[Coco] How to trick Disk BASIC?, or Drivewire sans disk controller...

[Joel Ewy]

Hey everyone,

I tried an experiment that hasn't yet achieved complete success.  Maybe 
somebody has some ideas about how to make it work.

As a result of some discussion on the forum on coco3.com I decided to 
try modifying an Orchestra 90CC cart so that it could be used as a 
Drivewire client without a disk controller.  ( 
http://www.coco3.com/community/2010/01/can-a-coco-3-sound-like-a-c64/comment-page-2/#comments 
)

The ROM on my Orch 90 is a 28-pin ROM, which makes it easy to do this 
modification without a socket adapter.  I was successful in 
non-destructively desoldering the original ROM and installing a socket.  
I then tested the Orch 90 with the original ROM put back in the socket.  
William Tell Overture.

Pin 26 on the Orch 90's ROM is left NC.  I wired it via a toggle switch 
to VCC and GND so I can select the upper 8K or lower 8K of a 27128 (16K) 
EPROM.  In one half of the EPROM I put a copy of the original Orchestra 
90 ROM, and in the other half I put a copy of the Drivewire 3 HDB-DOS.

When I switch it to Orch 90 it works fine.  But HDB-DOS apparently isn't 
happy that it isn't in an actual disk controller -- I don't get the Disk 
BASIC screen, but a garbled text screen.  The same thing happens if I 
put in a 2764 with the patched Disk BASIC out of a Disto Super 
Controller II -- the garbled screen looks identical.

I assume that the Disk BASIC ROM is checking the floppy disk controller 
hardware and not finding what it expects.  Is there some sanity checking 
done in Disk BASIC that could be skipped if we just want to run from a 
Drivewire server and have no need of actually accessing real floppy 
drives?  One of the main objectives here is to do without real floppy 
drives, controller, or an MPI.

JCE