[ibis-macro] Re: Analog Buffer Model Inside DLL

  • From: "Todd Westerhoff" <twesterh@xxxxxxxxxx>
  • To: <Arpad_Muranyi@xxxxxxxxxx>, <ibis-macro@xxxxxxxxxxxxx>
  • Date: Wed, 12 Dec 2012 18:05:50 -0500 (EST)

Arpad,



I think you and I are in agreement:



·         This flow is not supported in IBIS 5.1

·         Subsequent revisions of the spec could consider supporting this



What I’m pointing out is that the approach suggested changes the assumption 
of how analog and algorithmic models are partitioned, which I consider to be 
a fundamental assumption (perhaps THE fundamental assumption) in IBIS-AMI. 
If we revisit that, other solutions are possible. We just  have to be 
pragmatic about the time and cost associated with changing the spec, and 
whether it’s worth it.



Which is, as you correctly note, a separate discussion.



Thanks,



Todd.



Todd Westerhoff

VP, Software Products

Signal Integrity Software Inc. • www.sisoft.com

6 Clock Tower Place • Suite 250 • Maynard, MA 01754

(978) 461-0449 x24  •  twesterh@xxxxxxxxxx



“I want to live like that”

                                             -Sidewalk Prophets



From: ibis-macro-bounce@xxxxxxxxxxxxx 
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Muranyi, Arpad
Sent: Wednesday, December 12, 2012 5:15 PM
To: ibis-macro@xxxxxxxxxxxxx
Subject: [ibis-macro] Re: Analog Buffer Model Inside DLL



Todd,



The original question from Greg was:



“What nasty things are likely to happen if someone puts the analog buffer 
model inside the DLL?

At the very least, the impulse response will be incorrect.  Are there any 
circumstances under

which this can work correctly?



This spawned a bunch of replies ranging from “why not”

to “impossible”, mostly on theoretical bases.  You

may be right that this may not be practical at the

moment, but that’s not what the question was about.



Whether it is worth solving or not could be discussed

in a separate thread.  Who knows, we might find out

that it is worth considering it…



Thanks,



Arpad

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





From: Todd Westerhoff [mailto:twesterh@xxxxxxxxxx]
Sent: Wednesday, December 12, 2012 4:07 PM
To: Muranyi, Arpad
Cc: ibis-macro@xxxxxxxxxxxxx
Subject: Re: [ibis-macro] Re: Analog Buffer Model Inside DLL



... and revisiting one of the fundamental assumptions on which all of 
IBIS-AMI is based.



Which, based on past experience, is expensive, both in terms of time and 
effort.



I therefore assert that this is a problem that isn't worth solving.



Todd.





-- 



Todd Westerhoff

VP, Software Products

SiSoft

6 Clock Tower Place, Suite 250

Maynard, MA 01754

(978) 461-0449 x24

twesterh@xxxxxxxxxx

www.sisoft.com





“I want to live like that"

                                             -Sidewalk Prophets




On Dec 12, 2012, at 5:01 PM, "Muranyi, Arpad" <Arpad_Muranyi@xxxxxxxxxx> 
wrote:

Todd,



I did not suggest that this was possible under the

umbrella of the current v5.1 IBIS specification.



In one of my responses I stated:



“We would also need to revisit the AMI flow a

little bit, but that’s just detail.”



which implies a spec change, as far as I can tell…



Thanks,



Arpad

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



From: Todd Westerhoff [mailto:twesterh@xxxxxxxxxx]
Sent: Wednesday, December 12, 2012 3:56 PM
To: Muranyi, Arpad
Cc: ibis-macro@xxxxxxxxxxxxx
Subject: Re: [ibis-macro] Re: Analog Buffer Model Inside DLL



Arpad,



We have a published spec that says the analog model is to be included in the 
calculation of that channel impulse response.



Anything else is not compliant.



Todd.



-- 



Todd Westerhoff

VP, Software Products

SiSoft

6 Clock Tower Place, Suite 250

Maynard, MA 01754

(978) 461-0449 x24

twesterh@xxxxxxxxxx

www.sisoft.com





“I want to live like that"

                                             -Sidewalk Prophets




On Dec 12, 2012, at 4:21 PM, "Muranyi, Arpad" <Arpad_Muranyi@xxxxxxxxxx> 
wrote:

Todd,



This is not super-theoretical-science in the clouds.



It can be done just as practically and “easily” as the

EQ, DFE and CDR AMI algorithms can be done in the DLL-s.

It involves the same kind of algorithm knowledge, and

programming skill.



The question is, do we want to let model makers to do

this, and possibly get a bunch of bad models from

inexperienced people, or should we, the EDA vendors

still have the opportunity to sell our expertise and

provide higher quality and more reliable solutions to

our customers and AMI model users.



Thanks,



Arpad

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



From: ibis-macro-bounce@xxxxxxxxxxxxx 
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Todd Westerhoff
Sent: Wednesday, December 12, 2012 2:54 PM
To: Dmitriev-Zdorov, Vladimir; 'Gregory R Edlund'
Cc: ibis-macro@xxxxxxxxxxxxx
Subject: [ibis-macro] Re: Analog Buffer Model Inside DLL



Vladimir,



Not clear to me how you propose to handle the reflections associated with 
discontinuities at the point where the TX and RX analog circuits interface 
to the channel.  More importantly, even if it’s theoretically possible, that 
doesn’t make it practical.



