Perform signal escape routing in smaller regions

compiler/router/signal_escape_router.py

@@ -5,6 +5,7 @@
 #
 from openram import debug
 from openram.base.vector import vector
+from openram.base.vector3d import vector3d
 from openram import OPTS
 from .graph import graph
 from .graph_shape import graph_shape
@@ -75,9 +76,51 @@ class signal_escape_router(router):
         self.replace_layout_pins()
 
 
+    def prepare_path(self, path):
+        """
+        Override the `prepare_path` method from the `router` class to prevent
+        overflows from the SRAM layout area.
+        """
+
+        ll, ur = self.bbox
+        nodes = super().prepare_path(path)
+        new_nodes = []
+        for i in range(len(nodes)):
+            node = nodes[i]
+            c = node.center
+
+            # Haven't overflown yet
+            if ll.x < c.x and c.x < ur.x and ll.y < c.y and c.y < ur.y:
+                new_nodes.append(node)
+                continue
+
+            # Snap the pin to the perimeter and break the iteration
+            ll_diff_x = abs(c.x - ll.x)
+            ll_diff_y = abs(c.y - ll.y)
+            ur_diff_x = abs(c.x - ur.x)
+            ur_diff_y = abs(c.y - ur.y)
+            min_diff = min(ll_diff_x, ll_diff_y, ur_diff_x, ur_diff_y)
+
+            if min_diff == ll_diff_x:
+                fake_center = vector3d(ll.x + self.half_wire, c.y, c.z)
+            if min_diff == ll_diff_y:
+                fake_center = vector3d(c.x, ll.y + self.half_wire, c.z)
+            if min_diff == ur_diff_x:
+                fake_center = vector3d(ur.x - self.half_wire, c.y, c.z)
+            if min_diff == ur_diff_y:
+                fake_center = vector3d(c.x, ur.y - self.half_wire, c.z)
+
+            node.center = fake_center
+            new_nodes.append(node)
+            break
+        return new_nodes
+
+
     def add_perimeter_fake_pins(self):
         """
         Add the fake pins on the perimeter to where the signals will be routed.
+        These perimeter fake pins are only used to replace layout pins at the
+        end of routing.
         """
 
         ll, ur = self.bbox
@@ -118,17 +161,44 @@ class signal_escape_router(router):
             self.fake_pins.append(pin)
 
 
-    def get_closest_perimeter_fake_pin(self, pin):
-        """ Return the closest fake pin for the given pin. """
+    def create_fake_pin(self, pin):
+        """ Create a fake pin on the perimeter orthogonal to the given pin. """
 
-        min_dist = float("inf")
-        close_fake = None
-        for fake in self.fake_pins:
-            dist = pin.distance(fake)
-            if dist < min_dist:
-                min_dist = dist
-                close_fake = fake
-        return close_fake
+        ll, ur = self.bbox
+        c = pin.center()
+
+        # Find the closest edge
+        ll_diff_x = abs(c.x - ll.x)
+        ll_diff_y = abs(c.y - ll.y)
+        ur_diff_x = abs(c.x - ur.x)
+        ur_diff_y = abs(c.y - ur.y)
+        min_diff = min(ll_diff_x, ll_diff_y, ur_diff_x, ur_diff_y)
+
+        # Keep the fake pin out of the SRAM layout are so that they won't be
+        # blocked by previous signals if they're on the same orthogonal line
+        if min_diff == ll_diff_x:
+            fake_center = vector(ll.x - self.track_wire * 2, c.y)
+            vertical = True
+        if min_diff == ll_diff_y:
+            fake_center = vector(c.x, ll.y - self.track_wire * 2)
+            vertical = False
+        if min_diff == ur_diff_x:
+            fake_center = vector(ur.x + self.track_wire * 2, c.y)
+            vertical = True
+        if min_diff == ur_diff_y:
+            fake_center = vector(c.x, ur.y + self.track_wire * 2)
+            vertical = False
+
+        # Create the fake pin shape
+        layer = self.get_layer(int(not vertical))
+        half_wire_vector = vector([self.half_wire] * 2)
+        nll = fake_center - half_wire_vector
+        nur = fake_center + half_wire_vector
+        rect = [nll, nur]
+        pin = graph_shape(name="fake",
+                          rect=rect,
+                          layer_name_pp=layer)
+        return pin
 
 
     def get_route_pairs(self, pin_names):
@@ -137,7 +207,7 @@ class signal_escape_router(router):
         to_route = []
         for name in pin_names:
             pin = next(iter(self.pins[name]))
-            fake = self.get_closest_perimeter_fake_pin(pin)
+            fake = self.create_fake_pin(pin)
             to_route.append((pin, fake, pin.distance(fake)))
         return sorted(to_route, key=lambda x: x[2])