Added emulation for frame 'jitter' based on inconsistent scanline

counts.  Thanks to Spiceware for the idea and implementation.

Tweaked 'MDM' autodetection; the identifying string can be in
either bank 0 or bank 1 (or both).


git-svn-id: svn://svn.code.sf.net/p/stella/code/trunk@3199 8b62c5a3-ac7e-4cc8-8f21-d9a121418aba

Changes.txt

@@ -23,6 +23,15 @@
     now, this applies mainly to the various decimal and binary fields.
     More widgets will be made editable in future releases.
 
+  * The TIA now emulates the jitter that occurs when scanline counts
+    are not consistent frame-over-frame.  Also, the DPC+ scheme now
+    emulates jitter that can occur when using its Fractional Datafetchers
+    if the DFxFRACINC registers are not re-initialized every frame.
+    Special thanks to SpiceWare for this implementation.
+
+  * Tweaked 'MDM' scheme autodetection to detect that the identification
+    string can be in either bank 0 or bank 1.
+
   * Changed 'hidecursor' commandline argument (and associated UI item) to
     'cursor'.  The new argument allows to set mouse cursor visibility
     separately for both UI and emulation modes.

src/emucore/Cart.cxx

@@ -894,9 +894,9 @@ bool Cartridge::isProbablyFE(const uInt8* image, uInt32 size)
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 bool Cartridge::isProbablyMDM(const uInt8* image, uInt32 size)
 {
-  // MDM cart is identified key 'MDMC' in the first 4K of ROM
+  // MDM cart is identified key 'MDMC' in the first 8K of ROM
   uInt8 signature[] = { 'M', 'D', 'M', 'C' };
-  return searchForBytes(image, 4096, signature, 4, 1);
+  return searchForBytes(image, 8192, signature, 4, 1);
 }
 
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

src/emucore/CartDPCPlus.cxx

@@ -412,7 +412,7 @@ bool CartridgeDPCPlus::poke(uInt16 address, uInt8 value)
     {
       //DFxFRACLOW - fractional data pointer low byte
       case 0x00:
-        myFractionalCounters[index] = (myFractionalCounters[index] & 0x0F0000) | ((uInt16)value << 8);
+        myFractionalCounters[index] = (myFractionalCounters[index] & 0x0F00FF) | ((uInt16)value << 8);
         break;
 
       // DFxFRACHI - fractional data pointer high byte

src/emucore/TIA.cxx

@@ -57,7 +57,9 @@ TIA::TIA(Console& console, Sound& sound, Settings& settings)
     myFrameCounter(0),
     myPALFrameCounter(0),
     myBitsEnabled(true),
-    myCollisionsEnabled(true)
+    myCollisionsEnabled(true),
+    myNextFrameJitter(0),
+    myCurrentFrameJitter(0)
 
 {
   // Allocate buffers for two frame buffers
@@ -141,6 +143,7 @@ void TIA::reset()
 
   myFrameCounter = myPALFrameCounter = 0;
   myScanlineCountForLastFrame = 0;
+  myNextFrameJitter = myCurrentFrameJitter = 0;
 
   myP0Mask = &TIATables::PxMask[0][0][0];
   myP1Mask = &TIATables::PxMask[0][0][0];
@@ -653,6 +656,39 @@ inline void TIA::endFrame()
     memset(myPreviousFrameBuffer + offset, 1, stride);
   }
 
+  // Account for frame jitter, skipping the first few frames
+  if(myFrameCounter > 3)
+  {
+    // Set the jitter amount for the current frame
+    myCurrentFrameJitter = myNextFrameJitter * 160;
+
+    // Calculate the jitter amount for the next frame.
+    // Jitter amount of a frame depends upon the difference
+    // between the scanline counts of the prior two frames.
+    myNextFrameJitter = myScanlineCountForLastFrame - previousCount;
+
+    if(myNextFrameJitter < 0)
+    {
+      myNextFrameJitter = --myNextFrameJitter >> 1;
+
+      // Make sure currentFrameBuffer() doesn't return a pointer that
+      // results in memory being accessed outside of the 160*320 bytes
+      // allocated for the frame buffer
+      if(myNextFrameJitter < -myFrameYStart)
+        myNextFrameJitter = myFrameYStart;
+    }
+    else if(myNextFrameJitter > 0)
+    {
+      myNextFrameJitter = ++myNextFrameJitter >> 1;
+
+      // Make sure currentFrameBuffer() doesn't return a pointer that
+      // results in memory being accessed outside of the 160*320 bytes
+      // allocated for the frame buffer
+      if(myNextFrameJitter > 320 - myFrameYStart - myFrameHeight)
+        myNextFrameJitter = 320 - myFrameYStart - myFrameHeight;
+    }
+  }
+
   // Recalculate framerate. attempting to auto-correct for scanline 'jumps'
   if(myAutoFrameEnabled)
   {

