( ESNUG 382 Item 10 ) ------------------------------------------- [11/15/01]
Subject: ( ESNUG 381 #14 ) Parasitics And PrimeTime In Hierarchical Mode
> By the way, I would also be really interested in knowing if others are
> able to run PrimeTime in a hierarchical mode using detailed parasitics.
> This involves using read_parasitics -increment to read in each block
> level dnet.spef file and then the top level. I have tried this and
> the tool gives a load of false errors since it has not gotten the full
> RC network yet. ... The report_annotated_parasitic command does not
> work well, so you have to write tcl scripts to figure out if all the
> parasitics are annotated. ... The compete_net_parasitic command is also
> error prone and should not be a global command.
>
> - Bruce Zahn
> Agere Systems Allentown, PA
From: Sumir Kalucha <kalucha@synopsys.com>
Hi John,
The false errors that Bruce Zahn is commenting about is due to the default
behavior of the read_parasitics command in PrimeTime.
During parasitic backannotation, PrimeTime checks to make sure there are no
nets that are incompletely backannotated with R's and C's. If there is an
incompletely backannotated net, PrimeTime will issue an error message,
specifically DES-026.
In the case of a hierarchical design, there are multiple parasitics files
that are incrementally read in one by one and stitched together by PrimeTime
(read_parasitics -increment). As these parasitic files are read in, an
incomplete backannotation check is performed. Naturally, all of the boundary
nets may be incompletely backannotated nets since other segments may reside
in parasitics files that have not been read in yet, so there will be a lot
of false error messages. The question is how can these false errors be
suppressed.
The suggestion by Al Jacoutot to use read_parasitics -quiet option works but
with the caveat that this will suppress both the false messages and the
valid messages. To check for valid messages, the following is a better fix:
read_parasitics -quiet -increment block1.spef
read_parasitics -quiet -increment block2.spef
read_parasitics -quiet -increment top.spef
report_annotated_parasitics -check
This flow allows the messages to be suppressed during the reading of
parasitics and still allows for a check of incompletely backannotated nets
after all files have been read in.
- Sumir Kalucha
Synopsys, Inc. Mountain View, CA
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