[ibis-interconn] Updated introduction to the Redriver Flow BIRD

From: Walter Katz <wkatz@xxxxxxxxxx>
To: "IBIS-Interconnect" <ibis-interconn@xxxxxxxxxxxxx>
Date: Fri, 24 Oct 2014 11:44:06 -0400 (EDT)
All,

 

The following is a new introduction to the Redriver Flow BIRD. Please
review.

 

ANALYSIS PATH/DATA THAT LED TO SPECIFICATION:
 

As currently written, the reference flow for a Redriver makes the
incorrect assumption that the downstream Rx equalization is determined
from the downstream Tx and the downstream channel. In order for the
downstream Rx to properly determine its equalization, the impulse response
input to the downstream Rx must also include the impulse response output
of the upstream Rx. The current flow is written because it assumes that
the downstream Tx equalization is determined by the downstream channel. 

 

The proposed revision corrects the Redriver statistical simulation flow.

 

A channel can have one or more Retimer and/or Redriver models between the
Source Tx and the Terminal Rx. This BIRD corrects the flows in sections of
the channel that contain only Redrivers between either the Source Tx or a
Retimer Tx and a the Primary Rx or a Retimer Rx. For the purpose of this
BIRD the Source Tx or Retimer Tx will be called the Upstream Tx, and the
Primary Rx or Retimer Rx will be called the Downstream Rx.
 
In addition, it is assumed that the Upstream Tx is not Adaptive and the
Downstream Rx is Adaptive. Adaptive means that the equalization performed
by the model is a function of its input.
 
The Upstream Tx and the Redriver Tx commonly have Init_Returns_Impulse =
True, and have either GetWave_Exists True or False. Cases where the
Upstream Tx or Redriver Tx(s) have Init_Returns_Impulse = False is not
considered in this BIRD. Cases where the Upstream Tx or the Redriver Tx(s)
have GetWave_Exists False is not specifically addressed in this BIRD,
other than the fact that if a Tx has GetWave_Exists False (with the
assumption that the Tx is not adaptive) the EDA tool can do the function
of the Tx GetWave by inputting a unit impulse response to the Tx AMI_Init
function, the output impulse response will then contain the Tx
equalization and the EDA tool can use this impulse response to emulate the
missing Tx GetWave functionality.
 
The situation for the Rx models is more complex. The Downstream Rx and
Redriver Rx(s) can have Rx Init_Returns_Impulse True and GetWave_Exits
True (Dual Model), Init_Returns_Impulse True and GetWave_Exits False (Init
Only Model), or Init_Returns_Impulse False GetWave_Exits True (GetWave
Only Model). This BIRD is limited to correcting the Statistical Flows when
all of the Rx models have Init_Returns_Impulse True. It should be noted
that Redrivers are often not LTI (e.g. they can amplify and saturate their
input). For this case, if the downstream Rx is Init Only and any of the
upstream Rx models are Dual Model the Time Domain flow is problematic and
is not considered in this BIRD.

 

 

Walter

 

Walter Katz

 <mailto:wkatz@xxxxxxxxxx> wkatz@xxxxxxxxxx

Phone 303.449-2308

Mobile 303.335-6156
[ibis-interconn] Updated introduction to the Redriver Flow BIRD

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