In generation of the PCI Express Core, there is an option to disable the calibration block. Should I ever use this option?
For normal operation, this option should not be checked.
This option is provided for board debugging purposes and even then, should not be used in most cases. It allows the user to turn off the calibration block instantiated by the core for each MGT. Checking this option does not physically remove the calibration block, but only disables it. For more information about the calibration block, please see (Xilinx Answer 22477).