From 6a59bb52c98b82e6cb012fcb17ac6cbd6c89fe5a Mon Sep 17 00:00:00 2001
From: Sour <mesenemu@gmail.com>
Date: Sun, 17 Jun 2018 11:28:41 -0400
Subject: [PATCH] Fixed issues with Sunsoft-4 emulation (Mapper 68) -
 Nantettatte roms with external PRG now work properly

---
 Core/BaseMapper.cpp | 17 +++++++-----
 Core/BaseMapper.h   |  2 ++
 Core/Sunsoft4.h     | 65 ++++++++++++++++++++++++++++++++++++++++++---
 3 files changed, 74 insertions(+), 10 deletions(-)

diff --git a/Core/BaseMapper.cpp b/Core/BaseMapper.cpp
index 959412b7..275380bb 100644
--- a/Core/BaseMapper.cpp
+++ b/Core/BaseMapper.cpp
@@ -400,6 +400,16 @@ void BaseMapper::InitializeChrRam(int32_t chrRamSize)
 	}
 }
 
+void BaseMapper::SetupDefaultWorkRam()
+{
+	//Setup a default work/save ram in 0x6000-0x7FFF space
+	if(HasBattery() && _saveRamSize > 0) {
+		SetCpuMemoryMapping(0x6000, 0x7FFF, 0, PrgMemoryType::SaveRam);
+	} else if(_workRamSize > 0) {
+		SetCpuMemoryMapping(0x6000, 0x7FFF, 0, PrgMemoryType::WorkRam);
+	}
+}
+
 bool BaseMapper::HasChrRam()
 {
 	return _chrRamSize > 0;
@@ -586,12 +596,7 @@ void BaseMapper::Initialize(RomData &romData)
 		}
 	}
 
-	//Setup a default work/save ram in 0x6000-0x7FFF space
-	if(HasBattery() && _saveRamSize > 0) {
-		SetCpuMemoryMapping(0x6000, 0x7FFF, 0, PrgMemoryType::SaveRam);
-	} else if(_workRamSize > 0) {
-		SetCpuMemoryMapping(0x6000, 0x7FFF, 0, PrgMemoryType::WorkRam);
-	}
+	SetupDefaultWorkRam();
 
 	InitMapper();
 	InitMapper(romData);
diff --git a/Core/BaseMapper.h b/Core/BaseMapper.h
index 9870bee2..a105823a 100644
--- a/Core/BaseMapper.h
+++ b/Core/BaseMapper.h
@@ -136,6 +136,8 @@ protected:
 
 	uint8_t GetPowerOnByte(uint8_t defaultValue = 0);
 	
+	void SetupDefaultWorkRam();
+
 	void RestoreOriginalPrgRam();
 	void InitializeChrRam(int32_t chrRamSize = -1);
 
diff --git a/Core/Sunsoft4.h b/Core/Sunsoft4.h
index e15182f3..954afade 100644
--- a/Core/Sunsoft4.h
+++ b/Core/Sunsoft4.h
@@ -8,6 +8,10 @@ class Sunsoft4 : public BaseMapper
 private:
 	uint8_t _ntRegs[2];
 	bool _useChrForNametables;
+	bool _prgRamEnabled;
+	uint32_t _licensingTimer;
+	bool _usingExternalRom;
+	uint8_t _externalPage = 0;
 
 	void UpdateNametables()
 	{
@@ -35,24 +39,66 @@ protected:
 	{
 		_useChrForNametables = false;
 		_ntRegs[0] = _ntRegs[1] = 0;
+		
+		_licensingTimer = 0;
+		_usingExternalRom = false;
+		_prgRamEnabled = false;
 
 		//Bank 0's initial state is undefined, but some roms expect it to be the first page
 		SelectPRGPage(0, 0);
+		SelectPRGPage(1, 7);
 
-		SelectPRGPage(1, -1);
+		UpdateState();
 	}
 
 	void StreamState(bool saving) override
 	{
 		BaseMapper::StreamState(saving);
 		
-		Stream(_ntRegs[0], _ntRegs[1], _useChrForNametables);
+		Stream(_ntRegs[0], _ntRegs[1], _useChrForNametables, _prgRamEnabled, _usingExternalRom, _externalPage);
 
 		if(!saving) {
 			UpdateNametables();
+			UpdateState();
 		}
 	}
 
+	void UpdateState()
+	{
+		if(!_prgRamEnabled) {
+			RemoveCpuMemoryMapping(0x6000, 0x7FFF);
+		} else {
+			SetupDefaultWorkRam();
+		}
+		
+		if(_usingExternalRom) { 
+			if(_licensingTimer == 0) {
+				RemoveCpuMemoryMapping(0x8000, 0xBFFF);
+			} else {
+				SelectPRGPage(0, _externalPage);
+			}
+		}
+	}
+
+	void ProcessCpuClock() override
+	{
+		if(_licensingTimer) {
+			_licensingTimer--;
+			if(_licensingTimer == 0) {
+				UpdateState();
+			}
+		}
+	}
+
+	void WriteRAM(uint16_t addr, uint8_t value) override
+	{
+		if(addr >= 0x6000 && addr <= 0x7FFF) {
+			_licensingTimer = 1024 * 105;
+			UpdateState();
+		}
+		BaseMapper::WriteRAM(addr, value);
+	}
+
 	void WriteRegister(uint16_t addr, uint8_t value) override
 	{
 		switch(addr & 0xF000) {
@@ -79,8 +125,19 @@ protected:
 				UpdateNametables();
 				break;
 			case 0xF000: 
-				SelectPRGPage(0, value & 0x0F); 
-				//_prgRamEnabled = (value & 0x10) == 0x10;
+				bool externalPrg = (value & 0x08) == 0;
+				if(externalPrg && GetPRGPageCount() > 8) {
+					_usingExternalRom = true;
+					_externalPage = 0x08 | ((value & 0x07) % (GetPRGPageCount() - 0x08));
+					SelectPRGPage(0, _externalPage);
+				} else {
+					_usingExternalRom = false;
+					SelectPRGPage(0, value & 0x07);
+				}
+
+				_prgRamEnabled = (value & 0x10) == 0x10;
+				UpdateState();
+
 				break;
 		}
 	}