diff --git a/BizHawk.Emulation/Consoles/Nintendo/Gameboy/Gambatte.cs b/BizHawk.Emulation/Consoles/Nintendo/Gameboy/Gambatte.cs
index 33cb2ed4c3..7c14e3d3a3 100644
--- a/BizHawk.Emulation/Consoles/Nintendo/Gameboy/Gambatte.cs
+++ b/BizHawk.Emulation/Consoles/Nintendo/Gameboy/Gambatte.cs
@@ -145,25 +145,10 @@ namespace BizHawk.Emulation.Consoles.GB
 				tracecb = null;
 			LibGambatte.gambatte_settracecallback(GambatteState, tracecb);
 
-			// todo: have the gambatte core actually call this at an appropriate time
-			if (scanlinecallback != null)
-			{
-				IntPtr vram = IntPtr.Zero;
-				IntPtr bgpal = IntPtr.Zero;
-				IntPtr sppal = IntPtr.Zero;
-				IntPtr oam = IntPtr.Zero;
-				int unused = 0;
-				if (!LibGambatte.gambatte_getmemoryarea(GambatteState, LibGambatte.MemoryAreas.vram, ref vram, ref unused)
-					|| !LibGambatte.gambatte_getmemoryarea(GambatteState, LibGambatte.MemoryAreas.bgpal, ref bgpal, ref unused)
-					|| !LibGambatte.gambatte_getmemoryarea(GambatteState, LibGambatte.MemoryAreas.sppal, ref sppal, ref unused)
-					|| !LibGambatte.gambatte_getmemoryarea(GambatteState, LibGambatte.MemoryAreas.oam, ref oam, ref unused))
-					throw new Exception();
-
-				scanlinecallback(vram, IsCGBMode(), LibGambatte.gambatte_cpuread(GambatteState, 0xff40), bgpal, sppal, oam);
-			}
-
 			LibGambatte.gambatte_runfor(GambatteState, VideoBuffer, 160, soundbuff, ref nsamp);
 
+			Console.WriteLine("===");
+
 			// upload any modified data to the memory domains
 
 			foreach (var r in MemoryRefreshers)
@@ -593,18 +578,36 @@ namespace BizHawk.Emulation.Consoles.GB
 		#endregion
 
 		#region ppudebug
+		public bool GetGPUMemoryAreas(out IntPtr vram, out IntPtr bgpal, out IntPtr sppal, out IntPtr oam)
+		{
+			IntPtr _vram = IntPtr.Zero;
+			IntPtr _bgpal = IntPtr.Zero;
+			IntPtr _sppal = IntPtr.Zero;
+			IntPtr _oam = IntPtr.Zero;
+			int unused = 0;
+			if (!LibGambatte.gambatte_getmemoryarea(GambatteState, LibGambatte.MemoryAreas.vram, ref _vram, ref unused)
+				|| !LibGambatte.gambatte_getmemoryarea(GambatteState, LibGambatte.MemoryAreas.bgpal, ref _bgpal, ref unused)
+				|| !LibGambatte.gambatte_getmemoryarea(GambatteState, LibGambatte.MemoryAreas.sppal, ref _sppal, ref unused)
+				|| !LibGambatte.gambatte_getmemoryarea(GambatteState, LibGambatte.MemoryAreas.oam, ref _oam, ref unused))
+			{
+				vram = IntPtr.Zero;
+				bgpal = IntPtr.Zero;
+				sppal = IntPtr.Zero;
+				oam = IntPtr.Zero;
+				return false;
+			}
+			vram = _vram;
+			bgpal = _bgpal;
+			sppal = _sppal;
+			oam = _oam;
+			return true;
+		}
+
 		/// <summary>
 		/// 
 		/// </summary>
-		/// <param name="vram"></param>
-		/// <param name="cgb"></param>
-		/// <param name="lcdc"></param>
-		/// <param name="bgpal"></param>
-		/// <param name="sppal"></param>
-		/// <param name="oam"></param>
-		public delegate void ScanlineCallback(IntPtr vram, bool cgb, int lcdc, IntPtr bgpal, IntPtr sppal, IntPtr oam);
-
-		ScanlineCallback scanlinecallback;
+		/// <param name="lcdc">current value of register $ff40 (LCDC)</param>
+		public delegate void ScanlineCallback(int lcdc);
 
