How do you correlate clock differences between ICC2 and PrimeTime?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
Compare clock creation, generated relationships, waveform, latency, uncertainty, case analysis, and mode scope without mixing command outputs.
Technical Explanation
When two tools disagree, compare the inputs and analysis context before comparing slack. Units, libraries, PVT, clocks, exceptions, and modes must line up first.
What To Check
• Warning sign: One tool sees a generated clock or exclusivity relation that the other does not. • Inspect: Keep at least two possible causes open, then use one named object and the active mode or scenario to separate them. • Correct: Correct the shared SDC or tool-specific application context, then compare the same endpoint and scenario.
Command Checks & Actions
• report_clocks: shows clock definitions and relationships
• report_case_analysis: shows constants applied for the active mode
• report_exceptions: shows timing exceptions and their scope
Run the commands in order. Each line answers a separate part of the check.Healthy, Suspicious & Hard-stop Results
• Expected: Compare clock creation, generated relationships, waveform, latency, uncertainty, case analysis, and mode scope without mixing command outputs. • Investigate: One tool sees a generated clock or exclusivity relation that the other does not. • Stop before floorplanning when required logic or timing coverage is missing or unexplained. Correct the shared SDC or tool-specific application context, then compare the same endpoint and scenario.
Common Mistake
Do not assume the check passed just because ICC2 continued: One tool sees a generated clock or exclusivity relation that the other does not. 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: One tool sees a generated clock or exclusivity relation that the other does not.
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: Correct the shared SDC or tool-specific application context, then compare the same endpoint and scenario. Then I would reopen the clean checkpoint and rerun the same evidence.”
Practical Example
Symptom: One tool sees a generated clock or exclusivity relation that the other does not. Corrective path: Correct the shared SDC or tool-specific application context, then compare the same endpoint and scenario.
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