From 3c8a6a4e19211004e4c545f9e1635294442798fa Mon Sep 17 00:00:00 2001
From: alyosha-tas <alexei.f.k@gmail.com>
Date: Sat, 4 Feb 2017 09:14:55 -0500
Subject: [PATCH] NES: Fix PPU timing and Race condition

---
 .../Consoles/Nintendo/NES/PPU.regs.cs         |  4 ++++
 .../Consoles/Nintendo/NES/PPU.run.cs          | 20 ++++++++++---------
 2 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/PPU.regs.cs b/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/PPU.regs.cs
index 155690b2c7..c89ed19a33 100644
--- a/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/PPU.regs.cs
+++ b/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/PPU.regs.cs
@@ -479,6 +479,10 @@ namespace BizHawk.Emulation.Cores.Nintendo.NES
 		//VRAM address register (write)
 		void write_2006(byte value)
 		{
+			if (ppur.status.cycle==256)
+			{
+				conflict_2006 = true;
+			}
 			if (!vtoggle)
 			{
 				ppur._vt &= 0x07;
diff --git a/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/PPU.run.cs b/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/PPU.run.cs
index 70345b5b38..1a6006f135 100644
--- a/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/PPU.run.cs
+++ b/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/PPU.run.cs
@@ -39,6 +39,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.NES
 		public int spriteHeight;
 		public byte[] soam = new byte[512]; // in a real nes, this would only be 32, but we wish to allow more then 8 sprites per scanline
 		public bool reg_2001_color_disable_latch; // the value used here is taken 
+		public bool conflict_2006;
 
 		struct TempOAM
 		{
@@ -124,19 +125,20 @@ namespace BizHawk.Emulation.Cores.Nintendo.NES
 					bgdata.pt_1 = ppubus_read(ppu_addr_temp, true, true);
 					runppu(1);
 
-					//horizontal scroll clocked at cycle 3 and then
-					//vertical scroll at 255
-					if (reg_2001.PPUON)
-					{
-						ppur.increment_hsc();
-						if (ppur.status.cycle == 255)
-							ppur.increment_vs();
-					}
+					
 					break;
 				case 7:
 					
 					runppu(1);
-					
+					//horizontal scroll clocked at cycle 3 and then
+					//vertical scroll at 256
+					if (reg_2001.PPUON)
+					{
+						ppur.increment_hsc();
+						if (ppur.status.cycle == 256 && !conflict_2006)
+							ppur.increment_vs();
+					}
+					conflict_2006 = false;
 					break;
 			} //switch(cycle)
 		}