Okay, I've been disassembling the May 10, 1993 Sonic CD prototype for a while today, and I've been following along with the Rex Sabio documents to see what all the stuff does as I'm not familiar with the Sega CD nearly as much as I am with the Mega Drive. Anyway, I'm good on BIOS calls, but what would a jsr to $7880 or $7800 do. I can't seem to find that anywhere in these documents but I see it several times in the (either IP or SP code, still figuring that one out). Also, here's some examples of what I've disassembled so far, tell me how I'm doing on accuracy of commenting. usercall0: What I'm assuming is the entrypoint? One of the file entries: So yeah, long post is long, but if anyone could help I'd really appreciate it ;-)