How do you estimate required placeable area from target utilisation?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
Divide the counted placeable object area by the declared target utilisation. The result is a mathematical starting point, not a final implementable core.
Technical Explanation
If 600000 um^2 of counted cells must occupy 60% of placeable area, more area is needed than the cell total itself. Illustrative calculation: required area = 600000 um^2 / 0.60 = 1000000 um^2. Then test rows, macros, channels, pins, power reservation, congestion, and timing.
Formula Or Decision Rule
Required area [um^2] = counted placeable area [um^2] / target utilisation [unitless].
What To Check
• Warning sign: The calculation fits numerically but leaves no legal rows or routing access around macros. • Inspect: choose one affected region, macro, row, pin, path, or net and trace the physical cause. • Correct: Increase or reshape the usable plan based on the failed resource, and document why the mathematical minimum was insufficient.
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: Divide the counted placeable object area by the declared target utilisation. The result is a mathematical starting point, not a final implementable core. • Suspicious: The calculation fits numerically but leaves no legal rows or routing access around macros. • Hard stop: required legality or physical feasibility is missing or unexplained. Increase or reshape the usable plan based on the failed resource, and document why the mathematical minimum was insufficient.
Common Mistake
Do not hide the symptom with an arbitrary utilisation, halo, channel, blockage, pin move, or die-size change. The calculation fits numerically but leaves no legal rows or routing access around macros.
What The Interviewer Is Testing
The interviewer is testing whether you can connect “How do you estimate required placeable area from target utilisation?” to measurable physical evidence and an owned correction.
Practical Example
Symptom: The calculation fits numerically but leaves no legal rows or routing access around macros. Corrective path: Increase or reshape the usable plan based on the failed resource, and document why the mathematical minimum was insufficient.
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