did you know that you can find free Cortex M0 development boards at the side of the road? folks call them disposable vapes but they're hackable, and i've reverse engineered a bunch of them! see https://github.com/schlae/VapeRE/
many of these vapes bring the ARM SWD lines out through the charging connector's CC lines. with a simple breakout board and an SWD dongle you can reprogram the firmware.
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