419 lines
14 KiB
C#
419 lines
14 KiB
C#
// <copyright file="IoRegisters.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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public sealed class IoRegisters : EightBit.Ram
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{
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public const int BASE = 0xFF00;
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// Port/Mode Registers
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public const int P1 = 0x0; // R/W Mask5
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public const int SB = 0x1; // R/W Mask8
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public const int SC = 0x2; // R/W Bit7 | Bit0
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// Timer control
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public const int DIV = 0x4; // R/W Mask8
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public const int TIMA = 0x5; // R/W Mask8
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public const int TMA = 0x6; // R/W Mask8
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public const int TAC = 0x7; // R/W Mask3
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// Interrupt Flags
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public const int IF = 0xF; // R/W Mask5
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public const int IE = 0xFF; // R/W Mask5
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// Sound Registers
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public const int NR10 = 0x10; // R/W Mask7
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public const int NR11 = 0x11; // R/W Bit7 | Bit6
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public const int NR12 = 0x12; // R/W Mask8
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public const int NR13 = 0x13; // W 0
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public const int NR14 = 0x14; // R/W Bit6
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public const int NR21 = 0x16; // R/W Bit7 | Bit6
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public const int NR22 = 0x17; // R/W Mask8
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public const int NR23 = 0x18; // W 0
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public const int NR24 = 0x19; // R/W Bit6
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public const int NR30 = 0x1A; // R/W Bit7
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public const int NR31 = 0x1B; // R/W Mask8
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public const int NR32 = 0x1C; // R/W Bit6 | Bit5
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public const int NR33 = 0x1D; // W 0
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public const int NR34 = 0x1E; // R/W Bit6
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public const int NR41 = 0x20; // R/W Mask6
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public const int NR42 = 0x21; // R/W Mask8
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public const int NR43 = 0x22; // R/W Mask8
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public const int NR44 = 0x23; // R/W Bit6
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public const int NR50 = 0x24; // R/W Mask8
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public const int NR51 = 0x25; // R/W Mask8
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public const int NR52 = 0x26; // R/W Mask8 Mask8
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public const int WAVE_PATTERN_RAM_START = 0x30;
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public const int WAVE_PATTERN_RAM_END = 0x3F;
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// LCD Display Registers
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public const int LCDC = 0x40; // R/W Mask8
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public const int STAT = 0x41; // R/W Mask7
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public const int SCY = 0x42; // R/W Mask8
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public const int SCX = 0x43; // R/W Mask8
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public const int LY = 0x44; // R Mask8 zeroed
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public const int LYC = 0x45; // R/W Mask8
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public const int DMA = 0x46; // W 0
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public const int BGP = 0x47; // R/W Mask8
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public const int OBP0 = 0x48; // R/W Mask8
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public const int OBP1 = 0x49; // R/W Mask8
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public const int WY = 0x4A; // R/W Mask8
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public const int WX = 0x4B; // R/W Mask8
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// Boot rom control
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public const int BOOT_DISABLE = 0x50;
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private readonly Bus bus;
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private readonly Register16 divCounter = new Register16(0xab, 0xcc);
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private readonly Register16 dmaAddress = new Register16();
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private int timerCounter = 0;
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private bool dmaTransferActive = false;
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private bool scanP15 = false;
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private bool scanP14 = false;
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private bool p15 = true; // misc keys
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private bool p14 = true; // direction keys
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private bool p13 = true; // down/start
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private bool p12 = true; // up/select
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private bool p11 = true; // left/b
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private bool p10 = true; // right/a
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public IoRegisters(Bus bus)
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: base(0x80)
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{
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this.bus = bus;
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this.bus.ReadingByte += this.Bus_ReadingByte;
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this.bus.WrittenByte += this.Bus_WrittenByte;
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}
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public event EventHandler<LcdStatusModeEventArgs> DisplayStatusModeUpdated;
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public bool BootRomDisabled { get; private set; } = false;
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public bool BootRomEnabled => !this.BootRomDisabled;
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public int TimerClock => this.TimerControl & (byte)Mask.Two;
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public bool TimerEnabled => !this.TimerDisabled;
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public bool TimerDisabled => (this.TimerControl & (byte)Bits.Bit2) == 0;
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public int TimerClockTicks
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{
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get
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{
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switch (this.TimerClock)
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{
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case 0b00:
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return 1024; // 4.096 Khz
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case 0b01:
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return 16; // 262.144 Khz
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case 0b10:
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return 64; // 65.536 Khz
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case 0b11:
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return 256; // 16.384 Khz
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}
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throw new InvalidOperationException("Invalid timer clock specification");
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}
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}
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private ref byte TimerControl => ref this.Reference(TAC);
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private ref byte TimerModulo => ref this.Reference(TMA);
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private ref byte TimerCounter => ref this.Reference(TIMA);
