Xilinx Virtex UltraScale+ FPGAs User Manual page 111

Table 68: Valid RS-FEC Operating Sub-Modes
FEC_RXn_BYPASS_INDICATION
FEC_RXn_BYPASS_CORRECTION
Sub-mode 1: Full Operation
In this sub-mode, the RS-FEC engine detects and corrects errors. If a codeword with up to 15
symbol errors is received, the errors are corrected. If a codeword with 16 or more symbol errors
is received, the erroneous data is flagged soon after the start of data output.
Sub-mode 2: Error Indication, No Error Correction
In this sub-mode, the RS-FEC engine detects errors but does not correct them. If a codeword
with one or more errors is received, no error correction is attempted, but the erroneous data is
flagged soon after the start of data output.
Sub-mode 3: Error Correction, No Error Indication
In this sub-mode, the RS-FEC engine detects and corrects errors. If a codeword with up to 15
symbol errors is received, the errors are corrected. If a codeword with 16 or more symbol errors
is received, no correction is possible, and the erroneous data is not flagged until after it has been
output.
Usage Model
When FEC is enabled in 50G mode, bit 0 of each RXDATA bus is the first bit received in time,
and bit 159 is the last bit received in time. The RXDATASTART signal is driven High whenever
the RXDATA for the associated slice contains the first 160 bits of a codeword. Output
codewords are always aligned so that bit 0 of a codeword is on bit 0 of the RXDATA bus.
When FEC is enabled in 100G mode, bit 0 of CH0_RXDATA is the first bit received in time, and
bit 159 of CH1_RXDATA is the last bit received in time. The CH0_RXDATASTART signal is driven
High whenever the RXDATA buses contain the first 320 bits of a codeword. Output codewords
are always aligned so that bit 0 of a codeword is on bit 0 of CH0_RXDATA. CH0_RXDATASTART
should be ignored in 100G mode.
The RXDATAISAM signal is driven High alongside RXDATASTART whenever the codeword
received on the associated slice contains an alignment marker. This signal is not active when the
FEC is configured in 50G raw mode. In 100G mode, CH1_RXDATAISAM should be ignored.
UG581 (v1.0) January 4, 2019
Virtex UltraScale+ GTM Transceivers
Control Signal
Chapter 4: Receiver
Sub-Modes
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0 0
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