--fanout: leave out pins a same-net pour on their layer already joins

Committed vias were checked for hole spacing, but a route's own vias are
not committed until it is done, so a route hopping layers (more of them
on 6 layers) could put two of its vias 0.41 mm apart, as th-eda's
6-layer flight controller showed. A via is now also checked against
layer changes earlier on its own route.

bench/diagnose.py

@@ -106,6 +106,15 @@ def _capture_conflicts() -> list:
     return log
 
 
+def _wall_name(wall, names) -> str:
+    if isinstance(wall, str):
+        if wall.startswith("fixed copper of net "):
+            net = int(wall.rsplit(" ", 1)[1])
+            return f"fixed copper of {names.get(net, net)}"
+        return wall
+    return names.get(wall, "pads/keepouts")
+
+
 def _gap(a, b) -> int:
     dx = max(b.ll.x - a.ur.x, a.ll.x - b.ur.x, 0)
     dy = max(b.ll.y - a.ur.y, a.ll.y - b.ur.y, 0)
@@ -118,6 +127,25 @@ def _fresh(seen) -> GridRouter:
     return router
 
 
+def _static_wall(router: GridRouter, node) -> str:
+    """What static copper closes a node: a keepout, copper already on the
+    board (a fixed via or track, by net), or a pad."""
+    if node in router._keepout:
+        return "keepout"
+    fixed = getattr(router, "_diag_fixed", None)
+    if fixed is None:
+        fixed = router._diag_fixed = {}
+        margin = router.clearance + router.half_width
+        for net, layers, box in router.board.get_fixed_copper():
+            for cell in router._cells_in_box(box, margin):
+                for layer in layers:
+                    fixed[(*cell, layer)] = net
+    net = fixed.get(node)
+    if net is not None:
+        return f"fixed copper of net {net}"
+    return "pads"
+
+
 def _flood(router: GridRouter, pin, net_no: int, conns) -> tuple[int, Counter]:
     """How many nodes a pin can reach through free cells (up to FLOOD_LIMIT),
     and which other nets' copper bounds the region."""
@@ -146,7 +174,7 @@ def _flood(router: GridRouter, pin, net_no: int, conns) -> tuple[int, Counter]:
                 for owner in owners:
                     walls[conns[owner].net_no] += 1
                 if not owners:
-                    walls[0] += 1  # a pad or keepout
+                    walls[_static_wall(router, n)] += 1
                 continue
             seen.add(n)
             frontier.append(n)
@@ -224,7 +252,9 @@ def diagnose(
                     if reach < FLOOD_LIMIT:
                         walled.append({
                             "pin": end, "reach": reach,
-                            "walls": [names.get(n, "pads/keepouts") for n, _ in walls.most_common(4)],
+                            "walls": [
+                                _wall_name(n, names) for n, _ in walls.most_common(4)
+                            ],
                         })
             row["kind"] = "walled-in" if walled else "congestion"
             if walled:

src/freeroute/board/build.py

@@ -23,6 +23,7 @@ the containment invariant, and pads are centre-symmetric in practice).
 from __future__ import annotations
 
 import math
+import re
 
 from freeroute.dsn.model import DsnBoard
 from freeroute.dsn.shapes import Circle, Path, Polygon, Rectangle, Shape
@@ -38,6 +39,9 @@ from .transform import CoordinateTransform
 
 __all__ = ["build_board"]
 
+# DSN units per micrometre, for drills KiCad gives in um in via padstack names
+_DSN_PER_UM = {"um": 1.0, "mm": 0.001, "mil": 1 / 25.4, "inch": 1 / 25400}
+
 
 def build_board(dsn: DsnBoard) -> BasicBoard:
     """Construct a :class:`BasicBoard` from a parsed :class:`DsnBoard`."""
@@ -503,10 +507,15 @@ def _insert_wiring(dsn: DsnBoard, board: BasicBoard, transform: CoordinateTransf
         location = transform.dsn_to_board_point(via.x, via.y)
         pad = _pad_tile(max(padstack.shapes, key=_shape_extent), transform)
         box = pad.bounding_box()
+        drill = re.search(r"_([\d.]+):([\d.]+)_um", via.padstack)
+        drill_board = (
+            round(transform.dsn_to_board(float(drill.group(2)) * _DSN_PER_UM.get(dsn.unit, 1.0)))
+            if drill else 0
+        )
         board.insert(
             Via(
                 net_nos=[numbers[via.net]], fixed=True, padstack_name=via.padstack,
-                location=location, layers=sorted(layers or signal_layers),
+                drill=drill_board, location=location, layers=sorted(layers or signal_layers),
                 shape=IntBox(box.ll.x + location.x, box.ll.y + location.y,
                              box.ur.x + location.x, box.ur.y + location.y),
             )

src/freeroute/board/items.py

@@ -117,6 +117,10 @@ class Via(Item):
     #: layer indices the via's pads occupy, and the largest pad as a box
     layers: list[int] = field(default_factory=list)
     shape: object = None
+    #: drill diameter in board units, when the padstack name gives it
+    drill: int = 0
+    #: placed by the router's fan-out, not on the board yet: written out
+    generated: bool = False
 
 
 @dataclass
@@ -130,6 +134,8 @@ class Trace(Item):
     layer: int = 0
     half_width: int = 0
     corners: list[IntPoint] = field(default_factory=list)
+    #: placed by the router's fan-out, not on the board yet: written out
+    generated: bool = False
 
     def is_empty(self) -> bool:
         return len(self.corners) < 2

src/freeroute/cli.py

@@ -30,8 +30,11 @@ from freeroute.ses import write_ses
 #: which optional flags each engine actually implements. Anything not listed for
 #: an engine is rejected by :func:`_validate` rather than quietly ignored.
 ENGINE_OPTIONS: dict[str, frozenset[str]] = {
-    "grid": frozenset({"rip_up", "max_passes", "seed", "orders", "promote", "access", "rollback"}),
-    "exact": frozenset({"shove", "diagonal", "rip_up", "max_passes", "seed", "orders", "promote", "access", "rollback"}),
+    "grid": frozenset({"rip_up", "max_passes", "seed", "orders", "promote", "access", "rollback", "fanout"}),
+    "exact": frozenset(
+        {"shove", "diagonal", "rip_up", "max_passes", "seed", "orders", "promote", "access",
+         "rollback", "fanout"}
+    ),
     "room": frozenset({"shove", "pack"}),
 }
 
@@ -47,6 +50,7 @@ _FLAG_NAMES = {
     "promote": "--promote-failures",
     "access": "--access-cost",
     "rollback": "--no-rollback",
+    "fanout": "--fanout",
 }
 
 
@@ -175,6 +179,30 @@ def build_parser() -> argparse.ArgumentParser:
         "connections a rip-up displaces are rerouted at once and the rip-up is undone "
         "if fewer connections end up routed",
     )
+    parser.add_argument(
+        "--hole-to-hole",
+        type=float,
+        default=0.25,
+        metavar="MM",
+        help="grid and exact engines: least distance between the edges of any two via "
+        "holes, of one net or two (KiCad's min_hole_to_hole; default 0.25)",
+    )
+    parser.add_argument(
+        "--fanout",
+        nargs="?",
+        const="all",
+        choices=["all", "supply"],
+        help="grid and exact engines: before routing, give every fine-pitch pin a stub "
+        "outward past its pad row (and a via to its plane, for a plane net), committed "
+        "as copper so later routes cannot wall it in; --fanout supply: plane pins only",
+    )
+    parser.add_argument(
+        "--fanout-min-pins",
+        type=int,
+        default=32,
+        metavar="N",
+        help="with --fanout: fan out only packages with at least N fine-pitch pins (default 32)",
+    )
     parser.add_argument(
         "--jobs",
         type=int,
@@ -205,6 +233,7 @@ def main(argv: list[str] | None = None) -> int:
             ("promote", args.promote_failures is not None),
             ("access", args.access_cost is not None),
             ("rollback", not args.rollback),
+            ("fanout", bool(args.fanout)),
         )
         if asked
     ]
@@ -239,6 +268,9 @@ def main(argv: list[str] | None = None) -> int:
             "resolution": 2 if args.grid_resolution is None else args.grid_resolution,
             "heuristic_weight": args.heuristic_weight,
             "access_cost": args.access_cost or 0.0,
+            "hole_to_hole_mm": args.hole_to_hole,
+            "fanout": args.fanout or False,
+            "fanout_min_pins": args.fanout_min_pins,
             "rollback": args.rollback,
         }
     elif args.engine == "grid":
@@ -249,6 +281,9 @@ def main(argv: list[str] | None = None) -> int:
             "edge_clearance_mm": args.edge_clearance,
             "resolution": 1 if args.grid_resolution is None else args.grid_resolution,
             "access_cost": args.access_cost or 0.0,
+            "hole_to_hole_mm": args.hole_to_hole,
+            "fanout": args.fanout or False,
+            "fanout_min_pins": args.fanout_min_pins,
             "rollback": args.rollback,
         }
     if args.engine == "room":
@@ -287,6 +322,14 @@ def main(argv: list[str] | None = None) -> int:
         print(f"freeroute: {len(missing)} connection(s) not routed:", file=sys.stderr)
         for net, a, b, _zone in missing:
             print(f"  {net}: {a} to {b}", file=sys.stderr)
+    if result.narrowed:
+        print(
+            f"freeroute: {len(result.narrowed)} connection(s) of a wider net class only fitted "
+            "at the default width; their nets are written at the default width:",
+            file=sys.stderr,
+        )
+        for net, a, b in result.narrowed:
+            print(f"  {net}: {a} to {b}", file=sys.stderr)
     if in_zone:
         print(
             f"freeroute: {len(in_zone)} more connection(s) left to a zone fill that may join them:",

src/freeroute/route/exact_router.py

@@ -31,7 +31,7 @@ from dataclasses import dataclass, field
 import math
 
 from freeroute.board.board import BasicBoard
-from freeroute.board.items import Pin
+from freeroute.board.items import Pin, Via
 from freeroute.board.search_tree import ShapeSearchTree, TreeShape
 from freeroute.geometry import (
     IntBox,
@@ -99,6 +99,9 @@ def route_board_exact(
     route_first: frozenset | None = None,
     access_cost: float = 0.0,
     rollback: bool = True,
+    net_widths: dict[int, int] | None = None,
+    via_drill: int | None = None,
+    hole_to_hole: int = 0,
 ) -> ExactRouteResult:
     """Route ``board`` orthogonally and verify the result with exact geometry.
 
