( ESNUG 301 Item 8 ) --------------------------------------------- [10/15/98]
Subject: ( ESNUG 300 #2 ) How To Handle Hierarchical Capacitance Problems?
> I was just wondering if you could answer a quick question for me. I'm
> having problems with violating capacitance constraints on nets in my
> hierarchical design. Performing
>
> report_constraint -max_capacitance -all_violators
>
> gives a number of violators, some I have resolved by doing set_load
> on those ports ... others just won't budge whatever I do. I've tried
> characterizing and re-reporting, characterizing and re-synthing but nothing
> works. Can you tell me what the recommended procedure is to resolve these
> types of violations ????
>
> - Gary Cook
> Sony Broadcast
From: Gary Cook <gc@adv.sonybpe.com>
John,
To further the solution to this problem I've discovered that my output
buffer type is being changed but is still not enough because my bus
(address bus) has a high fanout. (What I need to do then is to get Design
Compiler to insert buffers on the inputs of the sub-designs that the address
bus is connected to.)
I can't seem to be able to get Design Compiler to do this though ... tried
setting the load, capacitance, drive etc. on the input port but it doesn't
insert the required buffer.... any ideas???
- Gary Cook
Sony Broadcast
---- ---- ---- ---- ---- ---- ----
From: "Tom Harrington" <tharring@ford.com>
Have you tried using set_fanout_load and set_max_fanout, to get the total
fanout under control?
- Tom Harrington
Ford Microelectronics Colorado Springs, CO
---- ---- ---- ---- ---- ---- ----
From: Oren Rubinstein <oren@gigapixel.com>
Hi John,
As you know, every now and then my fingers itch and I have to answer one of
these questions. Concerning "What's The Technique To Handle Hierarchical
Capacitance Problems?" Try:
children = find(design, {*}, -hier)
set_max_transition 1.0 children + current_design
remove_attribute children dont_touch /* Just in case you have any */
compile -only_design_rule
And congratulations for the 300th posting of ESNUG! Over the years, you've
done a great job of keeping us all informed.
- Oren Rubinstein
GigaPixel Corp. Santa Clara, CA
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