Period Constraints
 
 
PERIOD
- PERIOD is the duration of the clock and can be configured to have different duty cycles
 - Derived clocks can be defined as a function of another clock (*,/)
 - PERIOD is preferred over FROM:TO constraints; The tools will have a faster runtime. PERIOD should cover most of design.
 - Period only covers from Sync. Elements to other Sync. Elements, like Flip flops to flip flops.