Why is zero reported timing violations insufficient for readiness?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
Slack covers only analysed paths in active scenarios; missing clocks, exceptions, constants, inactive modes, or absent paths can make the result artificially clean.
Technical Explanation
Treat this as a readiness check. It should produce named objects and a result that another engineer can repeat from the same handoff.
What To Check
• Warning sign: WNS is positive while coverage reports show missing or removed analysis. • Inspect: Keep at least two possible causes open, then use one named object and the active mode or scenario to separate them. • Correct: Use coverage and intent reports as the gate, restore missing analysis, and only then interpret slack.
Command Checks & Actions
• check_timing: finds missing or inconsistent timing setup
• report_scenarios: shows the MCMM scenario matrix and analysis status
• report_clocks: shows clock definitions and relationships
• report_exceptions: shows timing exceptions and their scope
• report_case_analysis: shows constants applied for the active mode
Run the commands in order. Each line answers a separate part of the check.Healthy, Suspicious & Hard-stop Results
• Expected: Slack covers only analysed paths in active scenarios; missing clocks, exceptions, constants, inactive modes, or absent paths can make the result artificially clean. • Investigate: WNS is positive while coverage reports show missing or removed analysis. • Stop before floorplanning when required logic or timing coverage is missing or unexplained. Use coverage and intent reports as the gate, restore missing analysis, and only then interpret slack.
Common Mistake
Do not assume the check passed just because ICC2 continued: WNS is positive while coverage reports show missing or removed analysis. 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: WNS is positive while coverage reports show missing or removed analysis.
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: Use coverage and intent reports as the gate, restore missing analysis, and only then interpret slack. Then I would reopen the clean checkpoint and rerun the same evidence.”
Practical Example
Symptom: WNS is positive while coverage reports show missing or removed analysis. Corrective path: Use coverage and intent reports as the gate, restore missing analysis, and only then interpret slack.
Continue practising