Interviewers score the narration separately from the debugging: a correct cause told as a ramble reads as luck. Tell it in four beats, about a minute each, with one framework step audible per beat.
Beat | Time | Say |
|---|---|---|
Symptom | 1 min | Assumption: rare illegal-state freeze at a known clock boundary, unreproducible on the bench. State the three facts and the prime suspect. |
Investigation | 1.5 min | Crossing audit first, structural report, legality, fanout. Name the step that found it and the expensive step you skipped. |
Mechanism and fix | 1.5 min | Mechanism in two sentences, then the synchroniser fix with its two rules: single fanout source, level versus pulse. |
Trade-off and evidence | 1 min | Latency cost of the stages, why recovery logic alone was not the fix, and the closing evidence: structural re-run plus metastability-aware simulation, with simulation labelled as support, not proof. |
End by inviting the follow-up you want: "the interesting question is what I would change in the review process so the raw crossing never reaches tape-out". That hands the interviewer the waiver-and-methodology thread, which is your strongest ground after this section. A level-4 close names the failure rate honestly: the fix makes escape arbitrarily unlikely, never impossible, which is exactly what Resolution Time and MTBF teaches.
The trade-off and honesty: the latency cost, why recovery logic alone was insufficient, and the explicit statement that the fix bounds the failure rate but never reaches zero, with each claim tied to its evidence.