I’ll admit I’m guessing here, but I expect Greg wants to solve a problem, 
not just establish that it should be possible to solve it.



Todd.



Todd Westerhoff

VP, Software Products

Signal Integrity Software Inc. • www.sisoft.com

6 Clock Tower Place • Suite 250 • Maynard, MA 01754

(978) 461-0449 x24  •  twesterh@xxxxxxxxxx



“I want to live like that”

                                             -Sidewalk Prophets



From: Dmitriev-Zdorov, Vladimir [mailto:vladimir_dmitriev-zdorov@xxxxxxxxxx]
Sent: Wednesday, December 12, 2012 2:39 PM
To: twesterh@xxxxxxxxxx; 'Gregory R Edlund'
Cc: ibis-macro@xxxxxxxxxxxxx
Subject: RE: [ibis-macro] Re: Analog Buffer Model Inside DLL



In an abstract/theoretical way, it is still possible that AMI DLL correctly 
takes care of the “impulse response” by adding its internal model to it. 
Then however it should not be an ‘impulse response’, but 2- or 4-port 
S-parameters representing the core portion of the channel, which does not 
include analog models. Each model then can ‘append’ its analog part to the 
S-parameters, and restore the resulting impulse response, if needed for 
equalization. Instead of returning the updated impulse response, the Init 
function (or how we call it) will return the updated touchstone file, which 
then is passed to the Rx model, with the same purpose.



The objection here is that Tx must have the complete channel info, with Rx 
analog model,  before its Init function can start thinking about 
equalization, but then ‘appending’ analog models could be either separated 
from Init, and organized as one more function, possibly combined with what 
Fangyi proposed about resolving dependences, or we could still do everything 
in just one function, but perform a few cycles of Initialization, for 
example: (Tx_Init(), Rx_Init()), (Tx_Init(), Rx_Init()) … which resembles 
“backchannel” communication on Init() stage.



Of course, the writer of the AMI model must be able to do some operations 
with touchstone files, such as appending the model to it, and converting it 
into transfer function, finding impulse response by IFFT, etc.



From: ibis-macro-bounce@xxxxxxxxxxxxx 
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Todd Westerhoff
Sent: Wednesday, December 12, 2012 11:51 AM
To: 'Gregory R Edlund'
Cc: ibis-macro@xxxxxxxxxxxxx
Subject: [ibis-macro] Re: Analog Buffer Model Inside DLL



Greg,



Ask yourself how the person writing an algorithmic model should accurately 
model the reflections associated with an unspecified channel.  If there’s a 
way to do that, I’d like to hear about it.



Todd.



Todd Westerhoff

VP, Software Products

Signal Integrity Software Inc. • www.sisoft.com

6 Clock Tower Place • Suite 250 • Maynard, MA 01754

(978) 461-0449 x24  •  twesterh@xxxxxxxxxx



“I want to live like that”

                                             -Sidewalk Prophets



From: Gregory R Edlund [mailto:gedlund@xxxxxxxxxx]
Sent: Wednesday, December 12, 2012 1:41 PM
To: Todd Westerhoff
Cc: ibis-macro@xxxxxxxxxxxxx
Subject: Re: [ibis-macro] Analog Buffer Model Inside DLL



Todd,

Thanks for the response.

So, there are no "mathematical tricks" one can play in the DLL to account 
for the absence of the analog buffer model in the impulse response?  You can 
tell I haven't taken enough time to think this through all the way.  I'm 
having a knee-jerk reaction to a discussion that's going on internally.  8-) 
I'm about to dig into the IBIS 5.1 flow material to support my position.  I 
just wanted to make sure I had my ducks in a row and get some outside 
corroboration.

Anyone else care to chime in?

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



<image001.gif>Todd Westerhoff ---12/12/2012 12:31:11 PM---Greg, That is not 
possible. The analog model, by definition, interacts with the channel and 
must be

From: Todd Westerhoff <twesterh@xxxxxxxxxx>
To: Gregory R Edlund/Rochester/IBM@IBMUS
Cc: "ibis-macro@xxxxxxxxxxxxx" <ibis-macro@xxxxxxxxxxxxx>
Date: 12/12/2012 12:31 PM
Subject: Re: [ibis-macro] Analog Buffer Model Inside DLL

  _____




Greg,

That is not possible. The analog model, by definition, interacts with the 
channel and must be included in the impulse response. The equalization, also 
by definition, is considered to be electrically isolated from the channel 
and is thus represented in the DLL.

Putting the analog model in the DLL violates a fundamental assumption of 
IBIS-AMI. You may get good-looking results, but they will be invalid.

Todd.


-- 

Todd Westerhoff
VP, Software Products
SiSoft
6 Clock Tower Place, Suite 250
Maynard, MA 01754
(978) 461-0449 x24
twesterh@xxxxxxxxxx
www.sisoft.com <http://www.sisoft.com/>


“I want to live like that"
                                             -Sidewalk Prophets


On Dec 12, 2012, at 1:13 PM, Gregory R Edlund <gedlund@xxxxxxxxxx> wrote:


What nasty things are likely to happen if someone puts the analog buffer 
model inside the DLL?  At the very least, the impulse response will be 
incorrect.

Are there any circumstances under which this can work correctly?

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

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