( ESNUG 354 Item 3 ) ---------------------------------------------- [6/1/00]

From: [ A Synopsys PhysOpt CAE ]
Subject: Overriding Computed Steiner Routing In PhysOpt & Design Compiler

John, please post this to ESNUG.

Some of my customers are asking me how to override the PhysOpt computed
Steiner routing for back-annotated nets.  Steiner back annotation can be
removed with the "remove_annotated_delay" & set_annotated_delay" commands.

In the example circuit:

                   +-----+
                  A|  G  |           +-----+
             ------+  A  |Z         A|  G  |
                  B|  T  +---netB----+  A  |Z            
             ------+  E  |          B|  T  +---netC-------
                   |  1  |      -----+  E  |
                   +-----+           |  2  |
                                     +-----+

You can change the delay on netB to 0.25 ns with the following commands:

  remove_annotated_delay -from [get_pins GATE1/Z] -to [get_pins GATE2/A]
  set_annotated_delay 0.25 -from [get_pins GATE1/Z] -to [get_pins GATE2/A]

WARNING: PhysOpt & Design Compiler will not override the existing delay 
value applied on a net if the new value is smaller than the previous value!
No warning is issued when one attempts to override smaller delay value on a
net, the command will be ignored.  Therefore, it is ALWAYS best to remove
the annotated delay before attempting to override the delay with the
set_annotated_delay command.

    - [ A Synopsys PhysOpt CAE ]