Atari 2600: Modified how memory read/writes are handled, to better emulate the address bus. Cleaned up some comments. Turned off CPU debugging. Added functions to read console switches and player 2 buttons.

M6532: Mostly re-written, this time based on the datasheet. 
TIA: Removed console debug outputs.

BizHawk.Emulation/Consoles/Atari/2600/Atari2600.Core.cs

@@ -58,45 +58,32 @@ namespace BizHawk
 		//   ROM
 		public byte ReadMemory(ushort addr)
 		{
-			ushort maskedAddr = (ushort)(addr & 0x1FFF);
+			addr = (ushort)(addr & 0x1FFF);
-			ushort pageNum = (ushort)(maskedAddr >> 6);
+			if ((addr & 0x1080) == 0)
-			if (pageNum < 0x40)
 			{
-				// if Page 0x02, or a mirror
+				return tia.ReadMemory(addr);
-				if (pageNum % 4 > 1)
+			}
-				{
+			else if ((addr & 0x1080) == 0x0080)
-					return m6532.ReadMemory(maskedAddr);
+			{
-				}
+				return m6532.ReadMemory(addr);
-				// if Page 0x01 or 0x02, or a mirror
-				else
-				{
-					return tia.ReadMemory(maskedAddr);
-				}
 			}
-			// ROM data
 			else
 			{
-				//Console.WriteLine("ROM read");
+				return rom[addr & 0x0FFF];
-				return rom[maskedAddr & 0x0FFF];
 			}
 		}
 
 		public void WriteMemory(ushort addr, byte value)
 		{
-			ushort maskedAddr = (ushort)(addr & 0x1FFF);
+			addr = (ushort)(addr & 0x1FFF);
-			ushort pageNum = (ushort)(maskedAddr >> 6);
+			if ((addr & 0x1080) == 0)
-			if (pageNum < 0x40)
 			{
-				if (pageNum % 4 > 1)
+				tia.WriteMemory(addr, value);
-				{
+			}
-					m6532.WriteMemory(maskedAddr, value);
+			else if ((addr & 0x1080) == 0x0080)
-				}
+			{
-				else
+				m6532.WriteMemory(addr, value);
-				{
-					tia.WriteMemory(maskedAddr, value);
-				}
 			}
-			// ROM data
 			else
 			{
 				Console.WriteLine("ROM write(?):  " + addr.ToString("x"));
@@ -106,7 +93,7 @@ namespace BizHawk
 		public void HardReset()
 		{
 			cpu = new MOS6507();
-			cpu.debug = true;
+			//cpu.debug = true;
 			cpu.ReadMemory = ReadMemory;
 			cpu.WriteMemory = WriteMemory;
 
@@ -114,7 +101,7 @@ namespace BizHawk
 			//tia = new TIA(this, frameBuffer);
 			tia = new TIA(this);
 			// Setup 6532
-			m6532 = new M6532(cpu, ram, this);
+			m6532 = new M6532(this);
 
 			//setup the system state here. for instance..
 			// Read from the reset vector for where to start
@@ -125,15 +112,6 @@ namespace BizHawk
 		public void FrameAdvance(bool render)
 		{
 			Frame++;
-			if (resetSignal)
-			{
-				//cpu.PC = cpu.ReadWord(MOS6507.ResetVector);
-				m6532.resetOccured = true;
-				//m6532.swchb &= 0xFE;
-				//cpu.FlagI = true;
-			}
-			//cpu.Execute(228);
-			//cpu.Execute(2000);
 
 			tia.frameComplete = false;
 			while (tia.frameComplete == false)
@@ -154,23 +132,8 @@ namespace BizHawk
 				}
 				
 			}
-			resetSignal = Controller["Reset"];
-			//clear the framebuffer (hack code)
-			if (render == false) return;
-			/*
-			for (int i = 0; i < 160 * 192; i++)
-			{
-				if (i < 64*256)
-					frameBuffer[i] = i % 256; //black
-				if (i >= 64*256 && i < 128*256)
-					frameBuffer[i] = (i % 256) << 8; //black
-				if (i >= 128*256)
-					frameBuffer[i] = (i % 256) << 16; //black
-			}
-				*/
 
