How do you compare equal-area floorplans with different aspect ratios?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
Keep area, constraints, macro set, PG assumptions, and evaluation settings constant; compare path length, row continuity, channel capacity, pin affinity, congestion, and change risk.
Technical Explanation
Equal area controls only capacity, not geometry. Test at least two shapes with the same object counts and reports. Explain each difference through physical distance or resource distribution.
Formula Or Decision Rule
For constant A: W = sqrt(A x AR), H = sqrt(A / AR).
What To Check
• Warning sign: One alternative wins timing because the constraints or scenario changed, not because of shape. • Inspect: choose one affected region, macro, row, pin, path, or net and trace the physical cause. • Correct: Restore identical conditions and compare named paths and hot spots.
Command Checks & Actions
• initialize_floorplan -control_type core -shape R -side_ratio {<width_ratio> <height_ratio>} -core_utilization <ratio>: creates the initial die, core, rows or site array, and tracks from declared controls
• report_design -floorplan: reports the floorplan state understood by the tool
Run only the commands needed for this question. Save the report with the floorplan version and analysis context.Healthy, Suspicious & Hard-stop Results
• Healthy: Keep area, constraints, macro set, PG assumptions, and evaluation settings constant; compare path length, row continuity, channel capacity, pin affinity, congestion, and change risk. • Suspicious: One alternative wins timing because the constraints or scenario changed, not because of shape. • Hard stop: required legality or physical feasibility is missing or unexplained. Restore identical conditions and compare named paths and hot spots.
Common Mistake
Do not hide the symptom with an arbitrary utilisation, halo, channel, blockage, pin move, or die-size change. One alternative wins timing because the constraints or scenario changed, not because of shape.
What The Interviewer Is Testing
The interviewer is testing whether you can connect “How do you compare equal-area floorplans with different aspect ratios?” 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 one alternative wins timing because the constraints or scenario changed, not because of shape. I would use the named objects and reports to decide whether to iterate, waive, or return the issue.”
Practical Example
Symptom: One alternative wins timing because the constraints or scenario changed, not because of shape. Corrective path: Restore identical conditions and compare named paths and hot spots.
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