When comparing the estimated and actual GT power on a board while running the SAMPLE or EXTEST instruction, additional power can be seen on the GT rails (MGTAVcc & MGTAVtt).
What is the reason for this?
When running the SAMPLE or EXTEST instruction in 7 Series, ALL GTs connected to the power rail whether used in the design or not will become active and run the instruction.
In situations where there are fewer used GTs in the active design than GTs connected to the power plane, this will mean that XPE will not have reported their power and so the actual versus estimated can be different.
In order to estimate accurately, all GTs connected to the power rails whether used or not should be entered into XPE.
This applies to the following boundary scan instructions:
More details on the boundary scan instructions in UltraScale can be found in (Xilinx Answer 56775)