How do you decide whether a row fragment is useful?

Short Answer

A row fragment reported by the tool is only "usable capacity" if a real cell can actually legally land there — the tool counting it toward total row area doesn't mean it's actually placeable. ), its site alignment, which voltage area it belongs to, and whether nearby keepouts or halos block access to it.

Technical Explanation

• These fragments show up constantly beside macros, in notches, around halos, and at block boundaries — anywhere a macro or blockage cuts a row short.
• The danger is that tiny, unusable fragments inflate your nominal row-area number, making utilisation and capacity estimates look better than the design can actually deliver.
• Treat "is this fragment useful" as its own explicit check during floorplan sign-off, not something you assume is covered by the overall utilisation report.

Formula Or Decision Rule

Usable row sites = floor(fragment length / site width), after legal exclusions.

What To Check

• Warning sign: Many fragments exist but placement demand concentrates elsewhere.
• Inspect: choose one affected region, macro, row, pin, path, or net and trace the physical cause.
• Correct: Trim or merge the cause, adjust macro/blockage geometry, and recompute usable row capacity.

Healthy, Suspicious & Hard-stop Results

• Healthy: Measure its legal length, site alignment, voltage-area ownership, nearby keepouts, and whether intended cells plus required spacing can fit.
• Hard stop: required legality or physical feasibility is missing or unexplained.

What The Interviewer Is Testing

” to measurable physical evidence and an owned correction.

Follow-up Question & Model Response

"* Candidate Model Response: Model response: “I would change it if the same controlled rerun shows that many fragments exist but placement demand concentrates elsewhere. ”