 		/// <summary>
 		/// set up callback
@@ -613,14 +616,25 @@ namespace BizHawk.Emulation.Consoles.GB
 		/// <param name="line">scanline</param>
 		public void SetScanlineCallback(ScanlineCallback callback, int line)
 		{
+			if (GambatteState == IntPtr.Zero)
+				// not sure how this is being reached.  tried the debugger...
+				return;
 			if (callback == null)
-				this.scanlinecallback = null;
+				scanlinecb = null;
 			else if (line < 0 || line > 153)
 				throw new ArgumentOutOfRangeException("line must be in [0, 153]");
 			else
-				this.scanlinecallback = callback;
+				scanlinecb = delegate()
+				{
+					callback(LibGambatte.gambatte_cpuread(GambatteState, 0xff40));
+					//callback(0);
+				};
+
+			LibGambatte.gambatte_setscanlinecallback(GambatteState, scanlinecb, 0);
 		}
 
+		LibGambatte.ScanlineCallback scanlinecb;
+
 		#endregion
 
 		public void Dispose()
diff --git a/BizHawk.Emulation/Consoles/Nintendo/Gameboy/LibGambatte.cs b/BizHawk.Emulation/Consoles/Nintendo/Gameboy/LibGambatte.cs
index 17e248e7a7..3877502c0d 100644
--- a/BizHawk.Emulation/Consoles/Nintendo/Gameboy/LibGambatte.cs
+++ b/BizHawk.Emulation/Consoles/Nintendo/Gameboy/LibGambatte.cs
@@ -167,13 +167,30 @@ namespace BizHawk.Emulation.Consoles.GB
 		[DllImport("libgambatte.dll", CallingConvention = CallingConvention.Cdecl)]
 		public static extern void gambatte_settracecallback(IntPtr core, TraceCallback callback);
 
+		/// <summary>
+		/// type of the scanline callback
+		/// </summary>
+		[UnmanagedFunctionPointer(CallingConvention.Cdecl)]
+		public delegate void ScanlineCallback();
+
+		/// <summary>
+		/// set a callback to occur when ly reaches a particular scanline (so at the beginning of the scanline).
+		/// when the LCD is active, typically 145 will be the first callback after the beginning of frame advance,
+		/// and 144 will be the last callback right before frame advance returns
+		/// </summary>
+		/// <param name="core">opaque state pointer</param>
+		/// <param name="callback">null to clear</param>
+		/// <param name="sl">0-153 inclusive</param>
+		[DllImport("libgambatte.dll", CallingConvention = CallingConvention.Cdecl)]
+		public static extern void gambatte_setscanlinecallback(IntPtr core, ScanlineCallback callback, int sl);
+
 		/// <summary>
 		/// Sets the directory used for storing save data. The default is the same directory as the ROM Image file.
 		/// </summary>
 		/// <param name="core">opaque state pointer</param>
 		/// <param name="sdir"></param>
-		[DllImport("libgambatte.dll", CallingConvention = CallingConvention.Cdecl)]
-		public static extern void gambatte_setsavedir(IntPtr core, string sdir);
+		//[DllImport("libgambatte.dll", CallingConvention = CallingConvention.Cdecl)]
+		//public static extern void gambatte_setsavedir(IntPtr core, string sdir);
 
