( ESNUG 377 Item 19 ) ------------------------------------------- [09/19/01]
From: "Derek Brasili" <derek.brasili@cavium.com>
Subject: How Do I Create Actual True Internal Clocks In Synopsys PrimeTime?
Hi, John,
I am running PrimeTime on a top level module. Under this top level module
it calls a P&R gatelevel netlist and a custom design DB file. Within this
top level module I create a clock called ECLK. This clock is generated
from a global clock called RCLK. Now ECLK will rise/fall 80 ps after RCLK
does. We have a clock expert that will give me all the information I need
for ECLK. Now I don't want PrimeTime to analyze ECLK. I want to define it
by "create_clock". PrimeTime will not let you do this because ECLK is an
internal net to this top level module! I found a TCL script on Synopsys's
website called "create_net_clock". This supposedly allows you to create
clocks on internal nets. But what it does is traces its way back to the pin
in the top level module that creates ECLK. This happens to be RCLK.
So then it actually puts the clocking information for ECLK onto RCLK, thus
wiping out the original waveform I put on RCLK using the "create_clock"
command. The only way I have found to make this work is to make ECLK a pin
in the toplevel module.
Does anyone have a way to create a clock in PrimeTime on an internal net?
- Derek Brasili
Cavium
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