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From: Peter Alfke on 5 Jul 2005 18:25
Alvin, I do not see why the routing would care about the difference
between an incrementer and an adder.
But your preference for registering shows the disadvantage of generics:
In Xilinx, the address is automatically registered in the BRAM.
External registering just adds one unnecessary level of pipelining.
Designing WITH the available features achieves better results than
ignoring the features and designing generically.
As time goes on, the newer chips have more sophisticated features ( DSP
blocks, Ethernet controllers), just like they sprouted SRL16s, BRAM
read-while-write, and 18 x 18 multipliers before. Unless the
synthesizer is ultra-smart, it will ignore such things.

Well, I am obviously biased. But I hate to see our best ideas go to
waste because designers don't use them for not being "generic".
Peter Alfke

From: Martin Thompson on 6 Jul 2005 06:48
"Andy Peters" <Bassman59a(a)yahoo.com> writes:

> Peter Alfke wrote:
> > Why would an adder be slower than an increment.
> > In Xilinx, I see no difference. It's all a matter of carry propagation
> > ( and it is pretty fast in either case.)
> > Or is this a case of generics and portability?
> > My analogy for generics is Fast Food. Throw a coin whether you go to
> > McDon or to BurgerKing. it's all the same mediocre or below stuff.
> > Same with a design that is fearful of being Xilinx specific. Using only
> > the ingredients that everybody has, means lowering yourself to the
> > lowest common denominator.
> > Have guts and be specific! There is more stuff than Altera ever dreamt
> > of. Sorry, couldn't resist the plug.
>
> Peter,
>
> I'm rather impressed that you were able to turn a comment about
> increment vs adder speed into a dis on both VHDL generics AND Altera.
>

I'll just chip in, although Peter can comment for himself I'm sure - I
read his comments on generics to be referring to "code written in a
generic manner not to take advantage of one vendors feature set". I
don't think he was referring to generics in the VHDL sense...

However, your examples of where VHDL generics can be used are great!

Cheers,
Martin

--
martin.j.thompson(a)trw.com
TRW Conekt, Solihull, UK
http://www.trw.com/conekt
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