From eb6636dfbe4d47f49acd873f10ef009a0762b838 Mon Sep 17 00:00:00 2001
From: bwmott <bwmott@8b62c5a3-ac7e-4cc8-8f21-d9a121418aba>
Date: Sun, 13 Jan 2002 04:26:42 +0000
Subject: [PATCH] Improved the emulation of values read from the TIA based on
 the results Eckhard Stolberg obtained from a real 2600 showing that the TIA
 always defines bits 6 & 7 and lets bits 0 to 5 float.

git-svn-id: svn://svn.code.sf.net/p/stella/code/trunk@26 8b62c5a3-ac7e-4cc8-8f21-d9a121418aba
---
 stella/src/emucore/TIA.cxx | 58 ++++++++++++++++++--------------------
 1 file changed, 28 insertions(+), 30 deletions(-)

diff --git a/stella/src/emucore/TIA.cxx b/stella/src/emucore/TIA.cxx
index fdc25a42e..91a3c0c03 100644
--- a/stella/src/emucore/TIA.cxx
+++ b/stella/src/emucore/TIA.cxx
@@ -13,7 +13,7 @@
 // See the file "license" for information on usage and redistribution of
 // this file, and for a DISCLAIMER OF ALL WARRANTIES.
 //
-// $Id: TIA.cxx,v 1.2 2001-12-30 18:38:54 bwmott Exp $
+// $Id: TIA.cxx,v 1.3 2002-01-13 04:26:42 bwmott Exp $
 //============================================================================
 
 #include <assert.h>
@@ -1560,53 +1560,51 @@ uInt8 TIA::peek(uInt16 addr)
   // Update frame to current color clock before we look at anything!
   updateFrame(mySystem->cycles() * 3);
 
-  uInt8 noise = mySystem->getDataBusState();
-  uInt8 noise1 = noise & 0x7F;
-  uInt8 noise2 = noise & 0x3F;
+  uInt8 noise = mySystem->getDataBusState() & 0x3F;
 
   switch(addr & 0x000f)
   {
     case 0x00:    // CXM0P
       return ((myCollision & 0x0001) ? 0x80 : 0x00) | 
-          ((myCollision & 0x0002) ? 0x40 : 0x00) | noise2;
+          ((myCollision & 0x0002) ? 0x40 : 0x00) | noise;
 
     case 0x01:    // CXM1P
       return ((myCollision & 0x0004) ? 0x80 : 0x00) | 
-          ((myCollision & 0x0008) ? 0x40 : 0x00) | noise2;
+          ((myCollision & 0x0008) ? 0x40 : 0x00) | noise;
 
     case 0x02:    // CXP0FB
       return ((myCollision & 0x0010) ? 0x80 : 0x00) | 
-          ((myCollision & 0x0020) ? 0x40 : 0x00) | noise2;
+          ((myCollision & 0x0020) ? 0x40 : 0x00) | noise;
 
     case 0x03:    // CXP1FB
       return ((myCollision & 0x0040) ? 0x80 : 0x00) | 
-          ((myCollision & 0x0080) ? 0x40 : 0x00) | noise2;
+          ((myCollision & 0x0080) ? 0x40 : 0x00) | noise;
 
     case 0x04:    // CXM0FB
       return ((myCollision & 0x0100) ? 0x80 : 0x00) | 
-          ((myCollision & 0x0200) ? 0x40 : 0x00) | noise2;
+          ((myCollision & 0x0200) ? 0x40 : 0x00) | noise;
 
     case 0x05:    // CXM1FB
       return ((myCollision & 0x0400) ? 0x80 : 0x00) | 
-          ((myCollision & 0x0800) ? 0x40 : 0x00) | noise2;
+          ((myCollision & 0x0800) ? 0x40 : 0x00) | noise;
 
     case 0x06:    // CXBLPF
-      return ((myCollision & 0x1000) ? 0x80 : 0x00) | noise1;
+      return ((myCollision & 0x1000) ? 0x80 : 0x00) | noise;
 
