( ESNUG 459 Item 10 ) ------------------------------------------- [12/14/06]
Subject: ( ESNUG 458 #1 ) Plus the "official" Cadence & Synopsys responses
> This is the method we have used for at least 3-4 years and it has been
> serving us well. However, Synopsys now requires us to use a PT-SI license
> to use report_timing -crosstalk_delta. ... Taking away this very valuable
> capability and forcing us to buy a much more expensive PT-SI license is
> outrageous! ... Where is the outrage?
>
> - Dean Ranger
> Toshiba San Jose, CA
From: Dave Desharnais <dez=user domain=cadence spot mom>
Hi, John,
Dean Ranger is not alone in his frustration outlined in ESNUG 458 #1. We
can help. Dean mentioned in his post that Toshiba already uses CeltIC NDC,
the de-facto industry standard SI signoff solution in their design flows.
Our Encounter Timing System (ETS) is a no-brainer here. Dean should just
use ETS. It's solace for disgruntled PrimeTime users. Problem solved.
- David Desharnais
Cadence San Jose, CA
---- ---- ---- ---- ---- ---- ----
From: Gordon Yip <gordon.yip=user domain=synopsys spot mom>
Hi John,
This was not a conspiracy to extract more dollars from our users. It
started out as a simple licensing clean up for PrimeTime-SI features; it
did make sense at the time because the "-crosstalk_delta" option to
"report_timing" was developed as a PrimeTime-SI feature. Seeing that a
customer is relying on this feature to make the CeltIC flow workable
with PT, we worked with the customer a few months ago and removed this
change. In 2006.06-SP3, this command option no longer required a
PrimeTime-SI license.
However, this back and forth, PrimeTime-CeltIC SDF-based SI flow still
has its issues in terms of productivity and accuracy. Going in and out
of separate tools, using multiple libraries, passing constraints, and
generating large SDF files can be a nightmare and really slow you down:
delay calculation and STA in PrimeTime, then passing SDF and constraints
from PrimeTime to feed CeltIC, then running incremental SI delay
calculation in CeltIC, then generating incremental SDF from CeltIC and
feeding it back for an STA update in PrimeTime. There are so many steps
needed that the chance of "pilot error" creeping into the process is
rather high. Since PrimeTime-SI is an integrated solution, users can
perform crosstalk delay and noise analysis in a single tool and run in a
single flow, all while using a single unified library. Gone is the back
and forth between tools and passing of SDF files and constraints, all of
which impacts designer productivity.
Then there are the debugging aspects. Using two tools to debug a problem
can also be a nightmare. The best place to report and view signal
integrity effects on timing is in a combined timing/signal integrity
tool. When there is a problem, users can immediately query and get all
of the design, timing, parasitic coupling, voltage bump and delta delay
information to investigate and debug the signal integrity problem
without having to go back to a separate tool and try to find the same
problem and match up the names, numbers, and results.
Most important is the effect on accuracy. It is next to impossible to
decouple delay calculation, STA and SI analysis with independent,
standalone tools and still get signoff-level accuracy for 90 nm and
below: there is just too much interdependence. Since PrimeTime-SI is an
integrated solution built on golden STA, it gives you the most accurate
analysis. Here's why:
- Accurate crosstalk and slew-aware timing windows. Accurate timing
windows are essential to accurate signal integrity analysis, but
these timing windows can change due to crosstalk effects. PrimeTime-SI
provides an integrated timing calculation with signal integrity that is
the most accurate and efficient way to calculate crosstalk-affected
timing windows. A separate timing calculation that is independent of the
signal integrity calculation cannot accurately account for how crosstalk
will effect the timing windows, and this can lead to a less-than-accurate
timing window; essentially a "crosstalk-unaware" timing window.
- Accurate handling of clock reconvergence pessimism. Crosstalk delta
delay is a dynamic effect that requires special handling for accurate
clock reconvergence pessimism removal in the timing analysis tool. A
flow between a standalone signal integrity tool and a separate timing
tool, however, uses an incremental SDF file that cannot pass along
information to indicate that the delta delay is a dynamic effect. Simply
using an incremental SDF file will result in an inaccurate and possibly
optimistic handling of the clock reconvergence pessimism removal within
the timing tool. Because of potentially optimistic results using this
SDF-based interface, there is a significant limitation of using
standalone timing and signal integrity tools. PrimeTime-SI inherently
and automatically passes on the proper information about crosstalk delta
delays to the clock reconvergence pessimism removal algorithm, which in
turn will properly and accurately handle crosstalk effects on the clock
network.
- Consistent handling of timing constraints, exceptions, and properties
between clock domains. PrimeTime-SI provides consistent interpretation
and properly applies the design constraints and exceptions for both
timing and signal integrity analysis. With the separate tool approach,
users run the risk of different interpretations, different precedent
rules, and different levels of support, all of which can lead to wrong
results, or worse, missed violations.
Furthermore, by using PrimeTime-SI, designers can take advantage of all
of PrimeTime's capabilities, which are automatically available in
PrimeTime-SI. These include:
- Distributed multi-scenario analysis (DMSA). PrimeTime's DMSA feature
is a very powerful capability that helps designers manage the complexity
of multiple PrimeTime and PrimeTime-SI runs for multiple modes and
corners by efficiently utilizing available machine and license
resources. Most important, DMSA then generates a single merged report
that provides a global view of the design across all runs.
- Path-based analysis. PrimeTime's analysis performs path-specific
recalculation using path-specific slews and aggressor/victim edges
(instead of windows), which improves the slack and reduces the number
of violations.
- Advanced bottleneck reports. PrimeTime-SI has bottleneck reporting
tools that combine timing and signal integrity information to report the
victim or aggressor bottlenecks which affect the most violating timing
paths. This allows designers to see SI bottlenecks and determine a fix
that can fix multiple timing paths.
These are just a few of the many advantages of PrimeTime-SI.
In the end, we would recommend that for signoff signal integrity analysis,
designers should use PrimeTime-SI since it is the integrated solution
built on golden STA.
- Gordon Yip
Synopsys Mountain View, CA
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