/// <summary>
/// Checks the PPU cycle and state and calls the scanLine() method when appropriate.
/// </summary>
public override void Tick()
{
PPU ppu = PPU.Instance;
if (ppu.Cycle != 280)
{
return;
}
if (ppu.Scanline > 239 && ppu.Scanline < 261)
{
return;
}
if (ppu.flagShowbackground == 0 && ppu.flagShowSprite == 0)
{
return;
}
scanLine();
}
/// <summary>
/// Put value in memory in the specified location
/// </summary>
/// <param name="location">Index to be written at</param>
/// <param name="value">Value to be written at given index</param>
public void WriteMemory(ushort address, byte value)
{
if (address < 0x2000)
{
memory[address % 0x0800] = value;
}
else if (address < 0x4000)
{
PPU ppu = PPU.Instance;
ppu.writeRegister((ushort)(0x2000 + address % 8), value);
}
else if (address < 0x4014)
{
//set APU register value
//throw new NotImplementedException();
}
else if (address == 0x4014)
{
PPU ppu = PPU.Instance;
ppu.writeRegister(address, value);
}
else if (address == 0x4015)
{
//throw new NotImplementedException();
}
else if (address == 0x4016)
{
input1.Write(value);
input2.Write(value);
}
else if (address == 0x4017)
{
//throw new NotImplementedException();
}
else if (address >= 0x6000)
{
mapper.write(address, value);
}
else
{
throw new Exception("Invalid memory access requested");
}
}
/// <summary>
/// PPU writes to an address location. Method throws exception if
/// PPU is given an address which leads to invalid memory access.
/// </summary>
/// <param name="addr"></param>
/// <param name="value"></param>
public void PpuWrite(ushort addr, byte value)
{
addr = (ushort)(addr % 0x4000);
if (addr < 0x2000)
{
mapper.write(addr, value);
}
else if (addr < 0x3F00)
{
PPU ppu = PPU.Instance;
byte mode = mapper.cart.Mirroring;
ppu.nameTableData[MirroredAddress(mode, addr) % 2048] = value;
}
else if (addr < 0x4000)
{
PPU ppu = PPU.Instance;
ppu.writePalette((ushort)(addr % 32), value);
}
else
{
throw new Exception("Invalid memory access requested");
}
}
/// <summary>
/// PPU reading from an address specified. Method throws an exception
/// if address specifies invalid memory access.
/// </summary>
/// <param name="addr"></param>
/// <returns></returns>
public byte PpuRead(ushort addr)
{
addr = (ushort)(addr % 0x4000);
if (addr < 0x2000)
{
return(mapper.read(addr));
}
else if (addr < 0x3F00)
{
PPU ppu = PPU.Instance;
byte mode = mapper.cart.Mirroring;
return(ppu.nameTableData[MirroredAddress(mode, addr) % 2048]);
}
else if (addr < 0x4000)
{
PPU ppu = PPU.Instance;
return(ppu.readPalette((ushort)(addr % 32)));
}
else
{
throw new Exception("Invalid memory access requested");
}
}
/// <summary>
/// Returns value held at the position passed in by the parameter
/// Check if memory location is valid
/// </summary>
/// <param name="location">Memory index to be returned</param>
/// <returns>Value held at index location</returns>
public byte ReadMemory(ushort address)
{
if (address < 0x2000)
{
return(memory[address % 0x0800]);
}
else if (address < 0x4000)
{
PPU ppu = PPU.Instance;
return(ppu.readRegister((ushort)(0x2000 + address % 8)));
}
else if (address == 0x4014)
{
PPU ppu = PPU.Instance;
return(ppu.readRegister(address));
}
else if (address == 0x4015)
{
throw new NotImplementedException();
}
else if (address == 0x4016)
{
return(input1.Read());
}
else if (address == 0x4017)
{
return(input2.Read());
}
else if (address >= 0x6000)
{
return(mapper.read(address));
}
else
{
throw new Exception("Invalid memory access requested");
}
}