Two equal-area aspect ratios disagree on timing and congestion. Which wins?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
Use a scorecard with identical definitions and methods. Choose the shape whose combined row usability, macro legality, channels, pin access, PG reservation, congestion, timing, and change risk best matches project priorities.
Technical Explanation
No single metric decides the floorplan. Timing may improve through shorter critical paths while congestion worsens through pin concentration. Identify the physical cause of each delta and the risk owner.
Formula Or Decision Rule
Decision rule: no hard stop, then compare weighted project risks with evidence.
What To Check
• Warning sign: The choice is made from WNS alone or the prettiest outline. • Inspect: choose one affected region, macro, row, pin, path, or net and trace the physical cause. • Correct: Align the experiments, document tradeoffs, and choose or iterate with owners.
Command Checks & Actions
• report_design -floorplan: reports the floorplan state understood by the tool
• report_congestion -mode summary: reports routing demand, capacity, overflow, or hot spots
• estimate_timing: performs early virtual timing estimation
• report_timing: reports timing paths in the active analysis context
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 a scorecard with identical definitions and methods. Choose the shape whose combined row usability, macro legality, channels, pin access, PG reservation, congestion, timing, and change risk best matches project priorities. • Suspicious: The choice is made from WNS alone or the prettiest outline. • Hard stop: required legality or physical feasibility is missing or unexplained. Align the experiments, document tradeoffs, and choose or iterate with owners.
Common Mistake
Do not hide the symptom with an arbitrary utilisation, halo, channel, blockage, pin move, or die-size change. The choice is made from WNS alone or the prettiest outline.
What The Interviewer Is Testing
The interviewer is testing whether you can connect “Two equal-area aspect ratios disagree on timing and congestion. Which wins?” 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 the choice is made from WNS alone or the prettiest outline. I would use the named objects and reports to decide whether to iterate, waive, or return the issue.”
Practical Example
Symptom: The choice is made from WNS alone or the prettiest outline. Corrective path: Align the experiments, document tradeoffs, and choose or iterate with owners.
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