RE: [10GBASE-CX4] Signal Detect - Proposed Text & Figures
Hi Dan,
A few points I'd like to clarify.
1. Missing definitions
-On 15m IB cable, the signal will be sometimes well below 125mvpp
(instantaneously) hence there should be a low pass definition, in terms of
poles/zeroes or multipliers. My understanding is that the figure describes
the signal envelope rather than the signal itself -so one way to
implement it is using an envelope detector.
- There should be some tolerance given for the analog voltages -
analog designers may have a fit with this definition.
2. Questions
Supposing that there is a CX4 signal at 50mvp2p envelope and the
receiver correctly decodes it
(but it doesn't pass the proposed signal detect) - whould you want
the receiver to disregard its input ?
-The IEEE XAUI standard does not define / use the signal detect
function - why should CX4 have it ?
- You can add the comparators either directly to the input therby
increasing the input capacitance and degrading performance,
or they can be added after the equalizer which probably will have a
gain and cause alot of headache to the designers.
As a result, not all XAUI chips will be CX4 compatible and will
require
3. Is the proposed Signal Detector really needed ?
-The XAUI standard provides couple of data validity guard bands:
-PCS SYNC machine checks for a certain pattern
-Alignment machine checks for Alignment validity
-PCS layer checks validity of framing and XAUI protocol
-PCS produces IDLES as long as there is not a valid XAUI
frame
These can be combined to yield an alternative "logical" signal
detect.
In this case we'll need to define in the conformance tests a
proceedure for ensuring that the receiver sensitivity is sufficient.
Thanks,
Ze'ev
-----Original Message-----
From: DOVE,DANIEL J (HP-Roseville,ex1) [mailto:dan.dove@hp.com]
Sent: Wednesday, January 29, 2003 9:19 PM
To: 10GBASE-CX4 (E-mail)
Subject: [10GBASE-CX4] Signal Detect - Proposed Text & Figures
Hi all,
After some review and comment, I have updated the proposed document.
Note; one big issue was that we need timing specs, but did not want to make
them so tight that they could not be read through the MII Management
Interface.
Otherwise, we would be forcing a hardware pin to ensure measureability.
Also, the amplitude numbers have been adjusted to achieve a reasonable
implementation requirement for the SIGNAL_DETECT comparators.
We still need to confirm the numbers and consider the text/figures, but I am
proposing that barring any major objections, Howard should incorporate this
into his working paper presentation.
If you have a concern about that, please contact me or use the reflector
to express your opinion.
Regards,
Dan
======================================
Principal Engineer, LAN PHY Technology
System Architect, Workgroup Switching
dan.dove@hp.com
hp ProCurve Networking Business
8000 Foothills Blvd. MS 5555
Roseville, CA 95747-5555
Phone: 916 785 4187
Fax : 916 785 1815
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<<SIGNAL_DETECT3.pdf>>