431 lines
16 KiB
C#
431 lines
16 KiB
C#
// <copyright file="Bus.cs" company="Adrian Conlon">
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// Copyright (c) Adrian Conlon. All rights reserved.
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// </copyright>
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namespace EightBit.GameBoy
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{
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using System;
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using System.Collections.Generic;
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public abstract class Bus : EightBit.Bus
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{
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public const int CyclesPerSecond = 4 * 1024 * 1024;
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public const int FramesPerSecond = 60;
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public const int CyclesPerFrame = CyclesPerSecond / FramesPerSecond;
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public const int TotalLineCount = 154;
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public const int CyclesPerLine = CyclesPerFrame / TotalLineCount;
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public const int RomPageSize = 0x4000;
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private readonly Rom bootRom = new Rom(0x100); // 0x0000 - 0x00ff
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private readonly List<Rom> gameRomBanks = new List<Rom>(); // 0x0000 - 0x3fff, 0x4000 - 0x7fff (switchable)
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private readonly List<Ram> ramBanks = new List<Ram>(); // 0xa000 - 0xbfff (switchable)
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private readonly UnusedMemory unmapped2000 = new UnusedMemory(0x2000, 0xff); // 0xa000 - 0xbfff
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private readonly Ram lowInternalRam = new Ram(0x2000); // 0xc000 - 0xdfff (mirrored at 0xe000)
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private readonly UnusedMemory unmapped60 = new UnusedMemory(0x60, 0xff); // 0xfea0 - 0xfeff
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private readonly Ram highInternalRam = new Ram(0x80); // 0xff80 - 0xffff
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private bool enabledLCD = false;
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private bool disabledGameRom = false;
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private bool rom = false;
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private bool banked = false;
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private bool ram = false;
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private bool battery = false;
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private bool higherRomBank = true;
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private bool ramBankSwitching = false;
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private int romBank = 1;
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private int ramBank = 0;
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private int allowed = 0;
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protected Bus()
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{
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this.IO = new IoRegisters(this);
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this.CPU = new LR35902(this);
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}
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public LR35902 CPU { get; }
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public Ram VRAM { get; } = new Ram(0x2000);
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public Ram OAMRAM { get; } = new Ram(0xa0);
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public IoRegisters IO { get; }
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public bool GameRomDisabled => this.disabledGameRom;
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public bool GameRomEnabled => !this.GameRomDisabled;
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public override void RaisePOWER()
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{
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base.RaisePOWER();
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this.CPU.RaisePOWER();
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this.CPU.RaiseINT();
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this.Reset();
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}
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public override void LowerPOWER()
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{
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this.CPU.LowerPOWER();
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base.LowerPOWER();
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}
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public void Reset()
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{
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this.IO.Reset();
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this.CPU.LowerRESET();
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}
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public void DisableGameRom() => this.disabledGameRom = true;
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public void EnableGameRom() => this.disabledGameRom = false;
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public void LoadBootRom(string path) => this.bootRom.Load(path);
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public void LoadGameRom(string path)
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{
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const int bankSize = 0x4000;
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this.gameRomBanks.Clear();
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this.gameRomBanks.Add(new Rom());
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var size = this.gameRomBanks[0].Load(path, 0, 0, bankSize);
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var banks = size / bankSize;
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for (var bank = 1; bank < banks; ++bank)
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{
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this.gameRomBanks.Add(new Rom());
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this.gameRomBanks[bank].Load(path, 0, bankSize * bank, bankSize);
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}
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this.ValidateCartridgeType();
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}
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public void RunRasterLines()
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{
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this.enabledLCD = (this.IO.Peek(IoRegisters.LCDC) & (byte)LcdcControls.LcdEnable) != 0;
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this.IO.ResetLY();
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this.RunRasterLines(DisplayCharacteristics.RasterHeight);
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}
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public void RunVerticalBlankLines()
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{
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var lines = TotalLineCount - DisplayCharacteristics.RasterHeight;
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this.RunVerticalBlankLines(lines);
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}
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public override MemoryMapping Mapping(ushort address)
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{
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if ((address < 0x100) && this.IO.BootRomEnabled)
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{
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return new MemoryMapping(this.bootRom, 0x0000, Mask.Sixteen, AccessLevel.ReadOnly);
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}
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if ((address < 0x4000) && this.GameRomEnabled)
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{
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return new MemoryMapping(this.gameRomBanks[0], 0x0000, 0xffff, AccessLevel.ReadOnly);
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}
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if ((address < 0x8000) && this.GameRomEnabled)
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{
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return new MemoryMapping(this.gameRomBanks[this.romBank], 0x4000, 0xffff, AccessLevel.ReadOnly);
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}
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if (address < 0xa000)
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{
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return new MemoryMapping(this.VRAM, 0x8000, 0xffff, AccessLevel.ReadWrite);
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}
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if (address < 0xc000)
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{
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if (this.ramBanks.Count == 0)
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{
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return new MemoryMapping(this.unmapped2000, 0xa000, 0xffff, AccessLevel.ReadOnly);
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}
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else
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{
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return new MemoryMapping(this.ramBanks[this.ramBank], 0xa000, 0xffff, AccessLevel.ReadWrite);
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}
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}
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if (address < 0xe000)
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{
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return new MemoryMapping(this.lowInternalRam, 0xc000, 0xffff, AccessLevel.ReadWrite);
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}
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if (address < 0xfe00)
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{
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return new MemoryMapping(this.lowInternalRam, 0xe000, 0xffff, AccessLevel.ReadWrite); // Low internal RAM mirror
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}
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if (address < 0xfea0)
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{
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return new MemoryMapping(this.OAMRAM, 0xfe00, 0xffff, AccessLevel.ReadWrite);
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}
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if (address < IoRegisters.BASE)
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{
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return new MemoryMapping(this.unmapped60, 0xfea0, 0xffff, AccessLevel.ReadOnly);