@@ -131,6 +134,9 @@ def route_board_exact(
         route_first=route_first,
         access_cost=access_cost,
         rollback=rollback,
+        net_widths=net_widths,
+        via_drill=via_drill,
+        hole_to_hole=hole_to_hole,
     )
     edge = 0 if edge_clearance is None else edge_clearance
     outline = board.outline
@@ -172,23 +178,32 @@ def route_board_exact(
 
     via_layers = frozenset(signal_layers)
     accepted: dict[int, _Accepted] = {}
+    fixed_vias = {
+        (item.net_nos[0], item.location)
+        for item in board.get_items()
+        if isinstance(item, Via) and item.fixed and item.net_nos
+    }
 
     # Verify connection by connection, so one conflicting segment of a
     # 25-pin supply net costs that one connection, not the whole net.
     rejected: list[tuple[int, str, str]] = []
     ends_list = result.connection_ends or [("?", "?", "")] * len(result.connections)
+    # each net is checked at the width it will be written at: its class's
+    # when all of its connections went in at that, else the default
+    net_half = dict(result.net_half)
     for (net_no, wires, vias), ends in sorted(
         zip(result.connections, ends_list, strict=False), key=lambda c: c[0][0]
     ):
-        boxes = _copper_boxes(wires, vias, half_width, via_layers, via_half)
-        wire_count = len(_copper_boxes(wires, [], half_width, via_layers, via_half))
+        wire_half = net_half.get(net_no, half_width)
+        boxes = _copper_boxes(wires, vias, wire_half, via_layers, via_half)
+        wire_count = len(_copper_boxes(wires, [], wire_half, via_layers, via_half))
         if any(
             tree.clearance_conflict(
                 box, net_no, layer, clearance, "wire" if i < wire_count else "via"
             )
             for i, (box, box_layers) in enumerate(boxes)
             for layer in box_layers
-        ) or _end_in_rule_area(tree, wires, half_width) or (
+        ) or _end_in_rule_area(tree, wires, wire_half) or (
             outline is not None and not all(outline.box_clear(b, edge) for b, _ in boxes)
         ):
             rejected.append((net_no, *ends))
@@ -197,7 +212,12 @@ def route_board_exact(
         if acc is None:
             acc = accepted[net_no] = _Accepted(wires=[], vias=[])
         acc.wires.extend(wires)
-        acc.vias.extend(vias)
+        # connections of one net that end on the same plane cell share its
+        # via: write it once, and never on top of a via already on the board
+        acc.vias.extend(
+            v for v in dict.fromkeys(vias)
+            if v not in acc.vias and not _on_fixed_via(net_no, v, fixed_vias, via_half)
+        )
         for box, box_layers in boxes:
             oid = next(owner)
             tree.insert(TreeShape(oid, net_no, box_layers, box, routed=True))
@@ -247,6 +267,17 @@ def route_board_exact(
     for net_no, acc in accepted.items():
         clean.wires[net_no] = acc.wires
         clean.vias[net_no] = acc.vias
+    # shove and the diagonal pass lay copper at the default width: nets they
+    # recovered, and nets whose traces shove pushed aside
+    reshaped = (set(accepted) - accepted_before_recovery) | {
+        net for net, acc in accepted.items() if acc.shove_count
+    }
+    if diagonal:
+        reshaped = set(accepted)
+    clean.net_half = {
+        net: half for net, half in net_half.items() if net in accepted and net not in reshaped
+    }
+    clean.narrowed = list(result.narrowed)
 
     drc_clean = tree.has_violation(clearance) is None
     return ExactRouteResult(result=clean, tree=tree, drc_clean=drc_clean, shoves=shoves)
@@ -615,6 +646,15 @@ def _end_in_rule_area(tree, wires, half_width) -> bool:
     return False
 
 
+def _on_fixed_via(net_no, point, fixed_vias, via_half) -> bool:
+    """A routed via that reuses a via already on the board: the grid put it
+    on the fixed via's cell, a little off its centre, and it is not written."""
+    return any(
+        net == net_no and abs(loc.x - point.x) <= via_half and abs(loc.y - point.y) <= via_half
+        for net, loc in fixed_vias
+    )
+
+
 def _copper_boxes(wires, vias, half_width, via_layers, via_half=None):
     via_half = via_half or half_width
     boxes: list[tuple[IntBox, frozenset[int]]] = []

src/freeroute/route/fanout.py

@@ -0,0 +1,229 @@
+"""Fan out fine-pitch pins before routing: commit each pin's way out as copper.
+
+On a dense board the pins of a fine-pitch package get walled in: their own
+neighbours' pads on either side, and other nets' copper that got there first
+across the only way out. Reserving the way out did not help (the reserved
+cells still had to be routed, and lost to congestion there); committing it
+does, which is what a person does by hand.
+
+Each fine-pitch pin of a perimeter package (QFP, QFN, LGA: pads on the edge,
+none inside) gets a straight stub outward, perpendicular to its side of the
+package, just past its pad row. A pin whose net has an inner plane also gets
+a via at the stub's end, staggered between neighbouring pins so their holes
+keep their spacing, and so reaches the plane with nothing left to route.
+Every stub and via is checked exactly against pads, keepouts, the board edge,
+copper already on the board and earlier fan-out, and left out where it would
+not fit. The result goes on the board as fixed copper of its net (marked
+``generated``), so the router starts from the stub's end or the via, and the
+session writes it out with the routes.
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+import math
+
+from freeroute.board.board import BasicBoard
+from freeroute.board.items import Pin, Trace, Via
+from freeroute.geometry import IntBox, IntPoint
+from freeroute.geometry.polyline import Polyline, PolylineShape, corner_box
+
+# a package is fanned out when it has this many pins and they are this close
+_MIN_PINS = 8
+_FINE_PITCH_FACTOR = 1.2  # neighbour centres within this many (trace + 2 clearance)
+
+
+@dataclass
+class FanoutRules:
+    trace_width: int
+    clearance: int
+    via_half: int
+    via_drill: int
+    hole_to_hole: int
+    edge_clearance: int
+    signal_layers: list[int]
+    via_padstack: str
+    #: smallest package fanned out (a big dense part is where pins get walled in)
+    min_pins: int = 32
+    #: fan out plane pins only (a stub and a via each), as a person would first
+    supply_only: bool = False
+
+
+def plan_fanout(board: BasicBoard, rules: FanoutRules) -> list:
+    """The stubs and vias to put on the board before routing."""
+    half = max(rules.trace_width // 2, 1)
+    # a net may have several plane zones (a main plane and an island)
+    planes: dict[int, list] = {}
+    for z in board.get_conduction_areas():
+        if z.net_nos and not board.layer_structure.arr[z.layer].is_signal:
+            planes.setdefault(z.net_nos[0], []).append(z)
+    # copper pours on the routing layers, by net: a pad inside one is joined
+    # by the fill, and a stub there would take the room its thermal spokes need
+    pours: dict[int, list] = {}
+    for z in board.get_conduction_areas():
+        if z.net_nos and board.layer_structure.arr[z.layer].is_signal:
+            pours.setdefault(z.net_nos[0], []).append(z)
+    placed = _Placed(board, rules)
+    by_net: dict[int, list[Pin]] = {}
+    for pin in board.get_pins():
+        for n in pin.net_nos:
+            by_net.setdefault(n, []).append(pin)
+    items: list = []
+    pitch = 2 * rules.via_half + rules.hole_to_hole
+    for pins in _packages(board, rules).values():
+        centre = IntPoint(
+            sum(p.location.x for p in pins) // len(pins), sum(p.location.y for p in pins) // len(pins)
+        )
+        for k, pin in enumerate(sorted(pins, key=lambda p: (p.location.x, p.location.y))):
+            net = pin.net_nos[0] if pin.net_nos else None
+            if net is None:
+                continue
+            layer = next(layer for layer in pin.layers if layer in rules.signal_layers)
+            if any(z.layer == layer and z.polygon is not None and z.polygon.contains(pin.location)
+                   for z in pours.get(net, [])):
+                continue  # the pour joins it
+            direction = _outward(pin.location, centre)
+            reach = _pad_reach(pin, direction) + rules.clearance + half + rules.trace_width
+            end = _step(pin.location, direction, reach)
+            plane = planes.get(net)
+            partners = [q for q in by_net.get(net, []) if q is not pin]
+            # a signal whose other pins are all on other layers has to change
+            # layer somewhere: do it at the stub's end, away from the pads
+            elsewhere = bool(partners) and all(layer not in q.layers for q in partners)
+            if plane is None and (rules.supply_only or not elsewhere):
+                if not rules.supply_only and placed.stub_fits(pin.location, end, layer, net, half):
+                    items.append(placed.add_stub(pin.location, end, layer, net, half))
+                continue
+            # stagger the via of every other pin along the side outward
+            options = [reach + rules.via_half + rules.clearance + (k % 2) * pitch,
+                       reach + rules.via_half + rules.clearance + ((k + 1) % 2) * pitch]
+            for d in options:
+                at = _step(pin.location, direction, d)
+                if plane is not None and not any(
+                    z.polygon is not None and z.polygon.contains(at) for z in plane
+                ):
+                    continue
+                if placed.stub_fits(pin.location, at, layer, net, half) and placed.via_fits(at, net):
+                    items.append(placed.add_stub(pin.location, at, layer, net, half))
+                    items.append(placed.add_via(at, net))
+                    break
+    return items
+
+
+def _packages(board: BasicBoard, rules: FanoutRules) -> dict[str, list[Pin]]:
+    """Fine-pitch perimeter packages: many single-layer pins, close together."""
+    by_ref: dict[str, list[Pin]] = {}
+    for pin in board.get_pins():
+        if pin.shape is None or not pin.component_ref:
+            continue
+        on = [layer for layer in pin.layers if layer in rules.signal_layers]
+        if len(on) != 1:
+            continue  # through-hole pins change layer for free
+        by_ref.setdefault(pin.component_ref, []).append(pin)
+    fine = _FINE_PITCH_FACTOR * (rules.trace_width + 2 * rules.clearance)
+    out = {}
+    for ref, pins in by_ref.items():
+        if len(pins) < max(rules.min_pins, _MIN_PINS):
+            continue
+        close = sum(
+            1 for p in pins
+            if min(math.hypot(p.location.x - q.location.x, p.location.y - q.location.y)
+                   for q in pins if q is not p) < fine * 2
+        )
+        if close >= len(pins) // 2:
+            out[ref] = pins
+    return out
+
+
+def _outward(point: IntPoint, centre: IntPoint) -> tuple[int, int]:
+    """Away from the package centre, along the nearer axis (its side's normal)."""
+    dx, dy = point.x - centre.x, point.y - centre.y
+    if abs(dx) >= abs(dy):
+        return (1 if dx >= 0 else -1, 0)
+    return (0, 1 if dy >= 0 else -1)
+
+
+def _pad_reach(pin: Pin, direction: tuple[int, int]) -> int:
+    """How far the pad reaches from its centre in ``direction``."""
+    box = pin.shape.bounding_box()
+    if direction[0] > 0:
+        return box.ur.x - pin.location.x
+    if direction[0] < 0:
+        return pin.location.x - box.ll.x
+    if direction[1] > 0:
+        return box.ur.y - pin.location.y
+    return pin.location.y - box.ll.y
+
+
+def _step(point: IntPoint, direction: tuple[int, int], distance: float) -> IntPoint:
+    return IntPoint(point.x + round(direction[0] * distance), point.y + round(direction[1] * distance))
+
+
+class _Placed:
+    """Copper a fan-out stub or via has to clear, growing as fan-out is placed."""
+
+    def __init__(self, board: BasicBoard, rules: FanoutRules) -> None:
+        self.board, self.rules = board, rules
+        self.copper: list[tuple[IntBox, frozenset[int], int]] = []  # box, layers, net
+        for pin in board.get_pins():
+            if pin.shape is not None:
+                net = pin.net_nos[0] if pin.net_nos else -1
+                self.copper.append((pin.shape.bounding_box(), frozenset(pin.layers), net))
+        for net, layers, box in board.get_fixed_copper():
+            self.copper.append((box, layers, net))
+        self.keepouts = [
+            (tile.bounding_box(), o.layer, o.blocks_wires, o.blocks_vias, o.clearance)
+            for o in board.get_obstacle_areas() for tile in o.tiles
+        ]
+        self.holes: list[tuple[IntPoint, int]] = []  # centre, radius
+        for item in board.get_items():
+            if isinstance(item, Via) and item.fixed:
+                self.holes.append((item.location, (item.drill or rules.via_drill) // 2))
+        for pin in board.get_pins():
+            if pin.shape is not None and sum(1 for layer in pin.layers if layer in rules.signal_layers) > 1:
+                b = pin.shape.bounding_box()
+                self.holes.append((pin.location, min(b.ur.x - b.ll.x, b.ur.y - b.ll.y) // 2))
+
+    def _clear(self, box: IntBox, layers: frozenset[int], net: int, kind: str) -> bool:
+        grown = box.offset(self.rules.clearance)
+        for other, other_layers, other_net in self.copper:
+            if other_net != net and layers & other_layers and other.overlaps(grown):
+                return False
+        for kbox, klayer, wires, vias, needs in self.keepouts:
+            if klayer not in layers or not (wires if kind == "wire" else vias):
+                continue
+            if kbox.overlaps(grown if needs else box):
+                return False
+        outline = self.board.outline
+        return outline is None or outline.box_clear(box, self.rules.edge_clearance)
+
+    def stub_fits(self, a: IntPoint, b: IntPoint, layer: int, net: int, half: int) -> bool:
+        boxes = list(PolylineShape(Polyline([a, b]), half).tiles()) + [corner_box(b, half)]
+        return all(self._clear(box, frozenset({layer}), net, "wire") for box in boxes)
+
+    def via_fits(self, at: IntPoint, net: int) -> bool:
+        h = self.rules.via_half
+        box = IntBox(at.x - h, at.y - h, at.x + h, at.y + h)
+        if not self._clear(box, frozenset(self.rules.signal_layers), net, "via"):
+            return False
+        mine = self.rules.via_drill // 2
+        return all(
+            math.hypot(c.x - at.x, c.y - at.y) >= mine + r + self.rules.hole_to_hole
+            for c, r in self.holes
+        )
+
+    def add_stub(self, a: IntPoint, b: IntPoint, layer: int, net: int, half: int) -> Trace:
+        for box in list(PolylineShape(Polyline([a, b]), half).tiles()) + [corner_box(b, half)]:
+            self.copper.append((box, frozenset({layer}), net))
+        return Trace(net_nos=[net], fixed=True, layer=layer, half_width=half, corners=[a, b],
+                     generated=True)
+
+    def add_via(self, at: IntPoint, net: int) -> Via:
+        h = self.rules.via_half
+        box = IntBox(at.x - h, at.y - h, at.x + h, at.y + h)
+        layers = list(self.rules.signal_layers)
+        self.copper.append((box, frozenset(layers), net))
+        self.holes.append((at, self.rules.via_drill // 2))
+        return Via(net_nos=[net], fixed=True, padstack_name=self.rules.via_padstack,
+                   location=at, layers=layers, shape=box, drill=self.rules.via_drill,
+                   generated=True)

