[Coco] Error in vcc or RGBDOS

[Robert Gault]

Robert Gault wrote:
> Bill Pierce wrote:
>>
>> I've noticed this myself a while back. After an I/O on the empty virtual
>> floppy (Fd-502), then DRIVEON, it seems to loose the VHD.
>>
>
> Ah, that is slightly different from what I understood Luis' problem to be.
>
> The same thing happens with MESS so there may be an error in the RGBDOS ROM for
> emulators. RGBDOS on real hardware does not exhibit this problem. After an I/O
> error with a floppy, there is no problem reading a hard drive or a different
> floppy drive.
> At first glance, I see no reason for this in the RGBDOS code. It is possible it
> is a result of the emulation process itself. I'll spend more time going through
> the RGBDOS source code and if I find a cause for this, I'll make a new ROM
> available.
>
>

I've got a start on the problem and there should be a way to alter the RGBDOS 
ROM to correct it.
It seems that the error result at $F0 is not being cleared correctly and carries 
over to subsequent disk I/O. However the is one scenario where it is 
self-correcting.

test case
floppy in drive0
.vhd mounted

DIR3
Gives unrecoverable error until a DIR0 after which disk I/O is normal.
DIR3
Gives unrecoverable error but a POKE &HF0,0 will yield normal disk I/O.

It looks like RGBDOS is not correctly reporting values to $F0.