RELEASED
PMC-Sierra, Inc.
PM9311/2/3/5 ETT1™ CHIP SET
Data Sheet
PMC-2000164
ISSUE 3
ENHANCED TT1™ SWITCH FABRIC
C.2.1.3
Link Errors
If the link has no errors then the Dataslice will always see valid sequences of either six control words or six
data words. In reality, errors will occur. The system designer must be aware of the implications of the
different errors.
•
If a single word is corrupted to map to an illegal 10b word then the Dataslice will set DIR bit 23 and
assert an interrupt signal to the OOB bus. If the error occurs at one of the Dataslices that deals
with the LCS header or magic packets (i.e., Dataslices 0, 1, or 2) then the error is communicated to
the Enhanced Port Processor which will ignore that cell.
•
•
If a word is corrupted to look like another valid word, then this will not be detected, unless it
corrupts the LCS header in which case the header CRC should detect it. If the user payload is
corrupted then the cell will still be carried through the switch to the egress linecard.
The Serdes recognizes the bit sequence 0011111xx as a comma character for byte alignment.
This bit sequence occurs in the K28.5 comma character and it is used for link synchronization as
described above. An error can potentially cause the 0011111xx bit sequence to appear anywhere
in the serial bit stream, causing the Serdes to re-align to the corrupted 0011111xx comma and thus
lose byte synchronization. This condition will cause a sequence of 8B/10B errors to be
encountered by the 8B/10B decoder and the Dataslice will raise the DIR23 decoder error interrupt.
The Serdes should re-acquire lock when the linecard next sends an Idle cell. To prevent fiber
optics bit errors from throwing the Serdes out of byte synchronization the Serdes byte sync enable
pin can be connected to a pin on the Dataslice that is accessible through the OOB. Once the
Serdes has locked onto the right byte boundary software can make sure that the Serdes will no
longer look for the 0011111xx comma character.
•
A subtle yet serious error can occur if an idle cell is corrupted in such a way that the comma
character as programmed in the Dataslice 8B/10B decoder lookup table appears anywhere other
than at the start of the cell or several data words in the same cell are corrupted into valid control
words. This can cause the entire cell to appear as a cell of the other type (data -> Idle or Idle ->
data). While improbable, this can have serious consequences that are discussed in the section on
Channel errors.
C.2.2 Channel
A channel consists of 121links and thus 12 logical Dataslices, each slice dealing with six bytes of the 72
byte cell.
C.2.2.1
Synchronization
Each of the 12 channels carry a part (6-bytes) of the same LCS cell. Although the 12 channels are all
operating at the same frequency, their phase may be offset with respect to each other. In other words, each
Dataslice may receive its 6-byte portion of the cell at a slightly different time from its neighboring Dataslices
on the same switch port. So that the 12 parts of a cell remain intact, and are all switched at the same time,
1. The EPP can support fourteen logical slices (i.e. seven Dataslice chips)
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
333
PMC [ PMC-SIERRA, INC ]