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}
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if (address < 0xff80)
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{
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return new MemoryMapping(this.IO, IoRegisters.BASE, 0xffff, AccessLevel.ReadWrite);
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}
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return new MemoryMapping(this.highInternalRam, 0xff80, 0xffff, AccessLevel.ReadWrite);
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}
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protected override void OnWrittenByte()
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{
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base.OnWrittenByte();
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var address = this.Address.Word;
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var value = this.Data;
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switch (address & 0xe000)
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{
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case 0x0000:
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// Register 0: RAMCS gate data
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if (this.ram)
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{
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throw new InvalidOperationException("Register 0: RAMCS gate data: Not handled!");
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}
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break;
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case 0x2000:
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// Register 1: ROM bank code
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if (this.banked && this.higherRomBank)
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{
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// assert((address >= 0x2000) && (address < 0x4000));
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// assert((value > 0) && (value < 0x20));
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this.romBank = value & (byte)Mask.Five;
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}
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break;
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case 0x4000:
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// Register 2: ROM bank selection
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if (this.banked)
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{
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throw new InvalidOperationException("Register 2: ROM bank selection: Not handled!");
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}
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break;
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case 0x6000:
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// Register 3: ROM/RAM change
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if (this.banked)
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{
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switch (value & (byte)Mask.One)
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{
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case 0:
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this.higherRomBank = true;
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this.ramBankSwitching = false;
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break;
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case 1:
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this.higherRomBank = false;
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this.ramBankSwitching = true;
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break;
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default:
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throw new InvalidOperationException("Unreachable");
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}
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}
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break;
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}
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}
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private void ValidateCartridgeType()
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{
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this.rom = this.banked = this.ram = this.battery = false;
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// ROM type
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switch (this.gameRomBanks[0].Peek(0x147))
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{
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case (byte)CartridgeType.ROM:
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this.rom = true;
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break;
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case (byte)CartridgeType.ROM_MBC1:
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this.rom = this.banked = true;
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break;
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case (byte)CartridgeType.ROM_MBC1_RAM:
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this.rom = this.banked = this.ram = true;
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break;
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case (byte)CartridgeType.ROM_MBC1_RAM_BATTERY:
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this.rom = this.banked = this.ram = this.battery = true;
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break;
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default:
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throw new InvalidOperationException("Unhandled cartridge ROM type");
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}
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// ROM size
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{
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var gameRomBanks = 0;
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var romSizeSpecification = this.Peek(0x148);
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switch (romSizeSpecification)
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{
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case 0x52:
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gameRomBanks = 72;
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break;
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case 0x53:
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gameRomBanks = 80;
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break;
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case 0x54:
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gameRomBanks = 96;
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break;
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default:
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if (romSizeSpecification > 6)
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{
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throw new InvalidOperationException("Invalid ROM size specification");
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}
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gameRomBanks = 1 << (romSizeSpecification + 1);
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if (gameRomBanks != this.gameRomBanks.Count)
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{
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throw new InvalidOperationException("ROM size specification mismatch");
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}
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break;
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}
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// RAM size
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{
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var ramSizeSpecification = this.gameRomBanks[0].Peek(0x149);
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switch (ramSizeSpecification)
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{
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case 0:
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break;
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case 1:
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this.ramBanks.Clear();
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this.ramBanks.Add(new Ram(2 * 1024));
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break;
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case 2:
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this.ramBanks.Clear();
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this.ramBanks.Add(new Ram(8 * 1024));
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break;
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case 3:
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this.ramBanks.Clear();
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for (var i = 0; i < 4; ++i)
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{
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this.ramBanks.Add(new Ram(8 * 1024));
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}
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break;
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case 4:
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this.ramBanks.Clear();
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for (var i = 0; i < 16; ++i)
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{
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this.ramBanks.Add(new Ram(8 * 1024));
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}
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break;
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default:
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throw new InvalidOperationException("Invalid RAM size specification");
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}
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}
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}
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}
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private void RunRasterLines(int lines)
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{
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for (var line = 0; line < lines; ++line)
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{
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this.RunRasterLine(CyclesPerLine);
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}
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}
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private void RunVerticalBlankLines(int lines)
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{
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/*
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Vertical Blank interrupt is triggered when the LCD
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controller enters the VBL screen mode (mode 1, LY=144).
