Clock uncertainty is the amount of uncertainty relative to an ideal clock.
Uncertainty can come from user-specified external clock uncertainty (
set_clock_uncertainty), system jitter, or duty cycle
distortion. Clock-modifying blocks such as the MMCM and PLL also contribute to clock
uncertainty in the form of Discrete Jitter, and Phase Error if multiple related clocks
The Clocking Wizard provides accurate uncertainty data for the specified device and can generate various MMCM clocking configurations for comparing different clock topologies. To achieve optimal results for the target architecture, Xilinx recommends regenerating clock generation logic using the Clocking Wizard rather than using legacy clock generation logic from prior architectures.