Change policy for vertical track protection of the H-Tree.

Formerly we were using Placement::Area::TrackAvoid() to shift cells terminals
out of the way of the reserved vertical track. With double height cells,
this is coming more complex and due to heavy tracks uses in some cells,
the shift required may becomes too great. Instead, we place filler cells
just underneath the reserved track to prevent their usage. This is a
supplemental constraint on the router, but the new version manage it
correctly.

* New: In cumulus/block.spares.Spares.trackAvoid() to place filler cells
    under a given vertical area.

cumulus/src/plugins/block/htree.py

@@ -106,7 +106,11 @@ class HTree ( object ):
             hLeafDepth = gaugeConf.horizontalDepth - 2
         gaugeConf.setStackPosition( contact, x, y )
         gaugeConf.createVertical  ( contact, forkContact, x, 0 )
-        gaugeConf.addTrackAvoid( Box( x, forkContact.getY(), x, y ) )
+        trackAvoidBox = Box( x, forkContact.getY(), x, y )
+        if forkContact.getY() > contact.getY():
+            trackAvoidBox.inflate( 0, 0, 0, self.spares.conf.sliceHeight )
+        gaugeConf.addTrackAvoid( trackAvoidBox )
+        self.spares.trackAvoid( trackAvoidBox )
         if len(leaf.buffers) > 1:
             tl1Contact = gaugeConf.rpAccessByPlugName( leaf.buffers[1], bufferConf.input, ckNet, GaugeConf.DeepDepth|GaugeConf.HAccess )
             tl2Contact = gaugeConf.rpAccessByPlugName( leaf.buffers[2], bufferConf.input, ckNet )

cumulus/src/plugins/block/spares.py

@@ -1103,8 +1103,8 @@ class Spares ( object ):
         trace( 540, ',+', '\tSpares.addStrayBuffer()\n' )
 
         sliceHeight = self.conf.sliceHeight 
-        x           = self.quadTree.toXPitch( position.getX() )
-        y           = self.quadTree.toYSlice( position.getY() )
+        x           = self.toXPitch( position.getX() )
+        y           = self.toYSlice( position.getY() )
         slice       = y // sliceHeight
         orientation = Transformation.Orientation.ID
         y = slice * sliceHeight
@@ -1134,6 +1134,37 @@ class Spares ( object ):
             raise ErrorMessage( 2, 'Spares.getFreeBufferUnder(): No more free buffers under {}.'.format(area) )
         return leaf.selectFree()
 
+    def trackAvoid ( self, box ):
+        """
+        Protect a vertical track by putting a vertical column of narrow filler
+        under it (usually tie). Used by the H-Tree (clock tree) in low-metal
+        nodes.
+        """
+        trace( 540, ',+', '\tSpares.trackAvoid() {}\n'.format( box ))
+        yoffset = 0
+        if self.conf.isCoreBlock:
+            yoffset = self.conf.icore.getTransformation().getTy()
+        sliceHeight = self.conf.sliceHeight 
+        x           = self.toXPitch( box.getXMin() ) - self.conf.sliceStep
+        ymin        = self.toYSlice( box.getYMin() )
+        ymax        = self.toYSlice( box.getYMax() )
+        sliceMin    = (ymin - yoffset) // sliceHeight
+        sliceMax    = (ymax - yoffset) // sliceHeight
+        orientation = Transformation.Orientation.ID
+        ymin        = sliceMin * sliceHeight
+        for row in range( sliceMin+1, sliceMax ):
+            orientation = Transformation.Orientation.ID
+            y = row * sliceHeight + yoffset
+            if row%2:
+                orientation = Transformation.Orientation.MY
+                y          += sliceHeight
+            transf   = Transformation( x, y, orientation )
+            instance = self.conf.feedsConf.createFeed( self.conf.corona )
+            instance.setTransformation( transf )
+            instance.setPlacementStatus( Instance.PlacementStatus.FIXED )
+            trace( 540, '\ttrackAvoid, feed: {} @{}\n'.format(instance,transf) )
+        trace( 540, '-' )
+
     def raddTransNet ( self, topNet, path ):
         """
         Add a net through a whole hierarchy of Instance/Cells. The master cells