Re: [f-cpu] IDU News; synthesis report

[Michael Riepe <michael@stud.uni-hannover.de>]

On Fri, Apr 11, 2003 at 10:46:54AM +0200, devik wrote:
[...]
> One other specific of FPGA is that each (or each two) LUT has private
> flip-flop. Thus it seems to me that ultra high throughtput units
> on FPGA could take it into account and be pipelined deeply (because
> these FFs come at no price).

I'm not sure that this is a good idea.

> Also is there some web page where could I learn things like types
> of adders and multipliers ?

Several.  One of them is `(Lecture notes on) Computer Arithmetic:
Principles, Architectures and VLSI Design' by Reto Zimmermann.  I don't
remember the URL but Google should find it.  It's a rather terse document
(mostly formulas and graphics) but it's quite complete.  If you just
look for `Reto Zimmermann', you'll probably also find other interesting
documents.

> > Earlier synthesis runs with Synopsys reported 389 MHz for IAdd and 458 MHz
> > for IMul64 (that were the previous versions; the current ones are probably
> 
> these are for ASIC ? As I some time ago discussed with nicO, how
> can one have 6 GHz adder like one in P4 ?
> Is the trick in hand placing transistors instead of using
> vhdl synthetizer ?

They probably use hand-tuned circuits and `dynamic' pipeline registers
which basically consist of a pass gate and a capacitor (it's like a
"sample&hold" circuit for digital data) and are fast compared to ordinary
flip-flops, which allows more fine-grained pipes.  They may also use
gates like AOI -- that's an and-or-invert gate which can be made just one
transistor "deep", by using the CMOS equivalent of a `wired-and' gate
(something similar is most likely also used in the `fast carry' chains
of FPGAs).  They can also fine-tune the fan-in, fan-out and delay of
gates by making individual transistors smaller or larger.  And of course
they use the latest-and-greatest manufacturing process, featuring high
resolution, copper wires, low-K dielectrics and other nice stuff.

-- 
 Michael "Tired" Riepe <Michael.Riepe@stud.uni-hannover.de>
 "All I wanna do is have a little fun before I die"
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