transform/unroll: support empty dictionaries

diff --git a/migen/transform/unroll.py b/migen/transform/unroll.py
index 6e517cd187d21db62baf956ff0794d4a1462e99c..0d0ef9ee92d82895c64fb1e4f75de80430b5bdcc 100644 (file)
--- a/migen/transform/unroll.py
+++ b/migen/transform/unroll.py
@@ -1,3 +1,5 @@
+from itertools import repeat
+
 from migen.fhdl.structure import *
 from migen.fhdl.structure import _Operator, _Slice, _Assign, _ArrayProxy
 
@@ -60,6 +62,7 @@ def _replace(node, rin, rout, mode=_UNDETERMINED):
                raise TypeError
 
 def _list_step_dicts(d):
+       assert(d)
        iterdict = dict((k, iter(v)) for k, v in d.items())
        r = []
        try:
@@ -78,11 +81,19 @@ def _variable_for(s, n):
        return Signal(s.bv, name=name, variable=True)
 
 def unroll_sync(sync, inputs, outputs):
-       sd_in = _list_step_dicts(inputs)
-       sd_out = _list_step_dicts(outputs)
+       assert(inputs or outputs)
+       if inputs:
+               sd_in = _list_step_dicts(inputs)
+       else:
+               sd_in = repeat({})
+       if outputs:
+               sd_out = _list_step_dicts(outputs)
+               io_var_dict = sd_out[-1].copy()
+       else:
+               sd_out = repeat({})
+               io_var_dict = {}
 
        r = []
-       io_var_dict = sd_out[-1].copy()
        for n, (di, do) in enumerate(zip(sd_in, sd_out)):
                do_var = dict((k, _variable_for(v, n)) for k, v in do.items())