Hackadoodle to change the initial value of the DIV register? This is probably a bad idea

BizHawk.Emulation.Cores/Consoles/Nintendo/Gameboy/Gambatte.ISettable.cs

@@ -132,6 +132,11 @@ namespace BizHawk.Emulation.Cores.Nintendo.Gameboy
 			[DeepEqualsIgnore]
 			private bool _equalLengthFrames;
 
+			[DisplayName("Initial DIV offset")]
+			[Description("Internal.  Probably doesn't work.  Leave this set to 0.  Accepts values from 0 to 65532 in steps of 4")]
+			[DefaultValue(0)]
+			public int InitialDiv { get; set; }
+
 			public GambatteSyncSettings()
 			{
 				SettingsUtil.SetDefaultValues(this);
@@ -146,6 +151,11 @@ namespace BizHawk.Emulation.Cores.Nintendo.Gameboy
 			{
 				return !DeepEquality.DeepEquals(x, y);
 			}
+
+			public uint GetInitialDivInternal()
+			{
+				return (uint)(InitialDiv & 0xfffc);
+			}
 		}
 	}
 }

BizHawk.Emulation.Cores/Consoles/Nintendo/Gameboy/Gambatte.cs

@@ -63,6 +63,8 @@ namespace BizHawk.Emulation.Cores.Nintendo.Gameboy
 
 				real_rtc_time = !DeterministicEmulation && _syncSettings.RealTimeRTC;
 
+				DivInternal = _syncSettings.GetInitialDivInternal();
+
 				LibGambatte.LoadFlags flags = 0;
 
 				switch (_syncSettings.ConsoleMode)
@@ -88,7 +90,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.Gameboy
 					flags |= LibGambatte.LoadFlags.MULTICART_COMPAT;
 				}
 
-				if (LibGambatte.gambatte_load(GambatteState, file, (uint)file.Length, GetCurrentTime(), flags) != 0)
+				if (LibGambatte.gambatte_load(GambatteState, file, (uint)file.Length, GetCurrentTime(), flags, DivInternal) != 0)
 				{
 					throw new InvalidOperationException("gambatte_load() returned non-zero (is this not a gb or gbc rom?)");
 				}
@@ -172,6 +174,8 @@ namespace BizHawk.Emulation.Cores.Nintendo.Gameboy
 		/// </summary>
 		private LibGambatte.Buttons CurrentButtons = 0;
 
+		private uint DivInternal = 0;
+
 		#region RTC
 
 		/// <summary>
@@ -322,7 +326,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.Gameboy
 
 			if (controller.IsPressed("Power"))
 			{
-				LibGambatte.gambatte_reset(GambatteState, GetCurrentTime());
+				LibGambatte.gambatte_reset(GambatteState, GetCurrentTime(), DivInternal);
 			}
 
 			if (Tracer.Enabled)

BizHawk.Emulation.Cores/Consoles/Nintendo/Gameboy/LibGambatte.cs

@@ -57,7 +57,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.Gameboy
 		/// <param name="flags">ORed combination of LoadFlags.</param>
 		/// <returns>0 on success, negative value on failure.</returns>
 		[DllImport("libgambatte.dll", CallingConvention = CallingConvention.Cdecl)]
-		public static extern int gambatte_load(IntPtr core, byte[] romdata, uint length, long now, LoadFlags flags);
+		public static extern int gambatte_load(IntPtr core, byte[] romdata, uint length, long now, LoadFlags flags, uint div);
 
 		/// <summary>
 		/// Load GB BIOS image.
@@ -124,7 +124,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.Gameboy
 		/// <param name="core">opaque state pointer</param>
 		/// <param name="now">RTC time when the reset occurs</param>
 		[DllImport("libgambatte.dll", CallingConvention = CallingConvention.Cdecl)]
-		public static extern void gambatte_reset(IntPtr core, long now);
+		public static extern void gambatte_reset(IntPtr core, long now, uint div);
 
 		/// <summary>
 		/// palette type for gambatte_setdmgpalettecolor

libgambatte/include/gambatte.h

@@ -60,7 +60,7 @@ public:
 	  * @param flags    ORed combination of LoadFlags.
 	  * @return 0 on success, negative value on failure.
 	  */
-	int load(const char *romfiledata, unsigned romfilelength, std::uint32_t now, unsigned flags = 0);
+	int load(const char *romfiledata, unsigned romfilelength, std::uint32_t now, unsigned flags, unsigned div);
 	
 	int loadGBCBios(const char* biosfiledata);
 	int loadDMGBios(const char* biosfiledata);
@@ -93,7 +93,7 @@ public:
 	/** Reset to initial state.
 	  * Equivalent to reloading a ROM image, or turning a Game Boy Color off and on again.
 	  */
-	void reset(std::uint32_t now);
+	void reset(std::uint32_t now, unsigned div);
 	
