Re: SPARTAN-3 vs. VIRTEX-II

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You can feel how you wish about your designs, but even the loss of the
64 bit dual ports and the 128 bit single port rams is not signficant.
To make a 64 bit dual port RAM requires 8 LUTs for ram (same as in VII)
and one LUT for the read mux and possibly two more LUTs for the WEs.
But if this is part of a larger ram block you are making half of the WEs
would have been required anyway.  So it is not a "large" amount of
logic, just a bit more.  

If you are making really large blocks where the longer runs on the
address and data can slow it down significantly, then you likely are
better off with the block rams.  

Considering the much lower price of the XC3S parts, all this sounds to
me like a benefit, not a liability.  Think of it as paying for the LUTs
that have RAM and getting the other LUTs for free  :)

--

Rick "rickman" Collins

snipped-for-privacy@XYarius.com
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Re: SPARTAN-3 vs. VIRTEX-II
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Ok, I agree with you, itīs not to much logic. But because these extra
delays maybe I have to duplicate the circuits.

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No, they are not large blocks, but I have 128 to 512 FIR filters (256
coefs) running in parallel, and the sampling rate is 2 megaHertz.
Throughput!

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I'm not complaining, and I know that Xilinx wil not make a special
Spartan3 just for me. But I have the right to express what I think,
and maybe I'm not alone. Maybe there are a lot of Luizes and Rays,
maybe Xilinx will hear us and maybe, at these nanometer scales where
the pads are so big, to have all the CLBs configurable as memory is
not so significant in silicon area.

Luiz Carlos Oenning Martins
KHOMP Solutions

Re: SPARTAN-3 vs. VIRTEX-II
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Yes, certainly you have the right to express your views and to let
Xilinx know what you need.  But I think you are responding to the idea
that "something" is missing without knowing for sure if it is really an
issue.  When you say above that adding the level of logic may slow down
the design, you first need to know how fast these parts run.  After all,
you are comparing 90 nm Spartan 3s to 150 nm VirtexIIs.  It is very
possible that the S3s will run faster even with the added delays.  

I am sorry if my "nagging" is annoying.  But I have watched a lot of
changes in FPGAs and have often felt they were not for the better.  But
somewhere around the Virtex or VirtexII parts I started to realize that
I needed to forget about how the parts were different and focus on how
to solve my design problems using them.  With that I have come to
understand that often what I saw as a limitation is more than made up
for in other areas.  I am sure that Xilinx does not remove functionality
without considering the trade offs very seriously.  

--

Rick "rickman" Collins

snipped-for-privacy@XYarius.com
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Re: SPARTAN-3 vs. VIRTEX-II
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It doesn't look like (using the projected speeds for MicroBlaze).

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It's ok.
Maybe some day we can take a drink and talk about this. Better, let's
invite Peter, he can pay that french champagne! (I like beer too) :)

Luiz Carlos

Re: SPARTAN-3 vs. VIRTEX-II
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I am not looking for champagne on a beer budget, but I would sure like
to be able to pour them both into the same glass.  That is I would like
to have one footprint that I an put a Spartan into for low cost or a
Virtex when I need high performance and large size.  

--

Rick "rickman" Collins

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Re: SPARTAN-3 vs. VIRTEX-II


<SNIP>
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Isn't that a bit of redneck perspective -champagne in Budweiser glass ? ;o)






Re: SPARTAN-3 vs. VIRTEX-II
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That's what we call a Fredneck around here...  :)

--

Rick "rickman" Collins

snipped-for-privacy@XYarius.com
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Re: SPARTAN-3 vs. VIRTEX-II
Peter --

I have no problem with the fact that these are 2 seperate product lines
which target 2 different needs, but when Xilinx states that "Spartan-3 is
basically Virtex-II, but whith a few things missing", I think Xilinx ought
to be considerate of it's customers and enumerate EXACTLY what those "....
few things missing" are. To paraphrase John Cooley (Synopsys & EDA Gadfly):
Customers can accept virtually any truth about a product as long as they
don't have to find out about it painfully.

I'm not asking for "champagne on a beer budget". What I am saying is: I've
spent a good amount of time studying champagne (Virtex-II), but I don't have
a lot of time right now to study beer (Spartan-3) from scratch. Since Xilinx
claims to be making beer by subtracting a few things from champagne, Xilinx
can save me a LOT OF TIME by just telling me what those few subtractions
are, and then I can quickly figure out if beer is what I need. My management
is experiencing a little sticker shock right now at the cost of champagne,
but if I get them hooked on the cost of beer, and we discover that beer
can't quite satisfy our tastes 6 months from now, that will be an enormous
source of grief & embarrassment that I want to avoid.

Can you comment on my list? Additions? Corrections?



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Re: SPARTAN-3 vs. VIRTEX-II
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As has been said before in the group, one of the best features
of Xilinx datasheets was the section on 'how this part differs
from the last generation.'  Is that too complex for management
to get it?





Re: SPARTAN-3 vs. VIRTEX-II
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French champagne, please! :)

Luiz Carlos

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