Fixed package pins fight the logical dataflow. What can floorplanning change?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
Treat package pins as constraints, then adapt macro locations, block pins, feedthroughs, aspect ratio, and routing corridors around them. Escalate only when the package interface itself is negotiable.
Technical Explanation
You cannot solve a fixed doorway by pretending it moved. Compare crossings, bus order, critical paths, macro affinity, power/ground distribution, and congestion. Preserve differential and analogue constraints.
Formula Or Decision Rule
Decision rule: accept the package only with a credible on-die route and owned timing/congestion risk.
What To Check
• Warning sign: Pins are moved locally without package approval. • Inspect: choose one affected region, macro, row, pin, path, or net and trace the physical cause. • Correct: Keep fixed constraints, redesign internal geography, or return a quantified package change request.
Command Checks & Actions
• report_pin_placement -format {layer side offset}: reports pin layer, side, and offset
• report_congestion -mode hot_spot: reports routing demand, capacity, overflow, or hot spots
• report_timing: reports timing paths in the active analysis context
Run only the commands needed for this question. Save the report with the floorplan version and analysis context.Healthy, Suspicious & Hard-stop Results
• Healthy: Treat package pins as constraints, then adapt macro locations, block pins, feedthroughs, aspect ratio, and routing corridors around them. Escalate only when the package interface itself is negotiable. • Suspicious: Pins are moved locally without package approval. • Hard stop: required legality or physical feasibility is missing or unexplained. Keep fixed constraints, redesign internal geography, or return a quantified package change request.
Common Mistake
Do not hide the symptom with an arbitrary utilisation, halo, channel, blockage, pin move, or die-size change. Pins are moved locally without package approval.
What The Interviewer Is Testing
The interviewer is testing whether you can connect “Fixed package pins fight the logical dataflow. What can floorplanning change?” 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 pins are moved locally without package approval. I would use the named objects and reports to decide whether to iterate, waive, or return the issue.”
Practical Example
Symptom: Pins are moved locally without package approval. Corrective path: Keep fixed constraints, redesign internal geography, or return a quantified package change request.
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