mac/last_be: Simplify LiteEthMACTXLastBE using an FSM, fix sink.ready…

… corner case.

liteeth/mac/last_be.py

@@ -17,22 +17,24 @@ def __init__(self, dw):
 
         # # #
 
-        ongoing = Signal(reset=1)
-        self.sync += [
+        self.submodules.fsm = fsm = FSM(reset_state="COPY")
+        fsm.act("COPY",
+            sink.connect(source, omit={"last", "last_be"}),
+            source.last.eq(sink.last_be),
             If(sink.valid & sink.ready,
-                If(sink.last,
-                    ongoing.eq(1)
-                ).Elif(sink.last_be,
-                    ongoing.eq(0)
+                # If last Byte but not last packet token.
+                If(sink.last_be & ~sink.last,
+                    NextState("WAIT-LAST")
                 )
             )
-        ]
-        self.comb += [
-            source.valid.eq(sink.valid & ongoing),
-            source.last.eq(sink.last_be),
-            source.data.eq(sink.data),
-            sink.ready.eq(source.ready)
-        ]
+        )
+        fsm.act("WAIT-LAST",
+            # Accept incoming stream until we receive last packet token.
+            sink.ready.eq(1),
+            If(sink.valid & sink.last,
+                NextState("COPY")
+            )
+        )
 
 # MAC RX Last BE -----------------------------------------------------------------------------------