GDS / OASIS interop

Reticle’s interchange formats are only as good as what other tools make of them. This chapter records how Reticle’s GDS round-trip compares against two independent external tools, and whether KLayout can read Reticle’s conformant-OASIS writer.

The harness

scripts/interop/ drives a comparison headless inside the pinned hpretl/iic-osic-tools container (KLayout 0.29.x + gdspy 1.6), re-runnable with scripts/interop/run-interop.ps1. It:

1. generates two fixtures with gdspy (1 dbu = 1 nm);
2. round-trips each fixture (read then re-export) through Reticle (a standalone reticle-roundtrip driver on the host), KLayout, and gdspy;
3. normalizes every output with a single authoritative reader - KLayout renders each shape to an integer-dbu polygon (so path-vs-box representation differences are neutralized), and instance transforms are read with gdspy, which exposes the raw GDS STRANS rotation/magnification directly; and
4. exports each fixture as conformant OASIS (oasis_std) and has KLayout read it.

Because one reader normalizes every writer’s output, a divergence is attributable to the tool that wrote the file. The committed report and its machine-generated companion live under docs/interop/ in the repository.

Tooling note. The packet named gdstk; it is not preinstalled in the image and PEP 668 blocks a clean in-container pip install, so the harness uses gdspy (its same-author predecessor, preinstalled) as the second tool and stays reproducible with no network. If Docker is unavailable the runner prints the exact skipped command and exits 3, so the comparison can be recorded as not-run while the writer, the second PDK, and the GenTech refactor still ship.

What the round-trip preserves

On the clean fixture (a rectangle, a Manhattan polygon, a 45° polygon, a path, a label, a cell reference, and a 2×2 array), Reticle, KLayout, and gdspy round-trip the design identically - rendered geometry, labels, and instances all match, and KLayout reads Reticle’s OASIS output.

The documented divergence

On the odd fixture (seeded with a 1 nm sliver, round and custom-extension paths, a degenerate-vertex polygon, and a reference rotated 45° with magnification 2×), the geometry all round-trips cleanly, but one divergence surfaces in instance transforms:

Reticle’s placement model, Orientation, encodes only the eight orthogonal orientations (R0/R90/R180/R270 and mirrors). A non-orthogonal STRANS angle has no exact representation, so Reticle’s GDS importer snaps 45° to the nearest orthogonal orientation (90°) rather than dropping it silently; the magnification and origin survive. This is a modelling limitation, not a reader/writer bug - Reticle is a Manhattan-plus-45°-fill layout tool whose instance transforms are orthogonal by design. It is called out here and in the committed report rather than hidden.

See the full report at docs/interop/gds-oasis-divergence-report.md.