How do you decide whether a row fragment is useful?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
Measure its legal length, site alignment, voltage-area ownership, nearby keepouts, and whether intended cells plus required spacing can fit.
Technical Explanation
A fragment is useful only if a real placement can use it without blocking access. Tiny fragments often appear beside macros, notches, halos, or boundaries. They inflate nominal row area without adding practical capacity.
Formula Or Decision Rule
Usable row sites = floor(fragment length / site width), after legal exclusions.
What To Check
• Warning sign: Many fragments exist but placement demand concentrates elsewhere. • Inspect: choose one affected region, macro, row, pin, path, or net and trace the physical cause. • Correct: Trim or merge the cause, adjust macro/blockage geometry, and recompute usable row capacity.
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: Measure its legal length, site alignment, voltage-area ownership, nearby keepouts, and whether intended cells plus required spacing can fit. • Suspicious: Many fragments exist but placement demand concentrates elsewhere. • Hard stop: required legality or physical feasibility is missing or unexplained. Trim or merge the cause, adjust macro/blockage geometry, and recompute usable row capacity.
Common Mistake
Do not hide the symptom with an arbitrary utilisation, halo, channel, blockage, pin move, or die-size change. Many fragments exist but placement demand concentrates elsewhere.
What The Interviewer Is Testing
The interviewer is testing whether you can connect “How do you decide whether a row fragment is useful?” 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 many fragments exist but placement demand concentrates elsewhere. I would use the named objects and reports to decide whether to iterate, waive, or return the issue.”
Practical Example
Symptom: Many fragments exist but placement demand concentrates elsewhere. Corrective path: Trim or merge the cause, adjust macro/blockage geometry, and recompute usable row capacity.
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