As we have all known for some time, Xilinx has had a habit of padding the logic cell counts in their data sheets to account for "effectiveness". This factor is 1.125 or 9 LCs per CLB in the newest parts. I still find this very odd, but mainly annoying because when I want the true LC count, I have to calculate it myself. Anyone else find this to be a bit rediculous?
Xilinx padding LC numbers, how do you feel about it?
Started by ●January 19, 2006
Reply by ●January 19, 20062006-01-19
Of course it's ridiculous! Marketing loves to make engineers hate the company. They want to make the *managers* look past their feeble engineers for approving brand X versus brand A (forgetting, of course, that most engineers have the lattitude to push for one brand due to the *engineering* tradeoffs). There are times when you need to shoot the engineer to ship the product (just one more tweak is *not* okay!) but thankfully the engineers get to be pissed off at marketing until they skew the preference toward the "other" brand's mismarketing BS. Ah, what a wonderful world. What would it be like, after all, if we have to pull our hair out with our CAD tools (PC, synth, P&R, sim) but didn't have to get the least bit upset about choosing the part in the first place? - John_H "rickman" <spamgoeshere4@yahoo.com> wrote in message news:1137702911.352529.98730@g47g2000cwa.googlegroups.com...> As we have all known for some time, Xilinx has had a habit of padding > the logic cell counts in their data sheets to account for > "effectiveness". This factor is 1.125 or 9 LCs per CLB in the newest > parts. I still find this very odd, but mainly annoying because when I > want the true LC count, I have to calculate it myself. > > Anyone else find this to be a bit ridiculous? >
Reply by ●January 19, 20062006-01-19
Rickman, why do you ask? Everybody in this newsgroup hates that method, but Xilinx Marketing thinks that it is a more meaningful metric when comparing different manufacturer's devices. And it is, like it or not. This reminds me of the way horsepower was measured for automobiles: Disconnect the gearbox, the generator, the waterpump, the airconditioner and everything else that might drain power. A red-blooded engineer would say: give me the horsepower where the tire meets the road.... Peter
Reply by ●January 19, 20062006-01-19
Rickman, why do you ask? Everybody in this newsgroup hates that method, but Xilinx Marketing thinks that it is a more meaningful metric when comparing different manufacturer's devices. And it is, like it or not. This reminds me of the way horsepower was measured for automobiles: Disconnect the gearbox, the generator, the waterpump, the airconditioner and everything else that might drain power. A red-blooded engineer would say: give me the horsepower where the tire meets the road.... Peter
Reply by ●January 19, 20062006-01-19
Peter Alfke wrote:> Rickman, why do you ask? > Everybody in this newsgroup hates that method, but Xilinx Marketing > thinks that it is a more meaningful metric when comparing different > manufacturer's devices. And it is, like it or not.How about you try and introduce the meaning of UNITS to them ? ie let them use LCeq for the marketing DOCS, and also have an absolute, physical count, of LC = X * Y on the die. As a radical idea, they could even publish the formula LCeq = LCactual * MarketingsIdeaOfLevelPlayingFieldFactor That way, everyone is happy :) The problems occur when one dept trys to use a std unit, but hijack it to mean something else. In the end no one knows where they are.... and everyone is annoyed. -jg
Reply by ●January 19, 20062006-01-19
Peter Alfke wrote:> Rickman, why do you ask?\I asked because I wanted to hear the the opinion of others. I read a recent Spartan 3 data sheet and noticed that there is now a footnote explaining they they are padding the number. I just find this pretty absurd. You compared it to car makers measuring horsepower, but that is a measurement that has parameters. Countings LCs is counting and adding a 12.5% fudge factor is marketing, not measurement. It would be more like a car maker saying his engines are 9 equivalent cylinders! But mainly it is frustrating to always have to calculate the correct number myself. At least marketing has not gotten to my calculator yet. :)> Everybody in this newsgroup hates that method, but Xilinx Marketing > thinks that it is a more meaningful metric when comparing different > manufacturer's devices. And it is, like it or not.That is silly for you to state this as a fact when it is just your opinion. Have you ever had a customer ask you to adjust your LC counts so they can compare them to the competition? Who says it is "a more meaningful metric"? Your marketing, that's who! It is one thing to accept that your company lets marketing inflate the numbers, but please don't insult me by trying to justify it. Am I alone in regard to finding this annoying?
