( ESNUG 342 Item 2 ) --------------------------------------------- [2/03/00]

From: Kayla R Klingman <kayla.r.klingman@tek.com>
Subject: Do NOT Use "set_dont_touch_network" On Clocks With DC 99.10 !!

Hi, John,

We found a bug in DC 99.10 where:

   1) You clock on the negedge of the clock 
   2) You have a constant as the data in to a flop
   3) And your clock has set_dont_touch_network on it

It would add buffers to the clock, even though you told DC to leave it
alone.  The answer that came back from R&D at Synopsys was:

     Get rid of the set_dont_touch_network on your clock.

In DC 99.10 they started assuming an ideal clock, so set_dont_touch_network
was redundant.  They got rid of the set_dont_touch_network and the extra
clock buffering went away.  We're still waiting to hear why we have
dangling gates, but simplify_constants -boundary_optimization gets rid of
them.

    - Kayla Klingman
      Tektronix, Inc.                                  Oregon