Low Latency E-Tile 40G Ethernet Intel® FPGA IP User Guide

ID 683486
Date 8/31/2021
Public
Document Table of Contents

4.1.3. Link Fault Signaling Interface

Link fault signaling reflects the health of the link. It operates between the remote Ethernet device Reconciliation Sublayer (RS) and the local Ethernet device RS. The link fault modules communicate status during the interframe period.
For unidirectional fault signaling, the core implements Clause 66 of the IEEE 802.3-2012 Ethernet Standard.

Local Fault (LF)

If an Ethernet PHY sublayer detects a fault that makes the link unreliable, it notifies the RS of the local fault condition. If unidirectional is not enabled, the core follows Clause 46. The RS stops sending MAC data, and continuously generates a remote fault status on the TX datapath. After a local fault is detected, the RX PCS modifies the MII data and control to send local fault sequence ordered sets. Refer to Link Fault Signaling Based On Configuration and Status below.

The RX PCS cannot recognize the link fault under the following conditions:

  • The RX PCS is not fully aligned.
  • The bit error rate (BER) is high.

Remote Fault (RF)

If unidirectional is not enabled, the core follows Clause 46. If the RS receives a remote fault status, the TX datapath stops sending MAC data and continuously generates idle control characters. If the RS stops receiving fault status messages, it returns to normal operation, sending MAC client data. Refer to Link Fault Signaling Based On Configuration and Status below.

Link Status Signals

The MAC RX generates two link fault signals: local_fault_status and remote_fault_status.
Note: These signals are real time status signals that reflect the status of the link regardless of the settings in the link fault configuration register.
This register is generated only if you turn on Enable link fault generation . The MAC TX interface uses the link fault status signals for additional link fault signaling.
Table 12.  Link Fault Signaling Based On Configuration and StatusFor more information about the LINK_FAULT register, refer to TX MAC Registers.
LINK_FAULT Register (0x405) Real Time Link Status Configured TX Behavior Comment
Bit [0] Bit [3] Bit [1] Bit [2]

LF Received

RF Received

TX Data

TX RF

1'b0 Don't care Don't care Don't care Don’t care Don’t care On Off

Disable Link fault signaling on TX.

RX still reports link status.

TX side Link fault signaling disabled on the link.

TX data and idle.

1'b1 1'b1 Don't care Don't care Don't care Don't care Off On

Force RF.

TX: Stop data. Transmit RF only

1'b1 1'b0 1'b1 1'b1 Don't care Don't care On Off

Unidir: Backwards compatible.

TX: Transmit data and idle. No RF.

1'b1 1'b0 1'b1 1'b0 1'b1 1'b0 On On

Unidir: LF received.

TX: Transmit data 1 column IDLE after end of packet and RF

1'b1 1'b0 1'b1 1'b0 1'b0 1'b1 On Off

Unidir: RF receives

TX: Transmit data and idle. No RF.

1'b1 1'b0 1'b1 1'b0 1'b0 1'b0 On Off

Unidir: No link fault

TX: Transmit data and idle. No RF.

1'b1 1'b0 1'b0 Don't care 1'b1 1'b0 Off On

Bidir: LF received

TX: Stop data. Transmit RF only.

1'b1 1'b0 1'b0 Don't care 1'b0 1'b1 Off Off

Bidir: RF received

TX: Stop data. Idle only. No RF.

1'b1 1'b0 1'b0 Don’t care 1'b0 1'b0 On Off

Bidir: No link fault

TX: Transmit data and idle. No RF.

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