Thread Links Date Links
Thread Prev Thread Next Thread Index Date Prev Date Next Date Index

Clause 48: unaligned 8b10b stream problem


I have a concern about turning off comma detection and not having a timer to indicate no recent commas.
I believe I am looking at this correctly.  Let me know if I am missing something.

If a valid 8b10b stream becomes out of alignment, I believe there is a chance that it would never be realigned.
It may be a statistically rare case, but I thought I would mention it.

Here is the case:
 - The interface is using maximum bandwidth for packets and is only transmitting minimum IPG.
 - A bit slip or bit insertion in the stream happens so that bit alignment is wrong.
 - Many of the valid codewords if shifted by one are still valid; this may not cause Loss of Sync.  D21.5 can be shifted and be fine.  LOSyn takes 4 codeblock violations which consists of 4 codewords.  An occasional codeword violation may not cause Loss of Sync to happen.
 - The IPG codewords shifted would not be valid, but they do not occur often enough (with min IPG) to cause Loss of Sync.  This would only definately cause 6 codeword violations or 2 codeblocks.
 - Since Loss of Sync never happened, the commas would never be detected and the stream would never be realigned.

I have not had a chance to see statistically how many codwords can be shifted and still be valid.  That is an important question.  The next question will be is if that number is ok to not change the state machine.

/Brian Cruikshank

Brian Cruikshank
Mindspeed Techologies
Conexant Systems
5555 Central Ave
Boulder, CO 80301
Phone: (303) 543-2023
Cell:      (303) 641-9528
Fax:      (303) 543-2099
Email: brian.cruikshank@xxxxxxxxxxxxx