I have been working on a Teensy 4.1 debugger mod for a month or so now and I figured it was in a good place to share my progress. This project started by de-soldering the MKL02 chip, soldering magnet wire onto each pin of the MKL02 and the Teensy to break them out to 16 pin headers on a breadboard. From there I jumpered the pins which were necessary for the teensy to function while leaving the J-tag pins free to be used by a J-Link.

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I was successful in programming and debugging using PlatformIO so I continued the project by designing a flex pcb which could be soldered onto the teensy QFN pads. This first attempt failed as too much of the pads were cut and upon soldering they came right off.

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Which brings us to the current revision. Fully functioning Teensy 4.1 debugging!

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If you see this Paul, I would love for debugging on the next Teensy to be a bit easier! Although this has been an interesting/fun project to work on so thanks for that.