-			//run one frame's worth of cpu cyclees (i.e. do the emulation!)
+			//if (render == false) return;
-			//this should generate the framebuffer as it goes.
 		}
 
 		public byte ReadControls1()
@@ -184,5 +147,38 @@ namespace BizHawk
 			if (Controller["P1 Button"]) value &= 0xF7;
 			return value;
 		}
+
+		public byte ReadControls2()
+		{
+			byte value = 0xFF;
+
+			if (Controller["P2 Up"]) value &= 0xEF;
+			if (Controller["P2 Down"]) value &= 0xDF;
+			if (Controller["P2 Left"]) value &= 0xBF;
+			if (Controller["P2 Right"]) value &= 0x7F;
+			if (Controller["P2 Button"]) value &= 0xF7;
+			return value;
+		}
+
+		public byte ReadConsoleSwitches()
+		{
+			byte value = 0xFF;
+
+			bool select = false;
+			bool reset = Controller["Reset"];
+			bool bw = false;
+			bool p0difficulty = true;
+			bool p1difficulty = true;
+
+			if (reset) value &= 0xFE;
+			if (select) value &= 0xFD;
+			if (bw) value &= 0xF7;
+			if (p0difficulty) value &= 0xBF;
+			if (p1difficulty) value &= 0x7F;
+
+			return value;
+		}
+
+
 	}
 }

BizHawk.Emulation/Consoles/Atari/2600/M6532.cs

@@ -8,104 +8,118 @@ namespace BizHawk.Emulation.Consoles.Atari
 	// Emulates the M6532 RIOT Chip
 	public partial class M6532
 	{
-		MOS6507 Cpu;
-		public byte[] ram;
-		public int timerStartValue;
-		public int timerFinishedCycles;
-		public int timerShift;
-
-		bool interruptEnabled = false;
-		bool interruptTriggered = false;
-
 		Atari2600 core;
 
-		public byte swchb = 0x0B;
+		public int timerCyclesRemaining = 0;
+		public int timerShift = 0;
+
+		bool interruptEnabled = false;
+		bool interruptFlag = false;
+
+		public byte ddra = 0x00;
+		public byte ddrb = 0x00;
 
 		public bool resetOccured = false;
-		public int totalCycles = 0;
 
-		public M6532(MOS6507 cpu, byte[] ram, Atari2600 core)
+		public M6532(Atari2600 core)
 		{
-			Cpu = cpu;
-			this.ram = ram;
 			this.core = core;
 
-			// Apparently this will break for some games (Solaris and H.E.R.O.). We shall see
+			// Apparently starting the timer at 0 will break for some games (Solaris and H.E.R.O.). We shall see
-			timerFinishedCycles = 0;
+			timerCyclesRemaining = 0;
-
+			interruptEnabled = false;
+			interruptFlag = false;
 		}
 
 		public void tick()
 		{
-			totalCycles++;
+			timerCyclesRemaining--;
+			if (timerCyclesRemaining == 0 && interruptEnabled)
+			{
+				interruptFlag = true;
+			}
 		}
 
 		public byte ReadMemory(ushort addr)
 		{
-			ushort maskedAddr;
+			// Register Select (?)
+			bool RS = (addr & 0x0200) != 0;
 
-			if ((addr & 0x1080) == 0x0080 && (addr & 0x0200) == 0x0000)
+			if (!RS)
 			{
-				maskedAddr = (ushort)(addr & 0x007f);
+				// Read Ram
-				Console.WriteLine("6532 ram read: " + maskedAddr.ToString("x"));
+				ushort maskedAddr = (ushort)(addr & 0x007f);
-				return ram[maskedAddr];
+				return core.ram[maskedAddr];
 			}
 			else
 			{
-				maskedAddr = (ushort)(addr & 0x0007);
+				ushort registerAddr = (ushort)(addr & 0x0007);
-				if (maskedAddr == 0x04 || maskedAddr == 0x06)
+				if (registerAddr == 0x00)
 				{
-					Console.WriteLine("6532 timer read: " + maskedAddr.ToString("x"));
+					// Read Output reg A
+					// Combine readings from player 1 and player 2
+					byte temp = (byte)(core.ReadControls1() & 0xF0 | ((core.ReadControls2() >> 4) & 0x0F));
+					temp = (byte)(temp & ~ddra);
+					return temp;
+				}
+				else if (registerAddr == 0x01)
+				{
+					// Read DDRA
+					return ddra;
+				}
+				else if (registerAddr == 0x02)
+				{
+					// Read Output reg B
+					byte temp = core.ReadConsoleSwitches();
+					temp = (byte)(temp & ~ddrb);
+					return temp;
 
