NSF Format Specification

Mirror of [[1]]

                           NES Music Format Spec
                           ---------------------

By: Kevin Horton khorton@iquest.net

NOTE:

---

Remember that I am very willing to add stuff and update this spec. If you find a new sound chip or other change let me know and I will get back with you. E-mail to the above address.

V1.61 - 06/27/2000 Updated spec a bit V1.60 - 06/01/2000 Updated Sunsoft, MMC5, and Namco chip information V1.50 - 05/28/2000 Updated FDS, added Sunsoft and Namco chips V1.32 - 11/27/1999 Added MMC5 register locations V1.30 - 11/14/1999 Added MMC5 audio bit, added some register info V1.20 - 09/12/1999 VRC and FDS prelim sound info added V1.00 - 05/11/1999 First official NSF specification file

This file encompasses a way to transfer NES music data in a small, easy to use format.

The basic idea is one rips the music/sound code from an NES game and prepends a small header to the data.

A program of some form (6502/sound emulator) then takes the data and loads it into the proper place into the 6502's address space, then inits and plays the tune.

Here's an overview of the header:

offset # of bytes Function

---

0000 5 STRING "NESM",01Ah ; denotes an NES sound format file 0005 1 BYTE Version number (currently 01h) 0006 1 BYTE Total songs (1=1 song, 2=2 songs, etc) 0007 1 BYTE Starting song (1= 1st song, 2=2nd song, etc) 0008 2 WORD (lo/hi) load address of data (8000-FFFF) 000a 2 WORD (lo/hi) init address of data (8000-FFFF) 000c 2 WORD (lo/hi) play address of data (8000-FFFF) 000e 32 STRING The name of the song, null terminated 002e 32 STRING The artist, if known, null terminated 004e 32 STRING The Copyright holder, null terminated 006e 2 WORD (lo/hi) speed, in 1/1000000th sec ticks, NTSC (see text) 0070 8 BYTE Bankswitch Init Values (see text, and FDS section) 0078 2 WORD (lo/hi) speed, in 1/1000000th sec ticks, PAL (see text) 007a 1 BYTE PAL/NTSC bits:

                bit 0: if clear, this is an NTSC tune
                bit 0: if set, this is a PAL tune
                bit 1: if set, this is a dual PAL/NTSC tune
                bits 2-7: not used. they *must* be 0

007b 1 BYTE Extra Sound Chip Support

                bit 0: if set, this song uses VRCVI
                bit 1: if set, this song uses VRCVII
                bit 2: if set, this song uses FDS Sound
                bit 3: if set, this song uses MMC5 audio
                bit 4: if set, this song uses Namco 106
                bit 5: if set, this song uses Sunsoft FME-07
                bits 6,7: future expansion: they *must* be 0

007c 4 ---- 4 extra bytes for expansion (must be 00h) 0080 nnn ---- The music program/data follows

This may look somewhat familiar; if so that's because this is somewhat sorta of based on the PSID file format for C64 music/sound.

Loading a tune into RAM

---

If offsets 0070h to 0077h have 00h in them, then bankswitching is *not* used. If one or more bytes are something other than 00h then bankswitching is used. If bankswitching is used then the load address is still used, but you now use (ADDRESS AND 0FFFh) to determine where on the first bank to load the data.

Each bank is 4K in size, and that means there are 8 of them for the entire 08000h-0ffffh range in the 6502's address space. You determine where in memory the data goes by setting bytes 070h thru 077h in the file. These determine the inital bank values that will be used, and hence where the data will be loaded into the address space.

Here's an example:

METROID.NSF will be used for the following explaination.

The file is set up like so: (starting at 070h in the file)

0070: 05 05 05 05 05 05 05 05 - 00 00 00 00 00 00 00 00 0080: ... music data goes here...

Since 0070h-0077h are something other than 00h, then we know that this tune uses bankswitching. The load address for the data is specified as 08000h. We take this AND 0fffh and get 0000h, so we will load data in at byte 0 of bank 0, since data is loaded into the banks sequentially starting from bank 0 up until the music data is fully loaded.

