check_feedthroughs reports unused, reused, and constraint violations together. How do you triage them?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
Separate classifications, inspect named nets and blocks, and compare each with intended topology, pin pairs, buffering, and reuse policy. The categories require different decisions.
Technical Explanation
One total count mixes waste, intentional reuse, and real interface defects. Run targeted checks and reports. For each net record original/created status, pure/mixed path, owner, timing need, and physical access.
Formula Or Decision Rule
Decision rule: every remaining item is intentional, legal, useful, and owned.
What To Check
• Warning sign: All feedthrough warnings are waived because some are intentional. • Inspect: choose one affected region, macro, row, pin, path, or net and trace the physical cause. • Correct: Remove unused/redundant paths, repair constraint violations, document justified reuse, and rerun targeted categories.
Command Checks & Actions
• check_feedthroughs -unused_feedthroughs -reused_feedthroughs -redundant -net_constraints -topo_constraints: checks targeted feedthrough classes and constraints
• report_feedthroughs -reporting_style net_based: reports feedthrough nets and traversed blocks
Run only the commands needed for this question. Save the report with the floorplan version and analysis context.Healthy, Suspicious & Hard-stop Results
• Healthy: Separate classifications, inspect named nets and blocks, and compare each with intended topology, pin pairs, buffering, and reuse policy. The categories require different decisions. • Suspicious: All feedthrough warnings are waived because some are intentional. • Hard stop: required legality or physical feasibility is missing or unexplained. Remove unused/redundant paths, repair constraint violations, document justified reuse, and rerun targeted categories.
Common Mistake
Do not hide the symptom with an arbitrary utilisation, halo, channel, blockage, pin move, or die-size change. All feedthrough warnings are waived because some are intentional.
What The Interviewer Is Testing
The interviewer is testing whether you can connect “check_feedthroughs reports unused, reused, and constraint violations together. How do you triage them?” 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 all feedthrough warnings are waived because some are intentional. I would use the named objects and reports to decide whether to iterate, waive, or return the issue.”
Practical Example
Symptom: All feedthrough warnings are waived because some are intentional. Corrective path: Remove unused/redundant paths, repair constraint violations, document justified reuse, and rerun targeted categories.
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