[SI-LIST] Re: New blog posting: Four things that drove me nuts about IBIS 5.1
- From: "Todd Westerhoff" <twesterh@xxxxxxxxxx>
- To: <colin_warwick@xxxxxxxxxxx>
- Date: Mon, 22 Oct 2012 09:11:35 -0400 (EDT)
Colin,
I think the guidelines are straighforward:
1) All AMI models support Time-Domain analysis.
2) AMI models with "Init_Returns_Impulse = True" support Statistical
Analysis
With the further clarification that:
3) AMI models with "Getwave_Exists = True" support waveform processing which
is usually (but not always) NLTV
4) AMI models with both "Init_Returns_Impulse = True" and "Getwave_Exists =
True" have algorithmic support for both simulation modes, such that
comparing the results of Statistical and Time-Domain simulations is a
worthwhile exercise.
Todd.
Todd Westerhoff
VP, Software Products
Signal Integrity Software Inc. â www.sisoft.com <http://www.sisoft.com/>
6 Clock Tower Place â Suite 250 â Maynard, MA 01754
(978) 461-0449 <callto:978%29%20461-0449> x24 â twesterh@xxxxxxxxxx
âI want to live like thatâ
-Sidewalk Prophets
-----Original Message-----
From: colin_warwick@xxxxxxxxxxx [mailto:colin_warwick@xxxxxxxxxxx]
Sent: Saturday, October 20, 2012 11:40 AM
To: twesterh@xxxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx
Subject: RE: [SI-LIST] Re: New blog posting: Four things that drove me nuts
about IBIS 5.1
Pressed "send" too soon... Sorry...
The thing I forgot to add is that I believe a lot of the confusion around
this topic is the word "mode" itself in the term "dual-mode model."
Here's the reason. We often use the word "mode" in connection with simulator
mode (e.g. bit-by-bit mode or statistical mode). The word "mode" in
"dual-mode model" sparks the incorrect conclusion that "a dual mode model is
necessary to take advantage of both modes of the simulator" in the mind of
the uninitiated. (And I included myself in that category, before Fangyi
patiently explained to me that an impulse-only model can run perfectly well
in both modes.)
A clearer term might be "dual-function model" or something...
Then we'd have a narrative like:
1) A GetWave-function-only model can run only in bit-by-bit mode.
2) An impulse-function-only model can run in both modes, and the impulse
function is used in both modes.
3) A dual-function model can also run in both modes, but the GetWave
function is used in bit-by-bit mode, and the impulse function is used in
statistical mode
-----Original Message-----
From: WARWICK,COLIN (A-Americas,ex1)
Sent: Saturday, October 20, 2012 10:46 AM
To: 'Todd Westerhoff'
Cc: 'si-list@xxxxxxxxxxxxx'
Subject: RE: [SI-LIST] Re: New blog posting: Four things that drove me nuts
about IBIS 5.1
Hi Todd,
Thanks for you feedback. I agree with you 100%.
I said "buyer beware" because I've come across several model consumers (and
even a few model builders) who were unaware of the trade-offs you mention,
so I wanted to highlight them in the app note.
The fact is that if the model builder provides GetWave it implies to me that
the IC has non-linearity and/or time-varying (adaptive) behavior, because,
if the IC were LTI, the model builder could have captured the behavior
completely with the impulse response only. Therefore, if the model builder
provides both a GetWave and an impulse response, in my mind the model
consumer should be aware that that impulse response is probably some kind of
approximation. For example, an adaptive peaking filter of the type you
mention may change dynamically in the GetWave code used during a bit-by-bit
simulation, but its response will be static in the output of the impulse
response code used in a given statistical simulation.
In summary, Agilent supports such models in both our model building and our
model consuming EDA tools. When used with the engineering judgment you
mention, we believe they have great value.
Best regards,
-- Colin Warwick
Product Manager for High Speed Digital, Agilent EEsof EDA
...feeds blog @ http://Signal-Integrity.TM.Agilent.com/feed/
...tweets @signalintegrity
-----Original Message-----
From: Todd Westerhoff [mailto:twesterh@xxxxxxxxxx]
Sent: Saturday, October 20, 2012 12:22 AM
To: WARWICK,COLIN (A-Americas,ex1)
Cc: si-list@xxxxxxxxxxxxx
Subject: Re: [SI-LIST] Re: New blog posting: Four things that drove me nuts
about IBIS 5.1
Colin,
In your table 1, you imply that an AMI model that processes both impulse
responses (Init) and waveform data (Getwave) is risky, with a "Buyer Beware"
note.
