[ibis-macro] Re: Back-channel BIRD discussion
- From: Kumar Keshavan <ckumar@xxxxxxxxxxx>
- To: "wkatz@xxxxxxxxxx" <wkatz@xxxxxxxxxx>, "Dmitriev-Zdorov, Vladimir" <vladimir_dmitriev-zdorov@xxxxxxxxxx>, "ibis-macro@xxxxxxxxxxxxx" <ibis-macro@xxxxxxxxxxxxx>
- Date: Tue, 8 Apr 2014 14:06:27 -0700
while some standards (i22 802.3) specifies particular training pattern (prbs
11) others like pcix do not.
Most modern devices are multi standard and the rx is robust enough and iare
designed to be not predicated and dependent on particular training pattern.
From: ibis-macro-bounce@xxxxxxxxxxxxx [ibis-macro-bounce@xxxxxxxxxxxxx] On
Behalf Of Walter Katz [wkatz@xxxxxxxxxx]
Sent: Tuesday, April 08, 2014 4:39 PM
To: Dmitriev-Zdorov, Vladimir; ibis-macro@xxxxxxxxxxxxx
Subject: [ibis-macro] Re: Back-channel BIRD discussion
Vladimir,
First, the Tx Init must be called to get the correct amplitude of the Impulse
Response (Tx Peak to Peak Voltage), and some high frequency affects (details on
the shape of the eye). Tx Peak to Peak voltages are programmable in each
standard and can range by as much as 50%.
Second, it depends on what you mean by “Rx training”. If you want the Rx
training to emulate the standard (and the silicon implementation of the
standard), then the Rx would need to know the PRBS pattern to use. If the IC
vendor chose to use Rx Init to implement this training pattern and “time domain
simulation”, then it would need that pattern hard coded in the DLL, or it would
need to be specified in a Usage In parameter. But it is also true that training
can be done with any reasonable input. If the Tx has 3 FFE taps, and the Rx has
4 DFE taps, then any PRBS7 would probably be reasonable enough. (Note that when
I describe an Rx as having 4 DFE taps, I am really saying that it can optimize
internally 4UI of the impulse response, not that it represent DFE equalization
specifically.
Walter
From: Dmitriev-Zdorov, Vladimir [mailto:vladimir_dmitriev-zdorov@xxxxxxxxxx]
Sent: Tuesday, April 08, 2014 4:22 PM
To: ibis-macro@xxxxxxxxxxxxx
Cc: wkatz@xxxxxxxxxx
Subject: Back-channel BIRD discussion
Hi Walter,
A couple comments/questions about the presentation.
I agree that Rx optimization (e.g. made in INIT) can do almost everything since
Rx knows the channel’s response. If Rx were to know how to set Tx equalization,
it could find the optimal tap coefficients and send them to Tx. This statement
remains true regardless of the backchannel support. Therefore there is a
question. Why in our regular flow we call Tx INIT prior to Rx INIT? Maybe we
should allow Rx INIT be first? Then, it can update impulse response
accordingly. If we have a mechanism to pass tap values from Rx to Tx, that’s
fine. If we don’t, then Tx can receive the impulse response modified by Rx
optimization and do the best it can.
Second is about making BCI file a property of Rx, a tempting idea, considering
that in the current BIRD BCI file should be read/understood by Tx, Rx and EDA
tool. The last is required in the current spec to allow EDA tool to generate
the training pattern, as required by the protocol. Making your proposal, do you
mean that Rx training can be made on any reasonable input, not only by that
specified by the back-channel communication protocol?
Vladimir
From: ibis-macro-bounce@xxxxxxxxxxxxx<mailto:ibis-macro-bounce@xxxxxxxxxxxxx>
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Ambrish Varma
Sent: Wednesday, April 02, 2014 6:56 AM
To: ibis-macro@xxxxxxxxxxxxx<mailto:ibis-macro@xxxxxxxxxxxxx>
Subject: [ibis-macro] Revised Backchannel BIRD
Hi All,
The latest version of the Backchannel BIRD (draft 8) has been uploaded on the
ATM website and is available here:
http://www.vhdl.org/ibis/macromodel_wip/archive/20140401/ambrishvarma/Backchannel%20support%20BIRD%20147%20draft%208/Backchannel_BIRD147_Draft8.docx
Or
http://tinyurl.com/o8cqyqr
This is the version that was discussed at the 04/01/2014 ATM and includes
support for AMI_Init/Statistical Backchannel training.
Please let me know if there are any questions.
Thanks,
Ambrish.
Ambrish Varma.
Cadence Design Systems.
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