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public void Reset()
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{
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this.Poke(NR52, 0xf1);
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this.Poke(LCDC, (byte)(LcdcControls.DisplayBackground | LcdcControls.BackgroundCharacterDataSelection | LcdcControls.LcdEnable));
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this.divCounter.Word = 0xabcc;
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this.timerCounter = 0;
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}
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public void TransferDma()
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{
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if (this.dmaTransferActive)
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{
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this.bus.OAMRAM.Poke(this.dmaAddress.Low, this.bus.Peek(this.dmaAddress));
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this.dmaTransferActive = ++this.dmaAddress.Low < 0xa0;
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}
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}
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public void TriggerInterrupt(Interrupts cause) => this.Reference(IF) |= (byte)cause;
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public void CheckTimers(int cycles)
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{
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this.IncrementDIV(cycles);
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this.CheckTimer(cycles);
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}
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public void IncrementDIV(int cycles)
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{
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this.divCounter.Word += (ushort)cycles;
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this.Poke(DIV, this.divCounter.High);
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}
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public void IncrementTIMA()
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{
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var updated = this.TimerCounter + 1;
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if ((updated & (int)Bits.Bit8) != 0)
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{
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this.TriggerInterrupt(Interrupts.TimerOverflow);
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updated = this.TimerModulo;
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}
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this.TimerCounter = Chip.LowByte(updated);
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}
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public void IncrementLY() => this.Poke(LY, (byte)((this.Peek(LY) + 1) % GameBoy.Bus.TotalLineCount));
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public void ResetLY() => this.Poke(LY, 0);
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public void UpdateLcdStatusMode(LcdStatusMode mode)
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{
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var current = this.Peek(STAT) & unchecked((byte)~Mask.Two);
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this.Poke(STAT, (byte)(current | (int)mode));
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this.OnDisplayStatusModeUpdated(mode);
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}
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public void DisableBootRom() => this.BootRomDisabled = true;
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public void EnableBootRom() => this.BootRomDisabled = false;
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public void PressRight()
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{
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this.ControlRightLines(false);
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this.TriggerKeypadInterrupt();
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}
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public void ReleaseRight() => this.ControlRightLines(true);
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public void PressLeft()
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{
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this.ControlLeftLines(false);
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this.TriggerKeypadInterrupt();
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}
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public void ReleaseLeft() => this.ControlLeftLines(true);
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public void PressUp()
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{
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this.ControlUpLines(false);
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this.TriggerKeypadInterrupt();
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}
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public void ReleaseUp() => this.ControlUpLines(true);
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public void PressDown()
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{
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this.ControlDownLines(false);
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this.TriggerKeypadInterrupt();
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}
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public void ReleaseDown() => this.ControlDownLines(true);
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public void PressA()
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{
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this.ControlALines(false);
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this.TriggerKeypadInterrupt();
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}
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public void ReleaseA() => this.ControlALines(true);
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public void PressB()
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{
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this.ControlBLines(false);
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this.TriggerKeypadInterrupt();
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}
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public void ReleaseB() => this.ControlBLines(true);
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public void PressSelect()
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{
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this.ControlSelectLines(false);
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this.TriggerKeypadInterrupt();
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}
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public void ReleaseSelect() => this.ControlSelectLines(true);
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public void PressStart()
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{
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this.ControlStartLines(false);
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this.TriggerKeypadInterrupt();
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}
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public void ReleaseStart() => this.ControlStartLines(true);
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private void ControlRightLines(bool value) => this.p14 = this.p10 = value;
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private void ControlLeftLines(bool value) => this.p14 = this.p11 = value;
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private void ControlUpLines(bool value) => this.p14 = this.p12 = value;
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private void ControlDownLines(bool value) => this.p14 = this.p13 = value;
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private void ControlALines(bool value) => this.p15 = this.p10 = value;
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private void ControlBLines(bool value) => this.p15 = this.p11 = value;
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private void ControlSelectLines(bool value) => this.p15 = this.p12 = value;
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private void ControlStartLines(bool value) => this.p15 = this.p13 = value;
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private void OnDisplayStatusModeUpdated(LcdStatusMode mode) => this.DisplayStatusModeUpdated?.Invoke(this, new LcdStatusModeEventArgs(mode));
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private void CheckTimer(int cycles)
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{
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if (this.TimerEnabled)
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{
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this.timerCounter -= cycles;
