ff transitions switch

src/kyupy/logic_sim.py

@@ -91,13 +91,16 @@ class LogicSim:
                     if line is not None: self.state_epoch[line.reader] = self.epoch
         return stimuli
 
-    def capture(self, responses):
+    def capture(self, responses, ff_transitions=False):
         """Capture the current values at the primary outputs and in the state-elements (flip-flops).
         For primary outputs, the logic value is stored unmodified in the given target array.
-        For flip-flops, the logic value is constructed from the previous state and the new state.
+        For flip-flops, the logic value is either stored unmodified (`ff_transitions=False`)
+        or constructed from the previous state and the new state (`ff_transitions=True`).
 
         :param responses: A bit-parallel storage target for the responses in a compatible shape.
         :type responses: :py:class:`~kyupy.logic.BPArray`
+        :param ff_transitions: If true, calculate and store the transitions between the previous state
+        (the currently assigned pattern) and the new state.
         :returns: The given responses object.
         """
         for node, resp in zip(self.interface, responses.data if hasattr(responses, 'data') else responses):
@@ -106,15 +109,16 @@ class LogicSim:
                 resp[...] = self.state[node.outs[0]]
             else:
                 resp[...] = self.state[node.ins[0]]
-            # FIXME: unclear why we should use outs for DFFs
-            #if self.m > 2 and 'dff' in node.kind.lower() and len(node.outs) > 0:
-            #    if node.outs[0] is None:
-            #        resp[1, :] = ~self.state[node.outs[1], 0, :]  # assume QN is connected, take inverse of that.
-            #    else:
-            #        resp[1, :] = self.state[node.outs[0], 0, :]
-            #    if self.m > 4:
-            #        resp[..., 2, :] = resp[..., 0, :] ^ resp[..., 1, :]
-            #    # We don't handle X or - correctly.
+            if not ff_transitions: continue
+            # outs of DFFs contain the previously assigned value (previous state)
+            if self.m > 2 and 'dff' in node.kind.lower() and len(node.outs) > 0:
+                if node.outs[0] is None:
+                    resp[1, :] = ~self.state[node.outs[1], 0, :]  # assume QN is connected, take inverse of that.
+                else:
+                    resp[1, :] = self.state[node.outs[0], 0, :]
+                if self.m > 4:
+                    resp[..., 2, :] = resp[..., 0, :] ^ resp[..., 1, :]
+                # FIXME: We don't handle X or - correctly.
 
         return responses