Using Both the SGMII MAC Mode and SGMII PHY Mode Configurations to interface to an External BASE-T PHY with a GMII interface - 16.2 English

1G/2.5G Ethernet PCS/PMA or SGMII LogiCORE IP Product Guide (PG047)

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16.2 English

The following figure shows the operation of SGMII auto-negotiation. 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 previous figure, using a twisted copper pair as its medium). This resolves the operational speed and duplex mode with the link partner. The BASE-T PHY transfers the link partner abilities though the MDIO interface to the core (in SGMII configuration and PHY mode).
  • The core (in SGMII configuration and PHY mode) then passes the results of the auto-negotiation process to the core (in SGMII configuration and MAC mode), by leveraging the 1000BASE-X auto-negotiation specification described in Overview of Operation. 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. There are no other differences and dealing with the results of auto-negotiation can be handled as described previously in Overview of Operation.