[Coco] Question about MPI behavior

[Robert Hermanek]

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