SGMII Auto-Negotiation - 7.2 English

AXI 1G/2.5G Ethernet Subsystem Product Guide (PG138)

Document ID
PG138
Release Date
2023-11-15
Version
7.2 English

The external SGMII capable PHY device performs auto-negotiation with its link partner on the PHY Link (Ethernet bus), resolving operational speed and duplex mode and then in turn performs a secondary auto-negotiation with the transceiver across the SGMII Link. This transfers the results of the PHY with Link Partner auto-negotiation across the SGMII to the AXI Ethernet Subsystem.

The results of the SGMII auto-negotiation can be read from the SGMII Management Auto-Negotiation Link Partner Ability Base register (Table 7 ). The speed of the subsystem should then be set to match.

There are two methods that can be used for the completion of an auto-negotiation cycle:

  1. Polling the auto-negotiation complete bit of SGMII Management Status register (Register 1, bit 5 Table 3).
  2. Using the auto-negotiation complete interrupt (Interrupt Status Register and SGMII Management Auto-Negotiation Interrupt Control register, Table 12).

When placed into loopback, data is routed from the transmitter to the receiver path at the last possible point in the PCS/PMA sublayer. When placed into loopback, a constant stream of Idle code groups is transmitted through the transceiver.

Loopback in this position allows test frames to be looped back within the system without allowing them to be received by the link partner (the device connected on the other end of the Ethernet). The transmission of Idles allows the link partner to remain in synchronization so that no fault is reported.