-					// Calculate the current value on the timer
+					/*
-					int timerCurrentValue = timerFinishedCycles - totalCycles;
+					// TODO: Rewrite this!
+					bool temp = resetOccured;
+					resetOccured = false;
+					return (byte)(0x0A | (temp ? 0x00 : 0x01));
+					 * */
+				}
+				else if (registerAddr == 0x03)
+				{
+					// Read DDRB
+					return ddrb;
+				}
+				else if ((registerAddr & 0x5) == 0x4)
+				{
+					// Bit 0x0080 contains interrupt enable/disable
+					interruptEnabled = (addr & 0x0080) != 0;
 
-					interruptTriggered = false;
+					// The interrupt flag will be reset whenever the Timer is access by a read or a write
-
+					// However, the reading of the timer at the same time the interrupt occurs will not reset the interrupt flag
-					// If the timer has not finished, shift the value down for the game
+					// (M6532 Datasheet)
-					if (totalCycles < timerFinishedCycles)
+					if (timerCyclesRemaining != 0)
 					{
-						return (byte)(((timerCurrentValue) >> timerShift) & 0xFF);
+						interruptFlag = false;
+					}	
+
+					// If there is still time on the timer (or its 0), return the lowest byte
+					if (timerCyclesRemaining >= 0)
+					{
+						return (byte)(((timerCyclesRemaining) >> timerShift) & 0xFF);
 					}
-					// Other wise, return the last 8 bits from how long ago it triggered
 					else
 					{
-						interruptTriggered = true;
+						return (byte)(timerCyclesRemaining & 0xFF);
-						return (byte)(timerCurrentValue & 0xFF);
 					}
-				}
-				else
-				{
-					Console.WriteLine("6532 register read: " + maskedAddr.ToString("x"));
-					if (maskedAddr == 0x00) // SWCHA
-					{
-						return core.ReadControls1();
-						//return 0xFF;
-					}
-					else if (maskedAddr == 0x01) // SWACNT
-					{
-						
-					}
-					else if (maskedAddr == 0x02) // SWCHB
-					{
-						bool temp = resetOccured;
-						resetOccured = false;
-						return (byte)(0x0A | (temp ? 0x00 : 0x01));
-					}
-					else if (maskedAddr == 0x03) // SWBCNT
-					{
 
-					}
+				}
-					else if (maskedAddr == 0x05) // interrupt
+				else if ((registerAddr & 0x5) == 0x5)
+				{
+					// Read interrupt flag
+					if (interruptEnabled && interruptFlag)
 					{
-						if ((timerFinishedCycles - totalCycles >= 0)|| (interruptEnabled && interruptTriggered))
+						return 0x00;
-						{
+					}
-							return 0x00;
+					else
-						}
+					{
-						else
+						return 0x80;
-						{
-							return 0x80;
-						}
 					}
 				}
 			}
@@ -115,39 +129,81 @@ namespace BizHawk.Emulation.Consoles.Atari
 
 		public void WriteMemory(ushort addr, byte value)
 		{
-			ushort maskedAddr;
+			// Register Select (?)
+			bool RS = (addr & 0x0200) != 0;
 
