RE: D1.1 Clause 49 State Machine comments, part 2.
Alex,
The answer to your first set of questions was covered in the July proposal.
To get hamming distance on the end delimiter of the packet, you need to
check that both the block with the T and the block after it are appropriate.
Otherwise, a two bit error could change a data block to a control block
with one of the T type codes. If an error changed a data block into a
false T, then the next block would have been a D or a T. It takes another
at least two bit error to turn that block into an S or a C so we have a
4 bit hamming distance.
On S, we get the equivalent check by only allowing a transition to S when
the last block was T or C. If an S occurs after a D, S or E, then we
transtion
to E.
None of this is new. The notation for it was different in the state diagrams
from the proposal. Instead of checking next, they showed a delay of the
output
and sent the E when they received a D or T after a T. I changed to this
because
it is more consistant with the way that the check of the next code was done
after T in 1 Gig and I felt it was easier to understand.
I changed Z to C because XGMII calls these control not Z so it didn't seem
right for a PCS to start calling XGMII characters by a name like Z. Also,
it doesn't matter that the encoding of a character is different on one
medium from the encoding on another. The character still retains its
meaning.
For instance, the character /E/ is represented by a control bit plus 8 bits
containing 0xFE on XGMII, by 10 bits containing K30.7 (which is 011110 1000
or 100001 0111) on XAUI and X PCS, and by 7 bits containing 0x1e on R PCS;
but on all of them it is /E/. The control character, meaning the information
it is carrying, doesn't change but its representation changes. Therefore,
it still has its name.
Pat
-----Original Message-----
From: Alex Deng [mailto:adeng@xxxxxxxxx]
Sent: Thursday, November 02, 2000 2:35 PM
To: pat_thaler@xxxxxxxxxxx
Cc: stds-802-3-hssg@xxxxxxxx; Alex Deng; Sharat Prasad
Subject: D1.1 Clause 49 State Machine comments, part 2.
Hi Pat,
One more question:
Figure 49-11 --Transmit state machine:
Could you please explain a little bit about
when (T_TYPE(tx_raw)=T, why do you need to see if (T_TYPE_NEXT=(E+D+T))?
If you need to do this stuff to T, then I think you should do the same stuff
to
S, that means:
when(T_TYPE(tx_raw)=S, you need to see if (T_TYPE_NEXT=(E+S+T)), right?
The similar question apply to Figure 49-12--Receive state machine.
By the way, Figure 49-5 --64b/66b Block Formats:
The Input Data side, I think it's better to use "Z0,...Z7", not "C0,...C7",
just
like what in your
July's presentation, because C0 in Input Data side and C0 in Block Payload
side
are different,
but "D0,...D7" are same.
Regards,
--Alex Deng