Tighten routing policy with channel spacing and tie-net fallback

src/layout.js

@@ -18,7 +18,7 @@ const NET_CLASS_PRIORITY = {
 const LABEL_TIE_CLASSES = new Set(["power", "ground", "bus"]);
 const DEFAULT_RENDER_MODE = "schematic_stub";
 const ROTATION_STEPS = [0, 90, 180, 270];
-const MIN_CHANNEL_SPACING_STEPS = 2;
+const MIN_CHANNEL_SPACING_STEPS = 3;
 const LANE_ORDER = ["power", "clock", "signal", "analog", "ground", "bus", "differential"];
 
 function toGrid(value) {
@@ -1190,7 +1190,7 @@ function uniquePoints(points) {
   return [...map.values()];
 }
 
-function routeLabelTieNet(net, pinNodes, context) {
+function routeLabelTieNet(net, pinNodes, context, fallbackReason = null) {
   const routes = [];
   const tiePoints = [];
 
@@ -1239,7 +1239,7 @@ function routeLabelTieNet(net, pinNodes, context) {
       total_bends: 0,
       detour_ratio: 1,
       used_label_tie: true,
-      fallback_reason: null
+      fallback_reason: fallbackReason
     }
   };
 }
@@ -1493,6 +1493,9 @@ function shouldUseLabelTie(net, pinNodes, context) {
   const span = Math.abs(maxX - minX) + Math.abs(maxY - minY);
 
   if (context.renderMode === "explicit") {
+    if (context.busNetNames.has(net.name) && (pinNodes.length >= 3 || span > GRID * 36)) {
+      return true;
+    }
     return LABEL_TIE_CLASSES.has(net.class) && pinNodes.length > 2;
   }
 
@@ -1517,6 +1520,26 @@ function shouldUseLabelTie(net, pinNodes, context) {
   return false;
 }
 
+function shouldFallbackToTieByQuality(net, pinNodes, routed) {
+  if (!routed || routed.mode !== "routed") {
+    return false;
+  }
+  const stats = routed.route_stats ?? {};
+  const detour = Number(stats.detour_ratio ?? 1);
+  const bends = Number(stats.total_bends ?? 0);
+  const totalLength = Number(stats.total_length ?? 0);
+  const directLength = Number(stats.direct_length ?? totalLength);
+  const spanRatio = directLength > 0 ? totalLength / directLength : 1;
+
+  if (pinNodes.length >= 4 && (detour > 2.25 || bends >= 7)) {
+    return true;
+  }
+  if ((net.class === "analog" || net.class === "signal") && pinNodes.length >= 3 && spanRatio > 2.7) {
+    return true;
+  }
+  return false;
+}
+
 function routeAllNets(model, placed, placedMap, bounds, options) {
   const obstacles = buildObstacles(model, placed);
   const edgeUsage = new Map();
@@ -1551,10 +1574,14 @@ function routeAllNets(model, placed, placedMap, bounds, options) {
       busNetNames
     };
 
-    const routed = shouldUseLabelTie(net, pinNodes, routeContext)
+    let routed = shouldUseLabelTie(net, pinNodes, routeContext)
       ? routeLabelTieNet(net, pinNodes, routeContext)
       : routePointToPointNet(net, pinNodes, routeContext);
 
+    if (shouldFallbackToTieByQuality(net, pinNodes, routed)) {
+      routed = routeLabelTieNet(net, pinNodes, routeContext, "quality_policy");
+    }
+
     routedByName.set(net.name, {
       net,
       isBusMember: busNetNames.has(net.name),