How do you distinguish an intentional open from broken connectivity?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
Trace the object to interface intent, tie-off policy, black-box boundary, and synthesis log; intention requires recorded ownership.
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: An unused output is harmless, but a floating enable has the same superficial 'open' label. • Inspect: Compare one named object across the related reports; the same object should tell a consistent story. • Correct: Fix functional opens upstream; waive only named, reviewed objects with a reason and rerun criterion.
Command Checks & Actions
• check_netlist: reports structural connectivity problems
• report_ports -verbose [get_ports *]: shows boundary constraints and electrical assumptions
Run the commands in order. Each line answers a separate part of the check.Healthy, Suspicious & Hard-stop Results
• Expected: Trace the object to interface intent, tie-off policy, black-box boundary, and synthesis log; intention requires recorded ownership. • Investigate: An unused output is harmless, but a floating enable has the same superficial 'open' label. • Stop before floorplanning when required logic or timing coverage is missing or unexplained. Fix functional opens upstream; waive only named, reviewed objects with a reason and rerun criterion.
Common Mistake
Do not assume the check passed just because ICC2 continued: An unused output is harmless, but a floating enable has the same superficial 'open' label. 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: An unused output is harmless, but a floating enable has the same superficial 'open' label.
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: Fix functional opens upstream; waive only named, reviewed objects with a reason and rerun criterion. Then I would reopen the clean checkpoint and rerun the same evidence.”
Practical Example
Symptom: An unused output is harmless, but a floating enable has the same superficial 'open' label. Corrective path: Fix functional opens upstream; waive only named, reviewed objects with a reason and rerun criterion.
Continue practising