(WIP, DO NOT MERGE, breaks Dune music) Tried to fix DOTT having no music half the time (OPL3 issue)

src/Spice86.Core/Emulator/Devices/Sound/Opl3Fm.cs

@@ -178,6 +178,12 @@ public override byte ReadByte(ushort port) {
     }
 
     private byte PortRead(ushort port) {
+        // Some tests revealed it taking 1.5us to read an AdLib port.
+        // Expected by a lot of OPL music drivers in their startup routine, such as the one from 'Day of the Tentacle'
+        // Without this the driver decides the OPL can't be used and no music is played.
+        // Unlike the SB DSP reset delay which produces another (expected) response in SB port read path in the mean time,
+        // this wait is blocking.
+        _clock.Delay(TimeSpan.FromMicroseconds(1.5));
         switch (_mode) {
             case OplMode.Opl2:
                 // We allocated 4 ports, so just return -1 for the higher ones.

src/Spice86.Core/Emulator/VM/Clock/ClockBase.cs

@@ -65,4 +65,7 @@ protected virtual void OnResumeCore() { }
     /// Called by <see cref="Dispose"/> before finalization is suppressed. Override to release additional resources.
     /// </summary>
     protected virtual void OnDisposeCore() { }
+
+    /// <inheritdoc />
+    public abstract void Delay(TimeSpan timeSpan);
 }

src/Spice86.Core/Emulator/VM/Clock/CyclesClock.cs

@@ -7,6 +7,7 @@
 /// </summary>
 public class CyclesClock : ClockBase {
     private readonly State _cpuState;
+    private TimeSpan _delay;
 
     public CyclesClock(State cpuState, long cyclesPerSecond, int? jitterSeed, DateTimeOffset startTime)
         : base(ClockJitter.Create(jitterSeed), startTime) {
@@ -19,5 +20,10 @@ public CyclesClock(State cpuState, long cyclesPerSecond, int? jitterSeed, DateTi
 
     /// <inheritdoc/>
     public override double ElapsedTimeMs =>
-        (double)_cpuState.Cycles * 1000 / CyclesPerSecond + _jitter.Advance();
+        (double)_cpuState.Cycles * 1000 / CyclesPerSecond + _jitter.Advance() + _delay.Microseconds;
+
+    /// <inheritdoc/>
+    public override void Delay(TimeSpan timeSpan) {
+        _delay += timeSpan;
+    }
 }

src/Spice86.Core/Emulator/VM/Clock/EmulatedClock.cs

@@ -8,6 +8,7 @@
 public class EmulatedClock : ClockBase {
     private int _ticks;
     private readonly Stopwatch _stopwatch = new();
+    private TimeSpan _delay;
 
     public EmulatedClock(int? jitterSeed, DateTimeOffset startTime)
         : base(ClockJitter.Create(jitterSeed), startTime) {
@@ -21,7 +22,7 @@ public override double ElapsedTimeMs {
             if (_ticks++ % 100 != 0) {
                 return field;
             }
-            field = _stopwatch.Elapsed.TotalMilliseconds + _jitter.Advance();
+            field = _stopwatch.Elapsed.TotalMilliseconds + _jitter.Advance() + _delay.Microseconds;
             return field;
         }
     }
@@ -34,4 +35,9 @@ public override double ElapsedTimeMs {
 
     /// <inheritdoc/>
     protected override void OnDisposeCore() => _stopwatch.Stop();
+
+    /// <inheritdoc/>
+    public override void Delay(TimeSpan timeSpan) {
+        _delay += timeSpan;
+    }
 }

src/Spice86.Core/Emulator/VM/Clock/IEmulatedClock.cs

@@ -27,6 +27,14 @@ public interface IEmulatedClock : IDisposable {
     /// </summary>
     bool IsPaused { get; }
 
+    /// <summary>
+    /// Advance the clock by the specified amount of time.
+    /// </summary>
+    /// <remarks>
+    /// Used to simulate blocking I/O delays
+    /// </remarks>
+    void Delay(TimeSpan timeSpan);
+
     /// <summary>
     /// Called when the emulator is paused.
     /// </summary>

tests/Spice86.Tests/Emulator/Devices/Sound/Opl3ReadDelayTest.cs

@@ -0,0 +1,45 @@
+namespace Spice86.Tests.Emulator.Devices.Sound;
+
+using FluentAssertions;
+
+using NSubstitute;
+
+using Spice86.Core.Emulator.CPU;
+using Spice86.Core.Emulator.Devices.Sound;
+using Spice86.Core.Emulator.VM;
+using Spice86.Core.Emulator.VM.Clock;
+using Spice86.Shared.Interfaces;
+
+using System;
+
+using Xunit;
+
+[Trait("Category", "Sound")]
+public class Opl3ReadDelayTest {
+
+    [Fact]
+    public void Opl3ReadDelayIsAMicroSecondAndAHalf() {
+        //Arrange
+        State state = new(CpuModel.INTEL_80386);
+        ILoggerService loggerService = Substitute.For<ILoggerService>();
+        CyclesClock clock = new CyclesClock(state, 3000, null, DateTimeOffset.Now);
+        Opl3Fm opl3fm = new(new(OplMode.Opl3, 0x220, SbMixer: true),
+            new SoftwareMixer(Audio.Filters.AudioEngine.Dummy,
+            new PauseHandler(loggerService)),
+            state,
+            clock,
+            new Core.Emulator.IOPorts.IOPortDispatcher(new(), state, loggerService, false),
+            false,
+            loggerService);
+        state.Cycles = 100;
+
+        //Act
+        double before = clock.ElapsedTimeMs;
+        _ = opl3fm.ReadByte(0x330);
+        double after = clock.ElapsedTimeMs;
+
+        //Assert
+        double diff = after - before;
+        diff.Should().BeApproximately(1.5, 1);
+    }
+}