 		/// <summary>
 		/// Returns true if the currently loaded ROM image is treated as having CGB support.
diff --git a/BizHawk.MultiClient/GBtools/GBGPUView.cs b/BizHawk.MultiClient/GBtools/GBGPUView.cs
index 742d2216ec..dbb695a900 100644
--- a/BizHawk.MultiClient/GBtools/GBGPUView.cs
+++ b/BizHawk.MultiClient/GBtools/GBGPUView.cs
@@ -13,6 +13,15 @@ namespace BizHawk.MultiClient.GBtools
 	{
 		Emulation.Consoles.GB.Gameboy gb;
 
+		// gambatte doesn't modify these memory locations unless you reconstruct, so we can store
+		IntPtr vram;
+		IntPtr bgpal;
+		IntPtr sppal;
+		IntPtr oam;
+
+		bool cgb; // set once at start
+		int lcdc; // set at each callback
+
 		public GBGPUView()
 		{
 			InitializeComponent();
@@ -30,7 +39,16 @@ namespace BizHawk.MultiClient.GBtools
 			if (Global.Emulator is Emulation.Consoles.GB.Gameboy)
 			{
 				gb = Global.Emulator as Emulation.Consoles.GB.Gameboy;
-				if (gb.IsCGBMode())
+				cgb = gb.IsCGBMode();
+				lcdc = 0;
+				if (!gb.GetGPUMemoryAreas(out vram, out bgpal, out sppal, out oam))
+				{
+					gb = null;
+					if (Visible)
+						Close();
+				}
+
+				if (cgb)
 					label4.Enabled = true;
 				else
 					label4.Enabled = false;
@@ -302,8 +320,9 @@ namespace BizHawk.MultiClient.GBtools
 			b.UnlockBits(lockdata);
 		}
 
-		void ScanlineCallback(IntPtr vram, bool cgb, int lcdc, IntPtr bgpal, IntPtr sppal, IntPtr oam)
+		void ScanlineCallback(int lcdc)
 		{
+			this.lcdc = lcdc;
 			// set alpha on all pixels
 			unsafe
 			{
diff --git a/BizHawk.MultiClient/output/dll/libgambatte.dll b/BizHawk.MultiClient/output/dll/libgambatte.dll
index 3ba2573d65..43f431c686 100644
Binary files a/BizHawk.MultiClient/output/dll/libgambatte.dll and b/BizHawk.MultiClient/output/dll/libgambatte.dll differ
diff --git a/libgambatte/include/gambatte.h b/libgambatte/include/gambatte.h
index a0729dbea9..be67840072 100644
--- a/libgambatte/include/gambatte.h
+++ b/libgambatte/include/gambatte.h
@@ -86,6 +86,7 @@ public:
 	void setReadCallback(void (*callback)(unsigned));
 	void setWriteCallback(void (*callback)(unsigned));
 	void setTraceCallback(void (*callback)(void *));
+	void setScanlineCallback(void (*callback)(), int sl);
 
 	/** Sets the directory used for storing save data. The default is the same directory as the ROM Image file. */
 	void setSaveDir(const std::string &sdir);
diff --git a/libgambatte/src/cinterface.cpp b/libgambatte/src/cinterface.cpp
index 26735cf718..0858a6304d 100644
--- a/libgambatte/src/cinterface.cpp
+++ b/libgambatte/src/cinterface.cpp
@@ -83,6 +83,12 @@ __declspec(dllexport) void gambatte_settracecallback(void *core, void (*callback
 	g->setTraceCallback(callback);
 }
 
+__declspec(dllexport) void gambatte_setscanlinecallback(void *core, void (*callback)(), int sl)
+{
+	GB *g = (GB *) core;
+	g->setScanlineCallback(callback, sl);
+}
+
 __declspec(dllexport) void gambatte_setsavedir(void *core, const char *sdir)
 {
 	GB *g = (GB *) core;
diff --git a/libgambatte/src/cinterface.h b/libgambatte/src/cinterface.h
index 01b0c383d7..810347fc53 100644
--- a/libgambatte/src/cinterface.h
+++ b/libgambatte/src/cinterface.h
@@ -24,6 +24,8 @@ extern "C"
 
