64b/66b Synchronization / state machines
Hi Pat,
I was hoping you could shed some light on some questions I've been
having.
In reading clause 49 of D1.1 and comparing it to D1.0 I have noticed
that there is no longer a variable called sync_done. My main question
deals with D1.0 Fig 49-11 and D1.1 Fig 49-12 (i.e: The Receive state
machine). In D1.0, the criteria for going through the machine was that
sync_done = true. In the newer version, this has been reduced to
frame_lock = true. sync_done was defined as being = frame_lock *
!hi_ber. So, my question is why has the BER monitoring been removed as a
condition for the receive state machine? Is it that if there is a high
BER (>16 in ~125us) but we can still maintain frame_lock we don't care
about the BER and just continue doing our sequence monitoring? (Then why
monitor the BER at all?)
Another question I have is why the Transmit state machine was given the
3-bit error protection similar to the RX side (dealing with the D -> T).
I'm just curious why this was only put in now. Is it that we can't rely
on the XGMII being virtually fault free? (I think this was the original
reason why it wasn't in the first TX state machine)
Thanks,
-Dave
David Gross
Nortel Networks