src/freeroute/route/grid_router.py

@@ -31,7 +31,7 @@ import math
 import random
 
 from freeroute.board.board import BasicBoard
-from freeroute.board.items import ConductionArea, ObstacleArea, Pin
+from freeroute.board.items import ConductionArea, ObstacleArea, Pin, Via
 from freeroute.geometry import IntBox, IntPoint
 from freeroute.geometry.polyline import corner_box
 
@@ -61,7 +61,10 @@ class RouteResult:
     ``routed_net_numbers`` are the nets that got any wire or via.
     """
 
-    __slots__ = ("wires", "vias", "half_width", "unrouted", "connections", "connection_ends", "failed")
+    __slots__ = (
+        "wires", "vias", "half_width", "unrouted", "connections", "connection_ends", "failed",
+        "net_half", "narrowed",
+    )
 
     def __init__(self, half_width: int) -> None:
         self.wires: dict[int, list[tuple[int, list[IntPoint]]]] = {}
@@ -76,6 +79,10 @@ class RouteResult:
         self.connection_ends: list[tuple[str, str, str]] = []
         #: connections left unrouted: (net_no, one end, the other end)
         self.failed: list[tuple[int, str, str]] = []
+        #: half width of each net routed wider than the default (its class)
+        self.net_half: dict[int, int] = {}
+        #: connections of a wider class that only fitted at the default width
+        self.narrowed: list[tuple[int, str, str]] = []
 
     def add_wire(self, net_no: int, layer: int, path: list[IntPoint]) -> None:
         self.wires.setdefault(net_no, []).append((layer, path))
@@ -114,6 +121,8 @@ class _Connection:
         "a_end",
         "b_end",
         "path",
+        "narrow",
+        "half",
     )
 
     def __init__(self, index: int, net_no: int, a: Pin, b: Pin) -> None:
@@ -137,6 +146,10 @@ class _Connection:
         self.b_end: Pin | None = b
         # the node path last committed, so a rip-up can be undone
         self.path: list[Node] | None = None
+        # a connection of a wider class that did not fit at that width is
+        # routed at the default width instead; the half width it went in at
+        self.narrow = False
+        self.half = 0
 
 
 class GridRouter:
@@ -163,6 +176,9 @@ class GridRouter:
         route_first: frozenset | None = None,
         access_cost: float = 0.0,
         rollback: bool = True,
+        net_widths: dict[int, int] | None = None,
+        via_drill: int | None = None,
+        hole_to_hole: int = 0,
     ) -> None:
         self.board = board
         # Pin access: while a pin still has connections to route, the cells
@@ -223,6 +239,38 @@ class GridRouter:
         self.edge_clearance = 0 if edge_clearance is None else edge_clearance
         need = self.via_half + self.clearance + self.half_width
         self.via_reach = max(0, math.ceil(need / self.step) - 1)
+        # Net classes wider than the default: the grid is laid out for the
+        # default width, so a wider trace must also find the cells around its
+        # own free, out to its extra half width, and claims a wider halo.
+        self._net_half = {
+            net: max(width // 2, 1)
+            for net, width in (net_widths or {}).items()
+            if width // 2 > self.half_width
+        }
+        self._spread: list[tuple[int, int]] = []  # the current search's
+        self._cur_half = self.half_width
+        self._halo_by_half: dict[int, list[tuple[int, int]]] = {self.half_width: self._halo_offsets}
+        # Hole-to-hole spacing holds between any two vias, of one net or two.
+        # Other nets' vias are kept further apart already; a net's own vias
+        # (every pin of a supply dropping to its plane) are not, so a via
+        # must keep its drill plus the spacing from every via centre, except
+        # an own-net via at the very same cell, which it simply reuses.
+        drill = via_drill if via_drill else 2 * self.via_half
+        need = drill + max(hole_to_hole, 0)
+        self._via_drill, self._hole_gap, self._hole_need = drill, max(hole_to_hole, 0), need
+        reach = math.ceil(need / self.step)
+        self._hole_offsets = [
+            (dx, dy)
+            for dx in range(-reach, reach + 1)
+            for dy in range(-reach, reach + 1)
+            if (dx or dy) and math.hypot(dx, dy) * self.step < need
+        ]
+        self._via_nets: dict[Cell, dict[int, int]] = {}  # routed via centres
+        self._via_centres: list[IntPoint] | None = None  # cache for _hole_clear_at
+        self._fixed_vias: dict[Cell, int] = {}
+        # fixed vias sit anywhere, not on cell centres: exact hole checks
+        self._fixed_holes: list[tuple[IntPoint, int]] = []
+        self._fixed_via_points: set[tuple[int, IntPoint]] = set()
 
         if layers is None:
             layers = [i for i, layer in enumerate(board.layer_structure.arr) if layer.is_signal]
@@ -251,6 +299,28 @@ class GridRouter:
         self._halo: dict[Node, list[int]] = {}
         self._rasterize_obstacles()
         self._rasterize_fixed_copper()
+        for item in board.get_items():
+            if isinstance(item, Via) and item.fixed and item.net_nos:
+                self._fixed_vias[self._cell_of(item.location)] = item.net_nos[0]
+                self._fixed_via_points.add((item.net_nos[0], item.location))
+                # its own drill, from KiCad's padstack name (Via[0-3]_500:250_um)
+                reach = self._via_drill // 2 + (item.drill or self._via_drill) // 2 + self._hole_gap
+                self._fixed_holes.append((item.location, reach))
+        # Through-hole pads have holes too, and a route changes layer at one
+        # for free, so no via (of any net) goes within hole spacing of one.
+        # The DSN has no drill for a pad; its smaller half size stands in.
+        self._tht_holes: list[tuple[IntPoint, int]] = []
+        self._tht_block: set[Cell] = set()
+        for pin in board.get_pins():
+            if pin.shape is None or sum(1 for layer in pin.layers if layer in self.layers) < 2:
+                continue
+            box = pin.shape.bounding_box()
+            radius = min(box.ur.x - box.ll.x, box.ur.y - box.ll.y) // 2
+            reach = radius + self._via_drill // 2 + self._hole_gap
+            self._tht_holes.append((pin.location, reach))
+            ring = IntBox(pin.location.x, pin.location.y, pin.location.x, pin.location.y)
+            for cell in self._cells_in_box(ring, reach):
+                self._tht_block.add(cell)
 
