[ibis-macro] Re: AMI_Flows_6.pdf for today's ATM teleconference

  • From: "Muranyi, Arpad" <Arpad_Muranyi@xxxxxxxxxx>
  • To: "IBIS-ATM" <ibis-macro@xxxxxxxxxxxxx>
  • Date: Wed, 21 Apr 2010 21:35:12 -0700

Ambrish,
 
So is my understanding of what you are saying correct if I
summarize it this way:
 
You are only asking a different VISUAL representation of the
flow to accentuate the two separate paths, but the flow is
actually correct as I drew it for the presentation yesterday
(except for the question that follows)?
 
A (minor) detail question about your PDF attachment.
 
On the left side, the Stateye flow, you took out the
Tx Use_Init_Output Boolean.  Did you mean this, or is this
omission just part of the "crude representation" of the
flow (as you put it)?  If you meant it, do you mean to 
say that we should assume that this Boolean is always
True for the Stateye flow whether it says False in the
.ami file or not?  In other words, are you suggesting 
that this Boolean should only be meaningful for the TD
flow, otherwise it should be assumed to be True?
 
Thanks,
 
Arpad
==============================================================

________________________________

From: ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Ambrish Varma
Sent: Wednesday, April 21, 2010 11:08 PM
To: IBIS-ATM
Subject: [ibis-macro] Re: AMI_Flows_6.pdf for today's ATM teleconference



Arpad,

Your observations are correct. Use_Init_Output does allow the model
maker to have effectively the same algorithms in Init and Getwave. It's
a case of 'can' and 'should' as you pointed out in one of your earlier
mails. I keep pointing out to you the intent of section 2.1 and 2.2 and
the default value in the definition of Use_Init_Output and not the
possibilities. This is how I understand what the intent was: in section
2.1, we don't need a getwave, why - because init was necessary and
sufficient. In section 2.2, however, we do need a getwave - why -
because Init is NOT sufficient. 

But - as you said, we did leave the door open ...

 

When I wrote to you about separating the TD flow and the Stateye flow -
I meant separating it visually, in your slides - to fix the issue Walter
pointed out yesterday. Basically when the user wants a Stateye type
simulation, the EDA tool takes into account only Init and is done. The
path would look like this:

Obtain Channel Impulse Response (hAC(t)) --> Tx_Init call (hAC(t) x
hTEI(t))--> Rx_Init call (hAC(t) x hTEI(t) x hREI(t)) --> Stateye type
analysis. 

 

What you have already in the slide can be kept as is for TD simulation.
I have attached a crude representation.

 

Thanks,

-Ambrish.

 

________________________________

From: ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Muranyi, Arpad
Sent: Wednesday, April 21, 2010 7:24 PM
To: IBIS-ATM
Subject: [ibis-macro] Re: AMI_Flows_6.pdf for today's ATM teleconference

 

Ambrish,

 

I would like to see how you came to the conclusion that

"If you separate the Stateye flow with the TD flow, we will have what
the spec says currently".

 

I re-read the spec once again to find out how you came to that

conclusion, but my reading resulted in the opposite conclusion.

 

1)  pg. 181, 2.1 Linear, Time-invariant Equalization Model:

 

 

 

This implies (although not stated), that for the LTI (or Stateye) flow

the Init_Returns_Impulse Boolean must be set to true.

 

2)  On pg.182, 2.2 Nonlinear, and / or Time-variant Equalization Model 

    I read the following:

 

 

 

This is now talking about the non-LTI flow.  Note that it says that

"AMI_Init may also compute the impulse response of the block...".  

This means that the Init function can still return a modified impulse

response even if we are doing a non-LTI analysis with GetWave.

 

3)  pg. 144, GetWave_Exists says:

 

 

 

Note that is says "if Init_Returns_Impulse is set to "False"..."
basically

GetWave must exist.  This means that the only time Init is allowed not
to

return a modified impulse response is when we do a non-LTI analysis with

GetWave.  But notice that it doesn't say that if GetWave exits,
Init_Returns_Impulse

must be False, or in other words, it doesn't say that when we are ding a

non-LTI analysis with GetWave, the Init function is not allowed to
calculate

a modified impulse response.

 

There are several things we can conclude from this:

 

- if the Init function doesn't calculate the modified impulse response,

GetWave will have to include the algorithm to do that calculation

 

- the spec doesn't say anything that this algorithm may not be
duplicated

in the Init and GetWave functions, i.e. this duplication is not
forbidden

 

- this means that the model writer has a choice to put the algorithm 

that is responsible for calculating the modified impulse response into

either the Init or the GetWave function or both

 

- if there is a duplication of this algorithm in both Init and GetWave,

the model maker may set Use_Init_Output to False so that double counting

is prevented in the results

 

- with this approach one can build a parallel path for the LTI (or
Stateye)

and non-LTI (or TD) calculations within the same model without the
danger

of double counting for any effects

 

 

Clearly, the authors of the specification left it up to the model maker

to decide whether the modified impulse response is calculated in the

Init or the GetWave function or both.  One approach could be to "factor

it out" and put the LTI part of the algorithm into the Init function and

put the non-LTI portions of the algorithm into the GetWave function,

but one could also put the entire thing into the GetWave function and 

have a duplicate LTI algorithm or a similar LTI approximation in the

Init function.

 

This is what I am reading from the EXISTING specification.  I would like

to get a similar detailed analysis from you that explains how you
arrived

to the opposite conclusions based on the current specification.  I am
not

asking this to give you a hard time, I am making this request to find
out

why the existing specification can be interpreted in such completely

different ways so that we can fix the spec and eliminate the
possibilities

for such misinterpretations in the future.

 

Thanks,

 

Arpad

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

 

 

________________________________

From: Ambrish Varma [mailto:ambrishv@xxxxxxxxxxx] 
Sent: Wednesday, April 21, 2010 3:52 PM
To: Muranyi, Arpad
Subject: RE: [ibis-macro] Re: AMI_Flows_6.pdf for today's ATM
teleconference

Arpad,

If you separate the Stateye flow with the TD flow, we will have what the
spec says currently. I think the issue with what you had yesterday was
the mixing of the 2 flows together.

Let me know if you want me to elaborate. 

-Ambrish.

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