/// <summary>
/// Reads one byte from the specified bank, at the specified offset
/// </summary>
/// <param name="offset"></param>
/// <returns></returns>
public byte ReadByte(int offset)
{
// CHR ROM
if (offset < 0x2000)
{
return(_chrRom[offset]);
}
//PPU Registers
if (offset <= 0x3FFF)
{
return(ReadInterceptors.TryGetValue(offset, out currentReadInterceptor) ? currentReadInterceptor(offset) : (byte)0x0);
}
//Some UxROM boards from Nintendo have bus conflicts, we avoid these here
if (offset >= 0x6000 && offset < 0x8000)
{
return(0x0);
}
//16 KB switchable PRG ROM bank
if (offset <= 0xBFFF)
{
return(_prgRom[_prgBank0Offset + (offset - 0x8000)]);
}
//16 KB PRG ROM bank, fixed to the last bank
if (offset <= 0xFFFF)
{
return(_prgRom[_prgBank1Offset + (offset - 0xC000)]);
}
throw new ArgumentOutOfRangeException(nameof(offset), offset, "Maximum value of offset is 0xFFFF");
}
/// <summary>
/// Reads one byte from the specified bank, at the specified offset
/// </summary>
/// <param name="memoryType"></param>
/// <param name="offset"></param>
/// <returns></returns>
public byte ReadByte(enumMemoryType memoryType, int offset)
{
switch (memoryType)
{
case enumMemoryType.CPU:
return(_prgRom[CpuOffsetToPrgRomOffset(offset)]);
case enumMemoryType.PPU:
return(!ReadInterceptors.TryGetValue(offset, out currentReadInterceptor) ? _chrRom[offset] : currentReadInterceptor(offset));
default:
throw new ArgumentOutOfRangeException(nameof(memoryType), memoryType, null);
}
}
/// <summary>
/// Reads one byte from the specified bank, at the specified offset
/// </summary>
/// <param name="memoryType"></param>
/// <param name="offset"></param>
/// <returns></returns>
public byte ReadByte(int offset)
{
// CHR Bank 0 == $0000-$0FFF
// CHR Bank 1 == $1000-$1FFF
if (offset <= 0x1FFF)
{
var chrBankOffset = offset / 0x1000 == 0 ? _chrBank0Offset : _chrBank1Offset;
chrBankOffset += offset % 0x1000;
return(_chrRom[chrBankOffset]);
}
//PPU Registers
if (offset <= 0x3FFF)
{
return(ReadInterceptors.TryGetValue(offset, out currentReadInterceptor) ? currentReadInterceptor(offset) : (byte)0x0);
}
// PRG RAM Bank == $6000-$7FFF
if (offset >= 0x6000 && offset <= 0x7FFF)
{
if (!_usePrgRam)
{
throw new AccessViolationException($"Attempt to read PRG RAM when disabled. Offset ${offset:X4}");
}
return(_prgRam[offset - 0x6000]);
}
// PRG Bank 0 == $8000-$BFFF
// PRG Bank 1 == $C000-$FFFF
if (offset >= 0x8000 && offset <= 0xFFFF)
{
//Map address $8000 to our _prgRom start of 0x0000;
var prgBaseOffset = offset - 0x8000;
var prgBankOffset = prgBaseOffset / 0x4000 == 0 ? _prgBank0Offset : _prgBank1Offset;
prgBankOffset += prgBaseOffset % 0x4000;
return(_prgRom[prgBankOffset]);
}
throw new ArgumentOutOfRangeException(nameof(offset), offset, "Maximum value of offset is 0xFFFF");
}
/// <summary>
/// Reads one byte from the specified bank, at the specified offset
/// </summary>
/// <param name="memoryType"></param>
/// <param name="offset"></param>
/// <returns></returns>
public byte ReadByte(int offset)
{
//CHR ROM
if (offset < 0x2000)
{
return(_chrRom[offset]);
}
//PPU Interceptors (Read)
if (offset <= 0x3FFF)
{
return(ReadInterceptors.TryGetValue(offset, out currentReadInterceptor)
? currentReadInterceptor(offset)
: (byte)0x0);
}
//PRG ROM
if (offset <= 0xFFFF)
{
return(_prgRom[offset - 0x8000]);
}
throw new ArgumentOutOfRangeException(nameof(offset), offset, "Maximum value of offset is 0xFFFF");
}
