8-bit Game emulation

Transcript

3. Retro gaming Emulators Game frameworks
5. Games from 80’s and 90’s Popular theme
6. TV set game consoles Computer consoles Handheld game consoles
7. Simple graphics Recognizable style
11. Characteristic music and sounds Influencer of music streams
13. 8-bit data bus, 16-bit address bus 8-bit control bus
14. Z80 6502 family 6809
15. 16-bit address space Typically consist of Sometimes memory is mirrored
16. • Cycles (crystal) • Opcodes • Registers • Status flags • Stack (pointer)
17. Peripheral devices signal CPU Service routine handles interrupt logic Example: 6502 interrupt sequence
18. Sequence of opcodes Compiled by an assembler Essentially same today Memory addresses Instructions Operands Disassembly
19. Related to hardware Techniques
20. Built from multiple channels 8-bit resolution Channels
22. Handheld device Technical specifications
23. Mikey 65SC02 CPU ROM + timers Suzy Graphics and Math coprocessor, I/O RAM Memory Shift registers 16 MHz Oscillator
25. Comparable to virtualization Why would you emulate?
26. Well-known emulators Usually written in C/C++ Managed code is possible!
27. Documentation Binary ROM images Optional
28. Interpretation • Reproduce workings of CPU in code • Works with self- modifying code • Easiest Static translation • Translate native code to target • Compile time • Limited use with self-modifying code • Harder Dynamic translation • Like static, but runtime • Capabilities of target used best • Hardest to implement High level emulation • Use native hardware to emulate old API or electronics as soon as possible • Limited use
29. while (!stopEmulation) { ExecuteCPU(cyclesToExecute); GenerateInterrupts(); EmulateGraphics(); EmulateSound(); EmulateOtherHardware(); SynchronizeTime(); }
30. Execute logic Register variables Stack logic public abstract class ProcessorBase { public abstract void Initialize(); public abstract void Reset(); public abstract ulong Execute(int instructionsToExecute); public abstract object SignalInterrupt(InterruptType interrupt, params object[] details); } public byte A; // Accumulator (8 bits) public byte X; // X index register (8 bits) public byte Y; // Y index register (8 bits) public byte SP; // Stack Pointer (8 bits) public byte ProcessorStatus public byte Opcode; // Instruction opcode (8 bits) public ushort Address; // Instruction operand address public byte Data; // Instruction data public ushort PC; // Program Counter (16 bits)
31. public override ulong Execute(int instructionsToExecute) { if (IsSystemIrqActive) { IsAsleep = false; if (ActiveInterrupt == InterruptType.Nmi || (!I && ActiveInterrupt == InterruptType.Irq)) RunInterruptSequence(ActiveInterrupt); } // Fetch opcode Opcode = Memory.Peek(PC); SystemClock.CycleCount += 1 + timings[Opcode] * MemoryReadCycle; PC++; ExecuteOpcode(); } // Decode and execute switch (Opcode) { case 0x00: BRK(); break; case 0x01: ZeroPageIndexedIndirectX(); ORA(); break; case 0x05: ZeroPage(); ORA(); break; case 0x06: ZeroPage(); ASL(); break;
32. Demo: CPU
33. CPUs only see data Memory mapped registers public interface IMemoryAccess<TAddress, TData> { void Poke(TAddress address, TData value); TData Peek(TAddress address); } public class Ram64KBMemory: IMemoryAccess<ushort, byte>
34. public class SpriteControlBits0 { public byte ByteData { get; set; } // "B5 = H flip, 0 = not flipped" public bool HFlip { get { return (ByteData & HFlipMask) == HFlipMask; } set { ByteData = (byte)(value ? ByteData | HFlipMask : ByteData & (HFlipMask ^ 0xFF)); } } // "B7,B6 = bits/pixel-1 (1,2,3,4)" public byte BitsPerPixel { get { return (byte)((ByteData >> 6) + 1); } } } Other device (Suzy) Other device (Suzy) Memory Mapped Register Two views Bits mean things CPU Poke $FC80,C4
35. Demo: Memory
36. // High level copy Array.Copy(videoMemory, doubleBuffer1); // Low level copy IntPtr stream = GetAudioStream(); Marshal.Copy(emulator.AudioBuffer, 0, stream, length); Pixel oriented Concepts Video memory 1 2 3 4 5 6 2 22 5 6 6 6 6 66 6 1 1 1 1 1 4 44 2 4 4 4 1 63 6 6 6 6 6 5 Separate color palette