src/emucore/TIA.hxx

@@ -175,7 +175,7 @@ class TIA : public Device
       @return Pointer to the current frame buffer
     */
     uInt8* currentFrameBuffer() const
-      { return myCurrentFrameBuffer + myFramePointerOffset; }
+      { return myCurrentFrameBuffer + myFramePointerOffset + myCurrentFrameJitter; }
 
     /**
       Answers the previous frame buffer
@@ -616,6 +616,13 @@ class TIA : public Device
     // Whether TIA bits/collisions are currently enabled/disabled
     bool myBitsEnabled, myCollisionsEnabled;
   
+    // Derived from the difference between the scanline counts of the
+    // current and prior frames.  If non-zero the next frame should jitter.
+    Int32 myNextFrameJitter;
+  
+    // Jitter amount for the current frame
+    Int32 myCurrentFrameJitter;
+  
   private:
     // Following constructors and assignment operators not supported
     TIA() = delete;

src/macosx/stella.xcodeproj/project.pbxproj

@@ -1032,8 +1032,8 @@
 		DCD6FC9211C28C6F005DA767 /* PNGLibrary.hxx */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; name = PNGLibrary.hxx; path = ../common/PNGLibrary.hxx; sourceTree = SOURCE_ROOT; };
 		DCDA03AE1A2009BA00711920 /* CartWD.cxx */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; name = CartWD.cxx; path = ../emucore/CartWD.cxx; sourceTree = "<group>"; };
 		DCDA03AF1A2009BB00711920 /* CartWD.hxx */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; name = CartWD.hxx; path = ../emucore/CartWD.hxx; sourceTree = "<group>"; };
-		DCDAF4D818CA9AAB00D3865D /* SDL2.framework */ = {isa = PBXFileReference; lastKnownFileType = wrapper.framework; name = SDL2.framework; path = ../../../../../../Library/Frameworks/SDL2.framework; sourceTree = "<group>"; };
+		DCDAF4D818CA9AAB00D3865D /* SDL2.framework */ = {isa = PBXFileReference; lastKnownFileType = wrapper.framework; name = SDL2.framework; path = /Library/Frameworks/SDL2.framework; sourceTree = "<absolute>"; };
-		DCDAF4DA18CA9AF000D3865D /* SDL2.framework */ = {isa = PBXFileReference; lastKnownFileType = wrapper.framework; name = SDL2.framework; path = ../../../../../../Library/Frameworks/SDL2.framework; sourceTree = "<group>"; };
+		DCDAF4DA18CA9AF000D3865D /* SDL2.framework */ = {isa = PBXFileReference; lastKnownFileType = wrapper.framework; name = SDL2.framework; path = /Library/Frameworks/SDL2.framework; sourceTree = "<absolute>"; };
 		DCDE17F617724E5D00EB1AC6 /* ConfigPathDialog.cxx */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; name = ConfigPathDialog.cxx; path = ../gui/ConfigPathDialog.cxx; sourceTree = SOURCE_ROOT; };
 		DCDE17F717724E5D00EB1AC6 /* ConfigPathDialog.hxx */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; name = ConfigPathDialog.hxx; path = ../gui/ConfigPathDialog.hxx; sourceTree = SOURCE_ROOT; };
 		DCDE17F817724E5D00EB1AC6 /* SnapshotDialog.cxx */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; name = SnapshotDialog.cxx; path = ../gui/SnapshotDialog.cxx; sourceTree = SOURCE_ROOT; };