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

  • From: Scott McMorrow <scott@xxxxxxxxxxxxx>
  • To: Ambrish Varma <ambrishv@xxxxxxxxxxx>
  • Date: Thu, 29 Sep 2011 14:40:03 -0400

I might suggest that we add a section to the specification on Requirement for Documentation of Non-Fully Compliant Models
Requirement for Documentation of Non-Fully Compliant Models - If a model is not fully compliant with the IBIS-AMI specification, all model limitations must be fully documented within comment lines within the AMI file.
This way the limitations are recognized as not fully compliant with the specification, but are documented in a place that will always be included in the model tree. Limitations on samples per bit can be easily documented here. 


Scott

Scott McMorrow
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
(401) 284-1827 Business
(401) 284-1840 Fax

http://www.teraspeed.com

Teraspeed® is the registered service mark of
Teraspeed Consulting Group LLC


On 9/29/2011 2:01 PM, Ambrish Varma wrote:

I agree with Kumar and Scott,
The moment we add something like 'Samples per Bit' in the spec and legitimize 
models that only work at 1 particular number, I suspect model makers will start 
producing models based on that.


Here is some suggested text that could go in the new BIRD:

On page 186 in Section 10 after the lines:

| 3.1.2.4 sample_interval
|
| This is the sampling interval of the impulse_matrix. Sample_interval is
| usually a fraction of the highest data rate (lowest bit_time) of the
| device.  Example:
|
|   Sample_interval = (lowest_bit_time/64)

Add the following text:

| The fraction (64 in the above example) is a number that is decided by
| the EDA tool based on the rise time of the analog drivers, simulation
| speed,  or other factors. The AMI model must be able to produce valid     | 
results at any sample_interval.


Please add/amend anything to make it more meaningful - or even suggest 
something to add at some other place to make it absolutely clear to the AMI 
model maker what to expect.

Thanks,
Ambrish.

Ambrish Varma   |  Member of Consulting Staff
P: 978.262.6431   www.cadence.com






-----Original Message-----
From: ibis-macro-bounce@xxxxxxxxxxxxx [mailto:ibis-macro-bounce@xxxxxxxxxxxxx] 
On Behalf Of Walter Katz
Sent: Thursday, September 29, 2011 10:45 AM
To: scott@xxxxxxxxxxxxx; ibis-macro@xxxxxxxxxxxxx
Subject: [ibis-macro] Re: Samples per bit for AMI

Scott,

I do not disagree with your comments. I think you propose that IBIS 5.1
require that a model accept any samples per bit and that if the model
implementation does have such an internal limitation then the model should
do the Torque Conversion. SiSoft would accept this resolution.

Walter

-----Original Message-----
From: ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Scott McMorrow
Sent: Thursday, September 29, 2011 10:28 AM
To: ibis-macro@xxxxxxxxxxxxx
Subject: [ibis-macro] Re: Samples per bit for AMI

Walter

I'm on the same page as Kumar.  The EDA tool can set the sample_interval to
anything that it desires, to generate uniformly sampled data that is as
accurate as required.  A model that requires a fixed sample_interval is
contrary to the spec and is non-compliant.  There is nothing new here.  If a
model is non-compliant, it needs to be sent back to the model maker and get
fixed.  How is this different than any other non-compliant IBIS model?
Sometimes an IBIS model quality problem can be fixed by the user.  Sometimes
it cannot be fixed.  Any fix at the EDA
tool level using re-sampling is like putting lipstick on a pig.   In the
end, it's just a pig that does what it wants to do, not what it should do.

Scott

Scott McMorrow
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
(401) 284-1827 Business
(401) 284-1840 Fax

http://www.teraspeed.com

TeraspeedR is the registered service mark of Teraspeed Consulting Group LLC


On 9/29/2011 10:19 AM, Walter Katz wrote:

Kumar,

On page 188 of IBIS 5.0:

| 3.2.2 Arguments
| | 3.2.2.1 wave
|
| A vector of a time domain waveform, sampled uniformly at an interval
| specified by the ‘sample_interval’ specified during the init call.
| The wave is both input and output. The EDA platform provides the
| wave. The algorithmic model is expected to modify the waveform in
| place by applying a filtering behavior, for example, an equalization
| function, being modeled in the AMI_Getwave call.

The waveform in and out of AMI_GetWave is " sampled uniformly at an
interval specified by the ‘sample_interval’ specified during the init
call"

I think this is "uniformly sampled data". So your comment "Your
proposal will prevent the eda tool to pass continuous waveform as
accurately as possible." Is not logical and does not apply. What did
you mean by "Your proposal will prevent the eda tool to pass
continuous waveform as accurately as possible."

Walter


-----Original Message-----
From: ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of ckumar
Sent: Thursday, September 29, 2011 10:09 AM
To: Arpad_Muranyi@xxxxxxxxxx
Cc: IBIS-ATM
Subject: [ibis-macro] Re: Samples per bit for AMI

there are various ways of "digitizing". You probably meant uniformally
sampled data. Your proposal will prevent the eda tool to pass
continuous waveform as accurately as possible.

On Thu, 29 Sep 2011 13:54:40 +0000, "Muranyi, Arpad"
<Arpad_Muranyi@xxxxxxxxxx>   wrote:

Kumar,

Regarding: "It does not make any sense for the eda tool to be doing
the part of the models job.", I don't think this is what I am suggesting.
In the computer world there is no such thing as continuous waveform.
Everything is sampled, digitized.  I don't see how we can go without
knowing how things are digitized.

Thanks,

Arpad


======================================================================
===

-----Original Message-----
From: ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of ckumar
Sent: Thursday, September 29, 2011 7:25 AM
To: twesterh@xxxxxxxxxx
Cc: IBIS-ATM
Subject: [ibis-macro] Re: Samples per bit for AMI

I do not agree. Resampling may part of a adc(analog to digital

conversion)

which may be more or less complex. The key part is that the model
should treat the incoming waveform as an analog/continuous waveform
and take it from there. It does not make any sense for the eda tool
to be doing the part of the models job.

On Thu, 29 Sep 2011 08:10:46 -0400 (EDT), "Todd Westerhoff"
<twesterh@xxxxxxxxxx>   wrote:

I'm with Arpad on this (which should surprise no one).



This is a practical issue - there are models out there with

undocumented

requirements (e.g. samples per bit) and this is a standardized way
of documenting those requirements so that users (and tools) can do

something

about them.  The mere act of documenting a requirement should serve
as

a

hint to the model developer that generalizing the model might be a
good idea.



What bothers me most are models that have an undocumented
requirement,

run

when that requirement isn't met, but produce incorrect results.
What's the chance that the user notices a problem and does something
about it?
Virtually nil, in my experience.  The models that flatline or crash

(I've

seen both) are actually doing the user a favor.  Better to have no

result

than the wrong one.



No one is suggesting that having a fixed (or limited)
Samples_Per_Bit setting is a good idea.  We're not promoting bad
programming practices; we're trying to ensure good simulation
results.  If others are willing

to

tell system designers to wait while suppliers rewrite algorithmic

models,

great.  Seems silly to me, but maybe their users are more patient
than mine.



Todd.

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