[Coco] Question about MPI behavior

[Robert Gault]

Robert Hermanek wrote:
> I had an expectation that the following would work, but it apparently doesn't and I'm curious what people think:
>
> The plan:  I want to be able to boot up to HDB-DOS DW3 when I power up, but I also want to access real floppies, and also be able to use the original DOS in the drive controller when I want.  So I tried this configuration:
>
> 1)  Removed ROM from rs-232 pak and inserted HDB-DOS in it's place.
> 2)  Got out my MPI and upgraded it with PAL fix
> 3)  Plugged rs-232 Pak into slot 1, and a regular unmodified floppy controller into slot 4.
>
> Now, at this my expectation was:
>
> If I have my MPI selector on 1, I'll get HDB-DOS
> If I have my MPI selector on 4, I'll get unmodified DOS from the floppy controller.
>
> And that's exactly what happens.  And HDB-DOS can access drivewire images no problem, so I know it's working.  However, apparently the physical floppy drives cannot be accessed by HDB-DOS when I desire it, when the MPI selector is on 1.  My thought was that this would work:
>
> Boot up to HDB-DOS, then if I want to access a physical floppy hooked to the controller in slot 4, I can just use the standard commands:
>
> DRIVE OFF 0
> DIR 0
>
> But it hangs up on the DIR command, and there is no floppy acivity.  If I boot up to regular DOS on slot 4, then the floppy works fine.  It was my understanding that all the MPI selector did was choose which ROM to enable, but otherwise any conencted devices should still be available.  I used to have HDB-DOS ROM in a floppy controller directly, and it worked fine accessing these physical drives.  So I'm surprised that when it get loaded from another MPI slot and pak, it no longer works.  Thoughts?
>
> -Robert Hermanek
>

It should work and a very similar setup works for me.

FDC in slot4
Roger's SDMicro Drive Pak in slot1
A LOADM version of HDBDOS for Drivewire is on a "disk" in the SDMicro pak.

MPI selector on slot 1 which starts up the Pak and CoCoNet.
Select loading HDBDOS from a menu and HDBDOS starts.
DRIVE OFF does select real floppies.
DIR 0 does read disk0

I use a short Basic program as part of the LOADM routine to either clear or set 
the HDBDOS Offset values (they are typically $000000 for Drivewire) and with the 
offset=$5A000 and a .vhd drive in DW slot0, that drive will autostart AUTOEXEC.BAS.

The MPI switch selects both the ROM and disk I/O. You can send a value to $FF7F 
to split which slot has the ROM and which the FDC.
Perhaps something in your specific ROM has not correctly set $FF7F. You could 
try POKE &HFF7F,3  which would indicate the ROM is in slot1 and the I/O device 
in slot4.