By default, the Ethernet 1000BASE-X PCS/PMA or SGMII and QSGMII cores use DFE mode.
For DFE mode, it is recommended to update RXDFEXYDEN to '1'. This change enhances performance for medium and long reach applications with channel losses of 15 dB or higher at the Nyquist frequency.
For more information on this change, see Design Advisory for 7 Series FPGA GTX Transceiver - RXDFEXYDEN Port Update in DFE Mode (Xilinx Answer 58244).
In <core_name>_GTWIZARD_GT.v/vhd, the RXDFEXYDEN port should be changed from '0' to '1'.
This has been updated in the Vivado 2013.3 and later versions of the IP cores.
11/22/2013 - Initial release