Merge pull request #263 from antoinevg/antoinevg/fix-cdc

gateware: fix an order-of-operations bug with cdc.synchronize

luna/gateware/utils/cdc.py

@@ -53,19 +53,21 @@ def create_synchronizer(signal, output):
     # Otherwise, we'll need to make sure we only synchronize
     # elements with non-output directions.
     for name, layout, direction in signal.layout:
+        # Skip any output elements, as they're already
+        # in our clock domain, and we don't want to drive them.
+        if (direction == DIR_FANOUT):
+            m.d.comb += signal[name].eq(output[name])
+            continue
+        elif hasattr(signal[name], 'o') and ~hasattr(signal[name], 'i'):
+            m.d.comb += signal[name].o.eq(output[name])
+            continue
 
         # If this is a record itself, we'll need to recurse.
         if isinstance(signal[name], (Record, Pin)):
             synchronize(m, signal[name], output=output[name],
                     o_domain=o_domain, stages=stages)
             continue
 
-        # Skip any output elements, as they're already
-        # in our clock domain, and we don't want to drive them.
-        if (direction == DIR_FANOUT) or (hasattr(signal[name], 'o') and ~hasattr(signal[name], 'i')):
-            m.d.comb += signal[name].eq(output[name])
-            continue
-
         m.submodules += create_synchronizer(signal[name], output[name])
 
     return output

tests/test_cdc.py

@@ -8,6 +8,7 @@
 from unittest       import TestCase
 
 from amaranth import Module, Record, Signal
+from amaranth.lib.io import Pin
 from amaranth.hdl.rec import DIR_FANIN, DIR_FANOUT
 from luna.gateware.utils.cdc import synchronize, stretch_strobe_signal
 
@@ -39,6 +40,17 @@ def test_nested_record(self):
         ])
         synchronize(m, record)
 
+    def test_pins(self):
+        m = Module()
+        pins = {
+            "sig_in": Pin(1, "i"),
+            "sig_out": Pin(1, "o"),
+        }
+        record = Record([
+            (f_name, f.layout) for (f_name, f) in pins.items()
+        ], fields=pins)
+        synchronize(m, record)
+
 
 class StrobeStretcherTest(LunaGatewareTestCase):
     """ Test case for our strobe stretcher function. """