Re: PCcard DMA (detailled!)

From: Professor Dredd (
Date: 2001-04-11 03:01:27

This is one of the biggest challenges we face as C-64
users. The C-64 is not a card-cage design, its a
semi-closed architecture. This is one area the Apple
II line has a great advantage in.

Firstly the cart port is not electronically suited to
cart chaining due to excessive signal degredation (so
I understand), so plugging more than one cart into a
cart port expander is a hit/miss deal. It either
works, or doesn't, or only works if its close enough
to the motherboard (this I know from experience.) If a
new C-64 motherboard design is in the future, I hope
it makes some allowance for real expansion slots.

Second problem, there is no defined convention for how
the extra I/O space (the mirror registers) are to be
divvyed up to hardware expansion devices. Most
designers just seem to grab whatever's convenient, as
did Commodore with the C-128 MMU, 1750 REU and VDC. It
would be really cool if someone had a list of every
device that uses I/O space and where it is situated
for the purpose of avoiding confilicts in future

--- wrote:
> There would be a control unit at an as-yet undefined
> location,
> preferrably one located in one of the I/O pages. 
> This unit has the
> following functions (some optional, for later
> post-proof-of-concept
> implementation):
> The addressing spaces (memory OR io) can be mapped
> in 256 bytes at a time
> into one of the I/O pages.  My design assumes its
> the first non-cpu device
> on the cartport chain, so enabling this map will
> override whatever page you

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