How do you test floorplan sensitivity to cell-area growth?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
Recalculate required placeable area with the larger counted cell area, rebuild or resize the candidate, and compare rows, congestion, timing, and PG capacity using the same method.
Technical Explanation
Growth reserve should answer “what if the netlist gets larger?” with numbers. Illustrative example: 600000 um^2 growing by 8% becomes 648000 um^2; at U = 0.60 the mathematical placeable area becomes 1080000 um^2.
Formula Or Decision Rule
Anew = Aold x (1 + growth); required = Anew / U.
What To Check
• Warning sign: The plan has no continuous space for added buffers even though global whitespace exists. • Inspect: choose one affected region, macro, row, pin, path, or net and trace the physical cause. • Correct: Reshape or lower occupancy where growth must occur, then repeat the sensitivity run.
Command Checks & Actions
• 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: Recalculate required placeable area with the larger counted cell area, rebuild or resize the candidate, and compare rows, congestion, timing, and PG capacity using the same method. • Suspicious: The plan has no continuous space for added buffers even though global whitespace exists. • Hard stop: required legality or physical feasibility is missing or unexplained. Reshape or lower occupancy where growth must occur, then repeat the sensitivity run.
Common Mistake
Do not hide the symptom with an arbitrary utilisation, halo, channel, blockage, pin move, or die-size change. The plan has no continuous space for added buffers even though global whitespace exists.
What The Interviewer Is Testing
The interviewer is testing whether you can connect “How do you test floorplan sensitivity to cell-area growth?” 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 plan has no continuous space for added buffers even though global whitespace exists. I would use the named objects and reports to decide whether to iterate, waive, or return the issue.”
Practical Example
Symptom: The plan has no continuous space for added buffers even though global whitespace exists. Corrective path: Reshape or lower occupancy where growth must occur, then repeat the sensitivity run.
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