Hi Ross,
The PRU-ICSS subsystem includes, besides others (AM335X TRM Rev. K section 4.1.1):
• One Ethernet MII_RT module with two MII ports and configurable connections to PRUs
• One MDIO Port
These are separate and different from the CPSW Ethernet and are used for Industrial Ethernet protocols, e.g. EtherCAT. The PRU-ICSS MDIO signals are listed in Table 4-27 in the AM335X Datasheet Rev. G, the CPSW Ethernet MDIO signals are listed in Table 4-40.