Metroid has 6 4K banks in it, numbered 0 through 5. The 6502's address space has 8 4K bankswitchable blocks on it, starting at 08000h-08fffh, 09000h-09fffh, 0a000h-0afffh ... 0f000h-0ffffh. Each one of these is 4K in size, and the current bank is controlled by writes to 05ff8h thru 05fffh, one byte per bank. So, 05ff8h controls the 08000h-08fffh range, 05ff9h controls the 09000h-09fffh range, etc. up to 05fffh which controls the 0f000h-0ffffh range. When the song is loaded into RAM, it is loaded into the banks and not the 6502's address space. Once this is done, then the bank control registers are written to set up the inital bank values. To do this, the value at 0070h in the file is written to 05ff8h, 0071h is written to 05ff9h, etc. all the way to 0077h is written to 05fffh. This is should be done before every call to the init routine.

If the tune was not bankswitched, then it is simply loaded in at the specified load address, until EOF

Initalizing a tune

---

This is pretty simple. Load the desired song # into the accumulator, minus 1 and set the X register to specify PAL (X=1) or NTSC (X=0). If this is a single standard tune (i.e. PAL *or* NTSC but not both) then the X register contents should not matter. Once the song # and optional PAL/NTSC standard are loaded, simply call the INIT address. Once init is done, it should perform an RTS.

Playing a tune

---

Once the tune has been initalized, it can now be played. To do this, simply call the play address several times a second. How many times per second is determined by offsets 006eh and 006fh in the file. These bytes denote the speed of playback in 1/1000000ths of a second. For the "usual" 60Hz playback rate, set this to 411ah.

To generate a differing playback rate, use this formula:

        1000000

PBRATE= ---------

         speed

Where PBRATE is the value you stick into 006e/006fh in the file, and speed is the desired speed in hertz.

"Proper" way to load the tune

---

1) If the tune is bankswitched, go to #3.

2) Load the data into the 6502's address space starting at the specified

  load address. Go to #4.

3) Load the data into a RAM area, starting at (start_address AND 0fffh).

4) Tune load is done.

"Proper" way to init a tune

---

1) Clear all RAM at 0000h-07ffh.

2) Clear all RAM at 6000h-7fffh.

3) Init the sound registers by writing 00h to 04000-0400Fh, 10h to 4010h,

  and 00h to 4011h-4013h.

4) Set volume register 04015h to 00fh.

5) If this is a banked tune, load the bank values from the header into

  5ff8-5fffh.

6) Set the accumulator and X registers for the desired song.

7) Call the music init routine.

"Proper" way to play a tune

---

1) Call the play address of the music at periodic intervals determined

  by the speed words.  Which word to use is determined by which mode
  you are in- PAL or NTSC.

Sound Chip Support

---

Byte 007bh of the file stores the sound chip flags. If a particular flag is set, those sound registers should be enabled. If the flag is clear, then those registers should be disabled.

• VRCVI Uses registers 9000-9002, A000-A002, and B000-B002, write only.

Caveats: 1) The above registers are *write only* and must not disrupt music

           code that happens to be stored there.

        2) Major caveat:  The A0 and A1 lines are flipped on a few games!!
           If you rip the music and it sounds all funny, flip around 
           the xxx1 and xxx2 register pairs.  (i.e. 9001 and 9002)  9000
           and 9003 can be left untouched.  I decided to do this since it 
           would make things easier all around, and this means you only 
           will have to change the music code in a very few places (6).
           Esper2 and Madara will need this change, while Castlevania 3j
           will not for instance.
        
        3) See my VRCVI.TXT doc for a complete register description.

• VRCVII Uses registers 9010 and 9030, write only.

Caveats: 1) Same caveat as #1, above.

        2) See my VRCVII.TXT doc for a complete register description.

• FDS Sound uses registers from 4040 through 4092.

Caveats: 1) 6000-DFFF is assumed to be RAM, since 6000-DFFF is RAM on the

           FDS.  E000-FFFF is usually not included in FDS games because
           it is the BIOS ROM.  However, it can be used on FDS rips to help
           the ripper (for modified play/init addresses).

