Resurrecting ‘bricked’ NXP Kinetis Devices

Modern MCUs like the NXP Kinetis have security features which prevent reverse engineering, but can ‘brick’ devices too. Depending on the settings, it prevents read-out from the FLASH or reprogramming the device. While some of the protection is (mostly) not by-passable by design, in many case the devices looks like ‘bricked’ but still can be recovered. In this article I’ll get you some ways for a (hopefully) successful recovery.

J-Link EDU Mini recovering a tinyK22 with needle adapter
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McuOnEclipse Components: 26-Dec-2021 Release

I’m pleased to announce a new release of the McuOnEclipse components, available on SourceForge. This release includes several bug fixes, support for more devices, and updated components like FreeRTOS, MinINI, Percepio Tracealyzer and SEGGER SystemView.

SourceForge

SourceForge

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Standalone SWO

SWO (Single Wire Output) in ARM cores is probably one of the most under-used features. Which is surprising, because SWO can be very useful. In a nut shell: SWO is a single wire output pin/signal channel which can provide lots of different data, like PC sampling for coverage information, interrupt tracing data or ‘uart-like’ text packets.

SWO output from application
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Position-Independent Code with GCC for ARM Cortex-M

Welcome to ‘Alice in Wonderland‘! For a university research project using an ARM Cortex-M33 we are evaluating position-independent code as way to load applications or part of it with a bootloader. It sounds simple: just add -fPIC to the compiler settings and you are done.

Unfortunately, it is not that simple. That option opened up a ‘rabbit hole’ with lots of wonderful, powerful and strange things. Something you might not have been aware of what could be possible with the tools you have at hand today. Leading to the central question: how is position-independent code going to work with an embedded application on an ARM Cortex-M?

Let’s find out! Let’s start a journey through the wonderland…

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Recovering Cortex-M Microcontroller with a Power Glitch

If a Cortex microcontroller is unresponsive to a debug connection for various reasons, then this trick might help to recover that device for you. All you need is a debug probe from PEMICRO and a utility.

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Visual Studio Code for C/C++ with ARM Cortex-M: Part 1 – Installation

For a few months I’m learning and using Rust. I’m still learning, but I’m very impressed by the powerful and cool programming language, the vibrant ecosystem, the advanced concepts behind it and by the tools. With learning Rust I have been using the Visual Studio Code IDE and it works great for Rust. But I was wondering: could I use it for my ‘usual’ C/C++ development on ARM Cortex-M devices too? The answer is a clear ‘yes’, and this mini series of articles should get you up and running too.

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“java.net.SocketException: Connection reset”: Check your Windows Updates!

One of the most frustrating part developing embedded applications is if the debug connection fails somehow: with all the different factors like operating system, virtual machines, USB ports and hubs, debug probe and firmware a ‘connection failed’ is my nightmare. And this is probably the most frustrating parts for my students (and myself!)

I do have a growing list of tips & tricks in “Debugging Failure: Check List and Hints“, so check this list. What I just have added is an entry for

java.net.SocketException: Connection reset

It occurred for a few students when they wanted to use the on-board CMSIS-DAP LinkServer debug connection on the NXP LPC845-BRK.

NXP LPC845-BRK Board

NXP LPC845-BRK Board

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Tutorial: GNU Coverage with MCUXpresso IDE

If you are developing Linux or desktop applications with GNU tools, you  very likely are familiar with gcov: the GNU coverage tool. It collects data what parts of the code gets executed and represents that in different formats, great to check what is really used in the application code or what has been covered during multiple test runs.

Coverage Information with gcov

Coverage Information with gcov

line never executed

line never executed

GNU coverage is possible for resource constraint embedded systems too: it still needs some extra RAM and code space, but very well spent for gathering metrics and improves the firmware quality. As I wrote in “MCUXpresso IDE V11.3.0 for 2021” things are now easier to use, so here is a short tutorial how to use it.

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NXP published MCUXpresso SDK 2.9.0 on GitHub

There are many different aspects of Open Source projects: It is not only about the fact if the sources are available (‘open’). It is about the licensing terms (how permissible is it, what can I do with it), maintenance and continuous development (what has changed between releases), how and where is it delivered (Sourceforge, dedicated distribution, packaging) up to collaboration (how can I contribute or submit issues).

NXP has now published the MCUXpresso SDK on Github:

MCUXpresso SDK on GitHub

MCUXpresso SDK on GitHub

Something I was waiting for a long time.

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assert(), __FILE__, Path and other cool GNU gcc Tricks to be aware of

It is always good to have a close look what ends up in a microcontroller FLASH memory. For example using EHEP Eclipse plugin to inspect the binary file:

Source File Name in Binary Image

Source File Name in Binary Image

Obviously it has path and source file information in it. Why is that? And is this really needed?

What about:

  • Privacy: the path or file name might expose information (secret project name?) or might be used for reverse engineering?
  • Size: The strings add up to the final data/FLASH size, so this increases the need for ROM space?

So let’s have a look what is the reason for this and how it could be avoided or at least reduced.

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