This is the firmware I've been working on. Basically I wrote it because at the time (early 2023) there wasn't a "good" keyboard firmware like QMK or ZMK for the CH32V305. Now it supports keyboards, joysticks, and a rudimentary pointing device made out of a PS2-style analogue stick.

https://gitlab.com/hakfoo1/ch32v-keyboard/-/tree/fightstick?ref_type=heads

That branch has the mapping I used. Note this firmware has a keyboard-centric assumption that switches are wired as a matrix (between two sense lines), even if that matrix is 1x24, rather than just grounding a sense line individually.

The stick portion was one of those "Pandora Box" devices that was built into a cabinet and pre-wired to a crappy Android TV box.

I bought it because I figured it was probably cheaper than cutting a decent looking cabinet and buying the buttons off AliExpress. That also meant it came with a predefined cable harness to fit the Android box. In the hopes of making it tidy, and reversible, I ordered a little throwaway PCB that accepted the existing 40-pin plug and bridged it to a nanoCH32V305 breakout board. Of course, I made a design mistake, so the PCB had bodge wires, so not much was saved.

If you're starting from scratch, you could direct-wire to the MCU breakout board.