You can use an input port as the primary clock root as shown in the following figure.
Figure 1. create_clock for Input Ports
Constraint example:
create_clock -name SysClk -period 10 -waveform {0 5} [get_ports sysclk]In this example, the waveform is defined to have a 50% duty cycle. The -waveform argument is shown above to illustrate its usage
and is only necessary to define a clock with a duty cycle other than 50%. For more
information, see the create_clock Tcl command in the
Vivado
Design Suite Tcl Command Reference Guide (UG835). For a differential clock input
buffer, the primary clock only needs to be defined on the P-side of the pair.