 	/** @param palNum 0 <= palNum < 3. One of BG_PALETTE, SP1_PALETTE and SP2_PALETTE.
 	  * @param colorNum 0 <= colorNum < 4

libgambatte/src/cinterface.cpp

@@ -29,9 +29,9 @@ GBEXPORT void gambatte_destroy(GB *g)
 	delete g;
 }
 
-GBEXPORT int gambatte_load(GB *g, const char *romfiledata, unsigned romfilelength, long long now, unsigned flags)
+GBEXPORT int gambatte_load(GB *g, const char *romfiledata, unsigned romfilelength, long long now, unsigned flags, unsigned div)
 {
-	int ret = g->load(romfiledata, romfilelength, now, flags);
+	int ret = g->load(romfiledata, romfilelength, now, flags, div);
 	return ret;
 }
 
@@ -65,9 +65,9 @@ GBEXPORT void gambatte_setlayers(GB *g, unsigned mask)
 	g->setLayers(mask);
 }
 
-GBEXPORT void gambatte_reset(GB *g, long long now)
+GBEXPORT void gambatte_reset(GB *g, long long now, unsigned div)
 {
-	g->reset(now);
+	g->reset(now, div);
 }
 
 GBEXPORT void gambatte_setdmgpalettecolor(GB *g, unsigned palnum, unsigned colornum, unsigned rgb32)

libgambatte/src/gambatte.cpp

@@ -81,7 +81,7 @@ void GB::blitTo(gambatte::uint_least32_t *videoBuf, int pitch)
 	}
 }
 
-void GB::reset(const std::uint32_t now) {
+void GB::reset(const std::uint32_t now, const unsigned div) {
 	if (p_->cpu.loaded()) {
 		
 		int length = p_->cpu.saveSavedataLength();
@@ -94,7 +94,7 @@ void GB::reset(const std::uint32_t now) {
 		
 		SaveState state;
 		p_->cpu.setStatePtrs(state);
-		setInitState(state, !(p_->loadflags & FORCE_DMG), p_->loadflags & GBA_CGB, now);
+		setInitState(state, !(p_->loadflags & FORCE_DMG), p_->loadflags & GBA_CGB, now, div);
 		p_->cpu.loadState(state);
 		if (length > 0)
 		{
@@ -140,7 +140,7 @@ void GB::setLinkCallback(void(*callback)()) {
 	p_->cpu.setLinkCallback(callback);
 }
 
-int GB::load(const char *romfiledata, unsigned romfilelength, const std::uint32_t now, const unsigned flags) {
+int GB::load(const char *romfiledata, unsigned romfilelength, const std::uint32_t now, const unsigned flags, const unsigned div) {
 	//if (p_->cpu.loaded())
 	//	p_->cpu.saveSavedata();
 	
@@ -150,7 +150,7 @@ int GB::load(const char *romfiledata, unsigned romfilelength, const std::uint32_
 		SaveState state;
 		p_->cpu.setStatePtrs(state);
 		p_->loadflags = flags;
-		setInitState(state, !(flags & FORCE_DMG), flags & GBA_CGB, now);
+		setInitState(state, !(flags & FORCE_DMG), flags & GBA_CGB, now, div);
 		p_->cpu.loadState(state);
 		//p_->cpu.loadSavedata();
 	}

libgambatte/src/initstate.cpp

@@ -1146,7 +1146,7 @@ static void setInitialDmgIoamhram(unsigned char *const ioamhram) {
 
 } // anon namespace
 
-void gambatte::setInitState(SaveState &state, const bool cgb, const bool gbaCgbMode, const std::uint32_t now) {
+void gambatte::setInitState(SaveState &state, const bool cgb, const bool gbaCgbMode, const std::uint32_t now, const unsigned div) {
 	static const unsigned char cgbObjpDump[0x40] = {
 		0x00, 0x00, 0xF2, 0xAB, 
 		0x61, 0xC2, 0xD9, 0xBA, 
@@ -1198,7 +1198,7 @@ void gambatte::setInitState(SaveState &state, const bool cgb, const bool gbaCgbM
 	state.mem.ioamhram.ptr[0x140] = 0;
 	state.mem.ioamhram.ptr[0x144] = 0x00;
 	
-	state.mem.divLastUpdate = 0;
+	state.mem.divLastUpdate = 0 - div;
 	state.mem.timaLastUpdate = 0;
 	state.mem.tmatime = DISABLED_TIME;
 	state.mem.nextSerialtime = DISABLED_TIME;

libgambatte/src/initstate.h

@@ -22,7 +22,7 @@
 #include <cstdint>
 
 namespace gambatte {
-void setInitState(struct SaveState &state, bool cgb, bool gbaCgbMode, std::uint32_t now);
+void setInitState(struct SaveState &state, bool cgb, bool gbaCgbMode, std::uint32_t now, unsigned div);
 }
 
 #endif

libgambatte/src/savestate.h

@@ -38,7 +38,7 @@ struct SaveState {
 		void set(T *ptr, const unsigned long sz) { this->ptr = ptr; this->sz = sz; }
 		
 		friend class SaverList;
-		friend void setInitState(SaveState &, bool, bool, std::uint32_t);
+		friend void setInitState(SaveState &, bool, bool, std::uint32_t, unsigned);
 	};
 
 	struct CPU {