[ibis-macro] Re: Making IBIS responsive to the modeling needs of the industry ... new keyword [Specification]
- From: "Muranyi, Arpad" <Arpad_Muranyi@xxxxxxxxxx>
- To: "IBIS-ATM" <ibis-macro@xxxxxxxxxxxxx>
- Date: Fri, 5 Dec 2008 07:45:04 -0800
Walter,
I am not disputing the issues that there are lots of things out
there which IBIS hasn't addressed, and that EDA vendors have
developed their own way of shoehorning things into IBIS files
with proprietary methods.
But your reply doesn't answer my question. True, a new keyword
like [Specification] would help in making those proprietary
solutions official, but without describing what the content
and format of the file that it points to would not remove the
incompatibility problem, because these files would still not
be exchangeable between tools.
If my file describes the same eye opening diamond with a totally
different syntax as yours, we both may have an identical IBIS
file with the [Specification] keyword in it, but your tool is
still not going to be able to use my eye opening description and my
tool is not going to be able to use yours. This could be made to
work only if we wrote a spec for the eye opening description so
that the same file to which [Specification] points to could be
read by all EDA tools. I don't see how this [Specification]
keyword would be useful otherwise. But if we end up having to
write a specification for what goes into those external files,
I wonder why we need to go with external files at all? What is
the benefit of removing these things from the IBIS specification?
Relating to the subject line of this message, I agree we need to
do something to be responsive to the industry needs, but I don't
think that removing everything from the IBIS specification into
unspecified external files is the solution, unless we want to kill
IBIS completely and go our separate ways. We are starting to have
way too many proposals which go in this direction. The EMD proposal
suggests to put everything into external subcircuits without really
describing what the syntax of that subcircuit is (unless we end up
saying that it shall use the Interconnect-SPICE and nothing else).
There were similar suggestions in the C_comp discussions (final
stage subcircuit). This [Specification] keyword proposes another
external file without defining its format. IBIS-AMI does everything
outside the IBIS file also, but at least that one does define fairly
rigorously how the external files should interface with IBIS. (We
could even add *-AMS, ICM, PGK to this list if we want to be really
picky about how things started to be taken out of IBIS).
I am beginning to wonder, what the true motivations are behind these
recent suggestions. Do we want to make an empty egg-shell out of IBIS
that is pretty much useless for anything other than a nice display on a
shelf somewhere? Do we want every EDA tool to have their own
incompatible file formats again? If so, let's just close up shop
and say IBIS no longer exists. If not, let's try to find a more
standardized way to solve these problems.
Part of the problem is that all along the IBIS history we kept resorting
to minimalist changes, pushing off the real solutions to a later time.
These things have a tendency to accumulate and the longer we do this,
the bigger the problem-pile tends to get. When the pile gets too large
we either have to bite the bullet, take a big breath and start over, or
let the pile collapse under its own weight and leave it there. I feel
this is the situation we are approaching. The proposals we are
discussing
give me the impression of putting explosives into the pile and spread it
by explosions. The original pile may reduce in size or disappear, but
the result is a bunch of new smaller piles. These may turn into big
piles of their own at a later time if we are not make drastic changes
in how they are architected.
Arpad
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________________________________
From: Walter Katz [mailto:wkatz@xxxxxxxxxx]
Sent: Tuesday, December 02, 2008 7:00 PM
To: Muranyi, Arpad; 'IBIS-ATM'
Subject: RE: [ibis-macro] Re: Making IBIS responsive to the modeling
needs of the industry ... new keyword [Specification]
Arpad,
We passed around Cape Horne yesterday, and visited the Falkland Islands
(Malvenas) today. Seas surprisingly calm.
I understand your point, but right now IBIS is not being responsive to
the needs of the industry. If we could find a way to quickly implement
things like derating, masks, ... then this idea would not make sense.
But DDR2 derating has been around for 4 years and USB masks have been
around for close to that and IBIS has not been responsive.
For example, SiSoft has implemented all of the DDR2, DDR3 and DDR FB
design rules using |SiSoft IBIS keywords that meet JEDEC DDR rules. For
each new part that has a DDR compliant bus our customers need to include
these |SiSoft records. I expect that Mentor, Cadence, Agilent, Zuken,
... have done something similar. Each of us has implemented these DDR
rules in our own way. By having records such as "[Specification]
DDR2_667_CLKIN" SiSoft can point to our own private "Include" file that
has these DDR rules as we have implemented them. Other EDA companies can
point to their own "Include" files that implement this specification. As
new requirements get specified by Industry Standards Groups such as
JEDEC, all IC vendors need to do is have a standard way of having a
Model point to an industry standard, and this is what I am proposing.