 	__declspec(dllexport) void gambatte_settracecallback(void *core, void (*callback)(void *));
 
+	__declspec(dllexport) void gambatte_setscanlinecallback(void *core, void (*callback)(), int sl);
+
 	__declspec(dllexport) void gambatte_setsavedir(void *core, const char *sdir);
 
 	__declspec(dllexport) int gambatte_iscgb(void *core);
diff --git a/libgambatte/src/cpu.h b/libgambatte/src/cpu.h
index 640f518460..13711eef00 100644
--- a/libgambatte/src/cpu.h
+++ b/libgambatte/src/cpu.h
@@ -78,6 +78,10 @@ public:
 	void setTraceCallback(void (*callback)(void *)) {
 		tracecallback = callback;
 	}
+
+	void setScanlineCallback(void (*callback)(), int sl) {
+		memory.setScanlineCallback(callback, sl);
+	}
 	
 	void setSaveDir(const std::string &sdir) {
 		memory.setSaveDir(sdir);
@@ -110,7 +114,8 @@ public:
 	void setGameGenie(const std::string &codes) { memory.setGameGenie(codes); }
 	void setGameShark(const std::string &codes) { memory.setGameShark(codes); }
 
-	unsigned char ExternalRead(unsigned short addr) { return memory.read(addr, cycleCounter_); }
+	//unsigned char ExternalRead(unsigned short addr) { return memory.read(addr, cycleCounter_); }
+	unsigned char ExternalRead(unsigned short addr) { return memory.peek(addr); }
 	void ExternalWrite(unsigned short addr, unsigned char val) { memory.write(addr, val, cycleCounter_); }
 
 };
diff --git a/libgambatte/src/gambatte.cpp b/libgambatte/src/gambatte.cpp
index acb5a29b8c..5c295fbd98 100644
--- a/libgambatte/src/gambatte.cpp
+++ b/libgambatte/src/gambatte.cpp
@@ -107,6 +107,10 @@ void GB::setTraceCallback(void (*callback)(void *)) {
 	p_->cpu.setTraceCallback(callback);
 }
 
+void GB::setScanlineCallback(void (*callback)(), int sl) {
+	p_->cpu.setScanlineCallback(callback, sl);
+}
+
 void GB::setSaveDir(const std::string &sdir) {
 	p_->cpu.setSaveDir(sdir);
 }
diff --git a/libgambatte/src/memory.cpp b/libgambatte/src/memory.cpp
index 2405711180..4aaa934cf7 100644
--- a/libgambatte/src/memory.cpp
+++ b/libgambatte/src/memory.cpp
@@ -570,6 +570,32 @@ unsigned Memory::nontrivial_read(const unsigned P, const unsigned long cycleCoun
 	return ioamhram[P - 0xFE00];
 }
 
+unsigned Memory::nontrivial_peek(const unsigned P) {
+	if (P < 0xC000) {
+		if (P < 0x8000)
+			return cart.romdata(P >> 14)[P];
+
+		if (P < 0xA000) {
+			return cart.vrambankptr()[P];
+		}
+
+		if (cart.rsrambankptr())
+			return cart.rsrambankptr()[P];
+
+		return cart.rtcRead(); // verified side-effect free
+	}
+	if (P < 0xFE00)
+		return cart.wramdata(P >> 12 & 1)[P & 0xFFF];
+	if (P >= 0xFF00 && P < 0xFF80)
+		return nontrivial_ff_peek(P);
+	return ioamhram[P - 0xFE00];
+}
+
+unsigned Memory::nontrivial_ff_peek(const unsigned P) {
+	// some regs may be somewhat wrong with this
+	return ioamhram[P - 0xFE00];
+}
+
 void Memory::nontrivial_ff_write(const unsigned P, unsigned data, const unsigned long cycleCounter) {
 	if (lastOamDmaUpdate != DISABLED_TIME)
 		updateOamDma(cycleCounter);
diff --git a/libgambatte/src/memory.h b/libgambatte/src/memory.h
index 536a25f53f..9b01cbf8b9 100644
--- a/libgambatte/src/memory.h
+++ b/libgambatte/src/memory.h
@@ -66,6 +66,9 @@ class Memory {
 	void nontrivial_ff_write(unsigned P, unsigned data, unsigned long cycleCounter);
 	void nontrivial_write(unsigned P, unsigned data, unsigned long cycleCounter);
 	
