Why do row orientation and fragments matter?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
Row orientation must support the library’s legal cell orientations and power-rail alignment. Tiny row fragments consume bookkeeping space but may be unusable for real cells.
Technical Explanation
Alternating rows often help rail alignment, but the exact pattern is library and methodology dependent. Inspect the first-row choice, alternating pattern, multiple-height compatibility, fragments near macros, and row/voltage-area ownership.
Formula Or Decision Rule
Decision rule: keep only row segments that can legally accept intended cells and connect to the required supplies.
What To Check
• Warning sign: Rows flip incorrectly, extend through macros, or leave slivers too short for useful placement. • Inspect: choose one affected region, macro, row, pin, path, or net and trace the physical cause. • Correct: Recreate or trim rows using the approved site and row pattern; never assume one universal flip rule.
Command Checks & Actions
• create_site_array -name <array> -site <site> -boundary <boundary> -flip_alternate_row <true_or_false>: creates a bounded site array
• report_design -floorplan: reports the floorplan state understood by the tool
Run only the commands needed for this question. Save the report with the floorplan version and analysis context.Healthy, Suspicious & Hard-stop Results
• Healthy: Row orientation must support the library’s legal cell orientations and power-rail alignment. Tiny row fragments consume bookkeeping space but may be unusable for real cells. • Suspicious: Rows flip incorrectly, extend through macros, or leave slivers too short for useful placement. • Hard stop: required legality or physical feasibility is missing or unexplained. Recreate or trim rows using the approved site and row pattern; never assume one universal flip rule.
Common Mistake
Do not hide the symptom with an arbitrary utilisation, halo, channel, blockage, pin move, or die-size change. Rows flip incorrectly, extend through macros, or leave slivers too short for useful placement.
What The Interviewer Is Testing
The interviewer is testing whether you can connect “Why do row orientation and fragments matter?” to measurable physical evidence and an owned correction.
Practical Example
Symptom: Rows flip incorrectly, extend through macros, or leave slivers too short for useful placement. Corrective path: Recreate or trim rows using the approved site and row pattern; never assume one universal flip rule.
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