Why do macro orientation and alignment matter?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
Orientation changes which side the pins face; alignment determines whether the macro sits on required grids. A geometrically legal rotation can still damage dataflow or power access.
Technical Explanation
Turning a cabinet changes which way its doors open. For a macro, the “doors” are signal and power pins. Use only orientations allowed by the macro symmetry and compiler data. Check block-grid or FinFET-grid alignment where applicable.
Formula Or Decision Rule
Decision rule: an orientation must be library-legal, grid-legal, power-compatible, and helpful to pin access.
What To Check
• Warning sign: The macro is legal but its busiest pins face the boundary or another dense pin wall. • Inspect: choose one affected region, macro, row, pin, path, or net and trace the physical cause. • Correct: Choose an allowed orientation that supports dataflow and supplies, snap it correctly, and recheck access.
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: Orientation changes which side the pins face; alignment determines whether the macro sits on required grids. A geometrically legal rotation can still damage dataflow or power access. • Suspicious: The macro is legal but its busiest pins face the boundary or another dense pin wall. • Hard stop: required legality or physical feasibility is missing or unexplained. Choose an allowed orientation that supports dataflow and supplies, snap it correctly, and recheck access.
Common Mistake
Do not hide the symptom with an arbitrary utilisation, halo, channel, blockage, pin move, or die-size change. The macro is legal but its busiest pins face the boundary or another dense pin wall.
What The Interviewer Is Testing
The interviewer is testing whether you can connect “Why do macro orientation and alignment matter?” to measurable physical evidence and an owned correction.
Practical Example
Symptom: The macro is legal but its busiest pins face the boundary or another dense pin wall. Corrective path: Choose an allowed orientation that supports dataflow and supplies, snap it correctly, and recheck access.
Continue practising