[802.3ae_Serial] RE: CRPAT / CJPAT Pattern Question
This thread never really completed, so here is the suggested remedy I am
submitting with my letter ballot:
Time-stagger the payload portion of the patterns in the
lanes. I propose the staggering for CJPAT be such that lanes 0 & 2
remain as they are, but lanes 1 & 3 rotate 140 bytes each. This will
retain the special properties of this pattern within each lane.
I suggest CRPAT be rotated 3 bytes (~90 degrees per
repetition) per lane, although I have another comment that suggests
CRPAT has other potentially serious issues, and this change may cause
worse problems.
I THINK this addresses the thread, but I expect others will correct me
as appropriate. The suggested remedy does NOT invert the data (this is
not possible with 8B10B), but does attempt to provide a compromised
"mixing" of edges and frequencies.
*****
The "other" comment about CRPAT is
CRPAT may not meet its objectives of randomness unless disparity is
controlled (on each lane) as is done in Fibre Channel. However, this may
not be important, since this pattern is not referenced by other sections
of the standard.
The suggested remedy is
Option A: Delete section 48A.4.
Option B: Build up the pattern like CJPAT is where both disparities of
the pattern will exist, assuring that one is always correct. This would
take a few hours of effort.
Option C: Convince me that disparity is controlled such that the payload
portion starts positive.
Option D: Add a statement "The intended spectral density of this pattern
may not be achieved unless the ending running disparity of
START/PREAMBLE/SFD is controlled to be positive.
If option B, C, or D is chosen, then also add a note explaining that
"this pattern is not intended for compliance testing, but it may useful
for unspecified diagnostic purposes."
*****
Tom Lindsay
Stratos
-----Original Message-----
From: DAmbrosia, John F
Sent: Fri 6/15/2001 9:51 AM
To: Lindsay, Tom; Mike Jenkins
Cc: stds-802-3-hssg-serialpmd@ieee.org
Subject: RE: CRPAT / CJPAT Pattern Question
Tom,
Slipping by any number of bits would be preferrable.
i am thinking about any type of testing that would use the CJPAT
or CRPAT.
You could have this type of phenomenon happen on board level
testing.
John
-----Original Message-----
From: Lindsay, Tom [ mailto:tlindsay@stratoslightwave.com]
Sent: Friday, June 15, 2001 12:21 PM
To: DAmbrosia, John F; Mike Jenkins
Cc: stds-802-3-hssg-serialpmd@ieee.org
Subject: RE: CRPAT / CJPAT Pattern Question
John -
I just sent a note before I saw this.
Given the restrictions of 8B10B, slipping the pattern by a bit
is not
possible. It could easily be slipped by as little as 1 byte (10
bits),
but without disparity control, you may still not get the same
serial
pattern.
A basic question - are you thinking of a board level test or a
system
compliance test?
Tom
-----Original Message-----
From: DAmbrosia, John F [
mailto:john.dambrosia@tycoelectronics.com]
Sent: Friday, June 15, 2001 8:35 AM
To: 'Mike Jenkins'
Cc: stds-802-3-hssg-serialpmd@ieee.org
Subject: RE: CRPAT / CJPAT Pattern Question
Everyone,
THere are multiple issues here, so let me try to go through it
again. I
think we may be at a point where it is really an "implication "
thing
that
we can only try to inform about.
I would like to refer everyone to the presentation that was
given in St.
Louis -
http://grouper.ieee.org/groups/802/3/ae/public/may01/dambrosia_2_0501.pd
f
There are two aspects to the crosstalk analysis. The first part
looked
at
the noise values (both near and far-end)created in the HM-Zd
connector.
During this analysis worst-case switching patterns, intended to
maximize
the
amount of crosstalk, were used. You can see, how the worst case
switching
would be dependent on the connector pinout.
In the second part of the presentation, we ran a system
simulation of
the
XAUI channel. We used one pinout and either switched signals in
phase
or
out of phase with the signal under consideration. When adjacent
signals
are
switched in-phase, the overall performance of the system was
better than
when no adjacent signals were switched or when they were
switched out of
phase. In our simulation we assumed a bottom layer connection
(i.e.
traces
go through the via to the bottom layer). When assuming a top
layer
connection, this affect is even more dramatic.
So it was my concern that crosstalk between the 4 lanes in a
single
channel
would result in artifically improved performance, which would
improve
overall measured performance in a system environment where other
crosstalk
sources are then be factored in.
Perhaps another suggestion is to use the same data pattern for
each
lane,
but delay each by a bit? We can leverage off of CRPAT and
CJPAT, which
were
intended to test jitter, and include potential crosstalk
effects. I
don't
think a PRBS pattern will stress the jitter performance, since
this is
what
CJPAT is intended to do, right?
John
-----Original Message-----
From: Mike Jenkins [ mailto:jenkins@lsil.com]
Sent: Thursday, June 14, 2001 10:19 PM
Cc: stds-802-3-hssg-serialpmd@ieee.org
Subject: Re: CRPAT / CJPAT Pattern Question
All,
I want to step back a second to point out what this conversation
is aimed at. Changing the pattern on three lanes to see the
effect
at the receiver of the 4th lane is manipulating far-end
crosstalk
(FEXT). FEXT is much smaller than near-end crosstalk (NEXT)
because
the inductive and capacitive components subtract in FEXT but add
in NEXT. The NEXT for a receiver is created by the transmitters
in the same device as the receiver under test. If these
transmitters
are sending CRPAT (or whatever) asynchronously, all possible
combinations will occur to close the receiver eye.
Extraordinary
efforts to manipulate FEXT are probably for relatively rather
small
returns in additional eye closure.