     # --- grid helpers -------------------------------------------------------
 
@@ -386,6 +456,30 @@ class GridRouter:
         allow_ripup: bool,
         conns: list[_Connection],
         wire_keepout: bool = True,
+    ) -> float | None:
+        """:meth:`_enter_cost_base`, and for a trace wider than the default
+        the same for every cell its extra width reaches (the worst of them)."""
+        cost = self._enter_cost_base(cell, layer, net_no, allow_ripup, conns, wire_keepout)
+        if cost is None or not self._spread:
+            return cost
+        for dx, dy in self._spread:
+            c = (cell[0] + dx, cell[1] + dy)
+            if not (0 <= c[0] < self.cols and 0 <= c[1] < self.rows):
+                return None
+            more = self._enter_cost_base(c, layer, net_no, allow_ripup, conns, wire_keepout)
+            if more is None:
+                return None
+            cost = max(cost, more)
+        return cost
+
+    def _enter_cost_base(
+        self,
+        cell: Cell,
+        layer: int,
+        net_no: int,
+        allow_ripup: bool,
+        conns: list[_Connection],
+        wire_keepout: bool = True,
     ) -> float | None:
         """Cost to enter ``(cell, layer)`` for ``net_no``; ``None`` if blocked.
 
@@ -440,14 +534,101 @@ class GridRouter:
             for layer in self.layers:
                 if (*c, layer) in self._via_keepout:
                     return False
-                if self._enter_cost(c, layer, net_no, False, conns, wire_keepout=False) != 0.0:
+                if self._enter_cost_base(c, layer, net_no, False, conns, wire_keepout=False) != 0.0:
                     return False
-        return True
+        return self._holes_clear(cell, net_no)
+
+    def _near_path_via(self, node: Node, cell: Cell, came_from: dict) -> bool:
+        """A layer change earlier on the route that reaches ``node`` sits
+        within hole spacing of ``cell`` (and is not the same through via).
+        Committed vias are checked elsewhere; a route's own are not yet
+        committed while it is searched. Looks back far enough to cover the
+        hole spacing twice over, not along the whole route."""
+        limit = 4 * (math.ceil(self._hole_need / self.step) + 1)
+        need = self._hole_need / self.step
+        steps = 0
+        while node in came_from and steps < limit:
+            prev = came_from[node]
+            changes_layer = prev[:2] == node[:2] and prev[2] != node[2]
+            if changes_layer and node[:2] != cell and (
+                math.hypot(node[0] - cell[0], node[1] - cell[1]) < need
+            ):
+                return True
+            node = prev
+            steps += 1
+        return False
+
+    def _via_nets_at(self, cell: Cell) -> set[int]:
+        nets = {net for net, n in self._via_nets.get(cell, {}).items() if n > 0}
+        fixed = self._fixed_vias.get(cell)
+        if fixed is not None:
+            nets.add(fixed)
+        return nets
+
+    def _holes_clear(self, cell: Cell, net_no: int) -> bool:
+        """No via centre within hole-to-hole reach, but an own-net one here,
+        and no through-hole pad's hole within reach at all."""
+        if cell in self._tht_block:
+            return False
+        if self._fixed_holes:
+            here = self._cell_center(cell)
+            for loc, reach in self._fixed_holes:
+                d = math.hypot(loc.x - here.x, loc.y - here.y)
+                if d < reach and d > self.step:  # beyond its own cell: too close
+                    return False
+        if self._via_nets_at(cell) - {net_no}:
+            return False
+        cx, cy = cell
+        return not any(self._via_nets_at((cx + dx, cy + dy)) for dx, dy in self._hole_offsets)
 
     # --- A* search ----------------------------------------------------------
 
+    def _conn_half(self, conn: _Connection) -> int:
+        """The half width a connection is routed at: its class's, unless it
+        has fallen back to the default."""
+        return self.half_width if conn.narrow else self._net_half.get(conn.net_no, self.half_width)
+
+    def _spread_for(self, half: int) -> list[tuple[int, int]]:
+        """Cells a trace of ``half`` also needs free: those whose centre is
+        within its extra half width (plus half a cell, for the grid)."""
+        extra = half - self.half_width
+        if extra <= 0:
+            return []
+        reach = math.ceil(extra / self.step) + 1
+        limit = extra + self.step / 2
+        return [
+            (dx, dy)
+            for dx in range(-reach, reach + 1)
+            for dy in range(-reach, reach + 1)
+            if (dx or dy) and math.hypot(dx, dy) * self.step <= limit
+        ]
+
+    def _halo_for(self, half: int) -> list[tuple[int, int]]:
+        """Cells a committed trace of ``half`` claims from default-width traces."""
+        offsets = self._halo_by_half.get(half)
+        if offsets is None:
+            need = half + self.clearance + self.half_width
+            reach = math.ceil(need / self.step)
+            offsets = self._halo_by_half[half] = [
+                (dx, dy)
+                for dx in range(-reach, reach + 1)
+                for dy in range(-reach, reach + 1)
+                if (dx or dy) and math.hypot(dx, dy) * self.step < need
+            ]
+        return offsets
+
     def _search(
         self, conn: _Connection, allow_ripup: bool, conns: list[_Connection]
+    ) -> list[Node] | None:
+        half = self._conn_half(conn)
+        self._cur_half, self._spread = half, self._spread_for(half)
+        try:
+            return self._search_at_width(conn, allow_ripup, conns)
+        finally:
+            self._cur_half, self._spread = self.half_width, []
+
+    def _search_at_width(
+        self, conn: _Connection, allow_ripup: bool, conns: list[_Connection]
     ) -> list[Node] | None:
         goal_cell = self._group_target(conn.b_group)
         if not conn.b_group[0] and any(z.layer in self._power_layers for z in conn.b_group[1]):
@@ -503,6 +684,8 @@ class GridRouter:
                     pin = ends.get(node)
                     if ok and isinstance(pin, Pin) and self._walled(node):
                         ok = self._via_fits_at(pin.location, net_no)
+                if ok and self._near_path_via(source, cell, came_from):
+                    ok = False  # too close to a via earlier on this same route
                 if ok:
                     self._relax(source, target, g_via, goal_cell, g_score, came_from, open_heap)
                 continue
@@ -514,6 +697,8 @@ class GridRouter:
                     ok = via_ok.get(cell)
                     if ok is None:
                         ok = via_ok[cell] = self._via_placeable(cell, net_no, conns)
+                    if ok and self._near_path_via(current, cell, came_from):
+                        ok = False
                 else:
                     ok = True
                 if ok:
@@ -587,14 +772,30 @@ class GridRouter:
             ]
             copper += [(box, net) for net, _, box in self.board.get_fixed_copper()]
             self._static_copper = copper
-        return not any(net != net_no and box.overlaps(grown) for box, net in self._static_copper)
+        if any(net != net_no and box.overlaps(grown) for box, net in self._static_copper):
+            return False
+        return self._hole_clear_at(point)
 
-    def _stub_cells(self, pin_location: IntPoint, cell: Cell) -> list[Cell]:
+    def _hole_clear_at(self, point: IntPoint) -> bool:
+        """Hole spacing measured exactly from ``point`` to every via and
+        through-hole pad (a via moved into a pad is not on its cell's centre)."""
+        need = self._hole_need
+        if self._via_centres is None:  # rebuilt only after vias change
+            self._via_centres = [loc for _net, loc in self._fixed_via_points] + [
+                self._cell_center(c) for c, count in self._via_nets.items() if any(count.values())
+            ]
+        if any(math.hypot(c.x - point.x, c.y - point.y) < need for c in self._via_centres):
+            return False
+        return not any(
+            math.hypot(loc.x - point.x, loc.y - point.y) < reach for loc, reach in self._tht_holes
+        )
+
+    def _stub_cells(self, pin_location: IntPoint, cell: Cell, half: int | None = None) -> list[Cell]:
         """Cells where another net's trace would come too close to the stub."""
         from freeroute.board.outline import _point_segment
 
         end = self._cell_center(cell)
-        reach = 2 * self.half_width + self.clearance
+        reach = (half or self._cur_half) + self.half_width + self.clearance
         box = IntBox(
             min(pin_location.x, end.x), min(pin_location.y, end.y),
             max(pin_location.x, end.x), max(pin_location.y, end.y),
@@ -616,12 +817,12 @@ class GridRouter:
 
