From 3e14c07c5159e48124199315f2189d0df1a9ee33 Mon Sep 17 00:00:00 2001
From: alyosha-tas <alexei.f.k@gmail.com>
Date: Sat, 9 Apr 2016 09:33:13 -0400
Subject: [PATCH] implement PRG delay

---
 .../Consoles/Atari/2600/Tia/TIA.cs            | 46 ++++++++++++++++---
 1 file changed, 39 insertions(+), 7 deletions(-)

diff --git a/BizHawk.Emulation.Cores/Consoles/Atari/2600/Tia/TIA.cs b/BizHawk.Emulation.Cores/Consoles/Atari/2600/Tia/TIA.cs
index c1956a84ae..be1d67bf18 100644
--- a/BizHawk.Emulation.Cores/Consoles/Atari/2600/Tia/TIA.cs
+++ b/BizHawk.Emulation.Cores/Consoles/Atari/2600/Tia/TIA.cs
@@ -292,6 +292,11 @@ namespace BizHawk.Emulation.Cores.Atari.Atari2600
         private bool enam0_val = false;
         private bool enam1_val = false;
 
+        private int prg0_delay = 0;
+        private int prg1_delay = 0;
+        private byte prg0_val = 0;
+        private byte prg1_val = 0;
+
         private bool do_ticks = false;
         private byte _hsyncCnt;
 		private int _capChargeStart;
@@ -472,6 +477,34 @@ namespace BizHawk.Emulation.Cores.Atari.Atari2600
 
             }
 
+            // delay latch to player graphics registers
+            if (prg0_delay > 0)
+            {
+                prg0_delay++;
+                if (prg0_delay == 3)
+                {
+                    prg0_delay = 0;
+                    _player0.Grp = prg0_val;
+                    _player1.Dgrp = _player1.Grp;
+                }
+
+            }
+
+            if (prg1_delay > 0)
+            {
+                prg1_delay++;
+                if (prg1_delay == 3)
+                {
+                    prg1_delay = 0;
+                    _player1.Grp = prg1_val;
+                    _player0.Dgrp = _player0.Grp;
+
+                    // TODO: Find a game that uses this functionality and test it
+                    _ball.Denabled = _ball.Enabled;
+                }
+
+            }
+
             // Reset the RDY flag when we reach hblank
             if (_hsyncCnt <= 0)
 			{
@@ -1234,16 +1267,15 @@ namespace BizHawk.Emulation.Cores.Atari.Atari2600
 			}
 			else if (maskedAddr == 0x1B) // GRP0
 			{
-				_player0.Grp = value;
-				_player1.Dgrp = _player1.Grp;
+                prg0_val = value;
+                prg0_delay = 1;
+                
 			}
 			else if (maskedAddr == 0x1C) // GRP1
 			{
-				_player1.Grp = value;
-				_player0.Dgrp = _player0.Grp;
-
-				// TODO: Find a game that uses this functionality and test it
-				_ball.Denabled = _ball.Enabled;
+                prg1_val = value;
+                prg1_delay = 1;
+                
 			}
 			else if (maskedAddr == 0x1D) // ENAM0
 			{