Regards,
Mike
pat_thaler@agilent.com wrote:
>
> Michael,
>
> >From my experience testing crosstalk, single frequency
stimulus
signals
> would not be an effective way of testing crosstalk. Generally,
the
received
> crosstalk from a disturber such as an adjacent signal path is
the sum
of
> many crosstalk components each coupling in with its own phase.
Because
of
> this, the crosstalk is not a smooth function with frequency.
It
bounces
> around staying under an envelope where the envelope is the
amplitude
you
get
> when all the components add in phase. Therefore, testing
crosstalk at
a
few
> discrete frequencies doesn't tell you much about where the
envelope
lies.
>
> Generally one wants to test crosstalk with a signal containing
a broad
> spectrum of frequencies (e.g. CRPAT or even the normal idle
signal
since
we
> designed that to spread energy across the spectrum). One of
the
reasons
put
> forth in favor of having individual lane disables was that one
could
test
> crosstalk from one lane by disabling the other transmitters.
Therefore, we
> don't need to do any special patterns for crosstalk
measurement.
>
> Pat
>
> -----Original Message-----
> From: Michael Debie [ mailto:mdebie@wavecrest.com]
> Sent: Thursday, June 14, 2001 9:47 AM
> To: 'DAmbrosia, John F'; Michael Debie; 'Serial PMD reflector
(E-mail)'
> Subject: RE: CRPAT / CJPAT Pattern Question
>
> John,
>
> Absolutely agree. I was just simplifying my description to
one lane,
but,
I
> assumed we would test each lane individually. As far as the
pattern
> selection is concerned, the use of different patterns on each
lane
allows
us
> to see the contribution each of the other lanes has on cross
talk
noise.
> For example, suppose Lane 1 was driving a /5 clock like
pattern
(1111100000)
> the FFT of the jitter on the Lane under test would show a
spectral
line at
> Fc/10 and the amplitude of the spectral line would be the
pk-pk impact
on
DJ
> that Lane 1 has on the Lane Under Test (LUT?). We could set up
the
other 3
> lanes with varying degrees of clock like patterns and quickly
estimate
each
> lanes contribution to crosstalk on the LUT. We could perform
this
test on
> all 4 lanes to measure crosstalk contribution. It would also
be
interesting
> to sweep through several clock like frequencies on the non
tested
lanes to
> quantify the impact of crosstalk as a function of
instantaneous
frequency.
> The test in which we apply the same pattern on all of the non
tested
lanes
> will tell us how the crosstalk components combine.
>
> Regards,
> Michael
> -----Original Message-----
> From: DAmbrosia, John F [
mailto:john.dambrosia@tycoelectronics.com]
> Sent: Thursday, June 14, 2001 9:11 AM
> To: 'Michael Debie'; 'Serial PMD reflector (E-mail)'
> Subject: RE: CRPAT / CJPAT Pattern Question
>
> Michael,
> I think your second proposal makes more sense, but i think it
would
need
to
> go one step further. I think we should cycle which lane is
the
"different"
> lane like this-
>
> Pat 1A Pat 1B Pat 1C Pat 1D
> Lane A + - - -
> Lane B - + - -
> Lane C - - + -
> Lane D - - - +
>
> Where the "+" lane would be the pattern, and the "-" would be
the
> compliment. Thus, all channels get examined. If only 1 lane
is
tested,
> then the test is specific to the implemenation, where if all
lanes in
a
> channel get examined, then the performance of the channel is
fully
examined
> rather than 1/4 of it.
>
> John
>
> -----Original Message-----
> From: Michael Debie [ mailto:mdebie@wavecrest.com]
> Sent: Wednesday, June 13, 2001 5:41 PM
> To: DAmbrosia, John F
> Subject: RE: CRPAT / CJPAT Pattern Question
>
> John,
>
> A good diagnostic for cross talk would be to place different
frequency
clock
> like patterns on all of the lanes. This could tell us the
amplitude
of
> cross talk per other lane and where it comes from. Also, if
we run
the
same
> patterns on three lanes and one lane different, we could see
how the
other
> three lanes combine to effect cross talk on the lane under
test.
>
> Regards,
> m
>
> -----Original Message-----
> From: DAmbrosia, John F [
mailto:john.dambrosia@tycoelectronics.com]
> Sent: Wednesday, June 13, 2001 4:21 PM
> To: Serial PMD reflector (E-mail)
> Subject: CRPAT / CJPAT Pattern Question
>
> Everyone,
> The 10GEA XAUI Interoperability Group met this week, and were
discussing
the
> use of the CRPAT / CJPAT patterns for its testing. A general
observation
> was that the same data pattern appear on all 4 lanes
synchronously,
which
> means crosstalk is not really being testing, which was
probably being
> accounted for by connector crosstalk budget of 4%. Tyco
presented
data
>
http://grouper.ieee.org/groups/802/3/ae/public/may01/dambrosia_2_0501.pd
f
> that showed that crosstalk, which resulted from signals
switching
in-phase
> (i.e. high to low or low to high), could actually improve the
overall
> response of the system. Thus, the resultant eye is improved
and would
be
> best case, and not even nominal (all adjacent channels quiet).
>
> Obviously, there are a lot of system variables that come into
account
when
> considering crosstalk, but it would seem that we could improve
the
harshness
> of these patterns by not making all 4 channels have the same
data
patterns.
>
> John D'Ambrosia
> Manager, Semiconductor Relations
> Tyco Electronics Corporation
>
> Tel. 717.986.5692
> Mobile 717.979.9679
>
> email - john.dambrosia@tycoelectronics.com
>
>
--
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