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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Placing Code in Sections with managed GNU Linker Scripts

Managed linker scripts are great on one side: the simplify the otherwise complex GNU linker script handling. On the other side it requires knowledge how to tweak them in case ‘non-standard’ behavior is needed.

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SWO with ARM Cortex-M33

One major concern of embedded system development is performance. Microcontroller have more MHz than in the past, but embedded applications are all about timing and real-time aspects.

The challenge is: how to get data off the target in realtime? SWO can help with this….

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Using FatFS and MinINI with the NXP LPC55S16 EVK

For a research project we selected the NXP LPC55S16 but because it has due the silicon shortage it is not available probably for the next 52 weeks (yikes!) we can use the EVK Board.

The FatFS file system from Elm Chan is the de-facto file system for many embedded systems. As such it comes integrated with silicon vendor SDKs like the NXP MCUXpresso SDK. The problem is that the SDK only has examples for things on the board, and because that board does not have a SD card socket, no example for using FatFS with an SDK card is provided :-(. So I had to create one, and you can get it from GitHub.

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