[ibis-macro] Re: Samples per bit for AMI

  • From: "Walter Katz" <wkatz@xxxxxxxxxx>
  • To: <gedlund@xxxxxxxxxx>, <Arpad_Muranyi@xxxxxxxxxx>
  • Date: Thu, 29 Sep 2011 10:08:20 -0400 (EDT)

Greg,

 

If an AMI model does have a Sample_Per_Bit requirement, then the EDA tool
must do one of the following:

1.       Choose a samples per bit that satisfies all of the Tx and Rx
samples per bit requirements - not always possible when different models
have different samples per bit requirements.

2.       Choose a samples per bit for a simulation, and then run the
impulse response and waveforms through a Torque Converter (Gearbox) that
converts these waveforms to the model's required Samples_Per_Bit before
calling the model, and then run the output of the model back to the Torque
Converter backwards.

 

In the ideal world, if the internals of the model do have a
Samples_Per_Bit limitation, the model should be doing the Torque
Conversions described above.

 

According to IBIS 5.0 (and the proposed 5.1), a model which does have a
Samples Per Bit limitation is non-compliant. If we add a reserved
parameter Samples_Per_Bit in IBIS 5.2, then these models can be made
compliant to 5.2 if they specify Samples_Per_Bit in the .ami file.

 

Ken Willis made in a separate e-mail branch:

 

Good discussion. I agree it is good practice to document the model usage.
If the issue is really one of documentation, then I don't know if it is
something we have to put into the standard. Most of the IBIS-AMI model
kits have some readme or pdf documentation with them. This is not really
different than regular Spice or IBIS models that have been distributed for
many years. With AMI, you can even put comments into the .ami files
themselves. So there are ways to properly document the models, without
adding more keywords to the spec.

 

Unfortunately, model makers often do not document the Samples Per Bit
limitation, and in some cases do not realize they have a Samples Per Bit
limitation because they only test them at one Samples Per Bit. Also, it is
difficult for software to programmatically read these .pdf files and
extract Samples Per Bit limitations.

 

We certainly can add a compliance test to IBIS-AMI that would use the AMI
test benches to verify that a model works at any number of Samples Per
Bit.

 

Walter

 

 

From: ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Gregory R Edlund
Sent: Thursday, September 29, 2011 9:32 AM
To: Arpad_Muranyi@xxxxxxxxxx
Cc: IBIS-ATM; ibis-macro-bounce@xxxxxxxxxxxxx
Subject: [ibis-macro] Re: Samples per bit for AMI

 

Arpad,

Do you envision the new samples per bit parameter being used by the EDA
tool?  Or is it for documentation purposes?

There is another way to handle this scenario:  we could integrate samples
per bit into the quality check list, i.e. the model maker uses the quality
check list as a means of communication with the user.

Greg Edlund
Senior Engineer
Signal Integrity and System Timing
IBM Systems & Technology Group
3605 Hwy. 52 N  Bldg 050-3
Rochester, MN 55901



Inactive hide details for "Muranyi, Arpad" ---09/28/2011 06:44:32
PM---Hello everyone, I ran across yet another model today whi"Muranyi,
Arpad" ---09/28/2011 06:44:32 PM---Hello everyone, I ran across yet
another model today which was misbehaving

From: "Muranyi, Arpad" <Arpad_Muranyi@xxxxxxxxxx>
To: IBIS-ATM <ibis-macro@xxxxxxxxxxxxx>
Date: 09/28/2011 06:44 PM
Subject: [ibis-macro] Samples per bit for AMI
Sent by: ibis-macro-bounce@xxxxxxxxxxxxx

  _____  




Hello everyone,

I ran across yet another model today which was misbehaving
in our tool because it turned out that it would only work
with 64 samples per bit and the user unaware of this used a
different value.

When I wrote about this topic some time ago, I was wrestling
with another AMI model that would only work with 32 samples
per bit.  Neither of these models came with any documentation
on what samples per bit settings they will work with.  The
problem is that when such models are misbehaving, all kinds
of "fun stuff" is starting to happen, anywhere from crashes
to explosions  :-).

I believe that the most robust solution would be to add a
reserved parameter for samples per bit to the IBIS-AMI
specification so that the model makers would be forced to
document in the .ami parameter file sampling rate(s) the
model will work with.  Making blanket statements in the spec
is not going to guarantee  that the model maker will actually
do anything about it, they may not even read that part of
the specification at all...

Please look over the attached BIRD draft in which I attempt
to solve this problem by adding a reserved parameter to the
specification.

Questions, comments are welcome.

Thanks,

Arpad
==============================================================



[attachment "SamplingRateBIRD_01.pdf" deleted by Gregory R
Edlund/Rochester/IBM]

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