Low Latency 100-Gbps Ethernet IP Core User Guide

ID 683160
Date 4/15/2021
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3.2.12. Link Fault Signaling Interface

If you turn on Enable link fault generation in the LL 100GbE parameter editor, the LL 100GbE IP core provides link fault signaling as defined in the IEEE 802.3ba-2010 High Speed Ethernet Standard and Clause 66 of the IEEE 802.3-2012 Ethernet Standard, based on the LINK_FAULT_CONFIG register settings. The LL 100GbE MAC includes a Reconciliation Sublayer (RS) located between the MAC and the XLGMII or CGMII to manage local and remote faults. Link fault signaling on the Ethernet link is disabled by default but can be enabled by bit [0] 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 [1] of the LINK_FAULT_CONFIG register, the IP core conforms to Clause 66 of the IEEE 802.3-2012 Ethernet Standard. 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 802.3ba 2010 High Speed Ethernet Standard. 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.

Table 21.  Signals of the Link Fault Signaling InterfaceThese signals are available only if you turn on Enable link fault generation in the LL 100GbE parameter editor.

Signal Name

Direction

Description

remote_fault_status

Output

Asserted by the IP core when it detects a real-time remote fault in the RX MAC. The IP core asserts this signal regardless of the settings in the LINK_FAULT_CONFIG register.

This signal is clocked by clk_rxmac.

local_fault_status

Output

Asserted by the IP core when it detects a real-time local fault in the RX MAC. The IP core asserts this signal regardless of the settings in the LINK_FAULT_CONFIG register.

This signal is clocked by clk_rxmac.

unidirectional_en Output The IP core asserts this signal if it includes Clause 66 support for remote link fault reporting on the Ethernet link. Connects to the Unidir Enable field in bit [1] of the LINK_FAULT_CONFIG register at offset 0x405.

This signal is clocked by clk_txmac.

link_fault_gen_en Output The IP core asserts this signal if the PCS is enabled to generate a remote fault sequence on the Ethernet link when appropriate. Connects to the Link Fault Reporting Enable field in bit [0] of the LINK_FAULT_CONFIG register at offset 0x405.

This signal is clocked by clk_txmac.

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