How do connectivity and timing guide macro placement?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
Use flylines, bus width, path criticality, producer-consumer order, I/O affinity, clock/reset sources, and hierarchy to propose macro regions.
Technical Explanation
The goal is not minimum centre-to-centre distance for every pair; it is a routable, timing-aware dataflow. Correlate high-volume or critical connections with macro pin sides and available corridors. Check the standard-cell logic that must sit between macros.
Formula Or Decision Rule
Decision rule: prioritise connections whose delay or routing demand is hardest to absorb elsewhere.
What To Check
• Warning sign: A macro is near its partner but their active pin walls face away or across a blockage. • Inspect: choose one affected region, macro, row, pin, path, or net and trace the physical cause. • Correct: Move or orient the pair, preserve cell space between stages, then compare named paths and congestion.
Command Checks & Actions
• create_placement -floorplan -timing_driven -congestion: runs early floorplan placement when -floorplan is used
• 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: Use flylines, bus width, path criticality, producer-consumer order, I/O affinity, clock/reset sources, and hierarchy to propose macro regions. • Suspicious: A macro is near its partner but their active pin walls face away or across a blockage. • Hard stop: required legality or physical feasibility is missing or unexplained. Move or orient the pair, preserve cell space between stages, then compare named paths and congestion.
Common Mistake
Do not hide the symptom with an arbitrary utilisation, halo, channel, blockage, pin move, or die-size change. A macro is near its partner but their active pin walls face away or across a blockage.
What The Interviewer Is Testing
The interviewer is testing whether you can connect “How do connectivity and timing guide macro placement?” 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 macro is near its partner but their active pin walls face away or across a blockage. I would use the named objects and reports to decide whether to iterate, waive, or return the issue.”
Practical Example
Symptom: A macro is near its partner but their active pin walls face away or across a blockage. Corrective path: Move or orient the pair, preserve cell space between stages, then compare named paths and congestion.
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