware debugging requires a hardware debug probe, connected with a dedicated SWD/JTAG debug cable to the target device. This needs dedicated pins on the target device plus physical access to the device itself. In many cases, this is not possible in the final product. The hardware debug probes, cables, pins and high speed signals are costly. And worse they can introduce new problems and are prone to interference.
If there is a field bus like CAN connecting all the MCUs, why not use it for hardware debugging? Hardware debugging meaning programming the FLASH memory, halt the MCU, inspect the memory and registers, and step through the code?
Cortex-M Hardware Debugging over CAN
Yes, we can! With the help of a rather unknown hardware feature on ARM Cortex-M devices. We can use the ARM DebugMonitor Interrupt to control and debug the target system. As we would use a JTAG/SWD connection. Instead, we use the CAN bus :-).
I’m shifting more and more of my CI/CD testing infrastructure using the LinkServer runner. One reason is the LinkServer runner can run the test on-target. It can also collect GNO gcov coverage information at the same time. LinkServer is a suite of software tools for launching and managing GDB servers for NXP debug probes.
Test coverage is a very useful metric: it tells how much of your code has been covered by tests. Or the other way: it helps identifying areas of my code which has not been running tests. A new CMake extension in VS Code is available. It works with the new NXP LinkServer test runner to allow running tests on an embedded target. The really cool thing is: it collects and visualizes test data with coverage information in a single step:
The MCU-Link-MR from NXP is a CMSIS-DAP debug probe. It includes dedicated connection headers found on mobile robotic systems. These systems include the Pixhawk/PX4 drone and robotics hardware.
The NXP SDK is git based which is great. If I create a project with VS code, it references the SDK cloned locally.
Standard NXP SDK Project in VS Code
A standalone project structure is needed if you want to easily share a project with your team. It’s also necessary for sharing inside a classroom environment. This article shows how to use an NXP SDK project in standalone mode.
This is the second part describing how to use DevContainer for embedded applications with VS Code.
In Optimizing Embedded Development with VS Code and DevContainer I use VS Code with a docker ‘development’ container. The container is created with a recipe to install the development tools and SDK. With VS Code and DevContainer I have the same developer experience as I would develop locally on the host.
One thing not addressed in that earlier article is debugging. Using USB debug probes like a SEGGER J-Link or NXP MCU-Link is a challenge inside a container. This applies to any other debug probe as well.
The solution is to transform an USB based debug probe into one with a network connection:
Embedded System have a lifetime of 10 or 15 years. During that time the software and tools has to be maintained. This can be very challenging. Who knows if that compiler or tool used is still available in 10 years from now? Additionally installing and configuring the tool chain and environment for a new team member is difficult. Even worse: using a different host operating system for the cross development can produce different results or introduce issues.
VS Code running with DevContainer
One solution for all these problems is to use Docker images and containers. I can pack all the necessary tools and software into a virtual environment and container. But developing inside a container comes with many challenges. In this article I’ll show how Visual Studio Code or VS Code makes working with containers very easy. In this article I show how easy it is to use modern development tools and methodologies for embedded development.
NXP has released a new LinkServer software. It includes an interesting feature. The LinkServer test runner has been extended with a Semihosting console. This is not only very useful for on-target testing. With the Semihosting console, I have a bidirectional communication channel with the target. And I do not need any hardware pins or to run a debug session. All what I need is the CMSIS-DAP connection with the NXP LinkServer runner to have a command line shell: