Fix some bugs responsible for out-of-bounds array access crash on ym2612

BizHawk.Emulation/CPUs/Z80/Z80A.cs

@@ -3,7 +3,7 @@ using System.Globalization;
 using System.IO;
 
 // This Z80 emulator is a modified version of Ben Ryves 'Brazil' emulator.
-// It is MIT licensed (not public domain). (See Licenses)
+// It is MIT licensed.
 
 namespace BizHawk.Emulation.CPUs.Z80 
 {
@@ -33,6 +33,15 @@ namespace BizHawk.Emulation.CPUs.Z80
 			TotalExecutedCycles = 0;
 		}
 
+        /// <summary>
+        /// Reset the Z80 to its initial state, but don't modify cycle counters. For use where Z80 may be reset 
+        /// </summary>
+        public void SoftReset()
+        {
+            ResetRegisters();
+            ResetInterrupts();
+        }
+
         // Memory Access 
 
         public Func<ushort, byte> ReadMemory;

BizHawk.Emulation/Consoles/Sega/Genesis/MemoryMap.68000.cs

@@ -116,7 +116,7 @@ namespace BizHawk.Emulation.Consoles.Sega
             {
                 Z80Reset = (value & 1) == 0;
                 if (Z80Reset)
-                    SoundCPU.Reset();
+                    SoundCPU.SoftReset();
                 //Console.WriteLine("z80 reset: " + Z80Reset);
                 return;
             }
@@ -182,7 +182,7 @@ namespace BizHawk.Emulation.Consoles.Sega
             {
                 Z80Reset = (value & 0x100) == 0;
                 if (Z80Reset)
-                    SoundCPU.Reset();
+                    SoundCPU.SoftReset();
                 //Console.WriteLine("z80 reset: " + Z80Reset);
                 return;
             }

BizHawk.Emulation/Sound/YM2612.cs

@@ -28,6 +28,11 @@ namespace BizHawk.Emulation.Sound
         public void BeginFrame(int clock)
         {
             frameStartClock = clock;
+            while (commands.Count > 0)
+            {
+                var cmd = commands.Dequeue();
+                WriteCommand(cmd);
+            }
         }
 
         public void EndFrame(int clock)