Category Archives: NXP

Added Heap Memory Monitoring and Tracking to FreeRTOS V10.5

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We all should know it: dynamic memory usage can be dangerous. There can be memory fragmentation, use-after-free, out-of-memory and memory leaks. While I do prefer static memory allocation for embedded systems, using a dynamic memory allocation in some applications is not avoidable or just makes sense.

In one of my lecture modules we develop a ‘Boulder’ game, where the player has to collect underground diamonds and avoid moving monsters:

LPC845-BRK with OLED using dynamic memory allocation

I’ll show you have FreeRTOS memory usage can be tracked and monitored.

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Different Laser-Cut Enclosures for the MCU-Link

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The MCU-Link debug probe comes without an enclosure. To protect the hardware against ESD issues, I had created a 3D printed enclosure for it. That one worked fine, but takes some time to print it. If you have to build many enclosures for a full classroom setup, then a laser cutter is much faster. And to create some variations, I have decided to cut it with different materials and colors. To be environment friendly, extra glue is needed, and with recycled PMMA, different colors are possible too.

Different laser-cut enclosure: wood, and red, transparent, blue and green PMMA
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Changing the Startup: Custom initial PC and SP Register Setting with the Debugger

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By default, the debugger cares about the initial register settings after connecting to the target. But for special cases like using a bootloader combined with a loaded application, this requires a bit more than the usually ‘standard procedure’. For example I need to set both a custom program counter (PC) and stack pointer (SP).

How to set custom PC and SP for startup of the application
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Using Semihosting the direct Way

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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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IDE Custom C/C++ Local Build Environment

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On my host machine I have many different development environment installed. From different make, cmake and python versions up to different versions of GNU tool chains. Adding them to the PATH environment variable on Windows is really a bad thing: instead I want to keep my PATH as clean as possible. If I need to set up a different environment with different tools, then I prefer to have a ‘local’ environment.

PATH Setting
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Avoiding Stack Overflows: Application Monitoring the Stack Usage

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One of the biggest fears of embedded systems developers are stack overflows. FreeRTOS includes a cool feature to monitor and catch task stack overflows. But what about the MSP (Main Stack Pointer) on ARM, or the interrupt stack? What if not using an RTOS and running a bare-metal application?

Checking stack size used

There is a simple way monitoring stack usage at runtime, and for this I want to share the routines and what is now available inside the McuArm module.

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You_Shall_Not_Use_Printf: How to make sure no printf() is used

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Every embedded system developer should know by now, that using printf() is not a good thing for smaller systems. Printf() and the like are not only problematic from a code and data size perspective, they are infamous for vulnerability attacks too.

In this article I’ll show you multiple ways how to ban printf() or anything similar you want to avoid.

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Adding the Picolib C/C++ Standard Library to an existing GNU ARM Embedded Toolchain

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It looks like my previous article “Which Embedded GCC Standard Library? newlib, newlib-nano, …” stirred up something: I saw and knew about the Picolib created and maintained by Keith Packard, but never had the time to try it out. With the university grading mostly over, I have put aside a few hours to try it out. And the result is very interesting:

Footprint of different embedded libraries

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Debugging Embedded Targets with pyOCD and Eclipse

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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

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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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