> I thought it was because there was little to no documents for the GPUs/CPUs
ElSemi and Olivier Galibert figured it out pretty well. It's just that ElSemi's code is heavily tied to x86 32-bit (you'll notice there isn't a 64-bit version of his emulator, and forget about an ARM port) and thus it doesn't really drop into MAME in any meaningful way. Also, the fact that his emulator exists makes it less interesting to get it right in MAME.