LinkServer for Microcontrollers

GDB is the de-facto debugging engine and debug connection for micro-controllers these days: it is versatile and with its client-server architecture very flexible and powerful, and pretty much every debug probe and vendor (PEMICRO, SEGGER, OpenOCD, pyOCD, …) offers it. But a GDB server or command line implementation was not available for the NXP LinkServer family of debug probes (LPC-Link, MCU-Link, MCU-Link Pro). This has changed now: LinkServer is available as command line tool and can be used as GDB Server:

LinkServer as GDB Server with Eclipse

With the new LinkServer package I do not only get a gdb server implementation: I have now a command line tool I can use for automation and all kind of different things: programming boards, erasing flash, and so on.

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Booting J-Link as CMSIS-DAP Debug Probe

Mostly unnoticed (at least for myself), SEGGER has enabled some of the J-Link debug probes to support the CMSIS-DAP debug protocol.

SEGGER J-Link as CMSIS-DAP Debug Probe

This greatly enhances the use of J-Link debug probes for CMSIS-DAP based tools.

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Open Source picoLink: Raspberry Pi RP2040 CMSIS-DAP Debug Probe

One essential part of embedded development is the ability to debug the target application. The good thing with the Raspberry Pi Pico RP2040 Eco-system is: One can use another RP2040 Pico board as a debug probe to debug other ARM Cortex-M devices.

But instead using a Raspberry Pi Pico board with some wires, why not building a dedicated board? The result is a small, versatile and open source debugging probe which virtually can debug any ARM Cortex-M device as a standard ARM CMSIS-DAP probe:

picoLink Debug Probe debugging a Raspberry Pi Pico Board
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RP2040 with PIO and DMA to address WS2812B LEDs

I love the WS2812B (aka SK6812) addressable LEDs: they are inexpensive and available in different packages. I have used them in different projects, including the MetaClockClock one. I used the NXP Kinetis for these projects, but because they are not available any more, for a new project we had to choose a new microcontroller, with the Raspberry Pi Pico RP2040 as the winner.

Raspberry Pi Pico RP2040 driving WS2812B with PIO and DMA
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Using Semihosting the direct Way

Most embedded developers have probably used ‘semihosting’. And yes, it is generally seen as a bad thing. Maybe you have used it, without realizing what it really is and what it does. It is simple to add a printf() to the code (again: you should not use printf), and with the right standard library, it magically it shows up in a console view:

printf a hello world

That looks great, but what is behind this, to make it happen? Actually, it is really amazing technology. And it can be used for better things than just printing text.

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Debugging Embedded Targets with pyOCD and Eclipse

If doing embedded development, then the debugging solution is probably the most important single tool in the development chain. Because very debugging probe has its pros and cons, I usually have at least three different debug probes on my desk, simply to get the job done in all aspects.

What is true for the hardware debugging probes, is true for the gdb client and server side. I’m using mostly the P&E, SEGGER and CMSIS-DAP plugins (e.g. NXP LinkServer) and OpenOCD from the Eclipse IDE side. But there are more choices, for example pyOCD.

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ARM SWO ITM Console Bidirectional Standard I/O Retargeting

The ARM Cortex M architecture has many features which are underused, probably simply because engineers are not aware of it. SWO (Single Wire Output) is a single trace pin of the ARM Cortex-M CoreSight debug block. trace pin uses the ITM (Instruction Trace Macrocell) on ARM Cortex. It provides a serial output channel, at a high speed higher than the usual UART, because it is clocked at half or a quarter of the core clock frequency, depending on the core and implementation.

As such, it is an ideal high speed output channel to send text or data to the host. This is how it is usually used, but what is unknown to many: it can be used in a bidirectional way with the help of the debugger.

The topic of this article: how to redirect standard I/O like printf() or scanf() using the SWO ITM console: means both sending *and* receiving data over the SWO debug channel: that way I can use it as a kind of UART with a single pin only.

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NXP MCUXpresso IDE 11.7.0

It is the exam and grading time at the university, and the same time I’m preparing the lectures and labs for the new semester starting mid of February. I’m always heading for using the latest and greatest tools in my labs. A few days ago, NXP released the new version of the MCUXpresso IDE, version 11.7.0. Time to check it out…

NXP MCUXpresso IDE 11.7.0
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McuOnEclipse Components: 29-Dec-2022 Release

I’m pleased to announce a new release of the McuOnEclipse Processor Expert components, available on SourceForge.


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Fixing “REENT malloc succeeded” Assertion

One little nasty assertion in the GNU standard library appeared a few days ago, kind out of nowhere, reporting “REENT malloc succeeded”:

Obviously it was caused by the call to srand() which sets the ‘seed’ for the standard library (pseudo) random number generator. The assertion happens as well later for calling the rand() function.

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