How do rotation and mirroring change macro dataflow?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
They move pin walls relative to neighbours and may change supply-pin alignment. The macro outline can remain legal while routes become much longer.
Technical Explanation
Orientation changes the route entry points, not only the appearance. Use compiler-allowed orientations, symmetry data, power-pin requirements, snap points, and the direction of major buses. Repeated instances may need a consistent but not identical orientation.
Formula Or Decision Rule
Decision rule: minimise avoidable crossings and detours without violating macro legality.
What To Check
• Warning sign: A mirrored memory reverses bus order or points data pins into a blocked boundary. • Inspect: choose one affected region, macro, row, pin, path, or net and trace the physical cause. • Correct: Choose another allowed orientation or move the macro, then rerun pin-access and timing estimates.
Command Checks & Actions
• set_macro_constraints -allowed_orientations <orientation_list> <macro_collection>: records allowed macro or I/O placement constraints
• check_design -checks {dp_pre_macro_placement}: runs named design-planning check groups
Run only the commands needed for this question. Save the report with the floorplan version and analysis context.Healthy, Suspicious & Hard-stop Results
• Healthy: They move pin walls relative to neighbours and may change supply-pin alignment. The macro outline can remain legal while routes become much longer. • Suspicious: A mirrored memory reverses bus order or points data pins into a blocked boundary. • Hard stop: required legality or physical feasibility is missing or unexplained. Choose another allowed orientation or move the macro, then rerun pin-access and timing estimates.
Common Mistake
Do not hide the symptom with an arbitrary utilisation, halo, channel, blockage, pin move, or die-size change. A mirrored memory reverses bus order or points data pins into a blocked boundary.
What The Interviewer Is Testing
The interviewer is testing whether you can connect “How do rotation and mirroring change macro dataflow?” 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 mirrored memory reverses bus order or points data pins into a blocked boundary. I would use the named objects and reports to decide whether to iterate, waive, or return the issue.”
Practical Example
Symptom: A mirrored memory reverses bus order or points data pins into a blocked boundary. Corrective path: Choose another allowed orientation or move the macro, then rerun pin-access and timing estimates.
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