[Coco] V.PAGE

[Robert Gault]

Chuck Youse wrote:
> This byte in the device descriptor appears to be unused (or at least,
> not useful) on Coco OS-9 (both levels 1 and 2).  While it's set in the
> device descriptor, it appears to be cleared in the device static storage
> area (rather than copied from the descriptor) before the call to the
> driver's INIT routine during I$Attach (in both Level 1 and Level 2
> IOMAN).
> 
> I'd like to re-use this byte as the multi-pak slot indicator, as I can't
> see that that's in the device descriptor anywhere else and appears to be
> hard-coded into the respective device drivers.
> 
> Am I going to make something explode if I try to repurpose this byte?
> 
> C.
>

Nothing should explode but you may not want to hard code the slot. A 
more flexible scheme would be to use a driver data byte for each device 
installed in the MPI. It would be the responsibility of the device 
during its init phase to store the current value of the MPI I/O byte, 
search for itself scanning through the slots, and saving the found slot.
Each time the device (driver) runs, it swaps MPI slots as needed.

Of course if you are writing code exclusively for your own use, do 
whatever you want. If you will be writing code for distribution, you 
don't want to force a user into a specific MPI slot. Let your driver 
find the correct slot so the user is free to stuff the MPI at random.