rgbfix(1) — Game Boy checksum fixer

SYNOPSIS

rgbfix

[-CcjsVv] [-f fix_spec] [-i game_id] [-k licensee_str] [-l licensee_id] [-m mbc_type] [-n rom_version] [-p pad_value] [-r ram_size] [-t title_str] file

DESCRIPTION

The rgbfix program changes headers of Game Boy ROM images. It also performs other filetype operations, such as truncation. The arguments are as follows:

-C

Set the Game Boy Color–only flag: 0x143 = 0xC0. If both this and the -c flag are set, this takes precedence.

-c

Set the Game Boy Color–compatible flag: 0x143 = 0x80. If both this and the -C flag are set, -C takes precedence.

-f fix_spec

Fix certain header values that the Game Boy checks for correctness. Alternatively, intentionally trash these values by writing their binary inverse instead. fix_spec is a string containing any combination of the following characters:

l

Fix the Nintendo logo (0x104–0x133).

L

Trash the Nintendo logo.

h

Fix the header checksum (0x14D).

H

Trash the header checksum.

g

Fix the global checksum (0x14E–0x14F).

G

Trash the global checksum.

-i game_id

Set the game ID string (0x13F–0x142) to a given string of exactly 4 characters. If both this and the title are set, the game ID will overwrite the overlapping portion of the title.

-j

Set the non-Japanese region flag: 0x14A = 1.

-k licensee_str

Set the new licensee string (0x144–0x145) to a given string, truncated to at most two characters.

-l licensee_id

Set the old licensee code, 0x14B, to a given value from 0 to 0xFF. This value is deprecated and should be set to 0x33 in all new software.

-m mbc_type

Set the MBC type, 0x147, to a given value from 0 to 0xFF.

-n rom_version

Set the ROM version, 0x14C, to a given value from 0 to 0xFF.

-p pad_value

Pad the image to a valid size with a given pad value from 0 to 0xFF. rgbfix will automatically pick a size from 32KiB, 64KiB, 128KiB, ..., 8192KiB and give a warning thereafter. The cartridge size byte (0x148) will be changed to reflect this new size.

-r ram_size

Set the RAM size, 0x149, to a given value from 0 to 0xFF.

-s

Set the SGB flag: 0x146 = 3.

-t title

Set the title string (0x134–0x143) to a given string, truncated to at most 16 characters. It is recommended to use 15 characters instead, to avoid clashing with the CGB flag (-c or -C). If both this and the game ID are set, the game ID will overwrite the overlapping portion of the title.

-V

Print the version of the program and exit.

-v

Equivalent to -f lhg.

EXAMPLES

Most values in the ROM header are only cosmetic. The bare minimum requirements for a workable image are checksums, the Nintendo logo, and (if needed) the CGB/SGB flags. It is a good idea to pad the image to a valid size as well (“valid” meaning a multiple of 32KiB).

The following will make a plain, no-color Game Boy game without checking for a valid size:

$ rgbfix -v foo.gb

The following will make a SGB-enabled, color-enabled game with a title of “foobar”, and pad it to a multiple of 32KiB. (The Game Boy itself does not use the title, but some emulators or ROM managers might.)

$ rgbfix -vcs -l 0x33 -p 0 -t foobar baz.gb

The following will duplicate the header (sans global checksum) of the game “Survival Kids”:

$ rgbfix -cjsv -k A4 -l 0x33 -m 0x1B -p 0xFF -r 3 -t SURVIVALKIDAVKE SurvivalKids.gbc

SEE ALSO

rgbasm(1), rgblink(1), rgbds(7)

HISTORY

rgbfix was originally released by Carsten Sørensen as a standalone program called gbfix, and was later packaged in RGBDS by Justin Lloyd. It is now maintained by a number of contributors at https://github.com/rednex/rgbds.