4.2.4. Link Fault Signaling
If you enable Link Fault Generation Mode in the F-Tile Ethernet Intel® FPGA Hard IP parameter editor, the IP core provides link fault signaling as defined in the IEEE 802.3-2018 IEEE Standard for Ethernet.
The Ethernet MAC includes a Reconciliation Sublayer (RS) located between the MAC and the MII to manage local and remote faults. Link fault signaling on the Ethernet link is disabled by default but can be enabled by bit  of the link_fault_config register. When the link_fault_config register bits [1:0] have the value of 2'b01, link fault signaling is enabled in normal bidirectional mode. In this mode, the local RS TX logic transmits remote fault sequences in case of a local fault and transmits IDLE control words in case of a remote fault.
If you turn on bit  of the link_fault_config register, the IP core conforms to Clause 66 of the IEEE 802.3-2018 IEEE Standard for Ethernet. When link_fault_config[1:0] has the value of 2'b11, the IP core transmits the fault sequence ordered sets in the interpacket gaps according to the clause requirements.
The RS RX logic sets remote_fault_status or local_fault_status to 1 when the RS RX block receives remote fault or local fault sequence ordered sets. When valid data is received in more than 127 columns, the RS RX logic resets the relevant fault status (remote_fault_status or local_fault_status) to 0.
The IEEE standard specifies RS monitoring of RXC<7:0> and RXD<63:0> for Sequence ordered_sets. For more information, refer to Figure 81–9—Link Fault Signaling state diagram and Table 81-5—Sequence ordered_sets in the IEEE 802.3 2018 IEEE Standard for Ethernet. The variable link_fault is set to indicate the value of an RX Sequence ordered_set when four fault_sequences containing the same fault value are received with fault sequences separated by less than 128 columns and with no intervening fault_sequences of different fault values. The variable link_fault is set to OK following any interval of 128 columns not containing a remote fault or local fault Sequence ordered_set.