Allow ROMs < 64 bytes (Stella's internal page size) to work correctly. Fixes #564.

Changes.txt

@@ -29,16 +29,16 @@
   * Controllers can be changed during emulation (no ROM reload required
     anymore).
 
-  * Added support for Light Gun controller
+  * Added support for Light Gun controller.
 
-  * Added limitted KidVid support (8, 9 and 0 start the games)
+  * Added limited KidVid support (8, 9 and 0 start the games).
 
   * Removed superfluous controller option 'PADDLES_IDIR'.
 
   * Added configurable paddle dejittering.
 
   * Huge improvements to event remapping.
-    - Allow mapping of modifier-key and button-direction combinations.
+    - Allow mapping of modifier-key and button-direction combinations
     - One controller can use the same mappings as other controllers
     - Much more events can be remapped
     - Events can be filtered by type in UI
@@ -55,9 +55,9 @@
 
   * Added option to configure controller input repeat speed.
 
-  * Added high quality scaling
+  * Added high quality scaling.
 
-  * Made scanlines better aligned to scaling
+  * Made scanlines better aligned to scaling.
 
   * Added 'HiDPI' mode, which scales the UI by 2x when enabled.  This is
     meant for 4k and above monitors, but can actually be used at any
@@ -80,7 +80,7 @@
 
   * Added hotkey for sound on/off.
 
-  * Paths have been simplified: (TODO - finish this)
+  * Paths have been simplified:
     - The following file/directory locations are no longer configurable
       (statedir, nvramdir, cheatfile, palettefile, propsfile); they are
       now all under the base directory
@@ -143,15 +143,17 @@
 
   * Fixed cheatcode handling in 2K and 4K ROMs.
 
+  * Fixed bug where ROMs smaller than 64 bytes were not recognized.
+
   * Fixed bug where frying one ROM was continued with the next ROM.
 
   * Fixed not working 7800 pause key.
 
   * Enhanced UA bankswitching to support certain Brazilian carts.
 
-  * Fixed WD bankswitching
+  * Fixed WD bankswitching.
 
-  * Added FC bankswitching for Amiga's Power Play Arcade Video Game Album
+  * Added FC bankswitching for Amiga's Power Play Arcade Video Game Album.
 
   * Added auto-detection of display format based on filename.
 

src/emucore/Cart2K.cxx

@@ -31,15 +31,26 @@ Cartridge2K::Cartridge2K(const ByteBuffer& image, size_t size,
   while(mySize < size)
     mySize <<= 1;
 
-  // We can't use a size smaller than the minimum page size in Stella
-  mySize = std::max<size_t>(mySize, System::PAGE_SIZE);
-
   // Initialize ROM with illegal 6502 opcode that causes a real 6502 to jam
-  myImage = make_unique<uInt8[]>(mySize);
-  std::fill_n(myImage.get(), mySize, 0x02);
+  size_t bufSize = std::max<size_t>(mySize, System::PAGE_SIZE);
+  myImage = make_unique<uInt8[]>(bufSize);
+  std::fill_n(myImage.get(), bufSize, 0x02);
+
+  // Handle cases where ROM is smaller than the page size
+  // It's much easier to do it this way rather than changing the page size
+  if(mySize >= System::PAGE_SIZE)
+  {
+    // Directly copy the ROM image into the buffer
+    std::copy_n(image.get(), mySize, myImage.get());
+  }
+  else
+  {
+    // Manually 'mirror' the ROM image into the buffer
+    for(int i = 0; i < System::PAGE_SIZE; i += mySize)
+      std::copy_n(image.get(), mySize, myImage.get() + i);
+    mySize = System::PAGE_SIZE;
+  }
 
-  // Copy the ROM image into my buffer
-  std::copy_n(image.get(), size, myImage.get());
   createCodeAccessBase(mySize);
 
   // Set mask for accessing the image buffer