( ESNUG 286 Item 11 ) --------------------------------------------- [4/13/98]
From: bellman@azmda.sps.mot.com (Charles Bellman)
Subject: Seeking Accurate, Many Decimal Digits Delays On Inputs
John,
I have a method of verifying libraries in which I create an all-cells
testcase and part of the verification tool writes out an SDF file to compare
timing with other tools. I was wondering if anyone knows an easy way to
automatically set the drive at each pin such that I am assured that there
is, say, 0.5ns at all inputs. The set_drive command will work, but I need
to know the capacitance at each input port in order to set each pin's drive
correctly, e.g. set_drive <0.5ns/capacitance> <input_port>. The problem
is knowing each input's capacitance. I've tried to get the capacitance
attribute by using the 'get_attribute' command, unsuccessfully. I finally
wrote a Perl script to create a set of set_drive commands, based on a
report using the 'report_net' command. The problem with that is, the
resolution is only to 2 decimal places (load field):
Net Fanout Fanin Load Resistance Pins
------------------------------------------------------------
INPUT_1 1 1 0.01 0.00 2
INPUT_2 1 1 0.01 0.00 2
"Load" here may be 0.0149 or 0.0101 -- so you don't generate a very precise
drive value this way. I don't want to change my library input capacitances
from pF to fF right now. That would certainly help in the report. Any
other ideas?
- Chuck Bellman
Motorola NCSG SemiCustom
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