From 53f1808f735ce02044d2922e2b52b6ff78738b30 Mon Sep 17 00:00:00 2001
From: Souryo <mesenemu@gmail.com>
Date: Thu, 2 Jun 2016 20:35:08 -0400
Subject: [PATCH] MMC3: Implemented submapper 3 (MM-ACC) - fixes Incredible
 Crash Dummies -Also fixed a bug in NES 2.0 mapper ID code

---
 Core/MMC3.h            | 44 ++++++++++++++++++++++++++++++++++++++----
 Core/MapperFactory.cpp |  2 +-
 Core/PPU.cpp           |  8 ++++++--
 Core/RomData.h         |  2 +-
 4 files changed, 48 insertions(+), 8 deletions(-)

diff --git a/Core/MMC3.h b/Core/MMC3.h
index 16add8ba..8c4b2945 100644
--- a/Core/MMC3.h
+++ b/Core/MMC3.h
@@ -21,6 +21,8 @@ class MMC3 : public BaseMapper
 			RegE001 = 0xE001
 		};
 
+		uint8_t _subMapperID;
+
 		uint8_t _currentRegister;
 		uint8_t _chrMode;
 		uint8_t _prgMode;
@@ -36,6 +38,8 @@ class MMC3 : public BaseMapper
 		bool _wramEnabled;
 		bool _wramWriteProtected;
 
+		bool _needIrq;
+
 		struct {
 			uint8_t Reg8000;
 			uint8_t RegA000;
@@ -61,6 +65,8 @@ class MMC3 : public BaseMapper
 
 			_wramEnabled = false;
 			_wramWriteProtected = false;
+
+			_needIrq = false;
 		}
 
 	protected:
@@ -145,7 +151,7 @@ class MMC3 : public BaseMapper
 			BaseMapper::StreamState(saving);
 			Stream(_state.Reg8000, _state.RegA000, _state.RegA001, _currentRegister, _chrMode, _prgMode,
 				_irqReloadValue, _irqCounter, _irqReload, _irqEnabled, _lastCycle, _cyclesDown,
-				_wramEnabled, _wramWriteProtected, ArrayInfo<uint8_t>{_registers, 8});
+				_wramEnabled, _wramWriteProtected, ArrayInfo<uint8_t>{_registers, 8}, _needIrq);
 		}
 
 		virtual uint16_t GetPRGPageSize() { return 0x2000; }
@@ -208,12 +214,41 @@ class MMC3 : public BaseMapper
 			}
 		}
 
+		void TriggerIrq()
+		{
+			if(_subMapperID != 3) {
+				CPU::SetIRQSource(IRQSource::External);
+			} else {
+				//MM-ACC (Acclaim copy of the MMC3)
+				//IRQ will be triggered on the next falling edge of A12 instead of on the rising edge like normal MMC3 behavior
+				//This adds a 4 ppu cycle delay (until the PPU fetches the next garbage NT tile between sprites)
+				_needIrq = true;
+			}
+		}
+
+
 	public:
+		MMC3(uint8_t subMapperID)
+		{
+			_subMapperID = subMapperID;
+		}
+
+		MMC3()
+		{
+			_subMapperID = 0;
+		}
+
 		virtual void NotifyVRAMAddressChange(uint16_t addr)
 		{
 			uint32_t cycle = PPU::GetFrameCycle();
 
 			if((addr & 0x1000) == 0) {
+				if(_needIrq) {
+					//Used by MM-ACC (Acclaim copy of the MMC3), see TriggerIrq above
+					CPU::SetIRQSource(IRQSource::External);
+					_needIrq = false;
+				}
+
 				if(_cyclesDown == 0) {
 					_cyclesDown = 1;
 				} else {
@@ -233,14 +268,15 @@ class MMC3 : public BaseMapper
 						_irqCounter--;
 					}
 
-					if(ForceMmc3RevAIrqs() || EmulationSettings::CheckFlag(EmulationFlags::Mmc3IrqAltBehavior)) {
+					//SubMapper 2 = MM-ACC (Acclaim MMC3 clone)
+					if(_subMapperID != 2 && (ForceMmc3RevAIrqs() || EmulationSettings::CheckFlag(EmulationFlags::Mmc3IrqAltBehavior))) {
 						//MMC3 Revision A behavior
 						if((count > 0 || _irqReload) && _irqCounter == 0 && _irqEnabled) {
-							CPU::SetIRQSource(IRQSource::External);
+							TriggerIrq();
 						}
 					} else {
 						if(_irqCounter == 0 && _irqEnabled) {
-							CPU::SetIRQSource(IRQSource::External);
+							TriggerIrq();
 						}
 					}
 					_irqReload = false;
diff --git a/Core/MapperFactory.cpp b/Core/MapperFactory.cpp
index b146a5ca..8a6a9805 100644
--- a/Core/MapperFactory.cpp
+++ b/Core/MapperFactory.cpp
@@ -104,7 +104,7 @@ BaseMapper* MapperFactory::GetMapperFromID(RomData &romData)
 		case 1: return new MMC1();
 		case 2: return new UNROM();
 		case 3: return new CNROM(false);
-		case 4: return new MMC3();
+		case 4: return new MMC3(romData.SubMapperID);
 		case 5: return new MMC5();
 		case 7: return new AXROM();
 		case 9: return new MMC2();
diff --git a/Core/PPU.cpp b/Core/PPU.cpp
index 73bffaab..75c43842 100644
--- a/Core/PPU.cpp
+++ b/Core/PPU.cpp
@@ -644,8 +644,12 @@ void PPU::ProcessPreVBlankScanline()
 			if((_cycle - 260) % 8 == 0) {
 				//Cycle 260, 268, etc.  This is an approximation (each tile is actually loaded in 8 steps (e.g from 257 to 264))
 				LoadSpriteTileInfo();
-			} else if(_cycle == 257) {
-				_spriteIndex = 0;
+			} else if((_cycle - 257) % 8 == 0) {
+				//Garbage NT sprite fetch (257, 265, 273, etc.) - Required for proper MC-ACC IRQs (MMC3 clone)
+				_memoryManager->ReadVRAM(GetNameTableAddr());
+				if(_cycle == 257) {
+					_spriteIndex = 0;
+				}
 			}
 		}
 	} else if(_cycle == 321 && IsRenderingEnabled()) {
diff --git a/Core/RomData.h b/Core/RomData.h
index f0232b30..c2a7ebc5 100644
--- a/Core/RomData.h
+++ b/Core/RomData.h
@@ -71,7 +71,7 @@ struct NESHeader
 	{
 		switch(GetRomHeaderVersion()) {
 			case RomHeaderVersion::Nes2_0:
-				return (Byte8 & 0x0F << 4) | (Byte7 & 0xF0) | (Byte6 >> 4);
+				return ((Byte8 & 0x0F) << 4) | (Byte7 & 0xF0) | (Byte6 >> 4);
 			default:
 			case RomHeaderVersion::iNes:
 				return (Byte7 & 0xF0) | (Byte6 >> 4);