Thank you!! The documentation is pretty sad at the moment, but I'd love to talk about it! I do have a little info about the ROM hack in the readme here: https://github.com/heyspacebuck/pokepinball-romhack
Essentially: the game writes to registers 0xD803 and 0xD804 whenever a rumble needs to begin. I took the disassembled code from the Pokemon Reverse Engineering Team and, any time I saw writes to 0xD803/0xD804, I added two extra steps:
- load a byte of data into 0xFF01, the serial-port data register
- write 0x81 to 0xFF02; the serial-port control register
Writing 0x81 to the control register initiates the data transfer on the link cable, which takes about a millisecond. I don't know how to send more than one byte, yet x3 But this is sufficient for my peripheral for now! Lemme know if you have any other ideas that might be fun to set up, I'm excited to try making some ROMs from scratch soon!