May 27th - As most have heard, I'm finally feeling better and I've gone back to work on the XM, sadly my partner on this project - Mark (Groovybee) has moved onto some other work and is no longer involved in the XM it would seem. Mark has been great, he's been a real champion in helping on this project, but it has been a very long process and we all do these things for the love of the hobby, no one is obligated to stay on a project. However the Rev 3 design was based on idea's and features Marked wanted to incorporate into the XM design, and the BIOS is all Mark's work. Without Mark's involvement I cannot implement the logic he wanted to put into the design since I don't know what he wanted to lay it out as nor where he wished to tie in. Also some of the features may have required a further modified BIOS to support these features. I am not a 7800 Coder and I can't write the BIOS. Mark also has all of the sources to the BIOS so I couldn't alter it anyway. So I have decided on a compromise - I am going to take many of the benefits from the Rev 3 designs, go back to the Rev 2 which was a working platform and incorporate those Rev 3 improvements where feasible and then use the last stable BIOS Mark had delivered for the project and put everything together. Perry has a friend who is an Analog Audio guy looking over the Yamaha portion of the XM schematics to see if he can fix some of the shortcomings with the design.
So basically the final design will be a Rev 2.5 design. I've also decided that once the XM's are released I am putting all of the schematics into PD so those who'd like to tinker, hack and improve upon the XM design. Perhaps if Mark decides to get back involved in 7800 development at a later time, maybe he will release the BIOS as PD, but that is solely his decision and I would respect either way he would wish to go with that. My releasing of the schematics doesn't obligate him to release his BIOS. So I've started working on wedging the 68Pin 1504AS back into the Rev 3 boards, and re-routing the traces and removing all of the additional Bus partitioning and secondary Address Bus lines out of the design and getting to a Rev 2.5 'Hybrid' design which will be functional and do what was initially intended before feature-creep added to the design.
I will post more info in 2 weeks, I'll also see about bringing a working XM to the Too Many Games show June 14-16th in Pennsylvania.