             end = self._cell_center(cell)
             if end != pin.location:
-                for tile in PolylineShape(Polyline([pin.location, end]), self.half_width).tiles():
+                for tile in PolylineShape(Polyline([pin.location, end]), self._cur_half).tiles():
                     grown = tile.offset(self.clearance)
                     if any(k.overlaps(grown if needs else tile) for k, needs in keepouts):
                         return False
                 # the track's round end at the pin, for a rule area
-                cap = corner_box(pin.location, self.half_width)
+                cap = corner_box(pin.location, self._cur_half)
                 if any(not needs and k.overlaps(cap) for k, needs in keepouts):
                     return False
         if keepouts_only:
@@ -860,11 +1061,18 @@ class GridRouter:
             via_cells.append((path[-1][0], path[-1][1]))
         conn.trace_cells = [(cell, layer) for layer, cells in wire_segs for cell in cells]
         conn.via_cells = list(via_cells)
+        for cell in conn.via_cells:
+            count = self._via_nets.setdefault(cell, {})
+            count[conn.net_no] = count.get(conn.net_no, 0) + 1
+        if conn.via_cells:
+            self._via_centres = None
         for cell, layer in conn.trace_cells:
             self._cell_owner[(*cell, layer)] = conn.index
+        conn.half = half = self._conn_half(conn)
+        halo = self._halo_for(half)
         conn.halo_nodes = []
         for (cx, cy), layer in conn.trace_cells:
-            for dx, dy in self._halo_offsets:
+            for dx, dy in halo:
                 x, y = cx + dx, cy + dy
                 if 0 <= x < self.cols and 0 <= y < self.rows:
                     node = (x, y, layer)
@@ -881,7 +1089,7 @@ class GridRouter:
             if not isinstance(pin, Pin):
                 continue  # ended on a zone or a plane: no stub
             cell = cells[at]
-            for c in self._stub_cells(pin.location, cell):
+            for c in self._stub_cells(pin.location, cell, half):
                 node = (*c, layer)
                 if node not in self._cell_owner:
                     self._cell_owner[node] = conn.index
@@ -932,6 +1140,12 @@ class GridRouter:
                     del self._halo[node]
         conn.halo_nodes = []
         conn.trace_cells = []
+        for cell in conn.via_cells:
+            count = self._via_nets.get(cell)
+            if count and count.get(conn.net_no):
+                count[conn.net_no] -= 1
+        if conn.via_cells:
+            self._via_centres = None
         conn.via_cells = []
         conn.wires = []
         conn.vias = []
@@ -1012,6 +1226,7 @@ class GridRouter:
         best_count = -1
         best_snapshot: list[tuple[int, list, list]] | None = None
         best_unrouted = len(conns)
+        best_widths: tuple[dict[int, int], list] = ({}, [])
         # conns[i].index == i is what rip-up relies on, so shuffle a view
         order = list(conns)
         if self.seed is not None:
@@ -1031,13 +1246,25 @@ class GridRouter:
                 best_count = routed_count
                 best_unrouted = len(conns) - routed_count
                 best_snapshot = self._snapshot(conns)
+                best_widths = self._net_widths(conns)
             if routed_count == len(conns):
                 break
             if not changed:
                 break
-        return self._result_from(best_snapshot or [], best_unrouted)
+        result = self._result_from(best_snapshot or [], best_unrouted)
+        result.net_half, result.narrowed = best_widths
+        return result
 
     def _try_route(self, conn: _Connection, conns: list[_Connection]) -> bool:
+        if self._route_once(conn, conns):
+            return True
+        if conn.narrow or conn.net_no not in self._net_half:
+            return False
+        # a wider class that does not fit: route it at the default width
+        conn.narrow = True
+        return self._route_once(conn, conns)
+
+    def _route_once(self, conn: _Connection, conns: list[_Connection]) -> bool:
         path = self._search(conn, allow_ripup=False, conns=conns)
         if path is None:
             if not self.rip_up:
@@ -1101,7 +1328,9 @@ class GridRouter:
         # deterministic: fewer-pin nets first, then by net number
         for net_no in sorted(nets, key=lambda n: (len(pins_by_net.get(n, [])), n)):
             zones = zones_by_net.get(net_no, []) + planes_by_net.get(net_no, [])
-            groups = _connected_groups(pins_by_net.get(net_no, []), zones, plane_ids)
+            groups = _connected_groups(
+                pins_by_net.get(net_no, []), zones, plane_ids, self._fixed_pieces(net_no)
+            )
             hubs = [g for g in groups if any(id(z) in plane_ids for z in g[1])]
             if hubs:
                 # a plane net: every other group goes straight to the plane
@@ -1115,6 +1344,28 @@ class GridRouter:
                 conns.append(conn)
         return conns
 
+    def _fixed_pieces(self, net_no: int) -> list[_FixedPiece]:
+        """The net's tracks and vias already on the board, as connectivity."""
+        cache = getattr(self, "_fixed_cache", None)
+        if cache is None:
+            from freeroute.board.items import Trace
+            from freeroute.geometry.polyline import Polyline, PolylineShape, corner_box
+
+            cache = self._fixed_cache = {}
+            for item in self.board.get_items():
+                if not item.fixed or not item.net_nos:
+                    continue
+                if isinstance(item, Via) and item.shape is not None:
+                    piece = _FixedPiece(item.layers, [item.shape.bounding_box()], via=item)
+                elif isinstance(item, Trace) and not item.is_empty():
+                    boxes = list(PolylineShape(Polyline(item.corners), item.half_width).tiles())
+                    boxes += [corner_box(e, item.half_width) for e in (item.corners[0], item.corners[-1])]
+                    piece = _FixedPiece([item.layer], boxes, trace=item)
+                else:
+                    continue
+                cache.setdefault(item.net_nos[0], []).append(piece)
+        return cache.get(net_no, [])
+
     def _pins_by_net(self) -> dict[int, list[Pin]]:
         by_net: dict[int, list[Pin]] = {}
         for pin in self.board.get_pins():
@@ -1124,6 +1375,21 @@ class GridRouter:
                 by_net.setdefault(net_no, []).append(pin)
         return by_net
 
+    def _net_widths(self, conns: list[_Connection]) -> tuple[dict[int, int], list]:
+        """Half width of each wider-class net whose routed connections all went
+        in at it (a net is written at one width), and the connections that
+        had to fall back to the default."""
+        halves: dict[int, int] = {}
+        narrowed = []
+        for c in conns:
+            if not c.routed:
+                continue
+            halves[c.net_no] = min(halves.get(c.net_no, c.half), c.half)
+            if c.narrow:
+                narrowed.append((c.net_no, *_ends_of(c)))
+        wide = {net: half for net, half in halves.items() if half > self.half_width}
+        return wide, narrowed
+
     def _snapshot(self, conns: list[_Connection]) -> list[tuple]:
         return [
             (c.net_no, [(layer, list(pts)) for layer, pts in c.wires], list(c.vias),
@@ -1134,11 +1400,16 @@ class GridRouter:
 
     def _result_from(self, snapshot, unrouted: int) -> RouteResult:
         result = RouteResult(self.half_width)
+        written: set[tuple[int, IntPoint]] = set()
         result.unrouted = unrouted
         for net_no, wires, vias, ends in snapshot:
             for layer, points in wires:
                 result.add_wire(net_no, layer, points)
             for location in vias:
+                spot = (net_no, location)
+                if spot in written or spot in self._fixed_via_points:
+                    continue  # a via reused by another connection, or already on the board
+                written.add(spot)
                 result.add_via(net_no, location)
             result.connections.append((net_no, wires, vias))
             result.connection_ends.append(ends)
@@ -1189,13 +1460,50 @@ def _pin_touches_zone(pin: Pin, zone, plane: bool = False) -> bool:
     return any(zone.polygon.contains(c) for c in corners)
 
 
+def _touches(a: IntBox, b: IntBox) -> bool:
+    return not (a.ur.x < b.ll.x or b.ur.x < a.ll.x or a.ur.y < b.ll.y or b.ur.y < a.ll.y)
+
+
+def _fixed_joins_zone(piece, zone, plane: bool) -> bool:
+    """A through via inside a plane joins it; copper inside a zone on its
+    own layer joins that zone."""
+    if zone.polygon is None:
+        return False
+    if piece.via is not None:
+        if plane or zone.layer in piece.layers:
+            return zone.polygon.contains(piece.via.location)
+        return False
+    return zone.layer in piece.layers and any(
+        zone.polygon.contains(IntPoint((b.ll.x + b.ur.x) // 2, (b.ll.y + b.ur.y) // 2))
+        for b in piece.boxes
+    )
+
+
+class _FixedPiece:
+    """One track or via already on the board, as connectivity."""
+
+    __slots__ = ("layers", "boxes", "via", "trace")
+
+    def __init__(self, layers, boxes, via=None, trace=None) -> None:
+        self.layers = frozenset(layers)
+        self.boxes = boxes
+        self.via = via  # the Via item, for a via
+        self.trace = trace  # the Trace item, for a track
+
+
 def _connected_groups(
-    pins: list[Pin], zones: list, planes: frozenset = frozenset()
+    pins: list[Pin], zones: list, planes: frozenset = frozenset(), fixed: list | None = None
 ) -> list[tuple[list[Pin], list]]:
     """Pins and zones of one net that copper already joins: a pad in a zone
-    is connected to it, and two zones sharing a pad are one. Only the groups
-    need routing between them. Pin groups come first, in pin order."""
-    parent = list(range(len(pins) + len(zones)))
+    is connected to it, two zones sharing a pad are one, and copper already
+    on the board (tracks and vias, ``fixed``) joins whatever it touches. Only
+    the groups need routing between them. Pin groups come first, in pin
+    order. A group's fixed vias join its pins as extra route ends, so a
+    fanned-out pin is routed from its via; copper that touches no pin and no
+    zone adds nothing to route."""
+    fixed = fixed or []
+    n_pins, n_zones = len(pins), len(zones)
+    parent = list(range(n_pins + n_zones + len(fixed)))
 
     def find(i: int) -> int:
         while parent[i] != i:
@@ -1207,6 +1515,24 @@ def _connected_groups(
         for i, pin in enumerate(pins):
             if _pin_touches_zone(pin, zone, id(zone) in planes):
                 parent[find(i)] = find(len(pins) + j)
+    base = n_pins + n_zones
+    for k, piece in enumerate(fixed):
+        me = base + k
+        for i, pin in enumerate(pins):
+            if pin.shape is None or not piece.layers & set(pin.layers):
+                continue
+            pad = pin.shape.bounding_box()
+            if any(_touches(pad, b) for b in piece.boxes):
+                parent[find(i)] = find(me)
+        for j, zone in enumerate(zones):
+            if _fixed_joins_zone(piece, zone, id(zone) in planes):
+                parent[find(n_pins + j)] = find(me)
+        for k2 in range(k):
+            other = fixed[k2]
+            if piece.layers & other.layers and any(
+                _touches(a, b) for a in piece.boxes for b in other.boxes
+            ):
+                parent[find(base + k2)] = find(me)
     groups: dict[int, tuple[list[Pin], list]] = {}
     order: list[int] = []
     for i, pin in enumerate(pins):
@@ -1221,9 +1547,39 @@ def _connected_groups(
             groups[root] = ([], [])
             order.append(root)
         groups[root][1].append(zone)
+    for k, piece in enumerate(fixed):
+        root = find(base + k)
+        if root not in groups:
+            continue
+        if piece.via is not None:
+            groups[root][0].append(_via_end(piece.via))
+        elif piece.trace is not None:
+            # a track's ends are places a route may start: a fan-out stub's
+            # far end is outside the pad row the pin sat walled in by
+            for end in (piece.trace.corners[0], piece.trace.corners[-1]):
+                groups[root][0].append(_trace_end(piece.trace, end))
     return [groups[r] for r in order]
 
