I was debugging an STM32 project in a Discord voice chat. Someone in the chat mentioned that the CH32V003 10 cent microcontroller has an HSITRIM register for fine tuning the internal oscillator's frequency, and he jokingly mentioned transmitting FM with it. I said that HSITRIM dithering would be funny, and now here I am trying to turn this absurd shower thought into reality.

Yes, this could have been done purely using the SPI peripheral and DMA to spit out a delta-sigma modulated or undersampled (sampled at under the nyquist rate but still contains frequency components at the target frequency) bitstream, but using HSITRIM to modulate the output is more in line with the spirit of the component abuse challenge. It also gives me the opportunity to use DMA to drive a peripheral DMA was never meant to drive but it can anyways due to the wonders of memory mapped IO.

Is it practical?
Nope!

Is it fun?
Hopefully!