When using v1.8 of the Virtex-6 FPGA GTH Transceiver Wizard, BUFFER_CONFIG_LANEx[15:0] should manually be set to manual adjustment mode based on the TX/RX_FABRIC_WIDTH settings (as documented in Table 3-4 of the Virtex-6 FPGA GTH Transceivers User Guide (UG371)).
NOTE: Somevalues for RX_BUFFER_CONFIG[3:0]in table 3-4 of the user guide v2.2 are not correct. The correct values, as marked in the table in this Answer Record should be used. This is to be updated in a future revision of theVirtex-6 FPGA GTH Transceivers User Guide (UG371).
This has been fixedinv1.9of the Virtex-6 FPGA GTH Transceiver Wizard where this is setto manual mode. Please keep in mind that v1.9 of the wizardonly supports Production Silicon. For the updated wizard with this fix that supports ES Silicon, theVirtex-6 FPGA GTH Transceiver Wizard v1.7 Rev2should be used.