What makes a macro channel usable?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
A channel is usable only when its width and geometry support signal tracks, facing pins, power straps, vias, shielding, buffers where needed, and technology spacing.
Technical Explanation
Visible white space is not automatically routable space. Macro-to-macro, macro-to-boundary, and macro-to-cell spacing serve different purposes. Notches and concave corners can remove practical access.
Formula Or Decision Rule
Decision rule: channel capacity after PG and blockage reservation must exceed the expected directional demand with legal access.
What To Check
• Warning sign: The channel is open in the drawing but straps and pin access consume all usable tracks. • Inspect: choose one affected region, macro, row, pin, path, or net and trace the physical cause. • Correct: Measure demand and capacity, then change spacing, orientation, pin plan, PG reservation, or layer use and rerun.
Command Checks & Actions
• create_channel_congestion_map -channel_width_threshold <width>: estimates congestion in channel regions
• report_congestion -mode summary: reports routing demand, capacity, overflow, or hot spots
Run only the commands needed for this question. Save the report with the floorplan version and analysis context.Healthy, Suspicious & Hard-stop Results
• Healthy: A channel is usable only when its width and geometry support signal tracks, facing pins, power straps, vias, shielding, buffers where needed, and technology spacing. • Suspicious: The channel is open in the drawing but straps and pin access consume all usable tracks. • Hard stop: required legality or physical feasibility is missing or unexplained. Measure demand and capacity, then change spacing, orientation, pin plan, PG reservation, or layer use and rerun.
Common Mistake
Do not hide the symptom with an arbitrary utilisation, halo, channel, blockage, pin move, or die-size change. The channel is open in the drawing but straps and pin access consume all usable tracks.
What The Interviewer Is Testing
The interviewer is testing whether you can connect “What makes a macro channel usable?” to measurable physical evidence and an owned correction.
Practical Example
Symptom: The channel is open in the drawing but straps and pin access consume all usable tracks. Corrective path: Measure demand and capacity, then change spacing, orientation, pin plan, PG reservation, or layer use and rerun.
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