The GT wizard always generates this code based on the assumption that gtrefclk0_in is used as the CPLL reference clock.
When another reference clock is actually being supplied to the CPLL, this will defeat the purpose of the code.
If another reference clock is being used and gtrefclk0_in does not have a valid clock applied to it, the CPLL will remain powered down indefinitely.
After the GTX wrapper has been generated as described in the text of XAPP 592, the lowest level GTX wrapper (the wrapper used by SDI), must be edited manually to use the proper reference clock in this code segment.
Both SDI demos that are supplied here use gtrefclk1_in as the CPLL reference clock.
The k7gtx_sdi_wrapper_gt.v file supplied for these demos has already been edited to use gtrefclk1_in in this CPLL power down code.
Please see the XAPP592 readme.txt file for more details.