[Coco] PAK ROM Memory and the MPI

[Robert Gault]

There are some minor errors in the previous answer.

The MPI is controlled via $FF7F where the most significant nibble selects the expansion ROM and 
interrupts while the least significant nibble selects the I/O at $FF40-$FF5F.
$FF7F      value        slot
             $00          1   front
             $11          2
             $22          3
             $33          4   rear
possible    $nm          mixed slots
ex          $30          I/O via slot 4 ($FF40-$FF5F) with PAK ROM at slot 1

ROM MEMORY
Coco 1 or 2 ROM $8000-$FEFF
Coco 3      ROM $8000-$FDFF as $FF90 is normally set to constant DRAM at $FExx but is adjustable.

Jim Snider wrote "Maximizing the Multi-PAK" which describes the above and a table of addresses and 
the devices that use them in the Coco memory map.
Unfortunately I don't think Jim's paper is available for download.

Robert


RETRO Innovations wrote:
> On 10/16/2019 9:01 AM, Walter Zambotti wrote:
>> Got some good news about the performance improvements I am making to OVCC.
>>
>> No I didn't make the assembly any better!
>>
>> One of OVCC projects/goals was to implement Linux MMAP Memory Mapping (Some of you might remember
>> I tried something similar on Windows using AWE which was not a success).
>>
>> Apart from MMAP being much simpler than AWE it supports memory sharing which allows a memory page
>> to be mapped several times to different addresses.  This really suits OS9 on the CoCo.
>>
>> Anyway I have a prototype running and performance is up about 33%+. (Soon to be released)
>>
>> I can make it a little bit faster and much cleaner but first I need to know how the ROM mapping
>> works in the CoCo in relation to PAK ROM.
>>
>> I believe PAKS can have ROMS (8-18k) and those ROMS can be mapped into the address space from
>> $8000-$BFFF.
> Coco3 can map from 8000 - $feff, I believe, but Coco1/2 can only map the $c000-$ffef segment.
>>
>> What complicates this is the MPI.
>>
>> If the MPI contains multiple PAKS each with it's own ROM I can see in (O)VCC that the PAK that is
>> selected gets its ROM mapped.
>>
>> The MPI also has a port register that allows the slot selector to be change programmatically.
>>
>> If this slot is programmatically changed should/would this change the ROM that was mapped into
>> memory?
> Yep.
>>
>> Also what is the purpose of the spare slot select?
> It's for IO (so, you can have different things from an IO range mapped into $ff40-$ff5f per slot.
>>
>> Walter
>>
>>
>>
>