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This happens once per frame, so this interrupt is
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triggered 59.7 times per second. During this period the
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VRAM and OAM can be accessed freely, so it's the best
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time to update graphics (for example, use the OAM DMA to
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update sprites for next frame, or update tiles to make
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animations).
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This period lasts 4560 clocks in normal speed mode and
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9120 clocks in double speed mode. That's exactly the
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time needed to draw 10 scanlines.
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The VBL interrupt isn't triggered when the LCD is
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powered off or on, even when it was on VBL mode.
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It's only triggered when the VBL period starts.
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*/
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if (this.enabledLCD)
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{
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this.IO.UpdateLcdStatusMode(LcdStatusMode.VBlank);
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if ((this.IO.Peek(IoRegisters.STAT) & (byte)Bits.Bit4) != 0)
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{
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this.IO.TriggerInterrupt(Interrupts.DisplayControlStatus);
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}
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this.IO.TriggerInterrupt(Interrupts.VerticalBlank);
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}
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this.RunRasterLines(lines);
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}
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private void RunRasterLine(int suggested)
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{
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/*
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A scanline normally takes 456 clocks (912 clocks in double speed
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mode) to complete. A scanline starts in mode 2, then goes to
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mode 3 and, when the LCD controller has finished drawing the
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line (the timings depend on lots of things) it goes to mode 0.
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During lines 144-153 the LCD controller is in mode 1.
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Line 153 takes only a few clocks to complete (the exact
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timings are below). The rest of the clocks of line 153 are
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spent in line 0 in mode 1!
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During mode 0 and mode 1 the CPU can access both VRAM and OAM.
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During mode 2 the CPU can only access VRAM, not OAM.
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During mode 3 OAM and VRAM can't be accessed.
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In GBC mode the CPU can't access Palette RAM(FF69h and FF6Bh)
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during mode 3.
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A scanline normally takes 456 clocks(912 clocks in double speed mode) to complete.
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A scanline starts in mode 2, then goes to mode 3 and , when the LCD controller has
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finished drawing the line(the timings depend on lots of things) it goes to mode 0.
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During lines 144 - 153 the LCD controller is in mode 1.
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Line 153 takes only a few clocks to complete(the exact timings are below).
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The rest of the clocks of line 153 are spent in line 0 in mode 1!
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*/
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this.allowed += suggested;
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if (this.enabledLCD)
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{
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if (((this.IO.Peek(IoRegisters.STAT) & (byte)Bits.Bit6) != 0) && (this.IO.Peek(IoRegisters.LYC) == this.IO.Peek(IoRegisters.LY)))
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{
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this.IO.TriggerInterrupt(Interrupts.DisplayControlStatus);
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}
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// Mode 2, OAM unavailable
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this.IO.UpdateLcdStatusMode(LcdStatusMode.SearchingOamRam);
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if ((this.IO.Peek(IoRegisters.STAT) & (byte)Bits.Bit5) != 0)
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{
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this.IO.TriggerInterrupt(Interrupts.DisplayControlStatus);
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}
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this.allowed -= this.CPU.Run(80); // ~19us
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// Mode 3, OAM/VRAM unavailable
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this.IO.UpdateLcdStatusMode(LcdStatusMode.TransferringDataToLcd);
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this.allowed -= this.CPU.Run(170); // ~41us
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// Mode 0
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this.IO.UpdateLcdStatusMode(LcdStatusMode.HBlank);
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if ((this.IO.Peek(IoRegisters.STAT) & (byte)Bits.Bit3) != 0)
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{
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this.IO.TriggerInterrupt(Interrupts.DisplayControlStatus);
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}
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this.allowed -= this.CPU.Run(this.allowed); // ~48.6us
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this.IO.IncrementLY();
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}
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else
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{
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this.allowed -= this.CPU.Run(this.allowed);
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}
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}
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}
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}
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