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Rep:Re: [f-cpu] New snapshot for EU_INC and EU_CMP



-----Message d'origine-----
De: Yann Guidon <whygee@f-cpu.org>
A: f-cpu@seul.org
Date: 30/07/02
Objet: Re: [f-cpu] New snapshot for EU_INC and EU_CMP

hi,

Michael Riepe wrote:
> On Mon, Jul 29, 2002 at 08:48:13PM +0200, Etienne LABARRE wrote:
> > Hi all,
> > New snapshot include a lot of changes and features :
> >
> > INC unit and CMP unit are now two different units, for simplify and
> > decrease latency
> >
> > Both units are based to the same component : find_lsb
> >  It's a binary tree for find the first null lsb in a word.
> >  It supports SIMD operations (size of chunk = 8, 16, 32, 64, 128,
256
> >  bits)
> >  It's based to only one function : and_reduce. It's is a standard
> >  function of ieee.std_logic_1164 library.
> 
> Did you find source code or documentation for package std_logic_misc?
> 
> I noted that you use ieee.numeric_std in your designs, which is a
> no-no. Or did you include it by mistake?

hmmm... this remembers me of the story....
what do we decide ? JaI is pretty optimistic.


> > For CMP unit, the data flow is :
> >  1 level of xor,
> >  1 level of mux,
> >  find_lsb : 3 level of 4-and, 1 level of mux
> >  2 level of mux,
> >  total is 8 levels.
> >  Critical datapath is for CMP, MIN, MAX, SORT operations.
> 
> I doubt that you can get away with 8 cycles. From my experience,
64-bit
> CMP alone needs 1 level of 2-xor, 3 levels of 4-and, 1 level of 2-xor,
> 1 level of 2-and plus 3 levels of 4-or, giving a total of 9 levels.

don't forget the wiring delays either !
running a wire from bit 0 to bit 63 will take nearly a cycle,
so from 0 to 255 will take 4 cycles :-/

>>>> Where did you find those numbers ?
nicO

>  Michael "Tired" Riepe <Michael.Riepe@stud.uni-hannover.de>
WHYGEE
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