The Semtech LR2021 is not a fixed-function ASIC. It contains an on-board microcontroller with updatable firmware, and researcher Alex Beale has reverse engineered it well enough to write and deploy custom code directly on the chip.
Beale used LLMs as a core part of the reverse engineering process, crediting them with making an otherwise near-impossible task tractable. The payoff is concrete: he can now run FFTs for a waterfall display on-chip, and operate a full mesh network node without any external microcontroller. The original writeup details exactly how he got there, and that process is worth reading in full.
This is the second major class of radio chip to fall to this kind of internal reverse engineering in recent months, following similar work on WiFi hardware. The pattern is becoming clear: dedicated radio chips are hiding programmable cores, and researchers are starting to use them.
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