Subject: RE: [IBIS-Users] Questions Regarding Bird 75.8
From: Todd Westerhoff (twesterh@cisco.com)
Date: Tue Jan 07 2003 - 11:36:39 PST
A HA!
After all this years, the quote I needed!
"IBIS is a very complex standard, and trying to extend it to handle
everything that needs to be modeled in every case is hopeless."
Which give me the chance to say (once again):
Kumar Was Right.
Sorry - couldn't help myself!
Todd ;-}
Todd Westerhoff
High Speed Design Specialist
Cisco Systems
1414 Massachusetts Ave - Boxboro, MA - 01719
email:twesterh@cisco.com
ph: 978-936-2149
============================================
"When did the choices get so hard, with so much more at stake?
Life gets mighty precious when there's less of it to waste"
- Bonnie Raitt, "Nick of Time"
-----Original Message-----
From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org]On
Behalf Of Reid, Chris
Sent: Tuesday, January 07, 2003 12:33 PM
To: 'Timothy Coyle'; ibis-users@eda.org
Subject: RE: [IBIS-Users] Questions Regarding Bird 75.8
Timothy,
I'm glad you are interested in Bird 75 and 77.
Yes, this is quite a leap for IBIS. Fundamentally it defines a way that
VHDL-AMS or SPICE models can be registered for use in an automated SI tool
by using an IBIS wrapper. This makes it possible to go far beyond what IBIS
alone can do in terms of modeling real device characteristics, for example
power and ground supplies inside the package.
As you know, SPICE models direct from vendors are difficult to use because
they tend to be poorly documented. The IBIS wrapper for these models, if
correctly constructed, will help eliminate this confusion.
I share your enthusiasm for IBIS models. They make SI simulations much
faster than SPICE, and in some cases even more accurate. It is not true
that IBIS models are only translations from SPICE. Many IBIS models are
made by measuring the actual device responses. In many cases the simulated
results are actually closer to actual device performance than the SPICE
models that are supposed to represent the part.
Thus, classic IBIS models should be used where possible because:
1) They are faster to simulate.
2) They are, at least in some cases, more accurate.
However, there are many devices IBIS cannot model. With these Birds, for
example, it is possible to model the whole component from input to output
with a mixture of IBIS, SPICE, and VHDL-AMS all working together to describe
some complex behavior.
IBIS is a very complex standard, and trying to extend it to handle
everything that needs to be modeled in every case is hopeless. Thus these
Birds.
In short, use classic IBIS models where possible. Otherwise use the new
[external model] and [external circuit] structures.
Chris
-----Original Message-----
From: Timothy Coyle [mailto:Timothy.Coyle@nsc.com]
Sent: Tuesday, January 07, 2003 8:30 AM
To: ibis-users@server.eda.org
Subject: [IBIS-Users] Questions Regarding Bird 75.8
Hello,
I have been trying to follow along with the multilingual model discussions.
I have read through the bird and have some comment/questions.
My comments are more towards the purpose of the bird rather than technical
content.
It seems the purpose of this bird undermines what IBIS was originally
intended for: an adequate substitute for SPICE. (for most situations) This
bird
seems to be the death of IBIS. Why would I bother using IBIS at all when I
can use SPICE? Was the intention to use faster, less complex IBIS "blocks",
combined with SPICE "blocks" for the more complex parts? A vendor can right
now give out encrypted SPICE models. Why try to include these SPICE models
into a complex IBIS format? If the goal is to try to tie together the
"best" of IBIS, SPICE, and hardware languages I'm not sure that is the
scope of the IBIS spec.
Most vendors don't want to give out SPICE models, even if they are
encrypted. Will this bird force the hand of vendors? Once end users realize
what this bird can do,
won't they want the original SPICE model or hardware language code for
every device? IBIS is merely a "translated" SPICE model. Why use imitation
when you can have
the real thing?
I also question the need for this bird. I think this bird takes a huge
leap, and the gap left behind will swallow the IBIS community. I believe
it was
only last year at DesignCon where several papers were presented showing how
many rudimentary errors there were in IBIS files on the web. To this
day, I do not know of any IBIS files that are on the web that are
accompanied by any correlation documentation. To me, IBIS, as a standard,
does not have
the respect that it deserves. It is constantly being misused and abused.
And while an enhancement bird like this might be beneficial, I would think
that the current
state of IBIS would garner more attention.
As a model creator myself, I find the scope of this bird confusing, and I
find the future of IBIS questionable.
Regards,
Tim
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