Re: PCcard (2)
Date: 2001-04-10 15:06:22

On Tue, 10 Apr 2001, Ruud Baltissen wrote:

> > If you need more detail, I have the definitive ISA
> > bus reference book ;)
> If it is not too much trouble, please do. I thought I had some edocs on DMA.
> Only to find out yesterday that the I didn't

Okay.  The section covering DMA is extremely detailled, so I'll take some
time to read and summarize before posting.

> My apologies. I was thinking about using a 6522 for the data- AND
> addressbus. I had the one for the addressbus in mind when reading your
> comment.

Okay.  I can see some serious bottleneck problems, and will discuss
alternatives this evening.

> Instead of "bigger" I meant "faster" indeed.
> Regardless of any method, I still have a problem. The idea for the card is
> to use both free I/O areas in $DE00/DFFF: one as data-window, the other for
> adressing the needed I/O. This I/O is needed for a) reading bits 8..15, b)
> supplying addresslines A8..23 and c) telling the card wether it is an I/O-
> or memory-operation.
> The question I have is: when performing a DMA, let's say reading data from
> an attached 1.44 MB floppy, should the data transfer from the floppy to the
> C64 or from the floppy to the memory attached to the PC-card (like
> video-memory)?

I think the idea of using offboard memory would be great.  You could hang a
mem controller off the isa bus, and have your cards dma to there, and
thereafter, use a second busmaster (which is controlled by the c64) to dma
data to the c64 when you're ready.  You could fetch data from floppies, etc,
without stalling the c= this way.

> Ideal would be to be able to use both methods but that involves some more
> hardware. I have an idea but it certainly would rule out the 6522's.

DO tell! :)
> Another idea: the PC-card needs 256+ bytes. This means that it hardly can be
> combined with another cart. Maybe it can be used together with the REU, but
> I'm not sure. My idea is to add a 74LS139 to the original C= which enables
> you to reduce the area occupied by the VIC-II from $D000/D3FF to $D000/D0FF.
> The other 3*256 bytes now can be used for your own purposes. With jumpers or
> a 2-pin connector one can choose which configuration is to be used for the
> PC-card.

I'd like to use this on my SCPU in the future.  Stay out of the vicII mirror
space.  However, feel welcome to use d700

> About compatibility: I don't know any valid reason why a good programmer
> would prefer the mirror addresses to program the VIC-II. So I presume all
> well written software should run on such an altered C=.
> IMHO the change can be performed on all C64's and C128's.

Sigh. heh


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