lib.cdc: avoid modifying synchronizers in their elaborate() method.

Author: whitequark

nmigen/lib/cdc.py

@@ -57,19 +57,22 @@ def __init__(self, i, o, *, o_domain="sync", stages=2, reset=0, reset_less=True)
         self.i = i
         self.o = o
 
-        self._o_domain = o_domain
-        self._stages = [Signal(self.i.shape(), name="stage{}".format(index),
-                               reset=reset, reset_less=reset_less)
-                        for index in range(stages)]
+        self._reset      = reset
+        self._reset_less = reset_less
+        self._o_domain   = o_domain
+        self._stages     = stages
 
     def elaborate(self, platform):
         if hasattr(platform, "get_ff_sync"):
             return platform.get_ff_sync(self)
 
         m = Module()
-        for i, o in zip((self.i, *self._stages), self._stages):
+        flops = [Signal(self.i.shape(), name="stage{}".format(index),
+                        reset=self._reset, reset_less=self._reset_less)
+                 for index in range(self._stages)]
+        for i, o in zip((self.i, *flops), flops):
             m.d[self._o_domain] += o.eq(i)
-        m.d.comb += self.o.eq(self._stages[-1])
+        m.d.comb += self.o.eq(flops[-1])
         return m
 
 
@@ -82,20 +85,21 @@ def __init__(self, arst, *, domain="sync", stages=2):
         self.arst = arst
 
         self._domain = domain
-        self._stages = [Signal(1, name="stage{}".format(i), reset=1)
-                        for i in range(stages)]
+        self._stages = stages
 
     def elaborate(self, platform):
         if hasattr(platform, "get_reset_sync"):
             return platform.get_reset_sync(self)
 
         m = Module()
         m.domains += ClockDomain("reset_sync", async_reset=True, local=True)
-        for i, o in zip((0, *self._stages), self._stages):
+        flops = [Signal(1, name="stage{}".format(index), reset=1)
+                 for index in range(self._stages)]
+        for i, o in zip((0, *flops), flops):
             m.d.reset_sync += o.eq(i)
         m.d.comb += [
             ClockSignal("reset_sync").eq(ClockSignal(self._domain)),
             ResetSignal("reset_sync").eq(self.arst),
-            ResetSignal(self._domain).eq(self._stages[-1])
+            ResetSignal(self._domain).eq(flops[-1])
         ]
         return m

nmigen/vendor/xilinx_7series.py

@@ -363,8 +363,11 @@ def get_diff_input_output(self, pin, p_port, n_port, attrs, invert):
 
     def get_ff_sync(self, ff_sync):
         m = Module()
-        for i, o in zip((ff_sync.i, *ff_sync._stages), ff_sync._stages):
-            o.attrs["ASYNC_REG"] = "TRUE"
+        flops = [Signal(ff_sync.i.shape(), name="stage{}".format(index),
+                        reset=ff_sync._reset, reset_less=ff_sync._reset_less,
+                        attrs={"ASYNC_REG": "TRUE"})
+                 for index in range(ff_sync._stages)]
+        for i, o in zip((ff_sync.i, *flops), flops):
             m.d[ff_sync._o_domain] += o.eq(i)
-        m.d.comb += ff_sync.o.eq(ff_sync._stages[-1])
+        m.d.comb += ff_sync.o.eq(flops[-1])
         return m

nmigen/vendor/xilinx_spartan_3_6.py

@@ -413,22 +413,27 @@ def get_diff_input_output(self, pin, p_port, n_port, attrs, invert):
 
     def get_ff_sync(self, ff_sync):
         m = Module()
-        for i, o in zip((ff_sync.i, *ff_sync._stages), ff_sync._stages):
-            o.attrs["ASYNC_REG"] = "TRUE"
+        flops = [Signal(ff_sync.i.shape(), name="stage{}".format(index),
+                        reset=ff_sync._reset, reset_less=ff_sync._reset_less,
+                        attrs={"ASYNC_REG": "TRUE"})
+                 for index in range(ff_sync._stages)]
+        for i, o in zip((ff_sync.i, *flops), flops):
             m.d[ff_sync._o_domain] += o.eq(i)
-        m.d.comb += ff_sync.o.eq(multireg._stages[-1])
+        m.d.comb += ff_sync.o.eq(flops[-1])
         return m
 
-    def get_reset_sync(self, resetsync):
+    def get_reset_sync(self, reset_sync):
         m = Module()
         m.domains += ClockDomain("reset_sync", async_reset=True, local=True)
-        for i, o in zip((0, *resetsync._stages), resetsync._stages):
-            o.attrs["ASYNC_REG"] = "TRUE"
+        flops = [Signal(1, name="stage{}".format(index), reset=1,
+                        attrs={"ASYNC_REG": "TRUE"})
+                 for index in range(reset_sync._stages)]
+        for i, o in zip((0, *flops), flops):
             m.d.reset_sync += o.eq(i)
         m.d.comb += [
-            ClockSignal("reset_sync").eq(ClockSignal(resetsync._domain)),
-            ResetSignal("reset_sync").eq(resetsync.arst),
-            ResetSignal(resetsync._domain).eq(resetsync._stages[-1])
+            ClockSignal("reset_sync").eq(ClockSignal(reset_sync._domain)),
+            ResetSignal("reset_sync").eq(reset_sync.arst),
+            ResetSignal(reset_sync._domain).eq(flops[-1])
         ]
         return m