Added a flag to the 6502 code to track if the last memory access was a

read or not.  Also modified the TIA code so that if the last access
wasn't a read then it does not do a WSYNC operation.  This allows the
emubug.bin ROM to execute and report "2600" instead of "EMU".


git-svn-id: svn://svn.code.sf.net/p/stella/code/trunk@1123 8b62c5a3-ac7e-4cc8-8f21-d9a121418aba

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 1.68 2006-08-12 02:42:09 bwmott Exp $
+// $Id: TIA.cxx,v 1.69 2006-08-31 02:31:28 bwmott Exp $
 //============================================================================
 
 #include <cassert>
@@ -2211,8 +2211,18 @@ void TIA::poke(uInt16 addr, uInt8 value)
 
     case 0x02:    // Wait for leading edge of HBLANK
     {
-      // Tell the cpu to waste the necessary amount of time
+      // It appears that the 6507 only halts during a read cycle so
-      waitHorizontalSync();
+      // we test here for follow-on writes which should be ignored as
+      // far as halting the processor is concerned.
+      //
+      // TODO - 08-30-2006: This halting isn't correct since it's 
+      // still halting on the original write.  The 6507 emulation
+      // should be expanded to include a READY line.
+      if(mySystem->m6502().lastAccessWasRead())
+      {
+        // Tell the cpu to waste the necessary amount of time
+        waitHorizontalSync();
+      }
       break;
     }
 

stella/src/emucore/m6502/src/M6502.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: M6502.cxx,v 1.16 2006-06-09 02:45:11 urchlay Exp $
+// $Id: M6502.cxx,v 1.17 2006-08-31 02:31:29 bwmott Exp $
 //============================================================================
 
 #include "M6502.hxx"
@@ -80,6 +80,9 @@ void M6502::reset()
   SP = 0xff;
   PS(0x20);
 
+  // Reset access flag
+  myLastAccessWasRead = true;
+
   // Load PC from the reset vector
   PC = (uInt16)mySystem->peek(0xfffc) | ((uInt16)mySystem->peek(0xfffd) << 8);
 }

stella/src/emucore/m6502/src/M6502.hxx

@@ -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: M6502.hxx,v 1.16 2005-12-09 01:16:13 stephena Exp $
+// $Id: M6502.hxx,v 1.17 2006-08-31 02:31:29 bwmott Exp $
 //============================================================================
 
 #ifndef M6502_HXX
@@ -41,7 +41,7 @@ typedef Common::Array<Expression*> ExpressionList;
   has a 64K addressing space.
 
   @author  Bradford W. Mott
-  @version $Id: M6502.hxx,v 1.16 2005-12-09 01:16:13 stephena Exp $ 
+  @version $Id: M6502.hxx,v 1.17 2006-08-31 02:31:29 bwmott Exp $ 
 */
 class M6502
 {
@@ -171,6 +171,13 @@ class M6502
     */
     uInt16 getPC() const { return PC; }
 
+    /**
+      Answer true iff the last memory access was a read.
+
+      @return true iff last access was a read.
+    */ 
+    bool lastAccessWasRead() const { return myLastAccessWasRead; }
+
   public:
     /**
       Overload the ostream output operator for addressing modes.
@@ -279,6 +286,9 @@ class M6502
     /// Table of system cycles for each instruction
     uInt32 myInstructionSystemCycleTable[256]; 
 
+    /// Indicates if the last memory access was a read or not
+    bool myLastAccessWasRead;
+
   protected:
     /// Addressing mode for each of the 256 opcodes
     static AddressingMode ourAddressingModeTable[256];

stella/src/emucore/m6502/src/M6502Hi.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: M6502Hi.cxx,v 1.15 2005-12-17 01:23:07 stephena Exp $
+// $Id: M6502Hi.cxx,v 1.16 2006-08-31 02:31:29 bwmott Exp $
 //============================================================================
 
 #include "M6502Hi.hxx"
@@ -62,7 +62,10 @@ inline uInt8 M6502High::peek(uInt16 address)
   }
 #endif
 
-  return mySystem->peek(address);
+
+  uInt8 result = mySystem->peek(address);
+  myLastAccessWasRead = true;
+  return result;
 }
 
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
@@ -85,6 +88,7 @@ inline void M6502High::poke(uInt16 address, uInt8 value)
 #endif
 
   mySystem->poke(address, value);
+  myLastAccessWasRead = false;
 }
 
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

stella/src/emucore/m6502/src/M6502Low.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: M6502Low.cxx,v 1.8 2006-02-05 02:49:47 stephena Exp $
+// $Id: M6502Low.cxx,v 1.9 2006-08-31 02:31:29 bwmott Exp $
 //============================================================================
 
 #include "M6502Low.hxx"
@@ -52,7 +52,9 @@ inline uInt8 M6502Low::peek(uInt16 address)
   }
 #endif
 
-  return mySystem->peek(address);
+  uInt8 result = mySystem->peek(address);
+  myLastAccessWasRead = true;
+  return result;
 }
 
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
@@ -68,6 +70,7 @@ inline void M6502Low::poke(uInt16 address, uInt8 value)
 #endif
 
   mySystem->poke(address, value);
+  myLastAccessWasRead = false;
 }
 
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -