genlib/cdc: add GrayDecoder

sbourdeauducq · sbourdeauducq · commit de2cbb62cfaf · 2016-08-02T15:43:59.000+08:00
diff --git a/migen/genlib/cdc.py b/migen/genlib/cdc.py
@@ -143,3 +143,17 @@ def __init__(self, width):
             self.q_binary.eq(self.q_next_binary),
             self.q.eq(self.q_next)
         ]
+
+
+class GrayDecoder(Module):
+    def __init__(self, width):
+        self.i = Signal(width)
+        self.o = Signal(width)
+
+        # # #
+
+        o_comb = Signal(width)
+        self.comb += o_comb[-1].eq(self.i[-1])
+        for i in reversed(range(width-1)):
+            self.comb += o_comb[i].eq(o_comb[i+1] ^ self.i[i])
+        self.sync += self.o.eq(o_comb)
