[Coco] Paul Barton's 8Meg board, Roger Taylor's DrivePak, and NitrOS-9

[Robert Gault]

Would I be lucky enough to have a reader who uses both the Barton 8-Meg board 
and Roger's DrivePak? Usually I use a 6309 512K Coco3 but was recently testing 
my 6309 8-Meg DrivePak system. It will work perfectly with NitrOS-9 3.3.0 until 
I try to load the DrivePak drivers. Then there is a complete hardware crash.

If found that 6809 NitrOS-9 v3.2.9 works fine with the 8-Meg board, so something 
has changed which I can't seem to find.

Roger's DrivePak uses $FF6C-$FF6E which has been assigned to a MOD pak in the 
OS-9 defs but I don't have those drivers installed. The software turns off the 
interrupts while accessing $FF6C-$FF6E in any case. Also there is no problem 
with a 512K system.
The Barton board uses $FF9B and $FFAx the same way, for the most part, as 
NitrOS-9 handles 2Megs.

  FF9B  Reserved.
         1MB and 2MB bits, Write only.
         Bit 7 - na
         Bit 6 - na
         Bit 5 - 8MB Memory Bit          NoCan3 bits for 8MB.
         Bit 4 - 4MB Memory Bit          NoCan3 bits for 8MB.
         Bit 3 - 8MB Video Bit           NoCan3 bits for 8MB.
         Bit 2 - 4MB Video Bit           NoCan3 bits for 8MB.
         Bit 1 - 2MB Video Bit   Disto & NoCan2/3 bits for 2MB.
         Bit 0 - 1MB Video Bit   Disto & NoCan2/3 bits for 1MB.

$FF9B must be set before $FFAx go get the full 8Megs.

I don't see why but there is some weird interaction between this hardware and 
v3.3.0. I will be testing older versions of NitrOS-9 to see if there is one that 
works.

Robert