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.