1.3.1.1 Word Alignment (Byte Boundary or Comma Detect)
(Ask a Question)The 8b10b PCS block performs the comma code-word detection and alignment operation. The comma character is used by the receive logic to align the incoming data stream into 10-bit words. The alignment comma descriptions (K28.1, K28.5, and K28.7) are defined in section 36.2.4.9 of the IEEE 802.3.2002.
A comma is identified when there is a match across any eight consecutive bits to {00111110} or {11000001} patterns. The only legal 10b characters, which contain series of bits are K28.1, K28.5, and K28.7. In 802.3 specification definition, there is no occurrence of two legal 10b characters sent in a sequence containing the comma pattern, which drastically reduces the chance that a symbol aligner can falsely lock. Alignment status per lane is indicated by the LANE#_RX_VAL output pin going to high only after the PMA CDR locks onto an incoming data stream.
Word Aligner can lock onto an incorrect alignment causing disparity errors and/or code violations from the 8b10b decoder. In this case, the word aligner needs to be reset to find a new alignment. This can be done by using the PCS_ARST_N reset. The fabric logic needs to monitor the LANE#_RX_CODE_VIOLATION and LANE#_RX_DISPERROR to determine when to issue a PCS_ARST_N and find a new alignment.