In transcode bypass mode, a subset of the statistics outputs defined in Table: Common Ports are generated regardless of the chosen sub-mode. The statistics and flags that pertain to the functioning of the alignment and deskew logic (the AM lock signals, lane alignment status, FIFO fill levels and lane mapping) are not valid in this mode. The symbol error counts for lanes 1, 2 and 3 are not valid; all symbol errors are counted instead on the lane 0 output. The statistics and flags related to the RS decoder are valid in this mode.
The codeword increment flags are interpreted differently in transcode bypass mode than in normal mode. This is to allow the user to distinguish between a codeword that could have been corrected and a codeword that could not have been corrected when operating in a sub-mode where correction is disabled.
In 802.3bj and other standards, it is common to use the presence of consecutive uncorrectable codewords to trigger a loss of alignment event. When error correction is disabled, any codeword with errors is reported as an uncorrected codeword. Using the uncorrected codeword flag to detect loss of alignment in this case results in an unacceptably low BER threshold for alignment loss. Therefore an additional pair of codeword conditions are reported on these signals when transcode bypass mode is active, to allow the implementation of such an algorithm.
For each codeword processed by the decoder, the corrected_cw_inc and uncorrected_cw_inc signals might therefore be High twice, once, or not at all. This behavior is irrespective of the error correction sub-mode setting.
To count codewords that were corrected by the RS-FEC decoder, the corrected_cw_inc output should be combined with the cw_inc output using an AND operation to provide a qualified counter increment signal. Similarly, to count codewords that were not corrected, the uncorrected_cw_inc output should be combined with the cw_inc output in the same manner.
The codeword statistics flags ( stat_rx_rsfec*_cw_inc ) output from the RS-FEC engine in transcode bypass mode should be interpreted as per Table: RS-FEC Engine in Transcode Bypass Mode .