( ESNUG 321 Item 5 ) ---------------------------------------------- [6/8/99]
Subject: ( ESNUG 317 #4 ) Tricking DC Into Buffering Every Output Port
> I would like to force design compiler to put a buffer on all output
> ports, and to not use the buffered output internal to the module. The
> obvious way to do this would be to do a
>
> set_max_fanout 1 all_outputs()
>
> but of course set_max_fanout can only be used on input ports (why???).
> I can usually get what I want with the right combination of loads and
> output delays on the output port, but there are cases where this
> doesn't always work. Ideas?
>
> - Will Leavitt
> Giganet, Inc.
From: Robert Wiegand <rwiegand@mailsrv.ensoniq.com>
John,
This has worked for me in the past: Start out by setting a max_fanout
on the design,
set_max_fanout max_fanout_number current_design
/* let max_fanout_number = 20 for example */
Then, set a fanout number on the output port equal to the max fanout of
the design:
set_load max_fanout_number -fanout_number output_port(s)
or
set_fanout_load max_fanout_number output_port(s)
It is now a design rule violation to hang any additional internal loads
on the net driving the output.
- Bob Wiegand
Ensoniq, Corp. Malvern, PA
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