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Re: [802.3_ISAAC] Clock Recovery Function



Hi George,

 

Good job cleaning up the diagrams to represent what is really happening. 

I recommend that we implement what you suggested before the WG to get the diagrams and descriptions

as accurate as possible. The changes looks good to me as it is written.

 

Thanks,

William

 

 

From: George Zimmerman <george@xxxxxxxxxxxxxxxxxxxx>
Sent: Tuesday, April 7, 2026 8:33 PM
To: STDS-802-3-ISAAC@xxxxxxxxxxxxxxxxx
Subject: [802.3_ISAAC] Clock Recovery Function

 

The notes at the bottom of Figures 201-3, 201-4, and 201-25 have been vexing us in comments and have spurred me to look into the definition of the clock recovery function.  The reality is that the description is kind of messed up, and has been for a very long time.  Our PHYs recover clock within PMA receive and use that to sample the received signal.  We may or may not use that for transmission, depending on whether we are loop-timed.

 

If we can get quick consensus on this, I would like to enter it as a late comment, on clause 201.  If not, I will quickly withdraw it and you can contact me to work any issues for initial WG ballot.

 

The comment would be:

Clock Recovery is actually a function within PMA Receive.  Loop timing is accomplished when we generate a transmit clock.  This has been a long-standing error in 802.3 standards, since clause 40.  Asymmetric functionality has added new functionality to clock recovery, and requires we fix this.

 

The General description changes the name of the Clock Recovery function (and block in block diagrams 201-3, 201-4, and 201-25) to TX Clock Generation, changes the names of the signals to recovered_rx_clock (from PMA Receive) and tx_symbol_clock (to PMA Transmit), and changes the text and title of 201.5.2.9 Clock Recovery function to TX Clock Generation function, with an appropriate description.  Other ancillary mentions of the blocks and signals are changed in the text as well.

 

See attached proposal.

 

Again, we have lots of work to do – if we don’t have quick consensus, I’ll withdraw this and wait, working offline. 

Note – I will be offline much of the day tomorrow for personal reasons.  Don’t expect lengthy (or necessarily quick) replies.

 

-george

 

George Zimmerman, Ph.D.

President & Principal

CME Consulting, Inc.

Experts in Advanced PHYsical Communications

george@xxxxxxxxxxxxxxxxxxxx

310-920-3860

 


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