private UInt16 ReadWord(UInt16 address)
{
byte low = CpuRead(address);
byte high = CpuRead((UInt16)(address + 1));
return(BitMagic.Combine(high, low));
}
private UInt16 StackPopWord()
{
byte low = StackPop();
byte high = StackPop();
return(BitMagic.Combine(high, low));
}
public bool IND()
{
byte low = CpuRead(PC++);
byte high = CpuRead(PC++);
UInt16 ptr = BitMagic.Combine(high, low);
byte addrLow, addrHigh;
// hardware bug
if (low == 0x00FF)
{
addrLow = CpuRead((ptr));
addrHigh = CpuRead((UInt16)(ptr & 0xFF00));
}
else
{
addrLow = CpuRead(ptr);
addrHigh = CpuRead((UInt16)(ptr + 1));
}
address = BitMagic.Combine(addrHigh, addrLow);
return(false);
}
public bool ABS()
{
byte low = CpuRead(PC++);
byte high = CpuRead(PC++);
address = BitMagic.Combine(high, low);
return(false);
}
public bool IZX()
{
byte t = CpuRead(PC++);
// address is in zero page
byte addrLow = CpuRead((UInt16)((t + X) & 0x00FF));
byte addrHigh = CpuRead((UInt16)((t + X + 1) & 0x00FF));
address = BitMagic.Combine(addrHigh, addrLow);
return(false);
}
// global system clock
public void Clock()
{
ppu.Clock();
if (clockCounter % 3 == 0)
{
if (dmaStarted)
{
if (dmaDummy)
{
if (clockCounter % 2 == 1)
{
dmaDummy = false;
}
}
else
{
if (clockCounter % 2 == 0)
{
UInt16 address = BitMagic.Combine(dmaPage, dmaAddress);
dmaData = CpuRead(address);
}
else
{
ppu.Oam[dmaAddress++] = dmaData;
// after 256 writes dmaAddress loops back to zero
if (dmaAddress == 0)
{
dmaStarted = false;
dmaDummy = true;
}
}
}
}
else
{
cpu.Clock();
}
}
if (ppu.EmitNmi)
{
cpu.NMI();
}
clockCounter++;
}
public bool IZY()
{
byte t = CpuRead(PC++);
// address is in zero page
byte addrLow = CpuRead((UInt16)(t & 0x00FF));
byte addrHigh = CpuRead((UInt16)((t + 1) & 0x00FF));
address = BitMagic.Combine(addrHigh, addrLow);
address += Y;
// if page is crossed
if (Page(address) != Page((UInt16)(addrHigh << 8)))
{
return(true);
}
return(false);
}