[Coco] PAK ROM Memory and the MPI

[RETRO Innovations]

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
>
>
>

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