README.md

@@ -4,8 +4,8 @@
 The EDA repo owns canvas editing, YAML export, login, and API routing. This
 repo owns the Nazca-based GDS build flow: it reads saved cell YAML files,
 loads the selected technology manifest, loads PDK GDS assets, registers
-routable pins, connects bundle links through `mxpic_forge.Route`, and exports
-the final GDS.
+routable pins, connects bundle links through `mxpic_forge.Route` when available
+or Nazca `interconnects.Interconnect` as a fallback, and exports the final GDS.
 
 ## High Level Flow
 
@@ -34,10 +34,12 @@ Canvas Build GDS
 -> downloadable <project>.gds
 ```
 
-If `mxpic_router`, `mxpic_forge`, Nazca, or optional `gdstk` are absent, the
+If `mxpic_router`, Nazca, or optional `gdstk` are absent, the
 EDA server can still run canvas and login pages. Build actions are where the
-router stack is required. For Build Layout, the YAML is still saved and SVG
-preview is skipped when the router stack is missing.
+router stack is required. `mxpic_forge` improves routing when present, but is
+not required because the router falls back to Nazca Interconnect. For Build
+Layout, the YAML is still saved and SVG preview is skipped when the required
+router stack is missing.
 
 ## Runtime Stack
 
@@ -51,18 +53,21 @@ require_router_stack()
 -> import mxpic_router
 -> import nazca
 -> optionally import gdstk for SVG preview
--> import mxpic_router.builder._import_mxpic_forge_route()
+-> import mxpic_router.builder._import_route_backend()
+   -> first tries mxpic_router.builder._import_mxpic_forge_route()
       -> adds sibling ../mxpic_forge to sys.path
       -> removes any already-loaded non-forge mxpic modules
       -> from mxpic import Route
+   -> if mxpic_forge is absent:
+      -> uses nazca.interconnects.Interconnect through a Route-compatible adapter
 ```
 
 Important package naming:
 
 - `mxpic_router` is this active router package.
 - `mxpic_router_legacy` is the old internal legacy package.
-- `mxpic` should resolve to `mxpic_forge`, because `mxpic_forge` provides
-  `Route`.
+- `mxpic` should resolve to `mxpic_forge` when that checkout is present,
+  because `mxpic_forge` provides the preferred `Route` backend.
 
 ## Inputs To mxpic_router
 
@@ -415,7 +420,7 @@ bundles:
 For each link:
 
 ```text
-builder._route_link(link, pin_map, Route, warnings)
+builder._route_link(link, pin_map, RouteBackend, warnings)
 -> route = Route(
        radius=link.radius or 10,
        width=link.width,
@@ -455,7 +460,7 @@ otherwise            -> bend_p2p
 missing method       -> fallback to sbend_p2p
 ```
 
