Why can a very low unconstrained-endpoint count coexist with poor coverage?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
False paths, case analysis, disabled arcs, inactive scenarios, or missing clocks can remove paths before they become unconstrained endpoints.
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: The dashboard reports few unconstrained endpoints while whole interfaces or modes are absent. • Inspect: Keep at least two possible causes open, then use one named object and the active mode or scenario to separate them. • Correct: Audit scenario status, clocks, exceptions, case analysis, disabled arcs, and expected path groups; stop until coverage is explained.
Command Checks & Actions
• 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
• report_disable_timing: shows timing arcs that cannot propagate
Run the commands in order. Each line answers a separate part of the check.Healthy, Suspicious & Hard-stop Results
• Expected: False paths, case analysis, disabled arcs, inactive scenarios, or missing clocks can remove paths before they become unconstrained endpoints. • Investigate: The dashboard reports few unconstrained endpoints while whole interfaces or modes are absent. • Stop before floorplanning when required logic or timing coverage is missing or unexplained. Audit scenario status, clocks, exceptions, case analysis, disabled arcs, and expected path groups; stop until coverage is explained.
Common Mistake
Do not assume the check passed just because ICC2 continued: The dashboard reports few unconstrained endpoints while whole interfaces or modes are absent. 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: The dashboard reports few unconstrained endpoints while whole interfaces or modes are absent.
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: Audit scenario status, clocks, exceptions, case analysis, disabled arcs, and expected path groups; stop until coverage is explained. Then I would reopen the clean checkpoint and rerun the same evidence.”
Practical Example
Symptom: The dashboard reports few unconstrained endpoints while whole interfaces or modes are absent. Corrective path: Audit scenario status, clocks, exceptions, case analysis, disabled arcs, and expected path groups; stop until coverage is explained.
Continue practising