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if (this.timerCounter <= 0)
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{
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this.timerCounter += this.TimerClockTicks;
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this.IncrementTIMA();
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}
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}
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}
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private void ApplyMask(ushort address, byte masking) => this.Poke(address, (byte)(this.Peek(address) | ~masking));
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private void TriggerKeypadInterrupt() => this.TriggerInterrupt(Interrupts.KeypadPressed);
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private void Bus_WrittenByte(object sender, System.EventArgs e)
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{
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var address = this.bus.Address.Word;
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var value = this.bus.Data;
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var port = (ushort)(address - BASE);
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switch (port)
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{
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case P1:
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this.scanP14 = (value & (byte)Bits.Bit4) == 0;
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this.scanP15 = (value & (byte)Bits.Bit5) == 0;
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break;
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case SB: // R/W
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case SC: // R/W
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break;
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case DIV: // R/W
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this.Poke(port, 0);
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this.timerCounter = this.divCounter.Word = 0;
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break;
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case TIMA: // R/W
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break;
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case TMA: // R/W
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break;
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case TAC: // R/W
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break;
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case IF: // R/W
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break;
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case LCDC:
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case STAT:
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case SCY:
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case SCX:
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break;
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case DMA:
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this.dmaAddress.Word = Chip.PromoteByte(value);
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this.dmaTransferActive = true;
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break;
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case LY: // R/O
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this.Poke(port, 0);
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break;
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case BGP:
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case OBP0:
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case OBP1:
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case WY:
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case WX:
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break;
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case BOOT_DISABLE:
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this.BootRomDisabled = value != 0;
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break;
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}
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}
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private void Bus_ReadingByte(object sender, System.EventArgs e)
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{
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var address = this.bus.Address.Word;
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var io = (address >= BASE) && (address < 0xff80);
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if (io)
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{
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var port = (ushort)(address - BASE);
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switch (port)
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{
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// Port/Mode Registers
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case P1:
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{
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var directionKeys = this.scanP14 && !this.p14;
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var miscKeys = this.scanP15 && !this.p15;
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var live = directionKeys || miscKeys;
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var rightOrA = (live && !this.p10) ? 0 : Bits.Bit0;
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var leftOrB = (live && !this.p11) ? 0 : Bits.Bit1;
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var upOrSelect = (live && !this.p12) ? 0 : Bits.Bit2;
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var downOrStart = (live && !this.p13) ? 0 : Bits.Bit3;
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var lowNibble = (byte)(rightOrA | leftOrB | upOrSelect | downOrStart);
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var highNibble = (byte)Chip.PromoteNibble((byte)Mask.Four);
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var value = (byte)(lowNibble | highNibble);
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this.Poke(port, value);
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}
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break;
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case SB:
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break;
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case SC:
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this.ApplyMask(port, (byte)(Bits.Bit7 | Bits.Bit0));
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break;
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// Timer control
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case DIV:
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case TIMA:
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case TMA:
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break;
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case TAC:
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this.ApplyMask(port, (byte)Mask.Three);
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break;
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// Interrupt Flags
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case IF:
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this.ApplyMask(port, (byte)Mask.Five);
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break;
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// LCD Display Registers
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case LCDC:
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break;
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case STAT:
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this.ApplyMask(port, (byte)Mask.Seven);
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break;
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case SCY:
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case SCX:
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case LY:
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case LYC:
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case DMA:
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case BGP:
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case OBP0:
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case OBP1:
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case WY:
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case WX:
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break;
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default:
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this.ApplyMask(port, 0);
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break;
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}
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}
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}
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}
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}
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