[Coco] The ZORK games

[Robert Gault]

A while ago there were some questions about getting the Zork games
http://www.colorcomputerarchive.com/coco/Disks/Games/Infocom%20Adventures/
to run with Drivewire4.

I've been looking at this and have at least gotten Zork-I to start. Infocom used 
a silly method of getting disk access. First the DOS command loaded T34 into 
memory at $2600. Then most of this memory was moved to $5000 which consisted 
essentially of a byte for byte copy of the DOS1.1 DSKCON routine. This routine 
copied code into memory at $1100-$2FFF starting at track0 sector1 and jumped to 
this code. Some of the new code loaded was another copy of DSKCON.

It is possible to write a short ml routine to load code starting at T0S1. This 
code now $1100 is patched so that DSKCON at $D75F is used instead of the game's 
disk I/O routine at $216C.

After a few moves (where you go around the house to find a window to open and 
try to enter) the patched game crashes. I suspect that another block of disk 
access code was loaded so that the HDBDOS DSKCON was no longer used.

Does anyone have access to Infocom information about how the games did disk I/O 
that would make patching them easier?

Robert