( ESNUG 206 Item 5 ) ---------------------------------------------- [1/13/95]
Subject: (ESNUG 191 #2 192 #1) "Anyone Using Synopsys's Static Timing Analyzer?"
>> And, is anyone really using Synopsys as a static timing analyzer?
>> I don't find it accurate.
>
> In internal tests we have found that with a correct SDF file, the timing
> analyzer is as good as the numbers back-annotated... I am interested in
> the limitations you found. Can you expand on this some more on ESNUG?
From: ann@sioux.apple.com (Ann Nunziata)
John, I need to clarify what I meant by accurate. By the other user's reply
I can see that he thought I meant that the actual numbers might not be
accurate. This was not our problem.
The problem was that Synopsys was not doing a very good job of handling the
elimination of multi-cycle paths. I could not get accurate results because
DC did not always handle my multi-cycle paths correctly. I carefully watched
a synthesis in progress and discovered that in some cases, DC would accept
the multi-cycle command, appear to work on it, but in reality, it really
didn't like how I specified the start or endpoints, so the directive was
ignored. The path kept showing up. Sometimes this could be corrected
switching from specifying a pin to specifying a cell, but it was not clear
why DC couldn't handle it since the from-list and to-lists are supposed to
handle clocks, ports, pins or cells. The main problem was that you didn't
know that DC didn't understand your multi-cycle command. It was pretty
frustrating, and not nearly as useful as a real static timing analyzer like
Motive. (Perhaps this problem has been corrected, we were using 3.0a at the
time.)
The other problem was that the more mulit-cycle paths specified, the more
likely to run very slow or even crash and burn, Synopsys-FATAL style.
- Ann Nunziata
Apple Computer
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