-Then it calls the selected `mxpic_forge.Route` method:
+Then it calls the selected route backend method:
 
 ```python
 route_method(
@@ -492,7 +497,7 @@ mxpic_router/eda_loader.py
 
 mxpic_router/builder.py
 -> import Nazca
--> import mxpic_forge Route
+-> import mxpic_forge Route or Nazca Interconnect fallback
 -> apply technology manifest
 -> load all project YAML specs
 -> build basic, project, and PDK instances
@@ -510,9 +515,11 @@ mxpic_router_legacy/
   definitions. The frontend route editor and Nazca build path both consume it.
 - Keep PDK component metadata YAML beside its GDS files. The router needs that
   metadata to recreate pins after `nd.load_gds`.
-- Avoid reintroducing an internal `mxpic` package inside this repo. The name
-  `mxpic` must continue to resolve to `mxpic_forge`.
+- Avoid reintroducing an internal `mxpic` package inside this repo. When the
+  forge checkout is present, the name `mxpic` must continue to resolve to
+  `mxpic_forge`.
 - When adding a new routing family or xsection, update `technology.yml` first,
-  then verify that `mxpic_forge.Route` supports the required route method.
+  then verify that the selected route backend supports the required route
+  method.
 - When adding a new component source, make sure it eventually contributes pins
   to `pin_map`; otherwise bundle links can load but cannot route.

mxpic_router/builder.py

@@ -19,7 +19,7 @@ def build_project_gds(
 ) -> dict:
     import nazca as nd
 
-    Route = _import_mxpic_forge_route()
+    Route = _import_route_backend(nd)
     manifest = load_technology_manifest(technology_manifest_path)
     apply_technology_manifest(manifest, nd)
 
@@ -573,6 +573,89 @@ def _safe_float(value, default=0.0):
         return default
 
 
+class _NazcaInterconnectRoute:
+    """Small mxpic_forge.Route-compatible adapter around Nazca Interconnect."""
+
+    backend_name = "nazca Interconnect"
+
+    def __init__(self, radius=None, width=None, xs=None, PCB=False):
+        self.radius = radius
+        self.width = width
+        self.xs = xs
+        self.PCB = PCB
+        self._interconnect = self._create_interconnect(radius=radius, width=width, xs=xs, PCB=PCB)
+
+    @staticmethod
+    def _create_interconnect(radius=None, width=None, xs=None, PCB=False):
+        import nazca as nd
+
+        return nd.interconnects.Interconnect(radius=radius, width=width, xs=xs, PCB=PCB)
+
+    def strt_p2p(self, pin1=None, pin2=None, width=None, xs=None, arrow=True, **kwargs):
+        return self._interconnect.strt_p2p(
+            pin1=pin1,
+            pin2=pin2,
+            width=self._route_width(width),
+            xs=self._route_xs(xs),
+            arrow=arrow,
+        )
+
+    def sbend_p2p(self, pin1=None, pin2=None, width=None, radius=None, xs=None, arrow=True, **kwargs):
+        return self._interconnect.sbend_p2p(
+            pin1=pin1,
+            pin2=pin2,
+            width=self._route_width(width),
+            radius=self._route_radius(radius),
+            xs=self._route_xs(xs),
+            arrow=arrow,
+        )
+
+    def ubend_p2p(self, pin1=None, pin2=None, width=None, radius=None, xs=None, arrow=True, **kwargs):
+        return self._interconnect.ubend_p2p(
+            pin1=pin1,
+            pin2=pin2,
+            width=self._route_width(width),
+            radius=self._route_radius(radius),
+            xs=self._route_xs(xs),
+            arrow=arrow,
+        )
+
+    def bend_p2p(self, pin1=None, pin2=None, width=None, radius=None, xs=None, arrow=True, **kwargs):
+        route_method = getattr(self._interconnect, "bend_strt_bend_p2p", None)
+        if route_method is None:
+            route_method = getattr(self._interconnect, "strt_bend_strt_p2p")
+        return route_method(
+            pin1=pin1,
+            pin2=pin2,
+            width=self._route_width(width),
+            radius=self._route_radius(radius),
+            xs=self._route_xs(xs),
+            arrow=arrow,
+        )
+
+    def _route_width(self, width):
+        return self.width if width is None else width
+
+    def _route_radius(self, radius):
+        return self.radius if radius is None else radius
+
+    def _route_xs(self, xs):
+        return self.xs if xs is None else xs
+
+
+def _import_route_backend(nd=None):
+    try:
+        route = _import_mxpic_forge_route()
+        setattr(route, "backend_name", getattr(route, "backend_name", "mxpic_forge Route"))
+        return route
+    except Exception:
+        if nd is None:
+            import nazca as nd
+        if not hasattr(nd, "interconnects") or not hasattr(nd.interconnects, "Interconnect"):
+            raise
+        return _NazcaInterconnectRoute
+
+
 def _import_mxpic_forge_route():
     forge_root = os.path.abspath(os.path.join(os.path.dirname(__file__), "..", "..", "mxpic_forge"))
     if os.path.isdir(forge_root) and forge_root not in sys.path:

tests/test_eda_router_contract.py

@@ -221,6 +221,62 @@ class EdaRouterPinsContractTest(unittest.TestCase):
         )
         self.assertEqual(_metadata_pins(metadata, r"D:\mxpic\some_project_layout"), {})
 
+    def test_route_backend_falls_back_to_nazca_interconnect_when_forge_is_absent(self):
+        import mxpic_router.builder as builder
+
+        class FakeInterconnect:
+            calls = []
+
+            def __init__(self, radius=None, width=None, xs=None, PCB=False):
+                self.radius = radius
+                self.width = width
+                self.xs = xs
+                self.PCB = PCB
+
+            def strt_p2p(self, **kwargs):
+                self.calls.append(("strt_p2p", kwargs))
+                return "straight"
+
+            def sbend_p2p(self, **kwargs):
+                self.calls.append(("sbend_p2p", kwargs))
+                return "sbend"
+
+            def ubend_p2p(self, **kwargs):
+                self.calls.append(("ubend_p2p", kwargs))
+                return "ubend"
+
+            def bend_strt_bend_p2p(self, **kwargs):
+                self.calls.append(("bend_strt_bend_p2p", kwargs))
+                return "bend"
+
+        class FakeInterconnects:
+            Interconnect = FakeInterconnect
+
+        class FakeNazca:
+            interconnects = FakeInterconnects
+
+        original_import = builder._import_mxpic_forge_route
+        original_create = builder._NazcaInterconnectRoute._create_interconnect
+        try:
+            builder._import_mxpic_forge_route = lambda: (_ for _ in ()).throw(ImportError("no forge"))
+            builder._NazcaInterconnectRoute._create_interconnect = staticmethod(
+                lambda **kwargs: FakeInterconnect(**kwargs)
+            )
+
+            route_backend = builder._import_route_backend(FakeNazca)
+            route = route_backend(radius=20, width=0.7, xs="strip", PCB=False)
+
+            self.assertEqual(route.backend_name, "nazca Interconnect")
+            self.assertEqual(route.strt_p2p(pin1="a", pin2="b", arrow=False), "straight")
+            self.assertEqual(route.bend_p2p(pin1="a", pin2="b", radius=10, arrow=False), "bend")
+            self.assertEqual(FakeInterconnect.calls[0][0], "strt_p2p")
+            self.assertEqual(FakeInterconnect.calls[0][1]["width"], 0.7)
+            self.assertEqual(FakeInterconnect.calls[1][0], "bend_strt_bend_p2p")
+            self.assertEqual(FakeInterconnect.calls[1][1]["radius"], 10)
+        finally:
+            builder._import_mxpic_forge_route = original_import
+            builder._NazcaInterconnectRoute._create_interconnect = original_create
+
 
 if __name__ == "__main__":
     unittest.main()