From 1c7fdf7529cb02ddcb349648423dcdfb5c6c58c2 Mon Sep 17 00:00:00 2001
From: zeromus <zeromus@zeromus.org>
Date: Sun, 18 Mar 2012 18:41:45 +0000
Subject: [PATCH] nes-pass 10-even_odd_timing and 05-nmi_timing

---
 .../Consoles/Nintendo/NES/PPU.cs              |  2 --
 .../Consoles/Nintendo/NES/PPU.regs.cs         |  6 ++--
 .../Consoles/Nintendo/NES/PPU.run.cs          | 36 ++++++++-----------
 3 files changed, 17 insertions(+), 27 deletions(-)

diff --git a/BizHawk.Emulation/Consoles/Nintendo/NES/PPU.cs b/BizHawk.Emulation/Consoles/Nintendo/NES/PPU.cs
index d17b321756..33f39b5569 100644
--- a/BizHawk.Emulation/Consoles/Nintendo/NES/PPU.cs
+++ b/BizHawk.Emulation/Consoles/Nintendo/NES/PPU.cs
@@ -147,8 +147,6 @@ namespace BizHawk.Emulation.Consoles.Nintendo
 				for (int i = 0; i < x; i++)
 				{
 					ppur.status.cycle++;
-					if (ppur.status.cycle == ppur.status.end_cycle)
-						ppur.status.cycle = 0;
 
 					//might not actually run a cpu cycle if there are none to be run right now
 					nes.RunCpuOne();
diff --git a/BizHawk.Emulation/Consoles/Nintendo/NES/PPU.regs.cs b/BizHawk.Emulation/Consoles/Nintendo/NES/PPU.regs.cs
index 96391b585f..c2fbb6a776 100644
--- a/BizHawk.Emulation/Consoles/Nintendo/NES/PPU.regs.cs
+++ b/BizHawk.Emulation/Consoles/Nintendo/NES/PPU.regs.cs
@@ -66,7 +66,7 @@ namespace BizHawk.Emulation.Consoles.Nintendo
 			{
 				public int sl;
 				public bool rendering { get { return sl >= 0 && sl < 241; } }
-				public int cycle, end_cycle;
+				public int cycle;
 			}
 
 			//uses the internal counters concept at http://nesdev.icequake.net/PPU%20addressing.txt
@@ -94,7 +94,8 @@ namespace BizHawk.Emulation.Consoles.Nintendo
 					ser.Sync("_ht", ref _ht);
 					ser.Sync("fh", ref fh);
 					ser.Sync("status.cycle", ref status.cycle);
-					ser.Sync("status.end_cycle", ref status.end_cycle);
+					int junk = 0;
+					ser.Sync("status.end_cycle", ref junk);
 					ser.Sync("status.sl", ref status.sl);
 				}
 
@@ -151,7 +152,6 @@ namespace BizHawk.Emulation.Consoles.Nintendo
 					fh = 0;
 					_fv = _v = _h = _vt = _ht = 0;
 					status.cycle = 0;
-					status.end_cycle = 341;
 					status.sl = 241;
 				}
 
diff --git a/BizHawk.Emulation/Consoles/Nintendo/NES/PPU.run.cs b/BizHawk.Emulation/Consoles/Nintendo/NES/PPU.run.cs
index 3fcc2f7b37..96aede18d2 100644
--- a/BizHawk.Emulation/Consoles/Nintendo/NES/PPU.run.cs
+++ b/BizHawk.Emulation/Consoles/Nintendo/NES/PPU.run.cs
@@ -97,11 +97,12 @@ namespace BizHawk.Emulation.Consoles.Nintendo
 				//NOTE:  Not having this here breaks a Super Donkey Kong game.
 				reg_2003 = 0;
 
-				//fceu/fceux had 12 here, but 15 was required to pass blargg's 05-nmi_timing.nes
-				const int delay = 15;
+				//this was repeatedly finetuned from the fceux days thrugh the old cpu core and into the new one to pass 05-nmi_timing.nes
+				//note that there is still some leniency. for instance, 4,2 will pass in addition to 3,3
+				const int delay = 6;
 				runppu(3);
 				bool nmi_destiny = reg_2000.vblank_nmi_gen && Reg2002_vblank_active;
-				runppu(delay - 3);
+				runppu(3);
 				if (nmi_destiny) TriggerNMI();
 				if (PAL)
 					runppu(70 * (kLineTime) - delay);
@@ -116,6 +117,8 @@ namespace BizHawk.Emulation.Consoles.Nintendo
 				int oamslot=0;
 				int oamcount=0;
 
+				idleSynch ^= true;
+
 				//render 241 scanlines (including 1 dummy at beginning)
 				for (int sl = 0; sl < 241; sl++)
 				{
@@ -422,35 +425,24 @@ namespace BizHawk.Emulation.Consoles.Nintendo
 
 					ppuphase = PPUPHASE.BG;
 
-					//I'm unclear of the reason why this particular access to memory is made.
-					//The nametable address that is accessed 2 times in a row here, is also the
-					//same nametable address that points to the 3rd tile to be rendered on the
-					//screen (or basically, the first nametable address that will be accessed when
-					//the PPU is fetching background data on the next scanline).
-					//(not implemented yet)
-					if (sl == 0)
-					{
-						if (idleSynch && reg_2001.show_bg && !PAL)
-							ppur.status.end_cycle = 340;
-						else
-							ppur.status.end_cycle = 341;
-						idleSynch ^= true;
-					}
-					else
-						ppur.status.end_cycle = 341;
-
 					//fetch BG: two tiles for next line
 					for (int xt = 0; xt < 2; xt++)
 						Read_bgdata(ref bgdata[xt]);
 
-					runppu(kFetchTime * 2);
+					//this sequence is tuned to pass 10-even_odd_timing.nes
+					runppu(kFetchTime);
+					bool evenOddDestiny = reg_2001.show_bg;
+					runppu(kFetchTime);
 
 					//After memory access 170, the PPU simply rests for 4 cycles (or the
 					//equivelant of half a memory access cycle) before repeating the whole
 					//pixel/scanline rendering process. If the scanline being rendered is the very
 					//first one on every second frame, then this delay simply doesn't exist.
-					if (ppur.status.end_cycle == 341)
+					if (sl == 0 && idleSynch && evenOddDestiny && !PAL)
+					{ }
+					else
 						runppu(1);
+					ppur.status.cycle = 0;
 				
 				} //scanline loop