( ESNUG 339 Item 4 ) --------------------------------------------- [1/13/00]
Subject: ( ESNUG 335 #2 338 #6 ) DC/PT 3-D Load-Dependent Lookup Tables
> Synopsys version 1999.10 supports 3-dimensional lookup tables for delay
> modeling. I hope to find out what other tools (e.g., Avanti, Cadence,
> etc.) already have or plan to have compatible timing modeling. What have
> you heard from your vendors? Are there characterization tools out there
> that can write .lib's with this syntax?
>
> - Andy Pagones
> Motorola Labs
From: Stefan Scharfenberg <Stefan.Scharfenberg@motorola.com>
Hi John,
Please allow me to comment on the 3-D Lookup Table discussion. I think Andy
made a good point and the Synopsys Library Compiler CAE's reply answers this
to a certain extend. What I always find difficult when creating libraries
is to find out how are certain ways to model the library or certain
constructs impacting other tools? The Synopsys .lib has become a very
popular format which can be parsed by many tools (from Synopsys and other
vendors). Along with this development additional commands and constructs
like the 3-D tables were added. These are very well described in the
Library Compiler Manuals, what is missing is a list or table of tools that
can read this information and actually use it in a meaningful way. Let me
give an example.
/* Library defaults */
slew_lower_threshold_pct_rise : 20.00 ;
slew_upper_threshold_pct_rise : 80.00 ;
slew_derate_from_library : 1.00 ;
input_threshold_pct_fall : 50.00 ;
output_threshold_pct_fall : 50.00 ;
input_threshold_pct_rise : 50.00 ;
output_threshold_pct_rise : 50.00 ;
slew_lower_threshold_pct_fall : 20.00 ;
slew_upper_threshold_pct_fall : 80.00 ;
The above lines are only meaningful to PrimeTime. There is no hint to this
in any documentation that I looked at, so a user may have the impression
that all Synopsys tool understand this.
- Stefan Scharfenberg
Motorola SoCDT Munich, Germany
---- ---- ---- ---- ---- ---- ----
> I'm the Library Compiler CAE. Since Andy brought this up, I would like to
> give a brief history of 3-D timing modeling plus some recommendations.
> We've had a lot of experience at Synopsys modeling unbuffered outputs.
>
> In the early days of DC, we modeled one output dependent on output loading
> another output, but no output-to-output timing arcs. Many people use this
> today, though fewer & fewer libraries heavily leverage unbuffered outputs.
>
> A few years ago we added setup & hold constraint 3-D tables. Some vendors
> requested them and 3-D constraint tables are generally used when we have
> load dependant constraints. Setup/Hold depends on loads on both Q & Qbar.
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> - [ The Synopsys Library Compiler CAE ]
From: [ Made In Taiwan ]
Hi, John. Anonymous, please.
I am wondering how this can be true: "Setup/Hold depends on loads on both Q
and Qbar." from the SYNOPSYS CAE' statment.
For DFF's, we see a master/slave architecture. Otherwise, it is a LATCH.
So, the setup time of a DFF should not be affected by LOADING, since the
loading is blocked and afftected only the slave stage.
Can anybody tell me what I am missing out ??
- [ Made In Taiwan ]
|
|
