From 9d51ac379405c2f825dea312cfa97d8954a21601 Mon Sep 17 00:00:00 2001
From: Max Korbel <max.korbel@intel.com>
Date: Tue, 1 Nov 2022 10:16:31 -0700
Subject: [PATCH] Fix bug related to clock divider simulation, fix #191

---
 lib/src/modules/conditional.dart | 22 ++++++----
 test/clock_divider_test.dart     | 69 ++++++++++++++++++++++++++++++++
 2 files changed, 84 insertions(+), 7 deletions(-)
 create mode 100644 test/clock_divider_test.dart

diff --git a/lib/src/modules/conditional.dart b/lib/src/modules/conditional.dart
index 589a3d52a..25e98144b 100644
--- a/lib/src/modules/conditional.dart
+++ b/lib/src/modules/conditional.dart
@@ -336,14 +336,22 @@ class Sequential extends _Always {
       clk.glitch.listen((event) async {
         // we want the first previousValue from the first glitch of this tick
         _preTickClkValues[i] ??= event.previousValue;
-        if (!_pendingExecute) {
-          unawaited(Simulator.clkStable.first.then((value) {
-            // once the clocks are stable, execute the contents of the FF
-            _execute();
-            _pendingExecute = false;
-          }));
+
+        if (Simulator.phase == SimulatorPhase.clkStable) {
+          // this could be an output of a flop driving the clock of this
+          // flop, so execute immediately (e.g. clock divider)
+          _execute();
+          _pendingExecute = false;
+        } else {
+          if (!_pendingExecute) {
+            unawaited(Simulator.clkStable.first.then((value) {
+              // once the clocks are stable, execute the contents of the FF
+              _execute();
+              _pendingExecute = false;
+            }));
+          }
+          _pendingExecute = true;
         }
-        _pendingExecute = true;
       });
     }
   }
diff --git a/test/clock_divider_test.dart b/test/clock_divider_test.dart
new file mode 100644
index 000000000..051113bd9
--- /dev/null
+++ b/test/clock_divider_test.dart
@@ -0,0 +1,69 @@
+import 'package:rohd/rohd.dart';
+import 'package:rohd/src/utilities/simcompare.dart';
+import 'package:test/test.dart';
+
+import '../example/example.dart';
+
+class ClockDivider extends Module {
+  Logic get clkOut => output('clkOut');
+  ClockDivider(Logic clkIn, Logic reset) : super(name: 'clockDivider') {
+    clkIn = addInput('clkIn', clkIn);
+    reset = addInput('reset', reset);
+    final clkOut = addOutput('clkOut');
+
+    Sequential(clkIn, [
+      If(
+        reset,
+        then: [clkOut < 0],
+        orElse: [clkOut < ~clkOut],
+      ),
+    ]);
+  }
+}
+
+class TwoCounters extends Module {
+  TwoCounters(Logic resetClks, Logic resetCounters) {
+    resetClks = addInput('resetClks', resetClks);
+    resetCounters = addInput('resetCounters', resetCounters);
+
+    final clk = SimpleClockGenerator(10).clk;
+    final clkDiv = ClockDivider(clk, resetClks).clkOut;
+
+    addOutput('cntFast', width: 8) <=
+        Counter(Const(1), resetCounters, clk, name: 'fastCounter').val;
+    addOutput('cntSlow', width: 8) <=
+        Counter(Const(1), resetCounters, clkDiv, name: 'slowCounter').val;
+  }
+}
+
+void main() {
+  test('clock divider', () async {
+    final mod = TwoCounters(Logic(), Logic());
+    await mod.build();
+    final vectors = [
+      Vector({'resetClks': 1, 'resetCounters': 1}, {}),
+      Vector({'resetClks': 0, 'resetCounters': 1}, {}),
+      Vector({'resetClks': 0, 'resetCounters': 1}, {}),
+      Vector(
+          {'resetClks': 0, 'resetCounters': 0}, {'cntSlow': 0, 'cntFast': 0}),
+      Vector(
+          {'resetClks': 0, 'resetCounters': 0}, {'cntSlow': 1, 'cntFast': 1}),
+      Vector(
+          {'resetClks': 0, 'resetCounters': 0}, {'cntSlow': 1, 'cntFast': 2}),
+      Vector(
+          {'resetClks': 0, 'resetCounters': 0}, {'cntSlow': 2, 'cntFast': 3}),
+      Vector(
+          {'resetClks': 0, 'resetCounters': 0}, {'cntSlow': 2, 'cntFast': 4}),
+      Vector(
+          {'resetClks': 0, 'resetCounters': 0}, {'cntSlow': 3, 'cntFast': 5}),
+      Vector(
+          {'resetClks': 0, 'resetCounters': 0}, {'cntSlow': 3, 'cntFast': 6}),
+    ];
+
+    await SimCompare.checkFunctionalVector(mod, vectors);
+    final simResult = SimCompare.iverilogVector(
+        mod.generateSynth(), mod.runtimeType.toString(), vectors,
+        signalToWidthMap: {'cntSlow': 8, 'cntFast': 8});
+    expect(simResult, equals(true));
+  });
+}