UNIF

UNIF (Universal NES Image Format) is a differently constrained and more descriptive format for holding NES and Famicom ROM images. It has not really caught on due to network effects. Nonetheless, certain games can only be stored as UNIF.

Since the standard has not been updated since 2000, this has not been updated to reflect more recent findings.

Format

UNIF images start with a 32-byte header:

 offset  length(bytes)  value
      0       4         "UNIF"
      4       4         le32, minimum version number required to parse all chunks in file
      8      28         all nuls

Followed by any number of Type+Length+Value blocks:

 offset  length(bytes)  value
      0       4         Type, varies, defined below
      4       4         le32, length
      8     length      content encoding varies by type

Types

The following Types are known:

Type	Length	Minimum version required	encoding	content meaning
MAPR	variable	1	null-terminated ASCII	A unique human-readable identifier specifying the exact hardware used; not an iNES mapper number, and not a full text description of the mapper; required
PRGn	variable, should be power of two	4	raw	the contents of the nth PRG ROM; at least PRG0 is required; n is in hexadecimal
CHRn	variable, should be power of two	4	raw	the contents of the nth CHR ROM
PCKn	4	5	le32	the CRC-32 of the nth PRG ROM
CCKn	4	5	le32	the CRC-32 of the nth CHR ROM
NAME	variable	1	null-terminated ASCII	the name of the game
WRTR	variable	unknown	null-terminated ASCII	unofficial? the name of the dumping software. Should be in the DINF Type instead
READ	variable	1	null-terminated ASCII	comments about the game, especially licensing information for homebrew
DINF	204	2	special	Dumping information- offset length(bytes) value 0 100 ASCIIZ dumper name 100 1 day-of-month of dump 101 1 month-of-year of dump 102 2 year of dump 104 100 ASCIIZ the name of the dumping software or mechanism
TVCI	1	6	byte	TV standard compatibility information- 0. NTSC only 1. PAL only 2. compatible with both
CTRL	1	7	byte	Controllers usable by this game (bitmask) 1. Joypad 2. Zapper 4. R.O.B. 8. Arkanoid 16. Power Pad 32. Fourscore 64. expansion (leave cleared) 128. expansion (leave cleared)
BATR	1	5	byte	Boolean specifying whether the RAM is battery-backed.
VROR	1	5	byte	Boolean specifying whether CHRn should be ignored and replaced with RAM
MIRR	1	5	byte	What CIRAM A10 is connected to: 0. PPU A11 (horizontal mirroring) 1. PPU A10 (vertical mirroring) 2. Ground (one-screen A) 3. Vcc (one-screen B) 4. Extra memory has been added (four-screen "mirroring") 5. Mapper controlled

Shortcomings

MAPR chunks are nominally supposed to use the text on the PCB. However, the same PCB can have different incompatible behavior, depending on how or what things are populated or jumpered. The workaround has been to add extra text the MAPR chunk (in this case, "HVC-UNROM+74HC08"). Some games have no identifying text on the PCB at all. Other games have only symbols in Japanese or Chinese.

For greater emulator compatibility, people sometimes use already-known-supported MAPR chunks to get something that's "close enough", rather than specifying a new MAPR for not-necessarily-identical behavior.

CTRL chunks do not specify which controller should be plugged into which port nor Famicom-only controllers.

BATR chunks do not disambiguate which RAM is battery-backed, if more than one is present.

There is no ability to specify PRG-RAM or CHR-RAM outside of the MAPR chunk. Two VRC4 using games use the exact same PCB, but one has 2KB PRG-RAM and the other doesn't.

References

Last published version of the standard: http://libunif.googlecode.com/files/UNIF_current.txt