[Coco] PAK ROM Memory and the MPI

[Walter Zambotti]

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.

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?

Also what is the purpose of the spare slot select?

Walter