When a BUFGMUX has 2 input clock signals, it is necessary to verify that both input signals have a PERIOD constraint applied or propagated from a clocking element.
Then in order to propagate the desired PERIOD constraint through the BUFGMUX, the word PRIORITY must be added to the constraint.
The input PERIOD constraints must be related for the PRIORITY keyword to impact the analysis correctly.
If the constraint is generated by a clocking element , it is possible that this constraint needs to be re-write by the customer adding the previous word (PRIORITY).
For instance, there is a BUFGMUX called MUX_UP with 2 input clocks (MUX_UP_1 & MUX_UP_1) and the desired PERIOD constraint after the BUFGMUX is "TS_clk_mux_up_1".
The following is an example of constraints applied to the BUFGMUX using the PRIORITY word:
If for any reason, the PERIOD constraint is still not being applied after the BUFGMUX, the best option is to over-write the constraint with the desired PERIOD constraint at the output of the BUFGMUX.