+	unsigned nontrivial_peek(unsigned P);
+	unsigned nontrivial_ff_peek(unsigned P);
+
 	void updateSerial(unsigned long cc);
 	void updateTimaIrq(unsigned long cc);
 	void updateIrqs(unsigned long cc);
@@ -119,6 +122,10 @@ public:
 		return cart.rmem(P >> 12) ? cart.rmem(P >> 12)[P] : nontrivial_read(P, cycleCounter);
 	}
 
+	unsigned peek(const unsigned P) {
+		return cart.rmem(P >> 12) ? cart.rmem(P >> 12)[P] : nontrivial_peek(P);
+	}
+
 	void write(const unsigned P, const unsigned data, const unsigned long cycleCounter) {
 		if (cart.wmem(P >> 12)) {
 			cart.wmem(P >> 12)[P] = data;
@@ -152,6 +159,10 @@ public:
 		this->writeCallback = callback;
 	}
 
+	void setScanlineCallback(void (*callback)(), int sl) {
+		display.setScanlineCallback(callback, sl);
+	}
+
 	void setEndtime(unsigned long cc, unsigned long inc);
 	
 	void setSoundBuffer(uint_least32_t *const buf) { sound.setBuffer(buf); }
diff --git a/libgambatte/src/video.cpp b/libgambatte/src/video.cpp
index 3aac3e4beb..d581304c57 100644
--- a/libgambatte/src/video.cpp
+++ b/libgambatte/src/video.cpp
@@ -71,7 +71,9 @@ LCD::LCD(const unsigned char *const oamram, const unsigned char *const vram, con
 	eventTimes_(memEventRequester),
 	statReg(0),
 	m2IrqStatReg_(0),
-	m1IrqStatReg_(0)
+	m1IrqStatReg_(0),
+	scanlinecallback(0),
+	scanlinecallbacksl(0)
 {
 	std::memset( bgpData, 0, sizeof  bgpData);
 	std::memset(objpData, 0, sizeof objpData);
@@ -772,6 +774,8 @@ inline void LCD::event() {
 	case LY_COUNT:
 		ppu.doLyCountEvent();
 		eventTimes_.set<LY_COUNT>(ppu.lyCounter().time());
+		if (scanlinecallback && ppu.lyCounter().ly() == scanlinecallbacksl)
+			scanlinecallback();
 		break;
 	}
 }
diff --git a/libgambatte/src/video.h b/libgambatte/src/video.h
index e58c910f28..b0cfca8560 100644
--- a/libgambatte/src/video.h
+++ b/libgambatte/src/video.h
@@ -150,6 +150,9 @@ class LCD {
 	void doCgbBgColorChange(unsigned index, unsigned data, unsigned long cycleCounter);
 	void doCgbSpColorChange(unsigned index, unsigned data, unsigned long cycleCounter);
 
+	void (*scanlinecallback)();
+	int scanlinecallbacksl;
+
 public:
 	LCD(const unsigned char *oamram, const unsigned char *vram_in, VideoInterruptRequester memEventRequester);
 	void reset(const unsigned char *oamram, const unsigned char *vram, bool cgb);
@@ -253,6 +256,8 @@ public:
 
 	unsigned long *bgPalette() { return ppu.bgPalette(); }
 	unsigned long *spPalette() { return ppu.spPalette(); }
+
+	void setScanlineCallback(void (*callback)(), int sl) { scanlinecallback = callback; scanlinecallbacksl = sl; }
 };
 
 }