The current default value for TXPIPPMSEL in UG482 (v1.8) and UG476 (v1.11.1) is '1'.
This is done to select the TXPIPPM controller to control the TX PI.
In far-end PMA loopback, the RX PI needs to control the TX PI.
This is not possible with TXPIPPMSEL=1 and bit errors might be seen on the link during the loopback.
When using far-end PMA loopback in 7 Series GTP and GTH, ensure that TXPIPPMSEL is set to '0'.
7 Series GTP/GTH user guides will be updated in a future release.
(UG576) for UltraScale GTH already reflects this change and it can be referred to for this topic.
10/15/2015 - Initial Release