Subject: Re[2]: Quest for IBIS models, A NOTE TO IBIS USERS

From: Donald Telian <[email-masked]>
Date: Fri, 24 Feb 95 12:09:10 PST

Text item: Text_1

IBISers,

I've been encouraged to see the latest chain of emails.  It shows me that there 
is a growing USER interest in IBIS models.

For a while now, I've seen the need for an "IBIS Users Group" (IUG!?, needs 
work, too blunt, and it has nothing to do with birds).  I almost started this 
myself, but it doesn't make sense given my current job objectives.

This group would focus on the USEABILITY of IBIS models, and push for the 
AVAILABILITY of IBIS models.  Accuracy has been well addressed, but useability 
can get easily overlooked.

As someone who is responsible for releasing IBIS Models, I (for one) would 
definitely pay attention to what such a group might come up with.  It's 
difficult to handle miscellaneous requests from all over, but if such a group 
came up with a prioritized list of what could and should happen with IBIS we 
could work with that.  I think simulation tool vendors would feel the same way. 

And how about a list of the "Top 10 Necessary IBIS Models", along with the 
manufacturer(s) who should provide them?  Model releases normally flow from a 
certain threshold of end user pull or customer demand.

Trying to look at the modeling problem from the user's perspective is part of 
what started IBIS in the first place, and the ball is now rolling.  It has been 
pointed out that the Open Forum is largely simulation companies.  That needed to
happen to coordinate model style.  Now that there's agreement on format, it's 
time for the users to organize, stand up, and define the next step.

Any takers?

Donald Telian
Intel Corporation

PS:  Time-wise, this probably makes more sense than everyone trying to push for 
models by themselves.

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Greg,

My experience in getting Spice and/or IBIS models has varied dramatically from
vendor to vendor.  As this might also be of some interest to the various tool
vendors, here's my feedback...

My starting point is usually the vendor's rep.  Inevitably the rep has no clue
what we're requesting, though they do come up to speed fairly quickly.  Within
a day or so I get feedback as to what's available.  An increasing number of
companies have Spice information readily available, and a small number have
v1.1 IBIS stuff available.  I've yet to see a v2.1 model (though Intel has
provided equivalent Quad and HSpice models for buffers that couldn't be
accurately modeled in the earlier format).  Interestingly enough, many of the
companies I've encountered that have IBIS models also are willing to provide
the original Spice info.

I make a point to try to get my hands on Spice models for several reasons
(even though I won't be using Spice to run the sims).  First off, we've had
some success in getting vendors to "guarantee" their Spice models.  I rarely
get guaranteed IBIS models (it's happened once, and wasn't a memorable
experience).  Secondly, I can gain some insight into the model accuracy by
looking through the netlist and device models.  Though this can be misleading
it can also be quite beneficial.  I have a big issue with non-guaranteed
models, but that's another subject.  Finally, with most Spice models you're
free to set the operating conditions (process point, voltage, and temperature)
according to the each system's specifications.  IBIS min/max conditions are
often predefined and accordingly are too conservative for some applications.

When Spice models aren't available or can't be obtained in an acceptable time
period (the lawyers got involved), I take one of two different approaches
depending on my needs.  Sometimes I'll ask for IBIS models, while other times
I'll ask the vendor to perform a series of buffer characterization sims and
simply send me the raw results.  The second approach has worked well when the
vendor doesn't have IBIS models, doesn't know what IBIS models are, has v1.1
models that aren't accurate enough, or has the wrong operating conditions in
their standard models.  These two approaches have worked well at times, while
other times the whole experience is a big pain in the [insert favorite
anatomical reference here].

As to Zeelan models, they could come in handy at times.  I've yet to purchase
a copy of their library for two reasons:  it doesn't contain min/max models
and doesn't contain all the parts I think it should (DRAMs, cache RAMs, etc.).
 There have been times, however, when it would've been beneficial to have
their library available.

As to industry trends, I've seen a positive shift over the last 6 months or
so.  In general most of the companies have a long way to go, but I get the
impression that more and more of 'em are heading the right way.  I know I've
been going to a lot of trouble to educate a number of 'em...

Mark Leonard
Lead Engineer, Signal Integrity Group
Compaq Computer Corporation