37. Logic to emulate Multiple channels mixed together Buffered output public void Output(ulong cycleCount, byte sample) { while (audioLastUpdateCycle + AUDIO_SAMPLE_PERIOD < cycleCount) { audioLastUpdateCycle += AUDIO_SAMPLE_PERIOD; // Output audio sample as little endian 16-bit Buffer[audioBufferIndex++] = 0; Buffer[audioBufferIndex++] = sample; if (audioBufferIndex >= Buffer.Length) { OnBufferReady(); audioBufferIndex = 0; } } }
38. Byte and short operators Struct layout Endianness (little and big) [StructLayout(LayoutKind.Explicit)] public struct Word { [FieldOffset(0)] public ushort Value; [FieldOffset(0)] public byte LowByte; [FieldOffset(1)] public byte HighByte; } if (BitConverter.IsLittleEndian) { scb.SCBNEXT.Value = BitConverter.ToUInt16(ramMemory, address); address += 2; } else { scb.SCBNEXT.Value = (ushort)(ramMemory[address++] + (ramMemory[address++] << 8)); }
39. Performance optimization Inlining by compiler Debug.WriteLine(If) is bad for performance Debug.WriteLineIf(GeneralSwitch.TraceVerbose, String.Format("CartAddressStrobe (strobe={0}) shifter=${1:x}", strobe, shiftRegister));
40. If anything: Test CPU implementation! Other candidates for unit testing
41. Demo: Unit tests
43. Targets multiple platforms: Add-in for Visual Studio 2010 Simplifies and abstracts DirectX
44. Not your average XNA game Requires relatively little code Game loop and timing
45. Reuse implementation Portable libraries helps
46. Windowed and full-screen Sprites represented by Texture2D Power of graphics engine and video card Separate effects from content
47. Emulator video buffer (RAM) Sprite data protected override void Draw(GameTime gameTime) { lcdScreen.SetData(emulator.LcdScreenDma, 0x0, 0x3FC0); spriteBatch.Begin(SpriteSortMode.Deferred, null, SamplerState.PointClamp, null, null); spriteBatch.Draw(lcdScreen, new Rectangle(0, 0, graphicsWidth, graphicsHeight), new Rectangle(0, 0, Suzy.SCREEN_WIDTH, Suzy.SCREEN_HEIGHT), Color.White); spriteBatch.End(); base.Draw(gameTime); }
48. Demo: Graphics
49. SoundEffect API DynamicSoundEffectInstance gunfireSound = Content.Load<SoundEffect>("PewPew"); DynamicSoundEffectInstance Game Buffer 5 Buffer 4 Buffer 3 Buffer 2 Buffer 1 Buffer 0 SubmitBuffer Low-level Audio Playback Engine Pending Buffers
50. public const int AUDIO_SAMPLE_FREQ = 22050; public const int AUDIO_BUFFER_SIZE = AUDIO_SAMPLE_FREQ / 4; public const int AUDIO_SAMPLE_PERIOD = LynxHandheld.SYSTEM_FREQ / AUDIO_SAMPLE_FREQ; Characteristics B0 B1 B2 B3 B4 B5 B6 B7 Sample Block1 Block2 Block3 Block4 Sample Sample Sample B0 B1 B2 B3 B4 B5 B6 B7 Left Sample Block1 Block2 Right Sample Left Sample Right Sample
51. private void InitializeAudio() { dynamicSound = new DynamicSoundEffectInstance(22050, AudioChannels.Mono); soundBuffer = new byte[dynamicSound.GetSampleSizeInBytes(TimeSpan.FromMilliseconds(250))]; emulator.Mikey.AudioFilter.BufferReady += new EventHandler<BufferEventArgs>(OnAudioFilterBufferReady); dynamicSound.Play(); }
52. Demo: Audio
53. Classes to match input device Static method retrieves state Keyboard Mouse Gamepad TouchPanel Accelerometer Microphone public override bool ExitGame { get { KeyboardState keyboard = Keyboard.GetState(PlayerIndex.One); return keyboard.IsKeyDown(Keys.F4); } } GamePadState gamePad = GamePad.GetState(PlayerIndex.One); return gamePad.Buttons.Back == ButtonState.Pressed;
54. GamePadState gamePad = GamePad.GetState(PlayerIndex.One); JoystickStates joystick = JoystickStates.None; if (gamePad.DPad.Down == ButtonState.Pressed) joystick |= JoystickStates.Down; if (gamePad.DPad.Up == ButtonState.Pressed) joystick |= JoystickStates.Up; if (gamePad.DPad.Left == ButtonState.Pressed) joystick |= JoystickStates.Left; if (gamePad.DPad.Right == ButtonState.Pressed) joystick |= JoystickStates.Right; Transfer input device state to emulator core Analog versus digital [Flags] public enum JoystickStates { Up = 0x80, Down = 0x40, Left = 0x20, Right = 0x10 }
55. Demo: All together
56. Game emulators in managed code are possible Fun to do XNA is an excellent game framework
57. App Hub XNA Game Studio 4.0 Portable Library Tools Codeplex Lynx Sharp-64 CrystalBoy Cogwheel Emu7800 My Nes Bonami Spelcomputer museum
58. Ask them now! OutOfTimeException? Ask them later? Does anyone like to participate in writing a Vectrex emulator?!