For XAUI v12.1 Rev. 3 and RXAUI v4.2 Rev 2 and earlier cores, the transceiver debug option brings out ports to enable the PRBS sequence in the transceiver.
When receiving the PRBS sequence, the XAUI core will not achieve synchronization or alignment.
The XAUI core has timeout logic to issue a GTRXRESET if synchronization has not completed.
This timeout results in the transceiver being periodically reset when PRBS is enabled.
Code can be added to disable the synchronization timeout counter when PRBS is enabled.
Please contact Xilinx for code to work around this issue if using PRBS for testing.
This has been fixed in the Vivado 2015.1 or later release of the cores.