     case 0x07:    // CXPPMM
       return ((myCollision & 0x2000) ? 0x80 : 0x00) | 
-          ((myCollision & 0x4000) ? 0x40 : 0x00) | noise2;
+          ((myCollision & 0x4000) ? 0x40 : 0x00) | noise;
 
     case 0x08:    // INPT0
     {
       Int32 r = myConsole.controller(Controller::Left).read(Controller::Nine);
       if(r == Controller::minimumResistance)
       {
-        return 0x80 | noise1;
+        return 0x80 | noise;
       }
       else if((r == Controller::maximumResistance) || myDumpEnabled)
       {
-        return noise1;
+        return noise;
       }
       else
       {
@@ -1614,11 +1612,11 @@ uInt8 TIA::peek(uInt16 addr)
         uInt32 needed = (uInt32)(t * 1.19E6);
         if(mySystem->cycles() > (myDumpDisabledCycle + needed))
         {
-          return 0x80 | noise1;
+          return 0x80 | noise;
         }
         else
         {
-          return noise1;
+          return noise;
         }
       }
     }
@@ -1628,11 +1626,11 @@ uInt8 TIA::peek(uInt16 addr)
       Int32 r = myConsole.controller(Controller::Left).read(Controller::Five);
       if(r == Controller::minimumResistance)
       {
-        return 0x80 | noise1;
+        return 0x80 | noise;
       }
       else if((r == Controller::maximumResistance) || myDumpEnabled)
       {
-        return noise1;
+        return noise;
       }
       else
       {
@@ -1640,11 +1638,11 @@ uInt8 TIA::peek(uInt16 addr)
         uInt32 needed = (uInt32)(t * 1.19E6);
         if(mySystem->cycles() > (myDumpDisabledCycle + needed))
         {
-          return 0x80 | noise1;
+          return 0x80 | noise;
         }
         else
         {
-          return noise1;
+          return noise;
         }
       }
     }
@@ -1654,11 +1652,11 @@ uInt8 TIA::peek(uInt16 addr)
       Int32 r = myConsole.controller(Controller::Right).read(Controller::Nine);
       if(r == Controller::minimumResistance)
       {
-        return 0x80 | noise1;
+        return 0x80 | noise;
       }
       else if((r == Controller::maximumResistance) || myDumpEnabled)
       {
-        return noise1;
+        return noise;
       }
       else
       {
@@ -1666,11 +1664,11 @@ uInt8 TIA::peek(uInt16 addr)
         uInt32 needed = (uInt32)(t * 1.19E6);
         if(mySystem->cycles() > (myDumpDisabledCycle + needed))
         {
-          return 0x80 | noise1;
+          return 0x80 | noise;
         }
         else
         {
-          return noise1;
+          return noise;
         }
       }
     }
@@ -1680,11 +1678,11 @@ uInt8 TIA::peek(uInt16 addr)
       Int32 r = myConsole.controller(Controller::Right).read(Controller::Five);
       if(r == Controller::minimumResistance)
       {
-        return 0x80 | noise1;
+        return 0x80 | noise;
       }
       else if((r == Controller::maximumResistance) || myDumpEnabled)
       {
-        return noise1;
+        return noise;
       }
       else
       {
@@ -1692,22 +1690,22 @@ uInt8 TIA::peek(uInt16 addr)
         uInt32 needed = (uInt32)(t * 1.19E6);
         if(mySystem->cycles() > (myDumpDisabledCycle + needed))
         {
-          return 0x80 | noise1;
+          return 0x80 | noise;
         }
         else
         {
-          return noise1;
+          return noise;
         }
       }
     }
 
     case 0x0C:    // INPT4
       return myConsole.controller(Controller::Left).read(Controller::Six) ?
-          (0x80 | noise1) : noise1;
+          (0x80 | noise) : noise;
 
     case 0x0D:    // INPT5
       return myConsole.controller(Controller::Right).read(Controller::Six) ?
-          (0x80 | noise1) : noise1;
+          (0x80 | noise) : noise;
 
     case 0x0e:
       return noise;