When operating in tri-mode, the PHY negotiates the highest speed available with its link partner. The user application can set the speed of the Ethernet MAC after auto-negotiation completes by doing the following:
- The user application can either monitor auto-negotiation interrupt from the external PHY or internal Ethernet 1G/2.5G PCS/PMA or SGMII core or poll for auto-negotiation (see the relevant PHY documentation).
- When auto-negotiation completes, the user application can read the MDIO auto-negotiation registers to obtain the negotiated speed.
- The user application then needs to set this speed in the Ethernet MAC configuration registers using the host interface.
If auto-negotiation is disabled, the Ethernet MAC, PHY, and the PHY link partner must all be set to the same speed.