Subject: RE: [IBIS-Users] Questions Regarding Bird 75.8
From: Muranyi, Arpad (arpad.muranyi@intel.com)
Date: Wed Jan 08 2003 - 10:36:09 PST
Al,
Thank you for your comments on BIRD75.8. I would like to respond
to it giving some answers and asking some questions.
1) Your request for examples are well taken. We are working on
them now, but can't promise them by this coming Friday's meeting.
Regarding your request for the examples demonstrating that this
approach is superior to a SPICE or *-AMS only approach I wonder
what kind of superiority you think of? A SPICE or *-AMS model
will result in the same waveforms and/or accuracy, regardless
whether they are embedded in this IBIS wrapper, or not. So from that
point of view I don't see any difference there. However, from the
user's perspective, there are some usage model differences which
makes the life of the user easier. The IBIS wrapper provides
additional information for the simulation tool, helping in automating
the measurement tasks, and providing information about reference
loads, etc... without effecting the model behavior itself. That
is the benefit of having these languages embedded in IBIS.
2) You mention that this approach is confusing. Could you please
elaborate on what the confusing part is, so that we could address
it if possible?
3) You say that "it doesn't even come close to solving the problem".
I am not sure what you are referring to. Could you please give a
problem statement as you see it? We can't solve a problem if we
have a different opinion on what it is...
4) The BIRD allows for an "old fashioned" model under the [Model]
statement to coexist with the new [External Model] keyword that
provides the SPICE or *-AMS description of a device. It is up to
the model maker to make a duplicate model of the device both ways.
If they write such a duplicate with the old [Model] keyword, tools
which cannot process the new keywords can simulate just like today.
If the model maker doesn't care to do that, you may be out of luck.
5) I do not understand your question: "How it is superior to
documenting an equivalence between the languages, like the
equivalence between Spice and Verilog-A is documented." Please
explain what you mean by "documenting equivalence between languages".
6) Regarding "How it impacts mixed mode simulators", it depends on
whether they have a parser that can read the IBIS file. They should
certainly be able to process the *-AMS portion of the IBIS file without
difficulty. However, in order to read and make use of the rest of the
information, an IBIS parser would need to be implemented. This should
not be a large undertaking, however.
7) Regarding "How such a model can be developed and tested", this is
a complicated question, because of the freedom these languages provide.
There are zillions of ways to write a model. One way would be an
equivalent IV and Vt table based equivalent in one of the AMS languages.
Another way would be to use the same data, but curve fit them to equations
and write those equations up in AMS syntax. For SPICE lovers, I could
imagine someone to write up the transistor equations in AMS syntax, and
provide the usual process file information and netlist of transistors
in the AMS file. I can also envision many other ways using higher level
behavioral techniques, some of which may even be proprietary and patentable.
However, your question is well taken, and guidelines in form of a cook book
should be written to get people started. I am certainly planning to extend
my IBIS class materials in this direction too.
I hope I answered some of your concerns. Please give me more information
on those questions I didn't understand so we can find the answers to those
too.
Thanks,
Arpad
============================================================================
-----Original Message-----
From: Al Davis [mailto:aldavis@ieee.org]
Sent: Wednesday, January 08, 2003 12:36 AM
To: ibis-users@eda.org
Subject: Re: [IBIS-Users] Questions Regarding Bird 75.8
Can someone please post examples of mixed IBIS-Spice,
IBIS-Verilog, and IBIS-VHDL models so we can review them?
I asked for this several times before and so far have gotten no
useful responses. If the proponents of this BIRD are serious,
they will have made some examples manually to demonstrate the
concept. It is only by doing so that you can know enough about
it to proceed further.
I agree with the need, but I agree with Timothy that this
approach is confusing. I further believe that it doesn't even
come close to solving the problem that it is intended to solve.
The examples should demonstrate that it works, and is superior
to a Spice only (or *-AMS only) approach.
If such examples cannot be produced and published, it should be
rejected. It is the responsibility of those who think it is
good to prove it.
The proponents should also be able to explain:
1. How this impacts simulators that use only the [Model]
portion of an IBIS file. (not [Component])
2. How it is superior to documenting an equivalence between the
languages, like the equivalence between Spice and Verilog-A is
documented.
3. How it impacts mixed-mode simulators.
4. How such a model can be developed and tested.
If these questions cannot be adequately answered in this public
forum, it should be rejected.
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