From: whitequark <cz@m-labs.hk>
Date: Tue, 10 Sep 2019 07:25:28 +0000 (+0000)
Subject: hdl.ast: warn if reset value is truncated.
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=be49d3c0269928b2549538b295781048a8eb904f;p=nmigen.git

hdl.ast: warn if reset value is truncated.

Fixes #183.
---

diff --git a/nmigen/hdl/ast.py b/nmigen/hdl/ast.py
index 0afa5d9..56671ed 100644
--- a/nmigen/hdl/ast.py
+++ b/nmigen/hdl/ast.py
@@ -665,6 +665,14 @@ class Signal(Value, DUID):
 
         if not isinstance(self.nbits, int) or self.nbits < 0:
             raise TypeError("Width must be a non-negative integer, not '{!r}'".format(self.nbits))
+
+        reset_nbits = bits_for(reset, self.signed)
+        if reset != 0 and reset_nbits > self.nbits:
+            warnings.warn("Reset value {!r} requires {} bits to represent, but the signal "
+                          "only has {} bits"
+                          .format(reset, reset_nbits, self.nbits),
+                          SyntaxWarning, stacklevel=2 + src_loc_at)
+
         self.reset = int(reset)
         self.reset_less = bool(reset_less)
 
diff --git a/nmigen/test/test_hdl_ast.py b/nmigen/test/test_hdl_ast.py
index 1fd70aa..9ad4d32 100644
--- a/nmigen/test/test_hdl_ast.py
+++ b/nmigen/test/test_hdl_ast.py
@@ -510,6 +510,17 @@ class SignalTestCase(FHDLTestCase):
         self.assertEqual(s1.reset, 0b111)
         self.assertEqual(s1.reset_less, True)
 
+    def test_reset_narrow(self):
+        with self.assertWarns(SyntaxWarning,
+                msg="Reset value 8 requires 4 bits to represent, but the signal only has 3 bits"):
+            Signal(3, reset=8)
+        with self.assertWarns(SyntaxWarning,
+                msg="Reset value 4 requires 4 bits to represent, but the signal only has 3 bits"):
+            Signal((3, True), reset=4)
+        with self.assertWarns(SyntaxWarning,
+                msg="Reset value -5 requires 4 bits to represent, but the signal only has 3 bits"):
+            Signal((3, True), reset=-5)
+
     def test_attrs(self):
         s1 = Signal()
         self.assertEqual(s1.attrs, {})