What are whitespace and target utilisation?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
Whitespace is the placeable area left after counted cells are assigned area. Target utilisation is the planned fraction of placeable area occupied by the explicitly counted objects.
Technical Explanation
Whitespace is working room for optimisation cells, routing access, and change; it is not automatically wasted silicon. A utilisation value is incomplete until its numerator and denominator are stated. Reserved channels and blocked regions can make local capacity much lower than the global number.
Formula Or Decision Rule
Target utilisation = counted placeable object area / planned placeable area.
What To Check
• Warning sign: A low global utilisation is quoted while one region has no usable whitespace. • Inspect: choose one affected region, macro, row, pin, path, or net and trace the physical cause. • Correct: Map local density and blocked area, then change the physical plan rather than trusting one average.
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: Whitespace is the placeable area left after counted cells are assigned area. Target utilisation is the planned fraction of placeable area occupied by the explicitly counted objects. • Suspicious: A low global utilisation is quoted while one region has no usable whitespace. • Hard stop: required legality or physical feasibility is missing or unexplained. Map local density and blocked area, then change the physical plan rather than trusting one average.
Common Mistake
Do not hide the symptom with an arbitrary utilisation, halo, channel, blockage, pin move, or die-size change. A low global utilisation is quoted while one region has no usable whitespace.
What The Interviewer Is Testing
The interviewer is testing whether you can connect “What are whitespace and target utilisation?” to measurable physical evidence and an owned correction.
Practical Example
Symptom: A low global utilisation is quoted while one region has no usable whitespace. Corrective path: Map local density and blocked area, then change the physical plan rather than trusting one average.
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