Reply by ●January 19, 20062006-01-19
Peter Alfke wrote:> Rickman, why do you ask? > Everybody in this newsgroup hates that method, but Xilinx Marketing > thinks that it is a more meaningful metric when comparing different > manufacturer's devices. And it is, like it or not.Actually Pete I don't think it is. It's a very arbitrary number where apples, dead tires, horse shit, and tree stumps are all given numerical values which have absolutely no relation to particular customers needs, and declared equal in decsion tree wieghting in ways certain customers would never do the wieghting. If the company would then derate the part for being unable route a fully used device, or power a fully used device, or cool a fully used device there might, maybe, in a long shot be a justification for the bloat factor. The reality is that certain applications do not do arrithmentics, do not need much if any carry chain, or multipliers, or even very many F5/F6 muxes, but do need a lot of LUT's. Being clear up front that you are offering 2 cases of applies, 4 dead tires, no horse shit, and one stump to sit on while eating your apples is a whole lot clearing than tring to figure out just how much shit you get for 37. Old School math ... John
Reply by ●January 20, 20062006-01-20
On a sunny day (Fri, 20 Jan 2006 10:53:31 +1300) it happened Jim Granville <no.spam@designtools.co.nz> wrote in <43d00a4b@clear.net.nz>:>Peter Alfke wrote: >> Rickman, why do you ask? >> Everybody in this newsgroup hates that method, but Xilinx Marketing >> thinks that it is a more meaningful metric when comparing different >> manufacturer's devices. And it is, like it or not. > >How about you try and introduce the meaning of UNITS to them ? > >ie let them use LCeq for the marketing DOCS, and also have an absolute, >physical count, of LC = X * Y on the die. > >As a radical idea, they could even publish the formula >LCeq = LCactual * MarketingsIdeaOfLevelPlayingFieldFactor > > >That way, everyone is happy :) > >The problems occur when one dept trys to use a std unit, >but hijack it to mean something else. In the end no one knows >where they are.... and everyone is annoyed. >How about 'feel gates'? After all my 10W PC speakers are 1000 'music watts'. And this FPGA has a 10 giga gates equivalent feel power? A. Nonymous.
Reply by ●January 20, 20062006-01-20
Jan Panteltje wrote:> On a sunny day (Fri, 20 Jan 2006 10:53:31 +1300) it happened Jim Granville > <no.spam@designtools.co.nz> wrote in <43d00a4b@clear.net.nz>:...snip...> >The problems occur when one dept trys to use a std unit, > >but hijack it to mean something else. In the end no one knows > >where they are.... and everyone is annoyed. > > > How about 'feel gates'? > After all my 10W PC speakers are 1000 'music watts'. > And this FPGA has a 10 giga gates equivalent feel power?Jan, I think you are agreeing with me, no? There is a difference between how many "gates" they claim and how many LCs they count. It is somewhat arbitrary how you convert from LCs to gates. You can justify a wide range of conversion numbers. But LCs are counted, not estimated or equivalized. It is just silly for marketing to think that engineers are going to use their "equivalized" LC numbers in any comparison with another vendor or even within their own products. It's like they think we are too ignorant to realize they are doing it. They are mistaken, aren't they?
Reply by ●January 22, 20062006-01-22
Guess I'm not the only one but I keep an excel file updated with all the key xilinx and altera parts that I'll likely use. 2 spreadsheet columns, 1 for fabric columns, 1 for fabric rows, excel calculates the product as well as subtracting the fabric cells taken up by PPC, etc, etc. I also add columns for number of multipliers, IOB delays, etc, etc, (again!). When I occasionally get a crack at a new project start, sort by the key architectural features, and end up with a shortlist of parts, usually narrowed down to 1 from A and 1 from X (I'm convinced they do it deliberately!). You soon learn to ignore the marketing BS... On 19 Jan 2006 12:35:11 -0800, "rickman" <spamgoeshere4@yahoo.com> wrote:>As we have all known for some time, Xilinx has had a habit of padding >the logic cell counts in their data sheets to account for >"effectiveness". This factor is 1.125 or 9 LCs per CLB in the newest >parts. I still find this very odd, but mainly annoying because when I >want the true LC count, I have to calculate it myself. > >Anyone else find this to be a bit rediculous? >
