On 8/13/07, Mark <[EMAIL PROTECTED]> wrote: > Timothy Normand Miller wrote: > > instructions. Also, in response to his question, I'm targetting the > > 3S4000 because it's convenient. In the real design, we'll target the > > XP10, which is a little slower. Either way, this tells us basically > > what we need to know. > > > Doesn't that make this whole discussion moot? The XP10 doesn't have > hard multipliers, as near as I can tell. Regardless, the architecture > and timing aren't necessarily even remotely similar (well, sure, they're > both island-style FPGAs using 4-LUTs... but that's still a big design > space).
Ugh. You're right. I thought it had dedicated multipliers, but Howard can't find any reference to that in the spec. There's no sense in trying to move the nanocontroller into the Xilinx, because the nanocontroller's also responsibile for controlling DMA. > > I'd be wary of putting to much stock in XST's timing estimates, anyhow. > Until you've got post-PAR timing, don't bank on it. The timing numbers I provided are post-PAR, but as you say, regarding the mulipliers, the point is moot. We need to rethink that whole thing. Should we do some early-SPARC-style multiplier stepping instructions? I'm not sure we can without 4-operand instructions. Another option would be to switch to the out-of-band approach. Write operand to the multiplier via the I/O space, and X clock cycles later, you can grab the product. > Finally, I don't think you mentioned the speed grade and package you're > using for the Spartan or the Lattice part. (Both are on the board, > right? I'm going off > http://wiki.duskglow.com/tiki-index.php?page=OGD1+components+guide.) For Xilinx, it's -5. I think we also picked the fastest XP10. > Your timing numbers will depend on that, too (even in XST's output, I > believe). Have those aspects been specified yet? I mean, at least the > package is presumably known. Well, I wanted a ballpark sense of what was worst in the design, and for that I doubt it'll make a lot of difference which device we target. When it comes down to shaving off the last few nanoseconds, then it'll matter a lot. What we want is a controller that's reasonably efficient across multiple architectures anyhow. -- Timothy Normand Miller http://www.cse.ohio-state.edu/~millerti Open Graphics Project _______________________________________________ Open-graphics mailing list [email protected] http://lists.duskglow.com/mailman/listinfo/open-graphics List service provided by Duskglow Consulting, LLC (www.duskglow.com)
