Xilinx recommends that you run simulations using a resolution of 1 ps. Some Xilinx primitive components, such as MMCM, require a 1 ps resolution to work properly in either functional or timing simulation.
Tip: Because most of the simulation time
is spent in delta cycles, there is no significant simulator performance gain by using
coarser resolution with the Xilinx simulation models.
There is no need to use a finer resolution, such as femtoseconds (fs) as some simulators will round the numbers while others will truncate the numbers.