From 9f7ee662f930a0e1b18b8c8606450681bc5179ac Mon Sep 17 00:00:00 2001
From: Sour <mesenemu@gmail.com>
Date: Sun, 24 May 2020 22:41:54 -0400
Subject: [PATCH] GB: APU - Implemented volume update behavior on register
 writes Fixes sound in Prehistorik intro

---
 Core/GbSquareChannel.h   | 27 ++++++++++++++++++++++++---
 Core/GbTypes.h           |  1 +
 UI/Interop/DebugState.cs |  7 +++----
 3 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/Core/GbSquareChannel.h b/Core/GbSquareChannel.h
index 68eadae..56e21ba 100644
--- a/Core/GbSquareChannel.h
+++ b/Core/GbSquareChannel.h
@@ -90,7 +90,7 @@ public:
 
 	void ClockEnvelope()
 	{
-		if(_state.EnvTimer > 0) {
+		if(_state.EnvTimer > 0 && !_state.EnvStopped) {
 			_state.EnvTimer--;
 
 			if(_state.EnvTimer == 0) {
@@ -98,6 +98,8 @@ public:
 					_state.Volume++;
 				} else if(!_state.EnvRaiseVolume && _state.Volume > 0) {
 					_state.Volume--;
+				} else {
+					_state.EnvStopped = true;
 				}
 
 				_state.EnvTimer = _state.EnvPeriod;
@@ -170,15 +172,33 @@ public:
 				_state.Duty = (value & 0xC0) >> 6;
 				break;
 
-			case 2: 
+			case 2: {
+				if(_state.EnvPeriod == 0 && !_state.EnvStopped){
+					//"If the old envelope period was zero and the envelope is still doing automatic updates, volume is incremented by 1"
+					_state.Volume++;
+				} else if(!_state.EnvRaiseVolume) {
+					//"otherwise if the envelope was in subtract mode, volume is incremented by 2"
+					_state.Volume += 2;
+				}
+				
+				bool raiseVolume = (value & 0x08) != 0;
+				if(raiseVolume != _state.EnvRaiseVolume) {
+					//"If the mode was changed (add to subtract or subtract to add), volume is set to 16 - volume."
+					_state.Volume = 16 - _state.Volume;
+				}
+
+				//"Only the low 4 bits of volume are kept after the above operations."
+				_state.Volume &= 0xF;
+
 				_state.EnvPeriod = value & 0x07;
-				_state.EnvRaiseVolume = (value & 0x08) != 0;
+				_state.EnvRaiseVolume = raiseVolume;
 				_state.EnvVolume = (value & 0xF0) >> 4;
 
 				if(!(value & 0xF8)) {
 					_state.Enabled = false;
 				}
 				break;
+			}
 
 			case 3:
 				_state.Frequency = (_state.Frequency & 0x700) | value;
@@ -204,6 +224,7 @@ public:
 
 					//Volume envelope timer is reloaded with period.
 					_state.EnvTimer = _state.EnvPeriod;
+					_state.EnvStopped = false;
 					
 					//Channel volume is reloaded from NRx2.
 					_state.Volume = _state.EnvVolume;
diff --git a/Core/GbTypes.h b/Core/GbTypes.h
index 5a5a231..0231500 100644
--- a/Core/GbTypes.h
+++ b/Core/GbTypes.h
@@ -219,6 +219,7 @@ struct GbSquareState
 	bool EnvRaiseVolume;
 	uint8_t EnvPeriod;
 	uint8_t EnvTimer;
+	bool EnvStopped;
 
 	uint8_t Duty;
 	uint16_t Frequency;
diff --git a/UI/Interop/DebugState.cs b/UI/Interop/DebugState.cs
index 73af342..f18bf4f 100644
--- a/UI/Interop/DebugState.cs
+++ b/UI/Interop/DebugState.cs
@@ -693,6 +693,7 @@ namespace Mesen.GUI
 		public byte H;
 		public byte L;
 
+		[MarshalAs(UnmanagedType.I1)] public bool EiPending;
 		[MarshalAs(UnmanagedType.I1)] public bool IME;
 		[MarshalAs(UnmanagedType.I1)] public bool Halted;
 	}
@@ -713,6 +714,7 @@ namespace Mesen.GUI
 		[MarshalAs(UnmanagedType.I1)] public bool StatIrqFlag;
 
 		public byte LyCompare;
+		[MarshalAs(UnmanagedType.I1)] public bool LyCoincidenceFlag;
 		public byte BgPalette;
 		public byte ObjPalette0;
 		public byte ObjPalette1;
@@ -735,10 +737,6 @@ namespace Mesen.GUI
 		public UInt32 FrameCount;
 
 		public byte CgbVramBank;
-		public UInt16 CgbDmaSource;
-		public UInt16 CgbDmaDest;
-		public byte CgbDmaLength;
-		[MarshalAs(UnmanagedType.I1)] public bool CgbHdmaMode;
 
 		public byte CgbBgPalPosition;
 		[MarshalAs(UnmanagedType.I1)] public bool CgbBgPalAutoInc;
@@ -768,6 +766,7 @@ namespace Mesen.GUI
 		[MarshalAs(UnmanagedType.I1)] public bool EnvRaiseVolume;
 		public byte EnvPeriod;
 		public byte EnvTimer;
+		[MarshalAs(UnmanagedType.I1)] public bool EnvStopped;
 
 		public byte Duty;
 		public UInt16 Frequency;