Nightmaretony wrote:
I ended up taking a page from the WDC development board and looking at the Xilinx XC9572 CPLD. It has an 84 pin PLCC package, so a socket is easy, it has .100 pin centers. It is like a smaller gate count version of the XC95108.
I used ExpressPCB for the first board revision, and I am using it once again. I have made changes in the design to make it much more generic and hacker friendly. You download the circuit layout and send out, cost is maybe 50 dollars or so for each, cost dropping for more. Ri9ght now, still job hunting but when it comes time, will make a couple and sell at my cost or something.
That's precisely my point -- $50 for each PCB. And if you screw up, well, oops, you're out $50.
And since I'm totally new with programmable logic, and since $50 is a *LOT* of money for me, I'm probably going to go with a solution from Xess. (specifically, I'm thinking of using
http://www.xess.com/prod034.php3 ) Although it costs $160, it's pre-fabricated, relatively easily programmed, and has 64 pins or so of I/O that I can couple to various external goodies.
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The one thing I REALLY REALLY like about using CPLDs is for a finished board, the logic paths can be changes by the reprogram, and it can be done multiple times. This way, instead of having to hit up cuts and jumpers on the board, it is a firmware change on the CPLD.
True -- but I'm talking about things like, for example, where I discovered the clock slew rate was too slow on my Kestrel 1p1 and 1p2. That type of thing cannot be fixed by reprogramming the CPLD.
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I already have a monster video card planned for this as well that can easily be run from the 6502. It is almost the same as the Elm one, but with 6502 based differences. For the job, I was planning 3 seperate video sources on a single external board, but that no longer matters now.
Funny -- after researching the Xess board, I'm planning on the following:
* Paging-capable MMU -- yes, Virginia, this system will support true virtual memory and memory protection!! Theoretically, if someone wanted to port it, it will run Linux. Since the CPU itself can only address 16MB of RAM, and the board has 32MB on it, I figure an MMU would be needed anyway, so might as well make it useful!
* Video architecture inspired by AGNUS and DENISE, but with some elements of ANTIC thrown in (like, a *slightly* richer Copper instruction set.
). Expect a minimal blitter as well.
* Audio architecture that is a mixture of PAULA and SID, or as close as I can come to it. It should have some amount of built-in synthesis capabilities, plus the ability to play waveforms from RAM.
The highest priority is the video architecture, of course, with the MMU being very close second. Audio, I'm not so concerned with -- that can be offloaded to a handful of ATmega chips, I think, via dedicated SPI links.