Function FCEUX_PPU_Loop

src/ppu.cpp:2106–2527

int framectr = 0;
int FCEUX_PPU_Loop(int skip) {

	if (new_ppu_reset) // first frame since reset, time to initialize
	{
		ppur.reset();
		spr_read.reset();
		new_ppu_reset = false;
	}

	//262 scanlines
	if (ppudead) {
		// not quite emulating all the NES power up behavior
		// since it is known that the NES ignores writes to some
		// register before around a full frame, but no games
		// should write to those regs during that time, it needs
		// to wait for vblank
		ppur.status.sl = 241;
		if (PAL)
			runppu(70 * kLineTime);
		else
			runppu(20 * kLineTime);
		ppur.status.sl = 0;
		runppu(242 * kLineTime);
		--ppudead;
		goto finish;
	}

	{
		PPU_status |= 0x80;
		ppuphase = PPUPHASE_VBL;

		//Not sure if this is correct.  According to Matt Conte and my own tests, it is.
		//Timing is probably off, though.
		//NOTE:  Not having this here breaks a Super Donkey Kong game.
		PPU[3] = PPUSPL = 0;
		const int delay = 20;	//fceu used 12 here but I couldnt get it to work in marble madness and pirates.

		ppur.status.sl = 241;	//for sprite reads

		//formerly: runppu(delay);
		for(int dot=0;dot<delay;dot++)
			runppu(1);

		if (VBlankON) TriggerNMI();
		int sltodo = PAL?70:20;
		
		//formerly: runppu(20 * (kLineTime) - delay);
		for(int S=0;S<sltodo;S++)
		{
			for(int dot=(S==0?delay:0);dot<kLineTime;dot++)
				runppu(1);
			ppur.status.sl++;
		}

		//this seems to run just before the dummy scanline begins
		PPU_status = 0;
		//this early out caused metroid to fail to boot. I am leaving it here as a reminder of what not to do
		//if(!PPUON) { runppu(kLineTime*242); goto finish; }