/// <summary>
/// Executes a single PPU step.
/// </summary>
public void Step()
{
// Trigger an NMI at the start of _scanline 241 if VBLANK NMI's are enabled
if (Scanline == 241) // && Cycle == 1)
{
_nmiOccurred = 1;
if (_nmiOutput != 0)
{
_console.Cpu.TriggerNmi();
}
Scanline = 242;
//Cycle = 0;
}
Cycle += 8;
//Cycle++;
// Reset cycle (and scanline if scanline == 260)
// Also set to next frame if at end of last _scanline
if (Cycle > 340)
{
if (Scanline >= 261) // Last scanline, reset to upper left corner
{
f ^= 1;
Scanline = 0;
Cycle = -1;
_console.DrawFrame();
}
else // Not on last scanline
{
Cycle = -1;
Scanline++;
}
}
}
// Updates scanline and cycle counters, triggers NMI's if needed.
void UpdateCounters()
{
// Trigger an NMI at the start of _scanline 241 if VBLANK NMI's are enabled
if (Scanline == 241 && Cycle == 1)
{
_nmiOccurred = 1;
if (_nmiOutput != 0)
{
_console.Cpu.TriggerNmi();
}
}
bool renderingEnabled = (_flagShowBackground != 0) || (_flagShowSprites != 0);
// Skip last cycle of prerender scanline on odd frames
if (renderingEnabled)
{
if (Scanline == 261 && f == 1 && Cycle == 339)
{
f ^= 1;
Scanline = 0;
Cycle = -1;
_console.DrawFrame();
return;
}
}
Cycle++;
// Reset cycle (and scanline if scanline == 260)
// Also set to next frame if at end of last _scanline
if (Cycle > 340)
{
if (Scanline == 261) // Last scanline, reset to upper left corner
{
f ^= 1;
Scanline = 0;
Cycle = -1;
_console.DrawFrame();
}
else // Not on last scanline
{
Cycle = -1;
Scanline++;
}
}
}
