When there is no Video Source connected, rx_mode_locked and rx_t_locked keeps toggling. What can cause this problem?
The problem is caused by a known issue for GT : (Xilinx Answer 68379)
It is fixed in the 2017.1 release.
The patch for 2016.4 can be downloaded from (Xilinx Answer 68741).
GT sometimes outputs a non null RXDATA when no cable is connected. The pattern of RXDATA is valid Data, so rx_mode_locked and rx_t_locked are asserted.
However, if the data pattern does not contain valid xyz logic, then rx_mode_locked and rx_t_locked lose lock after they are asserted.