memory: add Memory.window_patterns(), to simplify decoders.

Author: whitequark

nmigen_soc/csr/bus.py

@@ -330,14 +330,8 @@ def add(self, sub_bus, *, addr=None):
             raise ValueError("Subordinate bus has data width {}, which is not the same as "
                              "multiplexer data width {}"
                              .format(sub_bus.data_width, self.bus.data_width))
-
-        start, end, ratio = window_range = self._map.add_window(sub_bus.memory_map, addr=addr)
-        assert ratio == 1
-        pattern = "{:0{}b}{}".format(start >> sub_bus.addr_width,
-                                     self.bus.addr_width - sub_bus.addr_width,
-                                     "-" * sub_bus.addr_width)
-        self._subs[pattern] = sub_bus
-        return window_range
+        self._subs[sub_bus.memory_map] = sub_bus
+        return self._map.add_window(sub_bus.memory_map, addr=addr)
 
     def elaborate(self, platform):
         m = Module()
@@ -346,7 +340,8 @@ def elaborate(self, platform):
         r_data_fanin = 0
 
         with m.Switch(self.bus.addr):
-            for sub_pat, sub_bus in self._subs.items():
+            for sub_map, sub_pat in self._map.window_patterns():
+                sub_bus = self._subs[sub_map]
                 m.d.comb += sub_bus.addr.eq(self.bus.addr[:sub_bus.addr_width])
 
                 # The CSR bus interface is defined to output zero when idle, allowing us to avoid

nmigen_soc/memory.py

@@ -321,6 +321,23 @@ def windows(self):
         for window, window_range in self._windows.items():
             yield window, (window_range.start, window_range.stop, window_range.step)
 
+    def window_patterns(self):
+        """Iterate local windows and patterns that match their address ranges.
+
+        Non-recursively iterate windows in ascending order of their address.
+
+        Yield values
+        ------------
+        A tuple ``window, pattern`` describing the address range assigned to the window.
+        ``pattern`` is a ``self.addr_width`` wide pattern that may be used in ``Case`` or ``match``
+        to determine if an address signal is within the address range of ``window``.
+        """
+        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)
+            yield window, pattern
+
     @staticmethod
     def _translate(start, end, width, window, window_range):
         assert (end - start) % window_range.step == 0

nmigen_soc/test/test_memory.py

@@ -209,6 +209,17 @@ def test_iter_windows(self):
             (window_2, (0x1000, 0x2000, 1)),
         ])
 
+    def test_iter_window_patterns(self):
+        memory_map = MemoryMap(addr_width=16, data_width=16)
+        window_1 = MemoryMap(addr_width=10, data_width=8)
+        memory_map.add_window(window_1, sparse=False)
+        window_2 = MemoryMap(addr_width=12, data_width=16)
+        memory_map.add_window(window_2)
+        self.assertEqual(list(memory_map.window_patterns()), [
+            (window_1, "000000----------"),
+            (window_2, "0001------------"),
+        ])
+
     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))