[ENH] Updated the ConcatSignal conversion code to check for undriven … (#371)

* [ENH] Updated the ConcatSignal conversion code to check for undriven signals.

* [ENH] Added a test to check the undriven ConcatSignal converts sensibly.

myhdl/_ShadowSignal.py

@@ -196,8 +196,39 @@ class ConcatSignal(_ShadowSignal):
             else:
                 w = len(a)
             lo = hi - w
+
+            if isinstance(a, _Signal) and a._name is None:
+                # We have seen a bug when a concat signal is created in the
+                # following way:
+                #
+                #     sig_list = [Signal(False) for n in range(32)]
+                #     concat_sig = ConcatSignal(*reversed(sig_list))
+                #
+                # It seems that the _name attribute on the signals in sig_list
+                # is only updated if an assignment is made to them. Otherwise
+                # _name is left as None. We need to check for None and raise
+                # a warning.
+                from myhdl.conversion._misc import _error
+                from myhdl import ToVHDLWarning
+
+                if w == 1:
+                    warnings.warn(
+                        "%s: %s[%s]" % (_error.UndrivenSignal, self._name, lo),
+                        category=ToVHDLWarning)
+                else:
+                    warnings.warn(
+                        "%s: %s[%s:%s]" % (_error.UndrivenSignal, self._name, hi, lo),
+                        category=ToVHDLWarning)
+
             if w == 1:
-                if isinstance(a, _Signal):
+                if isinstance(a, _Signal) and a._name is not None:
+                    # Check that a._name is not None as None should not be
+                    # written into the converted code. If it is None then we
+                    # assume no assignment has been made to the signal
+                    # (otherwise the _name attribute would have been updated
+                    # by the _analyzeSigs function). In this situation the
+                    # signal should hold its init value (as handled in the
+                    # else branch).
                     if a._type == bool:  # isinstance(a._type , bool): <- doesn't work
                         lines.append("%s(%s) <= %s;" % (self._name, lo, a._name))
                     else:
@@ -205,7 +236,9 @@ class ConcatSignal(_ShadowSignal):
                 else:
                     lines.append("%s(%s) <= '%s';" % (self._name, lo, bin(ini[lo])))
             else:
-                if isinstance(a, _Signal):
+                if isinstance(a, _Signal) and a._name is not None:
+                    # Check that a._name is not None as None should not be
+                    # written into the converted code
                     lines.append("%s(%s-1 downto %s) <= %s;" % (self._name, hi, lo, a._name))
                 else:
                     lines.append('%s(%s-1 downto %s) <= "%s";' %
@@ -223,8 +256,39 @@ class ConcatSignal(_ShadowSignal):
             else:
                 w = len(a)
             lo = hi - w
+
+            if isinstance(a, _Signal) and a._name is None:
+                # We have seen a bug when a concat signal is created in the
+                # following way:
+                #
+                #     sig_list = [Signal(False) for n in range(32)]
+                #     concat_sig = ConcatSignal(*reversed(sig_list))
+                #
+                # It seems that the _name attribute on the signals in sig_list
+                # is only updated if an assignment is made to them. Otherwise
+                # _name is left as None. We need to check for None and raise
+                # a warning.
+                from myhdl.conversion._misc import _error
+                from myhdl import ToVerilogWarning
+
+                if w == 1:
+                    warnings.warn(
+                        "%s: %s[%s]" % (_error.UndrivenSignal, self._name, lo),
+                        category=ToVerilogWarning)
+                else:
+                    warnings.warn(
+                        "%s: %s[%s:%s]" % (_error.UndrivenSignal, self._name, hi, lo),
+                        category=ToVerilogWarning)
+
             if w == 1:
-                if isinstance(a, _Signal):
+                if isinstance(a, _Signal) and a._name is not None:
+                    # Check that a._name is not None as None should not be
+                    # written into the converted code. If it is None then we
+                    # assume no assignment has been made to the signal
+                    # (otherwise the _name attribute would have been updated
+                    # by the _analyzeSigs function). In this situation the
+                    # signal should hold its init value (as handled in the
+                    # else branch).
                     if a._type == bool:
                         lines.append("assign %s[%s] = %s;" % (self._name, lo, a._name))
                     else:
@@ -232,7 +296,9 @@ class ConcatSignal(_ShadowSignal):
                 else:
                     lines.append("assign %s[%s] = 'b%s;" % (self._name, lo, bin(ini[lo])))
             else:
-                if isinstance(a, _Signal):
+                if isinstance(a, _Signal) and a._name is not None:
+                    # Check that a._name is not None as None should not be
+                    # written into the converted code
                     lines.append("assign %s[%s-1:%s] = %s;" % (self._name, hi, lo, a._name))
                 else:
                     lines.append("assign %s[%s-1:%s] = 'b%s;" %

myhdl/test/conversion/general/test_ShadowSignal.py

@@ -103,6 +103,24 @@ def bench_ConcatSignalWithConsts():
 def test_ConcatSignalWithConsts():
     assert conversion.verify(bench_ConcatSignalWithConsts()) == 0
 
+@block
+def bench_ConcatSignalUndriven():
+
+    n_sigs = 32
+
+    sig_list = [Signal(False) for n in range(n_sigs)]
+    concat_sig = ConcatSignal(*reversed(sig_list))
+
+    @instance
+    def check():
+
+        yield delay(10)
+        print(concat_sig)
+
+    return check
+
+def test_ConcatSignalUndriven():
+    assert conversion.verify(bench_ConcatSignalUndriven()) == 0
 
 @block
 def bench_TristateSignal():