What is a feedthrough?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
A feedthrough is a signal that enters a block and leaves it without being logically consumed there. It may shorten a top-level route, but it spends pin, routing, and possibly buffering resources inside the block.
Technical Explanation
It is a corridor through a room that belongs to someone else. Feedthroughs can be original, created, buffered, reused, redundant, pure, mixed, or unused depending on design and tool classification.
Formula Or Decision Rule
Decision rule: use a feedthrough only when the top-level benefit justifies the block-level cost and ownership is explicit.
What To Check
• Warning sign: A detour is removed but the block gains crowded pin pairs or an illegal voltage-area crossing. • Inspect: choose one affected region, macro, row, pin, path, or net and trace the physical cause. • Correct: Review timing, pin alignment, routing capacity, reuse, and ownership; keep, reshape, buffer, or remove deliberately.
Command Checks & Actions
• check_feedthroughs -unused_feedthroughs -reused_feedthroughs -redundant: checks targeted feedthrough classes and constraints
• report_feedthroughs -include_original_feedthroughs -reporting_style net_based: reports feedthrough nets and traversed blocks
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 feedthrough is a signal that enters a block and leaves it without being logically consumed there. It may shorten a top-level route, but it spends pin, routing, and possibly buffering resources inside the block. • Suspicious: A detour is removed but the block gains crowded pin pairs or an illegal voltage-area crossing. • Hard stop: required legality or physical feasibility is missing or unexplained. Review timing, pin alignment, routing capacity, reuse, and ownership; keep, reshape, buffer, or remove deliberately.
Common Mistake
Do not hide the symptom with an arbitrary utilisation, halo, channel, blockage, pin move, or die-size change. A detour is removed but the block gains crowded pin pairs or an illegal voltage-area crossing.
What The Interviewer Is Testing
The interviewer is testing whether you can connect “What is a feedthrough?” to measurable physical evidence and an owned correction.
Practical Example
Symptom: A detour is removed but the block gains crowded pin pairs or an illegal voltage-area crossing. Corrective path: Review timing, pin alignment, routing capacity, reuse, and ownership; keep, reshape, buffer, or remove deliberately.
Continue practising