The SGMII and Gb Ethernet PCS IP "xmit_autoneg" signal does not have the same definition as the xmit variable defined by the 802.3 spec. The 802.3 spec uses the xmit variable to indicate CONFIGURATION (/C/) IDLE (/I/) or Data condition for transmit and receive.
The xmit_autoneg in the SGMII and Gb Ethernet PCS IP Core is only used to control the PCS receive logic during autonegotiation.
The xmit_autoneg output pin is normally connected to the xmit port of the PCS in GbE mode (seeTN1124 "LatticeECP2M SERDES/PCS Usage Guide" --> "Idle Insert for Gigabit Ethernet Mode" section).
During autonegotiation, the SGMII/GbE PC IP asserts the xmit_autoneg to allow the PCS receive logic to insert periodic /I2/ ordered sets in the direction of the CTC block in order to prevent the CTC from overrrunning during the Auto negotiation phase.