 
+def _trace_end(trace, end: IntPoint) -> Pin:
+    """An end of a fixed track as a place a route may start or end."""
+    from freeroute.geometry.polyline import corner_box
+
+    return Pin(
+        net_nos=list(trace.net_nos), fixed=True, name="track", component_ref="",
+        location=end, layers=[trace.layer], shape=corner_box(end, trace.half_width),
+    )
+
+
+def _via_end(via) -> Pin:
+    """A fixed via as a place a route may start or end (not a pad to route)."""
+    return Pin(
+        net_nos=list(via.net_nos), fixed=True, name="via", component_ref="",
+        padstack_name=via.padstack_name, location=via.location,
+        layers=list(via.layers), shape=via.shape,
+    )
+
+
 def _split_path(path: list[Node]) -> tuple[list[tuple[int, list[Cell]]], list[Cell]]:
     """Split a node path into per-layer wire segments and via cells."""
     wires: list[tuple[int, list[Cell]]] = []
@@ -1284,6 +1640,9 @@ def route_board(
     route_first: frozenset | None = None,
     access_cost: float = 0.0,
     rollback: bool = True,
+    net_widths: dict[int, int] | None = None,
+    via_drill: int | None = None,
+    hole_to_hole: int = 0,
 ) -> RouteResult:
     """Convenience wrapper: build a :class:`GridRouter` and route the board."""
     router = GridRouter(
@@ -1303,5 +1662,8 @@ def route_board(
         route_first=route_first,
         access_cost=access_cost,
         rollback=rollback,
+        net_widths=net_widths,
+        via_drill=via_drill,
+        hole_to_hole=hole_to_hole,
     )
     return router.route()

src/freeroute/route/pipeline.py

@@ -12,6 +12,8 @@ to DSN units (dividing by the resolution) for the SES ``(wire (path ...))`` and
 
 from __future__ import annotations
 
+import re
+
 from freeroute.board import build_board
 from freeroute.dsn import DsnBoard, parse_dsn
 from freeroute.ses import RoutedVia, RoutedWire, RoutingResult, write_ses
@@ -34,6 +36,25 @@ def _rule_width_dsn(dsn: DsnBoard) -> float:
     return rules[0].value if rules else _DEFAULT_WIDTH_DSN
 
 
+def _net_widths_board(dsn: DsnBoard, scale: int) -> dict[int, int]:
+    """Track width of every net whose class asks for more than the default,
+    in board units, by net number (build_board numbers nets in DSN order)."""
+    default = _rule_width_dsn(dsn)
+    by_name: dict[str, float] = {}
+    for net_class in dsn.net_classes:
+        if not net_class.width_rules:
+            continue
+        width = net_class.width_rules[0].value
+        if width > default:
+            for name in net_class.net_names:
+                by_name[name] = max(by_name.get(name, 0.0), width)
+    return {
+        i + 1: round(by_name[net.name] * scale)
+        for i, net in enumerate(dsn.nets)
+        if net.name in by_name
+    }
+
+
 def _rule_clearance_dsn(dsn: DsnBoard) -> float:
     for rule in dsn.structure_rules.clearance_rules:
         if not rule.class_pairs:  # the layer-wide default clearance
@@ -53,6 +74,56 @@ def _mm_to_board(dsn: DsnBoard, scale: int, value_mm: float | None) -> int | Non
     return round(value_mm / unit_mm * scale)
 
 
+def _via_drill_board(dsn: DsnBoard, scale: int) -> int | None:
+    """The via's drill in board units, from KiCad's padstack name
+    (``Via[0-1]_600:300_um`` is a 600 um pad with a 300 um drill); None when
+    the name does not say, and the pad size stands in for it."""
+    match = re.search(r"_([\d.]+):([\d.]+)_um", _via_padstack(dsn))
+    if not match:
+        return None
+    return round(float(match.group(2)) * _dsn_units_per_um(dsn) * scale)
+
+
+def _dsn_units_per_um(dsn: DsnBoard) -> float:
+    return {"um": 1.0, "mm": 0.001, "mil": 1 / 25.4, "inch": 1 / 25400}.get(dsn.unit, 1.0)
+
+
+def _place_fanout(
+    board, dsn, scale, layers, width, clearance, edge, hole_to_hole_mm, mode=True, min_pins=32
+) -> None:
+    """Put the fan-out's stubs and vias on the board, before routing."""
+    from .fanout import FanoutRules, plan_fanout
+
+    via_half = _via_half_board(dsn, scale) or max(width // 2, 1)
+    rules = FanoutRules(
+        trace_width=width,
+        clearance=clearance,
+        via_half=via_half,
+        via_drill=_via_drill_board(dsn, scale) or 2 * via_half,
+        hole_to_hole=_mm_to_board(dsn, scale, hole_to_hole_mm) or 0,
+        edge_clearance=edge or 0,
+        signal_layers=layers or [i for i, layer in enumerate(dsn.layers) if layer.is_signal],
+        via_padstack=_via_padstack(dsn),
+        min_pins=min_pins,
+        supply_only=mode == "supply",
+    )
+    for item in plan_fanout(board, rules):
+        board.insert(item)
+
+
+def _add_generated(result, board) -> None:
+    """The fan-out's copper goes into the session with the routes."""
+    from freeroute.board.items import Trace, Via
+
+    for item in board.get_items():
+        if not getattr(item, "generated", False) or not item.net_nos:
+            continue
+        if isinstance(item, Trace):
+            result.add_wire(item.net_nos[0], item.layer, list(item.corners))
+        elif isinstance(item, Via):
+            result.add_via(item.net_nos[0], item.location)
+
+
 def _via_half_board(dsn: DsnBoard, scale: int) -> int | None:
     """Half the via pad's size in board units, from the DSN's via padstack.
 
@@ -83,6 +154,9 @@ def route_dsn_board(
     seed: int | None = None,
     route_first: frozenset | None = None,
     access_cost: float = 0.0,
+    hole_to_hole_mm: float = 0.25,
+    fanout: bool | str = False,
+    fanout_min_pins: int = 32,
     rollback: bool = True,
 ) -> tuple[RouteResult, int, list[str]]:
     """Route a parsed :class:`DsnBoard`; return the board-unit result, the scale,
@@ -94,6 +168,9 @@ def route_dsn_board(
     edge_clearance_board = _mm_to_board(dsn, scale, edge_clearance_mm)
     width_board = round(_rule_width_dsn(dsn) * scale)
     clearance_board = round(_rule_clearance_dsn(dsn) * scale)
+    if fanout:
+        _place_fanout(board, dsn, scale, layers, width_board, clearance_board,
+                      edge_clearance_board, hole_to_hole_mm, fanout, fanout_min_pins)
     result = route_board(
         board,
         resolution=resolution,
@@ -108,7 +185,11 @@ def route_dsn_board(
         route_first=route_first,
         access_cost=access_cost,
         rollback=rollback,
+        net_widths=_net_widths_board(dsn, scale),
+        via_drill=_via_drill_board(dsn, scale),
+        hole_to_hole=_mm_to_board(dsn, scale, hole_to_hole_mm) or 0,
     )
+    _add_generated(result, board)
     return result, scale, [layer.name for layer in dsn.layers]
 
 
@@ -122,6 +203,9 @@ def _to_routing_result(route, dsn: DsnBoard, scale: int, layer_names: list[str])
     result = RoutingResult()
     for net_no, segments in route.wires.items():
         name = numbers_to_names.get(net_no, str(net_no))
+        # its class's width when every connection of the net went in at it
+        half = getattr(route, "net_half", {}).get(net_no)
+        net_width = 2 * half / scale if half else width_dsn
         for layer_index, path in segments:
             layer_name = layer_names[layer_index] if layer_index < len(layer_names) else "F.Cu"
             coords: list[float] = []
@@ -129,7 +213,7 @@ def _to_routing_result(route, dsn: DsnBoard, scale: int, layer_names: list[str])
                 coords.append(point.x / scale)
                 coords.append(point.y / scale)
             if len(coords) >= 4:
-                result.add_wire(name, RoutedWire(layer=layer_name, width=width_dsn, coords=coords))
+                result.add_wire(name, RoutedWire(layer=layer_name, width=net_width, coords=coords))
     for net_no, locations in route.vias.items():
         name = numbers_to_names.get(net_no, str(net_no))
         for loc in locations:
@@ -137,6 +221,9 @@ def _to_routing_result(route, dsn: DsnBoard, scale: int, layer_names: list[str])
     result.unrouted = [
         (numbers_to_names.get(n, str(n)), a, b, zone) for n, a, b, zone in getattr(route, "failed", [])
     ]
+    result.narrowed = [
+        (numbers_to_names.get(n, str(n)), a, b) for n, a, b in getattr(route, "narrowed", [])
+    ]
     return result
 
 
@@ -151,6 +238,9 @@ def build_routing_result(
     seed: int | None = None,
     route_first: frozenset | None = None,
     access_cost: float = 0.0,
+    hole_to_hole_mm: float = 0.25,
+    fanout: bool | str = False,
+    fanout_min_pins: int = 32,
     rollback: bool = True,
 ) -> RoutingResult:
     """Route ``dsn`` (grid track) and convert to a DSN-unit RoutingResult."""
@@ -159,6 +249,9 @@ def build_routing_result(
         edge_clearance_mm=edge_clearance_mm, resolution=resolution, seed=seed,
         route_first=route_first,
         access_cost=access_cost,
+        hole_to_hole_mm=hole_to_hole_mm,
+        fanout=fanout,
+        fanout_min_pins=fanout_min_pins,
         rollback=rollback,
     )
     return _to_routing_result(route, dsn, scale, layer_names)
@@ -178,6 +271,9 @@ def route_dsn_board_exact(
     seed: int | None = None,
     route_first: frozenset | None = None,
     access_cost: float = 0.0,
+    hole_to_hole_mm: float = 0.25,
+    fanout: bool | str = False,
+    fanout_min_pins: int = 32,
     rollback: bool = True,
 ) -> tuple[ExactRouteResult, int, list[str]]:
     """Route a parsed :class:`DsnBoard` with the exact-geometry (orthogonal,
@@ -190,6 +286,9 @@ def route_dsn_board_exact(
     edge_clearance_board = _mm_to_board(dsn, scale, edge_clearance_mm)
     width_board = round(_rule_width_dsn(dsn) * scale)
     clearance_board = round(_rule_clearance_dsn(dsn) * scale)
+    if fanout:
+        _place_fanout(board, dsn, scale, layers, width_board, clearance_board,
+                      edge_clearance_board, hole_to_hole_mm, fanout, fanout_min_pins)
     exact = route_board_exact(
         board,
         resolution=resolution,
@@ -207,7 +306,11 @@ def route_dsn_board_exact(
         route_first=route_first,
         access_cost=access_cost,
         rollback=rollback,
+        net_widths=_net_widths_board(dsn, scale),
+        via_drill=_via_drill_board(dsn, scale),
+        hole_to_hole=_mm_to_board(dsn, scale, hole_to_hole_mm) or 0,
     )
+    _add_generated(exact.result, board)
     return exact, scale, [layer.name for layer in dsn.layers]
 
