[Coco] NitrOS-9 and the MPI

[Robert Gault]

Darren A wrote:
> Does anyone know if NitrOS-9 provides any kind of support for the MPI? If a
> driver is associated with a cartridge that uses SCS* for address decoding,
> is it completely the responsibility of the driver to make sure the correct
> MPI slot is activated?
>
> Since the floppy controllers use SCS* for decoding I tried looking through
> the rb1773 code, but didn't find any evidence to indicate that it takes the
> MPI into consideration.
>
> Darren
>

Darren,

By default the floppy controller is in the fourth slot of the MPI. It will at 
least be in the slot that the selector switch is set to or NitrOS-9 will not 
boot. That being the case, there is no need for a floppy driver to alter the MPI 
slot selection.
It should be clear that any other driver needing to change an MPI slot needs to 
save the current MPI setting, select what is needed for the special driver 
operation, and return the MPI setting to the original when finished.

If you want an example of manipulating $FF7F, look at my swread.asm in 
3rdparty/utils/smartwatch. I don't assume the Smartwatch (c) will be in the 
floppy controller but could be in any rom pak. So the current MPI settings are 
saved, each slot is tried until the watch is found, that slot is saved, and the 
MPI toggled between floppy controller and watch location as needed.

Not all paks need to switch the MPI slot. It will depend on the addressing.

Robert