USXGMII In-Band Control and Status Signals

The USXGMII specification defines a method to exchange link information based on a modification of the IEEE Std. 802.3 Clause 37 defined auto-negotiation state machine. This method uses XGMII ordered sets with a Cisco-specific opcode of 0x03.

In the 10GBase-KR PCS this opcode is user programmable via the programming registers. The PCS supports autonomous hardware and software auto-negotiation modes as described in the USXGMII specification.