Metrology

reticle-metrology turns a laid-out Document into a small set of quantitative reports. Every measurement runs on the CPU with exact integer geometry (no GPU, no sampling), over the flattened top cell, and never mutates the document. It reads only the public APIs of reticle-model, reticle-geometry, and reticle-extract.

Reports

Area and perimeter per layer. For each layer that carries geometry, area::report unions that layer’s flattened shapes on the exact i_overlay integer engine (through reticle_geometry::polygon_boolean) and returns a LayerMetrics { layer, area, perimeter, shape_count }. Area is the covered area in DBU squared with overlaps counted once; perimeter is the total union boundary length in DBU, including the boundaries of holes. Both are exact for integer (manhattan) geometry. A property test cross-checks area and perimeter against an independent coordinate-compression oracle over 200 random rectangle layouts.

Connectivity statistics. connectivity::stats extracts nets with reticle-extract using the SKY130 via/contact stack, so conductors on different layers joined by a via count as one net. It reports net_count, net_sizes (shapes per net, largest first), total_shapes, and max_fanout (the largest net’s shape count).

Antenna ratio. antenna::check is a deliberately small screen of the antenna effect: for each net it computes connected_metal_area / gate_area over a SKY130 layer subset and flags nets above a threshold. The semantics and their limits are stated in full in the module documentation and repeated here so no one mistakes the screen for sign-off:

• gate_area is the union area of polysilicon (poly, 66/20) on the net, approximated as all poly, not poly intersected with diffusion.
• connected_metal_area is the union area of li1 (67/20) and met1..met4 (68/20, 69/20, 70/20, 71/20) on the net. Contacts and vias join nets but are not counted as metal.
• A net with no poly has no gate and is never flagged.

This reduces the whole net to a single total-metal-to-gate ratio. It does not model per-metal-layer cumulative ratios across fabrication steps, sidewall or perimeter terms, diffusion-diode protection, or partial-route (as-built) area. Treat a flag as “worth a closer look”, not as a rule violation.

Export

MetrologyReport::generate bundles all three reports; to_csv and to_markdown render the bundle deterministically (newline-only line endings, fixed number formatting), so the output is byte-stable and safe to diff. Golden tests pin both renderings.

Scope

This is the CPU half of the metrology work. A GPU density overlay was scoped and explicitly deferred (see the metrology decision record); it is not built here.