public MemoryBus(PPURegisters ppuRegisters)
{
PPURegisters = ppuRegisters;
//Randomize(wram);
//Randomize(zram);
//Randomize(VideoMemory);
//Randomize(ObjectAttributeMemory);
TileSet = new TileSet(VideoMemory);
SpriteOam = new SpriteOam(ppuRegisters, ObjectAttributeMemory, TileSet);
Timer = new Timer(this);
}
public byte this[int address]
{
get
{
if (address < 0)
{
throw new ArgumentOutOfRangeException("Address cannot be negative.");
}
else if (address < 0x4000)
{
if (address < 0x100 && IsBootRomMapped)
{
return(bootRom[address]);
}
return(cart[address]); //ROM bank 0 (16K)
}
else if (address < 0x8000)
{
return(cart[address]); //ROM bank 1-N (16K, switchable if cart has an MBC)
}
else if (address < 0xA000)
{
//VRAM (8K)
return(VideoMemory[address - 0x8000]);
}
else if (address < 0xC000)
{
//external RAM (8K)
return(cart[address - 0xA000]);
}
else if (address < 0xE000)
{
//internal work RAM (8K)
return(wram[address - 0xC000]);
}
else if (address < 0xFE00)
{
//internal work RAM shadow
return(wram[address - 0xE000]);
}
else if (address < 0xFEA0)
{
//sprite OAM (160 bytes)
return(ObjectAttributeMemory[address - 0xFE00]);
}
else if (address < 0xFF00)
{
//unusable memory range, should always read as zero
return(0);
}
else if (address < 0xFF80)
{
//various hardware I/O registers (PPU, APU, joypad, etc)
if (address == 0xFF00)
{
return(JoypadRegister.Read());
}
else if (address == 0xFF01)
{
return(serialData);
}
else if (address == 0xFF02)
{
return(serialControl);
}
else if (Timer.MappedToAddress(address))
{
return(Timer[address]);
}
else if (address == 0xFF0F)
{
return(InterruptFlags.Data);
}
else if (soundRegisters.MappedToAddress(address))
{
return(soundRegisters[address]);
}
else if (address == 0xFF40)
{
return(PPURegisters.LCDControl.Data);
}
else if (address == 0xFF41)
{
return(PPURegisters.LCDStatus.Data);
}
else if (address == 0xFF42)
{
return(PPURegisters.ScrollY);
}
else if (address == 0xFF43)
{
return(PPURegisters.ScrollX);
}
else if (address == 0xFF44)
{
return(PPURegisters.CurrentScanline);
}
else if (address == 0xFF45)
{
return(PPURegisters.CompareScanline);
}
else if (address == 0xFF47)
{
return(PPURegisters.BackgroundPalette.Data);
}
else if (address == 0xFF48)
{
return(PPURegisters.SpritePalette0.Data);
}
else if (address == 0xFF49)
{
return(PPURegisters.SpritePalette1.Data);
}
else if (address == 0xFF4A)
{
return(PPURegisters.WindowY);
}
else if (address == 0xFF4B)
{
return(PPURegisters.WindowX);
}
else
{
return(0xFF);
}
//else throw new NotImplementedException($"Unsupported read of address ${address:X4} (not all hardware I/O registers are implemented yet).");
}
else if (address < 0xFFFF)
{
//zero page (128 bytes)
return(zram[address - 0xFF80]);
}
else if (address == 0xFFFF)
{
return(InterruptEnable.Data);
}
else
{
throw new ArgumentOutOfRangeException("Address must be between $0000 and $FFFF");
}
}
set
{
if (address < 0)
{
throw new ArgumentOutOfRangeException("Address cannot be negative.");
}
else if (address < 0x8000)
{
//memory bank controllers intercept ROM writes and use them for bank switching and etc
cart[address] = value;
//why does Tetris write here when it doesn't use one?
//see: https://www.reddit.com/r/EmuDev/comments/5ht388/gb_why_does_tetris_write_to_the_rom/
}
else if (address >= 0x8000 && address < 0xA000)
{
//VRAM (8K)
var vramAddress = address - 0x8000;
bool isTilesetDirty = address < 0x9800 && VideoMemory[vramAddress] != value;
VideoMemory[vramAddress] = value;
if (isTilesetDirty)
{
TileSet.UpdateFromMemoryWrite(VideoMemory, vramAddress);
}
}
else if (address < 0xC000)
{
//external RAM (8K)
cart[address - 0xA000] = value;
}
else if (address < 0xE000)
{
//internal work RAM (8K)
wram[address - 0xC000] = value;
}
else if (address < 0xFE00)
{
//internal work RAM shadow
wram[address - 0xE000] = value;
}
else if (address < 0xFEA0)
{
//sprite OAM (160 bytes)
var oamAddress = address - 0xFE00;
bool isOamDirty = ObjectAttributeMemory[oamAddress] != value;
ObjectAttributeMemory[address - 0xFE00] = value;
if (isOamDirty)
{
SpriteOam.UpdateFromMemoryWrite(ObjectAttributeMemory, oamAddress);
}
}
else if (address < 0xFF00)
{
//unusable memory, but same games (like Tetris) write here (by mistake?)... so don't crash
//see: https://www.reddit.com/r/EmuDev/comments/5nixai/gb_tetris_writing_to_unused_memory/
}
else if (address < 0xFF80)
{
//various hardware I/O registers (PPU, APU, joypad, etc)
if (address == 0xFF00)
{
JoypadRegister.Write(value);
}
else if (address == 0xFF01)
{
serialData = value;
gameLinkConsole?.Print(value);
}
else if (address == 0xFF02)
{
serialControl = value;
}
else if (Timer.MappedToAddress(address))
{
Timer[address] = value;
}
else if (address == 0xFF0F)
{
InterruptFlags.Data = (byte)(value | 0b1110_0000); //upper 3 bits are unused and always read as 1
}
else if (soundRegisters.MappedToAddress(address))
{
soundRegisters[address] = value;
}
else if (address == 0xFF40)
{
PPURegisters.LCDControl.Data = value;
}
else if (address == 0xFF41)
{
PPURegisters.LCDStatus.Data = value;
}
else if (address == 0xFF42)
{
PPURegisters.ScrollY = value;
}
else if (address == 0xFF43)
{
PPURegisters.ScrollX = value;
}
else if (address == 0xFF44)
{
PPURegisters.CurrentScanline = value;
}
else if (address == 0xFF45)
{
PPURegisters.CompareScanline = value;
}
else if (address == 0xFF46)
{
OamDmaTransfer(value);
}
else if (address == 0xFF47)
{
PPURegisters.BackgroundPalette.Data = value;
}
else if (address == 0xFF48)
{
PPURegisters.SpritePalette0.Data = value;
}
else if (address == 0xFF49)
{
PPURegisters.SpritePalette1.Data = value;
}
else if (address == 0xFF50)
{
IsBootRomMapped = false;
}
else if (address == 0xFF4A)
{
PPURegisters.WindowY = value;
}
else if (address == 0xFF4B)
{
PPURegisters.WindowX = value;
}
//else throw new NotImplementedException($"Unsupported write to address ${address:X4} (not all hardware I/O registers are implemented yet).");
}
else if (address < 0xFFFF)
{
//zero page (128 bytes)
zram[address - 0xFF80] = value;
}
else if (address == 0xFFFF)
{
InterruptEnable.Data = value;
}
else
{
throw new ArgumentOutOfRangeException($"Unexpected write to address ${address:X4}");
}
}
}
