Understanding Multicycle Constraints

In a default single-cycle clock relationship, the two clocks are in phase and toggle together. The default setup and hold represent a one clock cycle capture window and is the same as setting a constraint of setup = 1 and hold = 0. The hold is checking one clock cycle before the capture clock edge. When you use the set_multicycle_path constraint, you are adjusting the capture window by shifting it, widening it, or both.

If you do not use a multicycle constraint, the software assumes you want the default, single-cycle relationship.

The constraints that represent the default are:

set_multicycle_path -setup -from a -to b 1
set_multicycle_path -hold -from a -to b 0