phy/sim_utils: support low wait times (0/1) in PulseTiming

litedram/phy/sim_utils.py

@@ -206,6 +206,48 @@ def log_level_getter(log_level):
 
 # Simulator ----------------------------------------------------------------------------------------
 
+class Timing(Module):
+    # slight modification of tXXDController
+    def __init__(self, t):
+        self.valid = Signal()
+        self.ready = Signal()
+
+        if t is None:
+            t = 0
+
+        if isinstance(t, Signal):
+            count = Signal.like(t)
+        else:
+            count = Signal(max=max(t, 2))
+
+        ready = Signal()
+        ready_reg = Signal()
+        self.comb += [
+            self.ready.eq(ready_reg | ready),
+            ready.eq((t == 0) & self.valid),
+        ]
+
+        self.sync += \
+            If(self.valid,
+                If(t == 0,
+                    ready_reg.eq(1)
+                ).Else(
+                    count.eq(t - 1),
+                    If(t == 1,
+                        ready_reg.eq(1)
+                    ).Else(
+                        ready_reg.eq(0)
+                    )
+                ),
+            ).Elif(~ready,
+                If(count > 1,
+                    count.eq(count - 1),
+                ),
+                If(count == 1,
+                    ready_reg.eq(1)
+                )
+            )
+
 class PulseTiming(Module):
     """Timing monitor with pulse input/output
 
@@ -214,20 +256,29 @@ class PulseTiming(Module):
     * countdown triggered by a low to high pulse on `trigger`
     * `ready` is initially low, only after a trigger it can become high
     * provides `ready_p` which is high only for 1 cycle when `ready` becomes high
+    * supports t values starting from 0, with t=0 `ready_p` will pulse in the same
+      cycle in which `trigger` is high
     """
     def __init__(self, t):
         self.trigger = Signal()
         self.ready   = Signal()
         self.ready_p = Signal()
 
-        ready_d = Signal()
+        trigger_d = Signal()
         triggered = Signal()
-        tctrl = tXXDController(t)
+        timing = Timing(t)
-        self.submodules += tctrl
+        self.submodules += timing
 
-        self.sync += If(self.trigger, triggered.eq(1)),
+        self.sync += [
-        self.comb += [
+            If(self.trigger, triggered.eq(1)),
-            self.ready.eq(triggered & tctrl.ready),
+            trigger_d.eq(self.trigger),
-            self.ready_p.eq(edge(self, self.ready)),
+        ]
-            tctrl.valid.eq(edge(self, self.trigger)),
+        self.comb += [
+            self.ready.eq((triggered & timing.ready) | ((t == 0) & self.trigger)),
+            self.ready_p.eq(reduce(or_, [
+                edge(self, self.ready),
+                (t == 0) & edge(self, self.trigger),
+                (t == 1) & edge(self, trigger_d),
+            ])),
+            timing.valid.eq(edge(self, self.trigger)),
         ]

test/test_sim_utils.py

@@ -0,0 +1,87 @@
+# This file is part of LiteDRAM.
+#
+# Copyright (c) 2021 Antmicro <www.antmicro.com>
+# SPDX-License-Identifier: BSD-2-Clause
+
+import unittest
+
+from migen import *
+
+from litedram.phy.sim_utils import PulseTiming
+
+class TestSimUtils(unittest.TestCase):
+    def pulse_timing_test(self, dut, *, trigger, ready, ready_p, generators=None):
+        generators = generators or []
+        assert len(trigger) == len(ready) == len(ready_p)
+
+        ready_hist = ""
+        ready_p_hist = ""
+
+        def generator():
+            nonlocal ready_hist, ready_p_hist
+            for i in range(len(trigger)):
+                yield dut.trigger.eq(int(trigger[i]))
+                yield
+                ready_hist += str((yield dut.ready))
+                ready_p_hist += str((yield dut.ready_p))
+
+        run_simulation(dut, [generator(), *generators])
+        self.assertEqual(ready_hist, ready)
+        self.assertEqual(ready_p_hist, ready_p)
+
+    def test_pulse_timing_basic(self):
+        self.pulse_timing_test(PulseTiming(4),
+            trigger = "01000000",
+            ready   = "00000111",
+            ready_p = "00000100",
+        )
+
+    def test_pulse_timing_1(self):
+        self.pulse_timing_test(PulseTiming(1),
+            trigger = "01000000",
+            ready   = "00111111",
+            ready_p = "00100000",
+        )
+
+    def test_pulse_timing_0(self):
+        self.pulse_timing_test(PulseTiming(0),
+            trigger = "01000000",
+            ready   = "01111111",
+            ready_p = "01000000",
+        )
+
+    def pulse_timing_signal_test(self, t, **kwargs):
+        class Dut(PulseTiming):
+            def __init__(self):
+                self.t = Signal(3)
+                super().__init__(self.t)
+        dut = Dut()
+        def generator():
+            yield
+            yield dut.t.eq(t)
+            yield
+        self.pulse_timing_test(dut, generators=[generator()], **kwargs)
+
+    def test_pulse_timing_signal(self):
+        self.pulse_timing_signal_test(
+            t       = 4,
+            trigger = "00100000000000000",
+            ready   = "00000011111111111",
+            ready_p = "00000010000000000",
+        )
+
+    def test_pulse_timing_signal_1(self):
+        self.pulse_timing_signal_test(
+            t       = 1,
+            trigger = "00100000000000000",
+            ready   = "00011111111111111",
+            ready_p = "00010000000000000",
+        )
+
+    def test_pulse_timing_signal_0(self):
+        self.pulse_timing_signal_test(
+            t       = 0,
+            trigger = "00100000000000000",
+            ready   = "00111111111111111",
+            ready_p = "00100000000000000",
+        )