How do you select target utilisation without using a universal percentage?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
Start from counted area, macro dominance, expected growth, physical-only cells, clock and hold buffering, spare strategy, routing access, PG reservation, voltage areas, and local density risk. Then test alternatives.
Technical Explanation
Target utilisation is an engineering hypothesis about usable capacity, not a process-node constant. Keep the numerator and denominator fixed while comparing candidates. Record every reserved resource and sensitivity to cell-area growth.
Formula Or Decision Rule
Sensitivity: required area changes from A/U1 to A/U2 when target utilisation changes from U1 to U2.
What To Check
• Warning sign: A copied percentage produces fragmented rows or severe local hot spots. • Inspect: choose one affected region, macro, row, pin, path, or net and trace the physical cause. • Correct: Choose a lower or reshaped target for the measured constraint, then rerun the same scorecard.
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: Start from counted area, macro dominance, expected growth, physical-only cells, clock and hold buffering, spare strategy, routing access, PG reservation, voltage areas, and local density risk. Then test alternatives. • Suspicious: A copied percentage produces fragmented rows or severe local hot spots. • Hard stop: required legality or physical feasibility is missing or unexplained. Choose a lower or reshaped target for the measured constraint, then rerun the same scorecard.
Common Mistake
Do not hide the symptom with an arbitrary utilisation, halo, channel, blockage, pin move, or die-size change. A copied percentage produces fragmented rows or severe local hot spots.
What The Interviewer Is Testing
The interviewer is testing whether you can connect “How do you select target utilisation without using a universal percentage?” 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 a copied percentage produces fragmented rows or severe local hot spots. I would use the named objects and reports to decide whether to iterate, waive, or return the issue.”
Practical Example
Symptom: A copied percentage produces fragmented rows or severe local hot spots. Corrective path: Choose a lower or reshaped target for the measured constraint, then rerun the same scorecard.
Continue practising