( ESNUG 402 Item 1 ) --------------------------------------------- [10/23/02]
From: Joe Gilray <jg@cvs.agilent.com>
Subject: Your Old Custom Cell Libraries & Newer Synopsys Versions Won't Mix
John,
Be careful when using old custom cell libraries with newer versions of
Synopsys tools.
We had an old custom cell library that we had used successfully for a while,
but when we switched to PrimeTime v2002.03-SP1 (or v2002.09) we found that
the SDF generated was very different from that generated by v2001.08-SP1-1.
We were seeing net delays that were in the -100 ps range and quite a few
RC-005 warnings.
With the help of the Support Center we tracked the problem down to the fact
that our custom cell library didn't have the voltage defined so PrimeTime
was using the default value of 5V! This problem didn't show up in older
versions of PrimeTime because they used only one set of thresholds.
You can check your libraries with 'report_lib' or by using:
report_delay_calculation -thresholds
which showed the following for our case (note the from-pin voltage)
Calculation Rise Rise Fall Fall Slew Rail
Thresholds: Delay Slew Delay Slew Derate Voltage
----------------------------------------------------------------
from-pin 50 20->80 50 80->20 1.000 5.000
to-pin 50 20->80 50 80->20 1.000 1.080
Another way to work around the problem is to use:
set lib_thresholds_per_lib false
but I hesitate to suggest it as a long-term solution as it could cause
analogous problems when there *are* libraries with individual thresholds.
The online docs for lib_thresholds_per_lib are very useful, too.
- Joe Gilray
Agilent Technologies Corvallis, OR
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