Exceptions tell STA that the default one-cycle relationship is wrong for some paths. They are powerful and dangerous: every exception removes or relaxes a check, and every wrong exception hides a real failure. This topic covers false paths, multicycle paths, point-to-point delay exceptions, and the audit and policy that keep them honest.
Lesson | After it you can... |
|---|---|
Say what a false path removes and when it is justified. | |
Set setup and hold multipliers correctly. | |
Replace a path requirement with an explicit delay limit. | |
Run an audit that catches overbroad or stale exceptions. |
The RTL view is in Multi-Cycle and False Paths; the CDC view of exceptions is in CDC Constraints and STA.
An extra (overbroad) one: a missing exception produces a visible violation, while an extra one silently removes a check and the report looks cleaner than it should.