MDM scheme now uses hotspots from $800-$BFF instead of $800-$FFF.

git-svn-id: svn://svn.code.sf.net/p/stella/code/trunk@3001 8b62c5a3-ac7e-4cc8-8f21-d9a121418aba

Changes.txt

@@ -15,7 +15,9 @@
 4.1.1 to 4.2: (xxx xx, 2014)
 
   * Fixed 'MDM' scheme to trigger bankswitching on writes to hotspots
-    (previously it only triggered on reads).
+    (previously it only triggered on reads).  Also, the scheme has been
+    modified as originally designed by E. Blink; hotspots are now in the
+    range $800-$BFF instead of $800-$FFF.
 
 -Have fun!
 

src/emucore/CartMDM.cxx

@@ -89,7 +89,8 @@ uInt8 CartridgeMDM::peek(uInt16 address)
 {
   // Because of the way we've set up accessing above, we can only
   // get here when the addresses are from 0x800 - 0xFFF
-  bank(address & 0x0FF);
+  if(address < 0xC00)
+    bank(address & 0x0FF);
 
   int hotspot = ((address & 0x0F00) >> 8) - 8;
   return myHotSpotPageAccess[hotspot].device->peek(address);
@@ -102,7 +103,8 @@ bool CartridgeMDM::poke(uInt16 address, uInt8 value)
   // about those below $1000
   if(!(address & 0x1000))
   {
-    bank(address & 0x0FF);
+    if(address < 0xC00)
+      bank(address & 0x0FF);
 
     int hotspot = ((address & 0x0F00) >> 8) - 8;
     myHotSpotPageAccess[hotspot].device->poke(address, value);

src/emucore/CartMDM.hxx

@@ -33,7 +33,10 @@
 
     http://atariage.com/forums/topic/56073-cheap-2k4k-x-in-1-menu-driven-multicart-for-atari-2600
 
-  The hotspots in this scheme are read/write at addresses $800 to $FFF, where
+  Note that this code implements a modified scheme (as designed by E. Blink).
+  In this version, the hotspots are from $800 to $BFF instead of $800 to $FFF.
+
+  The hotspots in this scheme are read/write at addresses $800 to $BFF, where
   the lower byte determines the actual 4K bank switch to.  In the current
   implementation, only 128 banks are supported, so selecting bank 128+ results
   in further bankswitching being locked.  A reset line is used to reset to