 
@@ -225,6 +328,9 @@ def build_exact_routing_result(
     seed: int | None = None,
     route_first: frozenset | None = None,
     access_cost: float = 0.0,
+    hole_to_hole_mm: float = 0.25,
+    fanout: bool | str = False,
+    fanout_min_pins: int = 32,
     rollback: bool = True,
 ) -> RoutingResult:
     """Route ``dsn`` (exact track) and convert to a DSN-unit RoutingResult."""
@@ -241,6 +347,9 @@ def build_exact_routing_result(
         seed=seed,
         route_first=route_first,
         access_cost=access_cost,
+        hole_to_hole_mm=hole_to_hole_mm,
+        fanout=fanout,
+        fanout_min_pins=fanout_min_pins,
         rollback=rollback,
     )
     return _to_routing_result(exact.result, dsn, scale, layer_names)

src/freeroute/ses/model.py

@@ -60,6 +60,9 @@ class RoutingResult:
     #: connections the router could not make: (net name, one end, other end,
     #: the zone both ends sit in or "") -- a zone's fill may join the latter
     unrouted: list[tuple[str, str, str, str]] = field(default_factory=list)
+    #: connections of a wider net class that only fitted at the default width
+    #: (net name, one end, other end); their net is written at the default
+    narrowed: list[tuple[str, str, str]] = field(default_factory=list)
 
     def net(self, name: str, *, create: bool = False) -> RoutedNet | None:
         """Return the :class:`RoutedNet` with ``name`` (creating it if asked)."""

tests/route/test_fanout.py

@@ -0,0 +1,78 @@
+"""--fanout: fine-pitch pins get their way out committed before routing."""
+
+from __future__ import annotations
+
+from freeroute.board import build_board
+from freeroute.board.items import Trace, Via
+from freeroute.dsn import parse_dsn
+from freeroute.route.fanout import FanoutRules, plan_fanout
+from freeroute.route.pipeline import route_dsn_board_exact
+
+# a 12-pad package, 3 pads a side at 0.5 mm pitch, over a GND plane on In1;
+# pad 1 (left side, top) is GND, the rest are signals to far connector pads
+_SIDES = {
+    "L": [(-2000, y, 0) for y in (500, 0, -500)],
+    "R": [(2000, y, 0) for y in (500, 0, -500)],
+    "T": [(x, 2000, 90) for x in (-500, 0, 500)],
+    "B": [(x, -2000, 90) for x in (-500, 0, 500)],
+}
+_PADS = [p for side in "LRTB" for p in _SIDES[side]]
+
+
+def _dsn():
+    pins = "\n      ".join(
+        f"(pin {'padv' if r else 'padh'} {i + 1} {x} {y})" for i, (x, y, r) in enumerate(_PADS)
+    )
+    far = " ".join(f"(place C{i} {3000 + 2000 * (i % 5)} {-12000 - 2000 * (i // 5)} front 0)" for i in range(11))
+    nets = "(net GND (pins U1-1))\n    " + "\n    ".join(f"(net S{i} (pins U1-{i + 2} C{i}-1))" for i in range(11))
+    return f"""(pcb pkg (parser) (resolution um 10) (unit um)
+  (structure
+    (layer F.Cu (type signal)) (layer In1.Cu (type power)) (layer In2.Cu (type power))
+    (layer B.Cu (type signal))
+    (boundary (path pcb 0  -15000 15000  25000 15000  25000 -25000  -15000 -25000  -15000 15000))
+    (plane GND (polygon In1.Cu 0  -14500 14500  24500 14500  24500 -24500  -14500 -24500  -14500 14500))
+    (via "Via[0-3]_450:200_um") (rule (width 150) (clearance 150)))
+  (placement (component Q (place U1 0 0 front 0)) (component P {far}))
+  (library
+    (image Q
+      {pins})
+    (image P (pin padc 1 0 0))
+    (padstack padh (shape (rect F.Cu -400 -125 400 125)) (attach off))
+    (padstack padv (shape (rect F.Cu -125 -400 125 400)) (attach off))
+    (padstack padc (shape (rect F.Cu -500 -500 500 500)) (attach off))
+    (padstack "Via[0-3]_450:200_um" (shape (circle F.Cu 450)) (shape (circle B.Cu 450)) (attach off)))
+  (network {nets}))"""
+
+
+def _rules(dsn):
+    s = dsn.resolution.value
+    return FanoutRules(trace_width=150 * s, clearance=150 * s, via_half=225 * s, via_drill=200 * s,
+                       hole_to_hole=250 * s, edge_clearance=0, signal_layers=[0, 3],
+                       via_padstack="Via[0-3]_450:200_um", min_pins=8)
+
+
+def test_every_pin_gets_a_stub_outward_past_its_pad():
+    dsn = parse_dsn(_dsn())
+    board = build_board(dsn)
+    items = plan_fanout(board, _rules(dsn))
+    stubs = [i for i in items if isinstance(i, Trace)]
+    assert len(stubs) == 12
+    for stub in stubs:
+        a, b = stub.corners
+        pin = next(p for p in board.get_pins() if p.location == a)
+        pad = pin.shape.bounding_box()
+        # outward: the stub ends further from the package centre, outside its pad
+        assert abs(b.x) + abs(b.y) > abs(a.x) + abs(a.y)
+        assert not (pad.ll.x <= b.x <= pad.ur.x and pad.ll.y <= b.y <= pad.ur.y)
+
+
+def test_a_plane_pin_gets_a_via_and_needs_no_route():
+    dsn = parse_dsn(_dsn())
+    board = build_board(dsn)
+    items = plan_fanout(board, _rules(dsn))
+    assert len([i for i in items if isinstance(i, Via)]) == 1
+    exact, _scale, _ = route_dsn_board_exact(dsn, resolution=2, fanout=True, fanout_min_pins=8)
+    gnd = next(i + 1 for i, n in enumerate(dsn.nets) if n.name == "GND")
+    assert not any(f[0] == gnd for f in exact.result.failed)
+    assert exact.drc_clean
+    assert len(exact.result.vias.get(gnd, [])) == 1  # the fan-out's, written out

tests/route/test_fixed_wiring.py

@@ -48,3 +48,61 @@ def test_other_nets_route_around_a_fixed_track():
             continue
         for p, q in zip(pts, pts[1:], strict=False):
             assert not (min(p.x, q.x) < wall < max(p.x, q.x)), "crossed the GND track on F.Cu"
+
+
+# --- fixed wiring as connectivity ------------------------------------------
+
+_FANOUT = """(pcb fanout (parser) (resolution um 10) (unit um)
+  (structure
+    (layer F.Cu (type signal)) (layer In1.Cu (type power)) (layer In2.Cu (type power))
+    (layer B.Cu (type signal))
+    (boundary (path pcb 0  0 0  30000 0  30000 -20000  0 -20000  0 0))
+    (plane GND (polygon In1.Cu 0  500 -500  29500 -500  29500 -19500  500 -19500  500 -500))
+    (via "Via[0-3]_600:300_um") (rule (width 150) (clearance 150)))
+  (placement (component S (place G1 5000 -10000 front 0) (place A 10000 -10000 front 0)
+                          (place B 25000 -11500 back 0)))
+  (library
+    (image S (pin smd 1 0 0))
+    (padstack smd (shape (rect F.Cu -300 -300 300 300)) (attach off))
+    (padstack "Via[0-3]_600:300_um" (shape (circle F.Cu 600)) (shape (circle B.Cu 600)) (attach off)))
+  (network (net GND (pins G1-1)) (net SIG (pins A-1 B-1)))
+  (wiring
+    (wire (path F.Cu 150  5000 -10000  5000 -11500) (net GND) (type route))
+    (via "Via[0-3]_600:300_um"  5000 -11500 (net GND) (type route))
+    (wire (path F.Cu 150  10000 -10000  10000 -11500) (net SIG) (type route))
+    (via "Via[0-3]_600:300_um"  10000 -11500 (net SIG) (type route))
+    (wire (path F.Cu 300  2000 -2000  8000 -2000) (net GND) (type route))))"""
+
+
+def test_a_pad_fanned_out_to_its_plane_needs_no_route():
+    dsn = parse_dsn(_FANOUT)
+    exact, _scale, _names = route_dsn_board_exact(dsn, resolution=2)
+    gnd = next(i + 1 for i, n in enumerate(dsn.nets) if n.name == "GND")
+    assert exact.result.failed == []
+    assert not exact.result.vias.get(gnd) and not exact.result.wires.get(gnd)
+
+
+def test_a_fanned_out_signal_is_routed_from_its_via():
+    # B is on the bottom face, level with A's fan-out via: starting from that
+    # via on B.Cu is the cheapest way, and needs no via of its own
+    dsn = parse_dsn(_FANOUT)
+    exact, scale, names = route_dsn_board_exact(dsn, resolution=2)
+    sig = next(i + 1 for i, n in enumerate(dsn.nets) if n.name == "SIG")
+    assert sig in exact.result.routed_net_numbers
+    assert not exact.result.vias.get(sig), "the fan-out via is already there"
+    assert {names[layer] for layer, _ in exact.result.wires[sig]} == {"B.Cu"}
+
+
+def test_the_session_never_repeats_copper_already_on_the_board():
+    # the JAR writes the DSN's wiring back into its session, and an applier
+    # then adds it a second time on top of itself; freeroute writes only
+    # what it routed
+    from freeroute.route.pipeline import build_exact_routing_result
+
+    fixed_vias = {(5000.0, -11500.0), (10000.0, -11500.0)}
+    fixed_paths = {(5000.0, -10000.0, 5000.0, -11500.0), (10000.0, -10000.0, 10000.0, -11500.0),
+                   (2000.0, -2000.0, 8000.0, -2000.0)}
+    result = build_exact_routing_result(parse_dsn(_FANOUT), resolution=2)
+    for net in result.nets:
+        assert not {(v.x, v.y) for v in net.vias} & fixed_vias
+        assert not {tuple(w.coords) for w in net.wires} & fixed_paths

