How do you create a repeatable early-congestion estimate?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
Use the same floorplan version, coarse placement, scenarios, layer availability, PG/blockage assumptions, global-route mode, and report settings for every alternative.
Technical Explanation
A congestion picture is comparable only when the experiment is controlled. Floorplan global routing estimates demand and capacity; it cannot prove detailed-route DRC closure or final timing.
Formula Or Decision Rule
Decision rule: archive inputs and settings with the map and report.
What To Check
• Warning sign: Two maps differ because one ignored blockages or used another floorplan checkpoint. • Inspect: choose one affected region, macro, row, pin, path, or net and trace the physical cause. • Correct: Reproduce both from the same baseline and rerun the identical route/report sequence.
Command Checks & Actions
• route_global -floorplan true -congestion_map_only true: runs an early floorplan global-route estimate
• report_congestion -mode summary: reports routing demand, capacity, overflow, or hot spots
Run only the commands needed for this question. Save the report with the floorplan version and analysis context.Healthy, Suspicious & Hard-stop Results
• Healthy: Use the same floorplan version, coarse placement, scenarios, layer availability, PG/blockage assumptions, global-route mode, and report settings for every alternative. • Suspicious: Two maps differ because one ignored blockages or used another floorplan checkpoint. • Hard stop: required legality or physical feasibility is missing or unexplained. Reproduce both from the same baseline and rerun the identical route/report sequence.
Common Mistake
Do not hide the symptom with an arbitrary utilisation, halo, channel, blockage, pin move, or die-size change. Two maps differ because one ignored blockages or used another floorplan checkpoint.
What The Interviewer Is Testing
The interviewer is testing whether you can connect “How do you create a repeatable early-congestion estimate?” to measurable physical evidence and an owned correction.
Follow-up Question & Model Response
Follow-up probe: What would make you change your decision? Model response: “I would change it if the same controlled rerun shows that two maps differ because one ignored blockages or used another floorplan checkpoint. I would use the named objects and reports to decide whether to iterate, waive, or return the issue.”
Practical Example
Symptom: Two maps differ because one ignored blockages or used another floorplan checkpoint. Corrective path: Reproduce both from the same baseline and rerun the identical route/report sequence.
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