Upon configuration, you must initiate the GTTXRESET and GTRXRESET in sequential mode; that is, RESETOVRD=1'b0 and GTRESETSEL=1'b0.
If RESETOVRD and GTRESETSEL are already defaulted to the above values, then the GT resets: GTTXRESET and GTRXRESET cannot be asserted until a minimum of
500 ns after the configuration is complete. To keep the timing aligned with Figure 2-12 in the
7 Series FPGAs GTS Transceivers User Guide, it might be best to delay the CPLLRESET and the QPLLRESET as well.

If RESETOVRD and GTXRESETSEL are
NOT defaulted to the above values, then you must do the following:
- Wait a minimum of 500 ns after GSR deassert.
- Set RESETOVRD and GTRESETSEL to 0.
- Wait another 300-500 ns.
- Assert resets.