memory: fix MemoryMap window patterns.

Author: Jean-François Nguyen

nmigen_soc/memory.py

@@ -385,9 +385,12 @@ def window_patterns(self):
         it is always 1.
         """
         for window, window_range in self._windows.items():
-            pattern = "{:0{}b}{}".format(window_range.start >> window.addr_width,
-                                         self.addr_width - window.addr_width,
-                                         "-" * window.addr_width)
+            const_bits = self.addr_width - window.addr_width
+            if const_bits > 0:
+                const_pat = "{:0{}b}".format(window_range.start >> window.addr_width, const_bits)
+            else:
+                const_pat = ""
+            pattern = "{}{}".format(const_pat, "-" * window.addr_width)
             yield window, (pattern, window_range.step)
 
     @staticmethod

nmigen_soc/test/test_memory.py

@@ -261,6 +261,14 @@ def test_iter_window_patterns(self):
             (window_2, ("0001------------", 1)),
         ])
 
+    def test_iter_window_patterns_covered(self):
+        memory_map = MemoryMap(addr_width=16, data_width=8)
+        window = MemoryMap(addr_width=16, data_width=8)
+        memory_map.add_window(window)
+        self.assertEqual(list(memory_map.window_patterns()), [
+            (window, ("----------------", 1)),
+        ])
+
     def test_align_to(self):
         memory_map = MemoryMap(addr_width=16, data_width=8)
         self.assertEqual(memory_map.add_resource("a", size=1), (0, 1))