Added graph creation and functions in base class and lower level modules.

compiler/modules/dff.py

@@ -50,3 +50,11 @@ class dff(design.design):
         #Calculated in the tech file by summing the widths of all the gates and dividing by the minimum width.
         return parameter["dff_clk_cin"]
 
+    def build_graph(self, graph, inst_name, port_nets):        
+        """Adds edges to graph. Handmade cells must implement this manually."""
+        #The cell has 5 net ports hard-coded in self.pin_names. The edges
+        #are based on the hard-coded name positions.
+        # The edges added are: clk->Q.
+        # Internal nodes of the handmade cell not considered, only ports. vdd/gnd ignored for graph.
+        graph.add_edge(port_nets[2],port_nets[1])
+