You've correctly identified that generating a good LTI approximation of NLTV
behavior requires skill on the part of the model developer - well beyond a
straightforward adaptation of internal Matlab code a semiconductor company
may already have on hand. What you haven't done, is identify the benefit
(why would anyone want to do this in the first place?) and whether people
have already done it.
Let's start with the benefit. Statistical simulations run 30-300x faster
than their time-domain (bit by bit) counterparts AND predict very low
probability events with much more precision. In the lead-in to your paper,
you mention the need to perform hundreds of simulations to explore a design
space. In our experience, that's actually a low number - it's more like
thousands to tens of thousands of simulations. One of our customers
estimated the time needed to run design space explorations in time-domain
(bit-by-bit) mode as 6 months on a 64 processor server farm. That's just
not tenable.
A good dual-mode model (your "Buyer Beware" case) allows Design Space
Exploration to be run in Statistical Mode. Thousands of cases can be
explored quickly in Statistical Mode to see which cases are worth investing
the time to run in Time-Domain Mode. In the webinar we presented with
Xilinx in 2009 (or 2010, I don't have access to my records at the moment),
we showed how 500 Statistical Simulations could be run in about 15 minutes
to narrow down a design space. Those simulations used a dual-mode AMI RX
with both DFE and an adaptive peaking filter. The simulations were run on a
single desktop computer with 4 non-hyperthreaded cores. The equivalent bit
by bit analysis (as your paper suggests) would likely have taken 8 hours or
more.
It's true that coding a dual-mode AMI model for a device with nonlinear and
adaptive behavior takes talent ... still, there are plenty of such models
out there. We've been delivering dual-mode AMI models and AMI model
development tools since 2008. We correlate the results of Statistical and
Time-Domain simulations on every model we create.
It's also true that users need to understand the limits of the two
simulation approaches, and to use good engineering judgement when reviewing
simulation results. When you consider the impact that reducing simulation
time by 30-300x can have on a design cycle, we believe the extra effort
required to produce a good dual-mode model is well worth it.
Todd.
Todd Westerhoff
VP, Software Products
Signal Integrity Software Inc. â www.sisoft.com
6 Clock Tower Place â Suite 250 â Maynard, MA 01754
(978) 461-0449 x24 â twesterh@xxxxxxxxxx
â I want to live like that â
-Sidewalk Prophets
----- Original Message -----
From: "colin warwick" <colin_warwick@xxxxxxxxxxx>
To: si-list@xxxxxxxxxxxxx
Sent: Friday, October 19, 2012 2:48:23 PM
Subject: [SI-LIST] Re: New blog posting: Four things that drove me nuts
about IBIS 5.1
Hi si-listers,
A couple of people asked for a clarification about what combinations
(statistical versus bit-by-bit mode, with the four true/false model flags)
were valid, and what happened in each of the resulting 32 cases. I tried to
capture all this in a table a placed it in the updated posting here:
http://signal-integrity.tm.agilent.com/2012/four-things-that-drove-me-nuts-about-ibis-5-1/
Feedback/corrections welcome!
Best regards,
-- Colin Warwick
Product Manager for High Speed Digital, Agilent EEsof EDA
...feeds blog @ http://Signal-Integrity.TM.Agilent.com/feed/
...tweets @signalintegrity
-----Original Message-----
From: WARWICK,COLIN (A-Americas,ex1)
Sent: Tuesday, September 25, 2012 3:06 PM
To: 'si-list@xxxxxxxxxxxxx'
Subject: New blog posting: Four things that drove me nuts about IBIS 5.1
Hi si-listers,
My new blog posting has the pseudo-provocative title "Four things that drove
me nuts about IBIS 5.1."
http://signal-integrity.tm.agilent.com/2012/four-things-that-drove-me-nuts-about-ibis-5-1/
It's about my struggle to understand IBIS AMI in general and the so-called
"flow BIRD" (BIRD 120) in particular.
Hope it helps!
-- Colin Warwick
Product Manager for High Speed Digital, Agilent EEsof EDA ...feeds blog @
http://Signal-Integrity.TM.Agilent.com/feed/
...tweets @signalintegrity
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