SGMII Standard - 2.6 English

1G/10G/25G Switching Ethernet Subsystem Product Guide (PG292)

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2.6 English

The following figure shows the operation of SGMII Auto-Negotiation as described in Overview of Operation.

Additional information about SGMII Standard Auto-Negotiation is provided in the following sections.

Figure 1. SGMII Auto-Negotiation

The SGMII capable PHY has two distinctive sides to Auto-Negotiation.

  • The PHY performs Auto-Negotiation with its link partner using the relevant Auto-Negotiation standard for the chosen medium (BASE-T Auto-Negotiation is shown in the preceding figure, using a twisted copper pair as its medium). This resolves the operational speed and duplex mode with the link partner.
  • The PHY then passes the results of the Auto-Negotiation process with the link partner to the core (in SGMII mode), by leveraging the 1000BASE-X Auto-Negotiation specification described in the 1000BASE-X Standard topic. This transfers the results of the Link Partner Auto-Negotiation across the SGMII and is the only Auto-Negotiation observed by the core.

This SGMII Auto-Negotiation function, summarized previously, leverages the 1000BASE-X PCS/PMA Auto-Negotiation function but contains two differences.

  • The duration of the Link Timer of the SGMII Auto-Negotiation is shrunk from 10 ms to 1.6 ms so that the entire Auto-Negotiation cycle is much faster
  • The information exchanged is different and now contains speed resolution in addition to duplex mode. See Register 5: Auto-Negotiation Link Partner Base in Configuration and Status Register Map for 1G Ethernet PCS/PMA. Speed and Duplex status bits of this register are also provided in status_vector.
  • There are no other differences and dealing with the results of Auto-Negotiation can be handled as described previously in the 1000BASE-X Standard topic.