        2) Bankswitching operates slightly different on FDS tunes.  
           5FF6 and 5FF7 control the banks 6000-6FFF and 7000-7FFF 
           respectively.  NSF header offsets 76h and 77h correspond to
           *both* 6000-7FFF *AND* E000-FFFF.  Keep this in mind!

• MMC5 Sound Uses registers 5000-5015, write only as well as 5205 and 5206,

           and 5C00-5FF5

Caveats: 1) Generating a proper doc file. Be patient.

        2) 5205 and 5206 are a hardware 8*8 multiplier.  The idea being
           you write your two bytes to be multiplied into 5205 and 5206
           and after doing so, you read the result back out.  Still working
           on what exactly triggers it (I think a write to either 5205
           or 5206 triggers the multiply).

        3) 5C00-5FF5 should be RAM to emulate EXRAM while in MMC5 mode.

Note: Thanks to Mamiya for the EXRAM info.

• Namco 106 Sound Uses registers 4800 and F800.

           This works similar to VRC7.  4800 is the "data" port which is
           readable and writable, while F800 is the "address" port and is
           writable only.

           The address is 7 bits plus a "mode" bit.  Bit 7 controls
           address auto-incrementing.  If bit 7 is set, the address will
           auto-increment after a byte of data is read or written from/to
           4800.

           $40 ffffffff f:frequency L
           $42 ffffffff f:frequency M
           $44 ---sssff f:frequency H s:tone length (8-s)*4 in 4bit-samples
           $46 tttttttt t:tone address(4bit-address,$41 means high-4bits of $20)
           $47 -cccvvvv v:linear volume 1+c:number of channels in use($7F only)
           $40-47:ch1 $48-4F:ch2 ... $78-7F:ch8
           ch2-ch8 same to ch1

           $00-3F(8ch)...77(1ch) hhhhllll tone data
           h:odd address data(signed 4bit)
           l:even address data(signed 4bit)

           real frequency = (f * NES_BASECYCLES) / (40000h * (c+1) * (8-s)*4 * 45)
           NES_BASECYCLES 21477270(Hz)

Note: Very Special thanks to Mamiya for this information!

• Sunsoft FME-07 Sound uses registers C000 and E000

           This is similar to the common AY 3-8910 sound chip that is
           used on tons of arcade machines, and in the Intellivision.

           C000 is the address port
           E000 is the data port

           Both are write-only, and behave like the AY 3-8910.

Note: Special thanks to Mamiya for this information as well

Caveats

---

1) The starting song number and maximum song numbers start counting at

  1, while the init address of the tune starts counting at 0.  To
  "fix", simply pass the desired song number minus 1 to the init
  routine.

2) The NTSC speed word is used *only* for NTSC tunes, or dual PAL/NTSC tunes.

  The PAL speed word is used *only* for PAL tunes, or dual PAL/NTSC tunes.

3) The length of the text in the name, artist, and copyright fields must

  be 31 characters or less!  There has to be at least a single NULL byte
  (00h) after the text, between fields.

4) If a field is not known (name, artist, copyright) then the field must

  contain the string "<?>" (without quotes).  

5) There should be 8K of RAM present at 6000-7FFFh. MMC5 tunes need RAM at

  5C00-5FF7 to emulate its EXRAM. 8000-FFFF Should be read-only (not 
  writable) after a tune has loaded.  The only time this area should be 
  writable is if an FDS tune is being played.

6) Do not assume the state of *anything* on entry to the init routine

  except A and X.  Y can be anything, as can the flags.  

7) Do not assume the state of *anything* on entry to the play routine either.

  Flags, X, A, and Y could be at any state.  I've fixed about 10 tunes
  because of this problem and the problem, above.

8) The stack sits at 1FFh and grows down. Make sure the tune does not

  attempt to use 1F0h-1FFh for variables. (Armed Dragon Villigust did and
  I had to relocate its RAM usage to 2xx)

9) Variables should sit in the 0000h-07FFh area *only*. If the tune writes

  outside this range, say 1400h this is bad and should be relocated. 
  (Terminator 3 did this and I relocated it to 04xx).

That's it!