Auto Negotiation

Each RX lane has its own auto-negotiation state machine as shown in Figure 1. APB interface manages the auto-negotiation function. The auto-negotiation function complies with IEEE Std. 802.3 Clause 37 for next page operation support and can be configured to support link status notifications.

Each port has interrupt pins to allow software notification when auto-negotiation completes or, in the case of a next page operation, to indicate further page data should be written through the APB.

The design should be held in reset as the clock frequency changes.

If you also use auto-negotiation for SGMII operation, the off-chip PHY can use auto-negotiation to exchange link status information. In this case, the link status information conveys the link state as well as the expected SGMII operating speed. If the speed indicated by the link status does not match the current configured speed, hold the selected port in reset and change the speed mode. On release of reset, the auto-negotiation process automatically restarts and the link status from the off-chip PHY should match the newly configured speed mode.