Disable 'jitter' effect in older DPC+ driver versions (fixes #429).

Changes.txt

@@ -59,6 +59,10 @@
 
   * Fixed 'Dancing Plate (Unknown) (PAL)' to use joystick.
 
+  * Allow the DPC+ scheme to not enable 'jitter' effect for certain older
+    DPC+ driver versions; this allows 'Epic Adventure' ROM to finally
+    work in Stella.
+
   * PNG image support is now conditionally compiled into Stella.  All
     major ports (Linux/macOS/Windows) have it enabled by default.
 

src/common/StateManager.cxx

@@ -27,7 +27,7 @@
 
 #include "StateManager.hxx"
 
-#define STATE_HEADER "06000002state"
+#define STATE_HEADER "06000003state"
 // #define MOVIE_HEADER "03030000movie"
 
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

src/emucore/CartDPCPlus.cxx

@@ -18,6 +18,7 @@
 #ifdef DEBUGGER_SUPPORT
   #include "Debugger.hxx"
 #endif
+#include "MD5.hxx"
 #include "System.hxx"
 #include "Thumbulator.hxx"
 #include "CartDPCPlus.hxx"
@@ -35,7 +36,8 @@ CartridgeDPCPlus::CartridgeDPCPlus(const BytePtr& image, uInt32 size,
     myAudioCycles(0),
     myARMCycles(0),
     myFractionalClocks(0.0),
-    myBankOffset(0)
+    myBankOffset(0),
+    myJitterEnabled(true)
 {
   // Image is always 32K, but in the case of ROM > 29K, the image is
   // copied to the end of the buffer
@@ -63,6 +65,11 @@ CartridgeDPCPlus::CartridgeDPCPlus(const BytePtr& image, uInt32 size,
        Thumbulator::ConfigureFor::DPCplus,
        this);
 
+  // Disable jitter on certain DPC+ driver versions
+  string driverMD5;
+  driverMD5 = MD5::hash(image, 3*1024);
+  myJitterEnabled = driverMD5 != "8dd73b44fd11c488326ce507cbeb19d1";
+
   setInitialState();
 }
 
@@ -398,7 +405,8 @@ bool CartridgeDPCPlus::poke(uInt16 address, uInt8 value)
     {
       //DFxFRACLOW - fractional data pointer low byte
       case 0x00:
-        myFractionalCounters[index] = (myFractionalCounters[index] & 0x0F00FF) | (uInt16(value) << 8);
+        myFractionalCounters[index] =
+          (myFractionalCounters[index] & (myJitterEnabled ? 0x0F00FF : 0x0F0000)) | (uInt16(value) << 8);
         break;
 
       // DFxFRACHI - fractional data pointer high byte
@@ -677,6 +685,9 @@ bool CartridgeDPCPlus::save(Serializer& out) const
 
     // Clock info for Thumbulator
     out.putLong(myARMCycles);
+
+    // Jitter effect
+    out.putBool(myJitterEnabled);
   }
   catch(...)
   {
@@ -738,6 +749,9 @@ bool CartridgeDPCPlus::load(Serializer& in)
 
     // Clock info for Thumbulator
     myARMCycles = in.getLong();
+
+    // Jitter effect
+    myJitterEnabled = in.getBool();
   }
   catch(...)
   {

src/emucore/CartDPCPlus.hxx

@@ -270,6 +270,12 @@ class CartridgeDPCPlus : public Cartridge
     // Indicates the offset into the ROM image (aligns to current bank)
     uInt16 myBankOffset;
 
+    // Indicates whether 'jitter' should be emulated
+    // This is the default option, and should always be enabled
+    // However, certain ROMs were released with older DPC+ ARM drivers,
+    // before the scheme was finalized; this allows those ROMs to run
+    bool myJitterEnabled;
+
   private:
     // Following constructors and assignment operators not supported
     CartridgeDPCPlus() = delete;