How do you audit multicycle setup and hold intent?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
Confirm the functional cycle relationship, start/end clocks, edge convention, and paired hold behaviour instead of applying a number mechanically.
Technical Explanation
A multicycle path is allowed more than one clock cycle by function. Setup and hold relationships must be derived together from the real protocol.
What To Check
• Warning sign: A setup multicycle is added without the corresponding intended hold treatment. • Inspect: Compare one named object across the related reports; the same object should tell a consistent story. • Correct: Derive both checks from the protocol, correct the SDC, and inspect full clock-expanded paths.
Command Checks & Actions
• report_exceptions: shows timing exceptions and their scope
• report_timing -path_type full_clock_expanded: shows a path and its timing calculation
Run the commands in order. Each line answers a separate part of the check.Healthy, Suspicious & Hard-stop Results
• Expected: Confirm the functional cycle relationship, start/end clocks, edge convention, and paired hold behaviour instead of applying a number mechanically. • Investigate: A setup multicycle is added without the corresponding intended hold treatment. • Stop before floorplanning when required logic or timing coverage is missing or unexplained. Derive both checks from the protocol, correct the SDC, and inspect full clock-expanded paths.
Common Mistake
Do not assume the check passed just because ICC2 continued: A setup multicycle is added without the corresponding intended hold treatment. Fix or narrowly justify the named objects, then rerun the same command.
What The Interviewer Is Testing
Be ready to explain why this matters before floorplanning: A setup multicycle is added without the corresponding intended hold treatment.
Follow-up Question & Model Response
Model response: “I would save the report, inspect one affected object in the correct block and scenario, and make or request this correction: Derive both checks from the protocol, correct the SDC, and inspect full clock-expanded paths. Then I would reopen the clean checkpoint and rerun the same evidence.”
Practical Example
Symptom: A setup multicycle is added without the corresponding intended hold treatment. Corrective path: Derive both checks from the protocol, correct the SDC, and inspect full clock-expanded paths.
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