[Coco] Utility of large MPI (was: Re: ROM Cart registers)

[Darren A]

On Mon, Feb 1, 2016 at 8:08 PM, RETRO Innovations wrote:

> Hmm, I think I am beginning to understand why folks are looking more for
> an all-in-one cart for the Coco.  It's a shame, but it looks like the
> utility of a 8 slot MPI is marginal.
>
> If you are using a GCCC or sIDE, al of $ff5x is dedicated
> $ff6x-$ff7e must be dedicated, because none of those addresses are gated
> by the MPI.
> $ff4x is really the only place to share the bus.  16 bytes is not a lot of
> space to share.
>
>

Wouldn't the opposite be true?  The small number of open addresses can
limit how much functionality you put on a single cartridge. The more MPI
slots, the more opportunities to re-use those addresses by carts with
lesser requirements. Think of the slot number as an extension of the I/O
address.

Of course it's also possible to design a mega-function cart which
implements its own sub-addressing mechanism within those 16 locations. It
makes both the hardware and software a little more complex, but is
certainly doable.

While an 8-slot MPI sounds kind of cool, the amount of space it would take
up and the expense of the larger board makes it more of a negative for me.


- Darren