All input and output delays should be referenced to a virtual clock.
If the input and output delays reference base clocks or PLL clocks rather than
virtual clocks, the intra- and inter-clock transfer clock uncertainties,
determined by derive_clock_uncertainty, are incorrectly applied to the I/O ports.
See mnl_timequest_cookbook.pdf for more info.
Istvan Csomortani
Sergiu Arpadi
Laszlo Nagy
Adrian Costina