[fceu.git] / Documentation / FAQ

FCE Ultra General User's FAQ
 preliminary version
------------------


Q: Why doesn't the NSF <insert name here> work(correctly) on FCE Ultra?
A: Some NSF rips are bad.  Some read from addresses that are not specified
   in the NSF specifications, expecting certain values to be returned.
   Others execute undocumented instructions that have no affect on
   less-accurate software NSF players, but will cause problems on NSF players 
   that emulate these instructions.  Also, the playback rate specified
   in the NSF header is currently ignored, though I haven't encountered
   any problems in doing this.


Q: Why doesn't the game <insert name here> work(correctly) on FCE Ultra?
A: Many factors can make a game not work on FCE Ultra:

	- If the ROM image is in the iNES format(typically files that have 
	  the extension "nes"), its header may be incorrect.  This 
	  incorrectness may also be because of garbage in the 
	  header.  Certain utilities used to put text in the reserved 
	  bytes of the iNES header, then those reserved bytes were 
	  later assigned functions.  FCE Ultra recognizes and 
  	  automatically removes(from the ROM image in RAM, not on the 
	  storage medium) SOME header junk.

	  If the game has graphical errors while scrolling, chances are
	  the mirroring is set incorrectly in the header.  
	  
	  You can try to edit the header with a utility(in the NES 
	  utilities section at http://zophar.net ) or a hex editor.

	- The on-cart hardware the game uses may not be emulated 
	  correctly.

	- Limitations of the ROM image format may prevent a game from
	  being emulated correctly without special code to recognize that
	  game.  This occurs quite often with many Koei MMC5(iNES mapper 5) 
	  and MMC1(iNES mapper 1) games in the iNES format.  FCE Ultra identifies
	  and emulates some of these games based on the ROM CRC32 value.

	- The ROM image may be encrypted.  The author of SMYNES seems to
	  have done this intentionally to block other emulators from 
	  playing "SMYNES only" games.
Commit	Line	Data
c62d2810	1	FCE Ultra General User's FAQ
	2	preliminary version
	3	------------------
	4
	5
	6	Q: Why doesn't the NSF <insert name here> work(correctly) on FCE Ultra?
	7	A: Some NSF rips are bad. Some read from addresses that are not specified
	8	in the NSF specifications, expecting certain values to be returned.
	9	Others execute undocumented instructions that have no affect on
	10	less-accurate software NSF players, but will cause problems on NSF players
	11	that emulate these instructions. Also, the playback rate specified
	12	in the NSF header is currently ignored, though I haven't encountered
	13	any problems in doing this.
	14
	15
	16	Q: Why doesn't the game <insert name here> work(correctly) on FCE Ultra?
	17	A: Many factors can make a game not work on FCE Ultra:
	18
	19	- If the ROM image is in the iNES format(typically files that have
	20	the extension "nes"), its header may be incorrect. This
	21	incorrectness may also be because of garbage in the
	22	header. Certain utilities used to put text in the reserved
	23	bytes of the iNES header, then those reserved bytes were
	24	later assigned functions. FCE Ultra recognizes and
	25	automatically removes(from the ROM image in RAM, not on the
	26	storage medium) SOME header junk.
	27
	28	If the game has graphical errors while scrolling, chances are
	29	the mirroring is set incorrectly in the header.
	30
	31	You can try to edit the header with a utility(in the NES
	32	utilities section at http://zophar.net ) or a hex editor.
	33
	34	- The on-cart hardware the game uses may not be emulated
	35	correctly.
	36
	37	- Limitations of the ROM image format may prevent a game from
	38	being emulated correctly without special code to recognize that
	39	game. This occurs quite often with many Koei MMC5(iNES mapper 5)
	40	and MMC1(iNES mapper 1) games in the iNES format. FCE Ultra identifies
	41	and emulates some of these games based on the ROM CRC32 value.
	42
	43	- The ROM image may be encrypted. The author of SMYNES seems to
	44	have done this intentionally to block other emulators from
	45	playing "SMYNES only" games.