[Coco] VI and VIRQ

[Robert Gault]

Mark Marlette wrote:

> Gene,
> 
> offset, virtual drive, etc.....Boisy is the expert on this feature...
> 
> Mark
> 

I'm not sure what software comes from Cloud-9, but here is what I do on 
my KenTon scsi system.

The only difference between the OS-9 section of an RGBDOS/HDBDOS hard 
drive and the Disk Basic section is the offset added to the LSN#. For 
most people, that offset is constant and stored in the DOS ROM.
To be able to read an OS-9 disk stored in the Disk Basic section of the 
hard drive, boot disk or otherwise, a new driver is needed that adds the 
Disk Basic + drive number offset to all LSN values.

In fact, I have made such a driver available in my RGBDOS for emulators 
package. If you have the source code for the driver you are currently 
using, it should be easy to modify it to add the required offset value. 
The biggest problem is deciding whether to permit access to all drive 
numbers or just the boot drive. I chose to permit access to any drive 
number so used a byte in the descriptor to store that value, changeable 
using dmode.