[ibis-macro] Re: Unanswered question from last week.
- From: David Banas <DBanas@xxxxxxxxxx>
- To: Walter Katz <wkatz@xxxxxxxxxx>, "ibis-macro@xxxxxxxxxxxxx" <ibis-macro@xxxxxxxxxxxxx>
- Date: Wed, 16 Apr 2014 16:34:47 +0000
Hi Walter,
Thanks for your response.
Please, see my replies in-line, below.
Thanks,
-db
From: Walter Katz [mailto:wkatz@xxxxxxxxxx]
Sent: Wednesday, April 16, 2014 4:34 AM
To: David Banas; ibis-macro@xxxxxxxxxxxxx
Subject: RE: [ibis-macro] Unanswered question from last week.
David,
Suppose a user sets up a simulation with Tx tap coefficients -.15,.85,0. for
taps -1, 0 and 1 respectively.
[David Banas] Ok.
And then suppose the Tx AMI_Init function changed the tap settings to
-.2,.75,-.05.
[David Banas] I will suppose no such thing. If the user has manually set tap
weights, then he is operating the model in "manual" mode and there should be no
danger of the model changing anything without his knowledge. In the scenario I
was proposing, the user is in complete control of how the Tx model operates. If
he wants to set the taps himself, he uses "manual" mode; if he wants the Tx
model to take a SWAG at it, he uses "auto" mode; if he wants the Tx to
participate in some sort of co-optimization training algorithm, he puts it in
that mode, etc.
There is no requirement in the spec that the Tap parameter be an InOut, so if
it was an In, how does the user know that the tap coefficients have changed?
And if they have changed, what have they changed to? How does the user know how
to program his BIOS to optimize the operation of the channel?
[David Banas] Although I have no objection to changing the type of the tap
weight parameters to InOut, I suppose he could read the simulation log. It
might be reasonable to expect that a model which exerts any control over the
tap weights be expected to report their final values in the msg parameter of
the AMI_Init() call, for instance.
Even if the Tap was InOut, and it reported to the user what the change was the
user is going to get a performance result using -.2,.75,-.05. which will give
him a more open eye at the input to the Rx but a worse eye at the output of the
Rx.
Your response, very importantly, included the following "and if the user has
opted to NOT use the Tx model 'co-opt' mode, but rather to use some 'auto'
feature of the Tx model". So you are saying that the Tx model NEEDS a 'auto
feature that can be turned on and off.
[David Banas] Nope. I'm saying that, if the Tx model happens to offer such an
operational mode to its user as a convenience, then its only obligation is tell
the user what tap weights it set, not the tool.
This is exactly what I said when I said for Redriver Tx and for Tx involved in
co-optimization.
[David Banas] But, I'm suggesting that an "auto" mode might have utility for
the user, completely outside of any re-driver or co-optimization context. It
might just be a nice convenience feature model makers add, in order to assist
their users "narrow the parameter space". And let's, please, be careful about
potentially legislating away a model maker's ability to provide such a
convenience.
I suggested a reserved parameter to turn the Tx self-optimization on and off.
So we either force the user to read the Tx Model users guide to figure this
out, or use a reserved parameter. In any case I believe the user should control
this, and not leave it solely up to the Tx model to make this decision as you
suggested in your question.
[David Banas] On this point (i.e. - The user should be in control of how the
model operates.), I think we're in violent agreement.
Walter
From: David Banas [mailto:DBanas@xxxxxxxxxx]
Sent: Tuesday, April 15, 2014 5:17 PM
To: Walter Katz; ibis-macro@xxxxxxxxxxxxx<mailto:ibis-macro@xxxxxxxxxxxxx>
Subject: RE: [ibis-macro] Unanswered question from last week.
I think my original question is more true to my intended inquiry, than either
alternative you propose.
And, understand that the case I'm envisioning is one in which the user doesn't
want EDA tool driven co-optimization to occur. (Otherwise, he'd do that.)
In such an instance, and if the user has opted to NOT use the Tx model 'co-opt'
mode, but rather to use some 'auto' feature of the Tx model, in which that
model chooses the optimum FIR coefficients based solely upon the channel
impulse response and not expecting to take part in any Tx/Rx co-optimization,
why must the Tx AMI_Init() function alert the EDA tool that it has done so?
(Mike M., that is what you were suggesting; right?)
Thanks,
-db
From: Walter Katz [mailto:wkatz@xxxxxxxxxx]
Sent: Tuesday, April 15, 2014 1:29 PM
To: David Banas; ibis-macro@xxxxxxxxxxxxx<mailto:ibis-macro@xxxxxxxxxxxxx>
Subject: RE: [ibis-macro] Unanswered question from last week.
David,
Your statement is not quite correct. I think the statement should be:
Why must the Tx .ami file tell the EDA tool, if it assisted the user in
choosing "optimum" tap weights?
or
Why must the Tx .ami file tell allow the EDA tool to tell the Tx AMI_Init() to
assist the user in choosing "optimum" tap weights?
The reason for letting the EDA tool know what the Tx AMI_Init() function is
doing (or controlling what the Tx AMI_Init() function is doing is important in
co-optimization, particularly in the statistical flow. The Rx AMI_Init needs to
know the Tx equalization used to generate the input to the Rx AMI_Init, and
when the Rx AMI_Init returns an optimized Tx tap coefficients, the Tx AMI_Init
function needs to be called with these coefficients, and the Tx AMI_Init must
use the equalization for these tap coefficients.
Does this answer your question?
Walter
From: ibis-macro-bounce@xxxxxxxxxxxxx<mailto:ibis-macro-bounce@xxxxxxxxxxxxx>
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of David Banas
Sent: Tuesday, April 15, 2014 2:30 PM
To: ibis-macro@xxxxxxxxxxxxx<mailto:ibis-macro@xxxxxxxxxxxxx>
Subject: [ibis-macro] Unanswered question from last week.
Hi all,
I asked a question, at the end of Walter's presentation last week, which I
don't think was ever answered. So, I'd like to ask it, again:
Why must the Tx AMI_Init() function tell the EDA tool, if it assisted the user
in choosing "optimum" tap weights?
(How, for instance, is this use case different than the user relying on, say,
MATLAB to help him find optimum tap weights and setting those MATLAB-prescribed
values in the AMI model, by hand?)
Thanks,
-db
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