Just look at the confusion we have created by the IBIS implementation of
VinH_AC, which kind-of satisfies the JEDEC measurement rules but in fact
does not because it handles slow and fast corners differently then the
JEDEC spec. (IBIS specifies a typ value and then uses a threshold
sensitivity to adjust for voltage corners, JEDEC specifies values for
each of the corners). I think the IBIS method could make more sense, but
customers require that their designs satisfy the JEDEC spec.
"[Specification]" is one way we can make IBIS responsive to the needs of
the IC/EDA/Customer community.
Does anyone have another approach to solve this problem?
Do we want to solve this problem?
Walter
-----Original Message-----
From: ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Muranyi, Arpad
Sent: Tuesday, December 02, 2008 1:49 PM
To: IBIS-ATM
Subject: [ibis-macro] Re: Making IBIS responsive to the modeling needs
of the industry ... new keyword [Specification]
Walter,
In general, this [Specification] proposal looks very much like
IBIS-AMI, adding one simple keyword to IBIS and do the rest outside.
In the case of AMI, we wrote a whole new specification to describe
what AMI actually is, describing parameters, the format of the
parameter files, etc... I feel we will need to do the same in
this case too. Otherwise how would a tool know how to parse the
content of the file that [Specification] points to.
So while this seems to be an easy fix in the IBIS specification,
I don't see any reduction of work, because somewhere it must be
defined what the file contains and what its syntax is. Or did I
miss something?
Another topic: This proposal is yet another example, where we are
diverting things from the IBIS specification to some other, external
file or specification. If we keep this trend up, there will be
nothing left in IBIS itself, except a bunch of pointers. This
makes me wonder again about the conversation we are doing on the
overhauling of IBIS... Any comments?
Thanks,
Arpad
=====================================================================
________________________________
From: ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Walter Katz
Sent: Tuesday, December 02, 2008 12:22 PM
To: 'IBIS-ATM'
Subject: [ibis-macro] Making IBIS responsive to the modeling needs of
the industry ... new keyword [Specification]
All,
I do not expect to be able to attend an ATM meeting until Dec 15. I read
last weeks minutes and cam up with an idea that might solve many of the
issues that we have been suffering through:
We are all aware of the difficulty of introducing new features to IBIS
(e.g. C_Comp, Derating, Masks, USB rules, JEDEC rules, On Die
S-parameters, LTI Differential Tx and Rx models, ...).
I would like to propose a simple solution that I think will solve this
problem by introducing a single new keyword to IBIS "[Specification]".
The format of a [Specification] record is simply:
[Specification] specification_name
[Specification] records can occur in the [Component] section, or [Model]
section. Each component and each model may have multiple [Specification]
records.
A specification_name can either be registered. It is registered by being
placed in an IBIS maintained registry of registered names along with a
specification_name.txt or specification_name.pdf document describing the
specification. If a specification_name is not registered, then the
specification_name.txt or specification_name.pdf needs to be supplied
along with the IBIS file.
I think the following example will explain the usefulness of this
concept. Consider a 667 MegHz, DDR2 memory part with the following
models: CLKIN, ADDCMD, DQ, DQS. The IBIS file might be:
[Model] CLKIN
[Specification] DDR2_667_CLKIN
[Model] ADDCMD
[Specification] DDR2_667_ ADDCMD
[Model] DQ
[Specification] DDR2_667_DQ
[Model] DQS
[Specification] DDR2_667_DQS_diff
The IBIS registry would contain the following entries for DDR2 667MegHz.
There would be other entries for other speed grades, DDR3, DDR4, ...
DDR2_667_CLKIN DDR2_667_CLKIN.txt
DDR2_667_ ADDCMD DDR2_667_ ADDCMD.txt
DDR2_667_DQ DDR2_667_DQ.txt
DDR2_667_DQS_diff DDR2_667_DQS_diff.txt
DDR2_667_CLKIN.txt might contain
JEDEC Standard No. 79-2C
Speed grade 667MegHz
Signal CK
This is sufficient information for an EDA tool to create a design kit
for this model. It will be up to the EDA tool to determine how it
implements this in its environment.
Similarly there can be [Specification] for eye masks, on die
s-parameters, "ladder C_comp", ... EDA tool vendors can implement
solutions to each of these problems in an appropriate way based on their
target market and their tool capabilities. The key point is that
[Specification] allows IC vendors to document in their IBIS [Model]s the
measurement/simulation requirements of their models without waiting for
IBIS to come up with new keywords/parameters, and allows EDA vendors to
address industry standard measurement rules in a timely manor.
USB, JEDEC, and other industry standard specifications fit naturally
into this scheme. Fancy C_Comp solutions can be more problematic, since
the [Specification] might be ties to a specific simulation methodology
or EDA tool, but it would at least document the solution used by the IC
vendor for their analysis. I would expect that IC vendors will learn to
write these [Specifications] in a way that would be supported by the EDA
tools that their customers use.
Walter Katz
Chief Scientist
Signal Integrity Software, Inc.
wkatz@xxxxxxxxxx
303.449-2308
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