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 -jbev - This message was sent through the cbm-hackers mailing list. To unsubscribe: echo unsubscribe | mail email@example.com.
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