-			if ((addr & 0x1080) == 0x0080 && (addr & 0x0200) == 0x0000)
+			// If the RS bit is not set, this is a ram write
+			if (!RS)
 			{
-				maskedAddr = (ushort)(addr & 0x007f);
+				ushort maskedAddr = (ushort)(addr & 0x007f);
-				Console.WriteLine("6532 ram write: " + maskedAddr.ToString("x"));
+				core.ram[maskedAddr] = value;
-				ram[maskedAddr] = value;
 			}
 			else
 			{
-				maskedAddr = (ushort)(addr & 0x0007);
+				// If bit 0x0010 is set, and bit 0x0004 is set, this is a timer write
-				if ((addr & 0x14) == 0x14)
+				if ((addr & 0x0014) == 0x0014)
 				{
-					int[] shift = new int[] {0,3,6,10};
+					ushort registerAddr = (ushort)(addr & 0x0007);
-					timerShift = shift[addr & 0x03];
 
-					// Store the number of cycles for the timer
+					// Bit 0x0080 contains interrupt enable/disable
-					timerStartValue = value << timerShift;
+					interruptEnabled = (addr & 0x0080) != 0;
 
-					// Calculate when the timer will be finished
+					// The interrupt flag will be reset whenever the Timer is access by a read or a write
-					timerFinishedCycles = timerStartValue + totalCycles;
+					// (M6532 datasheet)
 
-					Console.WriteLine("6532 timer write:  " + maskedAddr.ToString("x"));
+					if (registerAddr == 0x04)
-
+					{
-					interruptEnabled = ((addr & 0x08) != 0);
+						// Write to Timer/1
+						timerShift = 0;
+						timerCyclesRemaining = value << timerShift;
+						interruptFlag = false;
+					}
+					else if (registerAddr == 0x05)
+					{
+						// Write to Timer/8
+						timerShift = 3;
+						timerCyclesRemaining = value << timerShift;
+						interruptFlag = false;
+					}
+					else if (registerAddr == 0x06)
+					{
+						// Write to Timer/64
+						timerShift = 6;
+						timerCyclesRemaining = value << timerShift;
+						interruptFlag = false;
+					}
+					else if (registerAddr == 0x07)
+					{
+						// Write to Timer/1024
+						timerShift = 10;
+						timerCyclesRemaining = value << timerShift;
+						interruptFlag = false;
+					}
 				}
-				else if ((addr & 0x04) == 0 && (maskedAddr & 0x03) == 0x02)
+				// If bit 0x0004 is not set, bit 0x0010 is ignored and
+				// these are register writes
+				else if ((addr & 0x0004) == 0)
 				{
-					swchb = value; 
+					ushort registerAddr = (ushort)(addr & 0x0007);
-				}
+
-				else
+					if (registerAddr == 0x00)
-				{
+					{
-					Console.WriteLine("6532 register write: " + maskedAddr.ToString("x"));
+						// Write Output reg A
+					}
+					else if (registerAddr == 0x01)
+					{
+						// Write DDRA
+						ddra = value;
+					}
+					else if (registerAddr == 0x02)
+					{
+						// Write Output reg B
+					}
+					else if (registerAddr == 0x03)
+					{
+						// Write DDRB
+						ddrb = value;
+					}
 				}
 			}
 		}

BizHawk.Emulation/Consoles/Atari/2600/TIA.cs

@@ -642,7 +642,6 @@ namespace BizHawk.Emulation.Consoles.Atari
 		public byte ReadMemory(ushort addr)
 		{
 			ushort maskedAddr = (ushort)(addr & 0x000F);
-			Console.WriteLine("TIA read:  " + maskedAddr.ToString("x"));
 			if (maskedAddr == 0x00) // CXM0P
 			{
 				return (byte)((((player0.missile.collisions & CXP1) != 0) ? 0x80 : 0x00) | (((player0.missile.collisions & CXP0) != 0) ? 0x40 : 0x00));
@@ -686,7 +685,6 @@ namespace BizHawk.Emulation.Consoles.Atari
 		public void WriteMemory(ushort addr, byte value)
 		{
 			ushort maskedAddr = (ushort)(addr & 0x3f);
-			Console.WriteLine("TIA write:  " + maskedAddr.ToString("x"));
 
 			if (maskedAddr == 0x00) // VSYNC
 			{
@@ -698,7 +696,6 @@ namespace BizHawk.Emulation.Consoles.Atari
 				else
 				{
 					// When VSYNC is disabled, this will be the first line of the new frame
-					Console.WriteLine("TIA VSYNC Off");
 
 					// write to frame buffer
 					outputFrame();