Read this exception report line and tell me what happened: From { A B C }, To D, Setup 2, Hold *, Ignored f,o.
From PDVerse PrimeTime STA Interview Guide · pdVerse Mentor Guide
Ten-second Interview Answer
A set_multicycle_path 2 -from {A B C} -to D was only partially applied: f means an invalid startpoint (C) was dropped, o means another path (A) was overridden by a higher-priority exception, and only B->D actually carries the multicycle value 2.
Complete Technical Explanation
The report line reads { A B C } D 2 * f,o - startpoints A, B and C to endpoint D, a setup value of 2, no hold value, and an Ignored column carrying two codes. That combination tells you a set_multicycle_path 2 -from {A B C} -to D was accepted syntactically but only partly took effect. The f code says at least one specified startpoint is invalid - here C, so the C->D path was dropped from the exception entirely. The o code says at least one path was overridden by a higher-priority exception - here A->D, which is already covered by a false path, and a false path outranks a multicycle path in the exception precedence order. What is left is B->D, and that is the only path actually enforced with the multicycle value 2. So of the three startpoints you wrote, one was never valid, one is excused by something stronger, and one behaves as intended. The skill being tested is decoding a partially ignored exception rather than assuming that because the command was accepted the whole thing took effect. Every field in that line is telling you something, and the Ignored column is the one that matters most.
In Pd / Signoff
This is exactly what you read after applying a batch of exceptions from a spec: check the Ignored column on every reported exception rather than just confirming the command returned. An f usually points at a stale or misspelled instance name after a netlist change; an o tells you a higher-priority exception already owns that path, so your new constraint is doing nothing there.
Common Trap
Assuming a command that produced no error was fully applied. A collection-style -from {A B C} can be two-thirds inert - one startpoint invalid, another overridden - and the only evidence is the Ignored column codes, which is why exception reports need reading rather than glancing at.
Expect Next
Which exception types outrank a multicycle path, and what precedence order does PrimeTime apply?
Topic And Primetime Commands
Timing Exceptions / False Paths. set_multicycle_path
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