4.1.12. PHY Management (MDIO)
To access each PHY device, write the PHY address to the MDIO register (mdio_addr0/1) followed by the transaction data (MDIO Space 0/1). For faster access, the MAC function allows up to two PHY devices to be mapped in its register space at any one time. Subsequent transactions to the same PHYs do not require writing the PHY addresses to the register space thus reducing the transaction overhead. You can access the MDIO registers via the Avalon® memory-mapped interface.
For more information about the registers of a PHY device, refer to the specification provided with the device.
For more information about the MDIO registers, refer to the MAC Configuration Register Space section.