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