tests/route/test_net_widths.py

@@ -0,0 +1,42 @@
+"""Net classes wider than the default are routed at their width where it fits."""
+
+from __future__ import annotations
+
+from freeroute.dsn import parse_dsn
+from freeroute.route.pipeline import build_exact_routing_result
+
+_BOARD = """(pcb widths (parser) (resolution um 10) (unit um)
+  (structure
+    (layer F.Cu (type signal))
+    (boundary (path pcb 0  0 0  20000 0  20000 -10000  0 -10000  0 0))
+    {keepouts}
+    (rule (width 150) (clearance 150)))
+  (placement (component S (place P1 2000 -5000 front 0) (place P2 18000 -5000 front 0)))
+  (library (image S (pin pad 1 0 0)) (padstack pad (shape (rect F.Cu -600 -600 600 600)) (attach off)))
+  (network (net PWR (pins P1-1 P2-1))
+    (class Power PWR (rule (width 400) (clearance 150)))))"""
+
+# two keepouts leave a 0.65 mm channel: room for 0.15 mm (0.45), not for 0.4 mm (0.7)
+_CHANNEL = (
+    '(keepout "" (polygon F.Cu 0  9000 0  11000 0  11000 -4675  9000 -4675))\n'
+    '    (keepout "" (polygon F.Cu 0  9000 -5325  11000 -5325  11000 -10000  9000 -10000))'
+)
+
+
+def _route(keepouts=""):
+    return build_exact_routing_result(parse_dsn(_BOARD.format(keepouts=keepouts)), resolution=2)
+
+
+def test_a_wider_class_is_routed_and_written_at_its_width():
+    result = _route()
+    assert result.unrouted == [] and result.narrowed == []
+    widths = {w.width for net in result.nets for w in net.wires}
+    assert widths == {400.0}
+
+
+def test_a_wider_class_that_does_not_fit_falls_back_to_the_default():
+    result = _route(_CHANNEL)
+    assert result.unrouted == []
+    assert [net for net, _a, _b in result.narrowed] == ["PWR"]
+    widths = {w.width for net in result.nets for w in net.wires}
+    assert widths == {150.0}

tests/route/test_via_spacing.py

@@ -0,0 +1,136 @@
+"""Vias keep hole-to-hole spacing, even within one net."""
+
+from __future__ import annotations
+
+import itertools
+import math
+
+from freeroute.dsn import parse_dsn
+from freeroute.route.pipeline import route_dsn_board_exact
+
+# four GND pads 0.5 mm apart over a GND plane: each drops a via to the plane
+_DSN = """(pcb holes (parser) (resolution um 10) (unit um)
+  (structure
+    (layer F.Cu (type signal)) (layer In1.Cu (type power)) (layer In2.Cu (type power))
+    (layer B.Cu (type signal))
+    (boundary (path pcb 0  0 0  20000 0  20000 -20000  0 -20000  0 0))
+    (plane GND (polygon In1.Cu 0  500 -500  19500 -500  19500 -19500  500 -19500  500 -500))
+    (via "Via[0-3]_500:300_um") (rule (width 150) (clearance 150)))
+  (placement (component S (place G1 9000 -10000 front 0) (place G2 9500 -10000 front 0)
+                          (place G3 10000 -10000 front 0) (place G4 10500 -10000 front 0)))
+  (library
+    (image S (pin smd 1 0 0))
+    (padstack smd (shape (rect F.Cu -150 -300 150 300)) (attach off))
+    (padstack "Via[0-3]_500:300_um" (shape (circle F.Cu 500)) (shape (circle B.Cu 500)) (attach off)))
+  (network (net GND (pins G1-1 G2-1 G3-1 G4-1))))"""
+
+
+def test_a_nets_own_vias_keep_hole_to_hole_spacing():
+    dsn = parse_dsn(_DSN)
+    exact, scale, _ = route_dsn_board_exact(dsn, resolution=2)
+    assert exact.result.failed == []
+    vias = exact.result.vias[1]
+    assert len(set(vias)) == len(vias), "a via written twice"
+    need = (300 + 250) * scale  # drill + 0.25 mm, centre to centre
+    for a, b in itertools.combinations(vias, 2):
+        assert math.hypot(a.x - b.x, a.y - b.y) >= need, f"vias at {a} and {b} too close"
+
+
+def test_connections_sharing_a_plane_via_write_it_once():
+    # eight GND pads 0.4 mm apart: the hole spacing makes several of them
+    # end on the same plane via, which must come out once, not once each
+    pads = " ".join(f"(place G{i} {9000 + 400 * i} -10000 front 0)" for i in range(8))
+    pins = " ".join(f"G{i}-1" for i in range(8))
+    dsn = parse_dsn(
+        _DSN.replace(
+            "(place G1 9000 -10000 front 0) (place G2 9500 -10000 front 0)\n"
+            "                          (place G3 10000 -10000 front 0) (place G4 10500 -10000 front 0)",
+            pads,
+        )
+        .replace("(pins G1-1 G2-1 G3-1 G4-1)", f"(pins {pins})")
+        .replace("(rect F.Cu -150 -300 150 300)", "(rect F.Cu -125 -300 125 300)")
+    )
+    exact, _scale, _ = route_dsn_board_exact(dsn, resolution=2)
+    vias = exact.result.vias[1]
+    assert len(vias) < 8, "no via is shared, so this board no longer tests sharing"
+    assert len(set(vias)) == len(vias), "a shared via written more than once"
+
+
+def _router(dsn_text, via_drill_um=300):
+    from freeroute.board import build_board
+    from freeroute.route.grid_router import GridRouter
+    from freeroute.route.pipeline import _rule_clearance_dsn, _rule_width_dsn
+
+    dsn = parse_dsn(dsn_text)
+    s = dsn.resolution.value
+    return GridRouter(
+        build_board(dsn), trace_width=round(_rule_width_dsn(dsn) * s),
+        clearance=round(_rule_clearance_dsn(dsn) * s), resolution=2, orthogonal=True,
+        via_drill=via_drill_um * s, hole_to_hole=250 * s,
+    ), s
+
+
+_THT = """(pcb tht (parser) (resolution um 10) (unit um)
+  (structure (layer F.Cu (type signal)) (layer B.Cu (type signal))
+    (boundary (path pcb 0  0 0  20000 0  20000 -20000  0 -20000  0 0))
+    (via "Via[0-1]_500:300_um") (rule (width 150) (clearance 150)))
+  (placement (component T (place J1 10000 -10000 front 0)))
+  (library (image T (pin tht 1 0 0))
+    (padstack tht (shape (circle F.Cu 1700)) (shape (circle B.Cu 1700)) (attach off))
+    (padstack "Via[0-1]_500:300_um" (shape (circle F.Cu 500)) (shape (circle B.Cu 500)) (attach off)))
+  (network (net SIG (pins J1-1))))"""
+
+
+def test_no_via_goes_near_a_through_hole_pads_hole_even_of_its_own_net():
+    router, s = _router(_THT)
+    pin = router._cell_of(router.board.get_pins()[0].location)
+    assert not router._holes_clear(pin, 1)  # own net, right on the pad
+    far = (pin[0] + 40, pin[1])
+    assert router._holes_clear(far, 1)
+
+
+def test_a_via_in_a_pad_keeps_hole_spacing_from_a_fixed_via():
+    from freeroute.geometry import IntPoint
+
+    text = _THT.replace("(network (net SIG (pins J1-1))))",
+                        "(network (net SIG (pins J1-1)))\n"
+                        "  (wiring (via \"Via[0-1]_500:300_um\"  3000 -3000 (net SIG) (type route))))")
+    router, s = _router(text)
+    assert not router._hole_clear_at(IntPoint(3400 * s, -3000 * s))  # 0.4 mm < 0.55 mm
+    assert router._hole_clear_at(IntPoint(3600 * s, -3000 * s))
+
+
+def test_hole_spacing_from_a_fixed_via_is_measured_from_where_it_really_is():
+    # a fixed via off the grid with its own 0.25 mm drill, and the router's
+    # via a smaller 0.2 mm one (the flight controller's case): a new via needs
+    # its centre 0.1 + 0.125 + 0.25 = 0.475 mm away, measured exactly, where
+    # one rule for all vias gave 0.2 + 0.25 = 0.45 from the cell centres
+    text = _THT.replace("(network (net SIG (pins J1-1))))",
+                        "(network (net SIG (pins J1-1)) (net GND))\n"
+                        "  (wiring (via \"Via[0-1]_500:250_um\"  3030 -3030 (net GND) (type route))))")
+    text = text.replace(
+        '(attach off)))\n  (network',
+        '(attach off))\n    (padstack "Via[0-1]_500:250_um" (shape (circle F.Cu 500)) '
+        '(shape (circle B.Cu 500)) (attach off)))\n  (network',
+    )
+    router, s = _router(text, via_drill_um=200)
+    via = next(v for v in router.board.get_items() if getattr(v, "drill", 0))
+    assert via.drill == 250 * s
+    loc = via.location
+    for cell in [(x, y) for x in range(router.cols) for y in range(router.rows)]:
+        c = router._cell_center(cell)
+        d = math.hypot(c.x - loc.x, c.y - loc.y)
+        if router.step * 1.5 < d < 470 * s:
+            assert not router._holes_clear(cell, 1), f"{d / s:.0f} um from the fixed via"
+        elif 560 * s < d < 700 * s and cell not in router._tht_block:
+            assert router._holes_clear(cell, 1)
+
+
+def test_a_route_keeps_its_own_vias_apart():
+    # a route that changed layer at (10, 10) may not change layer again one
+    # cell away; the same cell is the same through via, and far is fine
+    router, _s = _router(_THT)
+    came_from = {(10, 10, 1): (10, 10, 0), (11, 10, 1): (10, 10, 1), (12, 10, 1): (11, 10, 1)}
+    assert router._near_path_via((12, 10, 1), (11, 10), came_from)
+    assert not router._near_path_via((12, 10, 1), (10, 10), came_from)
+    assert not router._near_path_via((12, 10, 1), (40, 10), came_from)

tests/test_cli.py

@@ -159,6 +159,7 @@ def test_cli_supported_combinations_are_accepted(tmp_path):
         "promote": ["--promote-failures", "2"],
         "access": ["--access-cost", "5"],
         "rollback": ["--no-rollback"],
+        "fanout": ["--fanout"],
     }
     for engine, options in ENGINE_OPTIONS.items():
         for option in options: