test: add test_timing_controllers with tXXDController test

test/test_timing_controllers.py

@@ -0,0 +1,40 @@
+# This file is Copyright (c) 2019 Florent Kermarrec <florent@enjoy-digital.fr>
+# License: BSD
+
+import unittest
+import random
+
+from migen import *
+
+from litedram.common import tXXDController
+
+class TestTimingControllers(unittest.TestCase):
+    def txxd_controller_test(self, txxd, loops):
+        def generator(dut, valid_rand):
+            prng = random.Random(42)
+            for l in range(loops):
+                while prng.randrange(100) < valid_rand:
+                    yield
+                yield dut.valid.eq(1)
+                yield
+                yield dut.valid.eq(0)
+
+        @passive
+        def checker(dut):
+            dut.ready_gaps = []
+            while True:
+                while (yield dut.ready) != 0:
+                    yield
+                ready_gap = 1
+                while (yield dut.ready) != 1:
+                    ready_gap += 1
+                    yield
+                dut.ready_gaps.append(ready_gap)
+
+        dut = tXXDController(txxd)
+        run_simulation(dut, [generator(dut, valid_rand=90), checker(dut)])
+        self.assertEqual(min(dut.ready_gaps), txxd)
+
+    def test_txxd_controller(self):
+        for i in range(2, 32):
+            self.txxd_controller_test(i, 512)