ROM Header

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Standard header

The following table shows the standard contents of the ROM header. Most of the structure of the header is defined by the IPL3 routines commonly used in commercial games (which are actually contained in the ROM itself); only a few fields are accessed by IPL2 (which is burned in PIF ROM) and are thus hard-coded for all possible valid N64 ROMs.

Offset Size Name Description
0x00 0x4 PI BSD DOM1 Configuration Flags These flags are used by IPL2 to configure access to the ROM (which is mapped in the PI DOM1 space, see memory map). IPL2 first configure the PI to its slowest speed to be able to read these 4 bytes, and then use them to configure the correct speed to access the ROM.

All known commercial games use 80 37 12 40 in these bytes.

These fields could be tuned in replica cartridges to adapt to the actual maximum physical speed that the ROM can be accessed, but please pay attention that many emulators expect to find the 4 "standard" values here and actually use them as a "fixed ID" to detect if the ROM dump was byte-swapped.

If you are an emulator author, please make sure that your emulator can load a ROM with arbitrary values in these first 4 bytes, and assume the ROM is in plain "big-endian" format (not byte swapped, not endian swapped). All modern homebrew ROMs should ship in plain format anyway, as the other formats are obsolete and strongly discouraged.

0x04 0x4 Clock Rate Constant value used by libultra versions 2.0I and earlier, to naively calculate how much real-time has passed based on the CPU's Count register.

The value is masked by 0xFFFFFFF0, then multiplied by 0.75 to account for the CPU clock's multiplier (1.5x) and that the Count register increments every 2 CPU cycles. However, if the masked value equals zero, libultra defaults to 0x03B9ACA0 (62,500,000) before multiplying by 0.75.

All known ROMs, except those listed below, have this field set to 0x0000000F.

Clock Rate libultra ver. Game Code Title
0x03B9ACAF 2.0D NCUP Cruis'n USA (Europe)
0x03B9ACAF 2.0D NCUE Cruis'n USA (USA) (Rev A)
0x03B9ACAF 2.0D NCUE Cruis'n USA (USA) (Rev B)
0x03B9ACAF 2.0D NCUE Cruis'n USA (USA)
0x03A07F5F 2.0G NDMP Doom 64 (Europe)
0x03A07F5F 2.0H NDMJ Doom 64 (Japan)
0x03A07F5F 2.0G NDME Doom 64 (USA) (Rev A)
0x03A07F5F 2.0G NDME Doom 64 (USA)
0x03B9ACAF 2.0G NXGP NBA Hangtime (Europe)
0x03B9ACAF 2.0G NXGE NBA Hangtime (USA)
0x03A07F5F 2.0I NRIP New Tetris, The (Europe)
0x03A07F5F 2.0I NRIE New Tetris, The (USA)
0x03A07F5F 2.0H NQKP Quake 64 (Europe)
0x03A07F5F 2.0H NQKE Quake 64 (USA)
0x03A07F5F 2.0F NFXJ Star Fox 64 (Japan)
0x03A07F5F 2.0H NFXE Star Fox 64 (USA) (Rev A)
0x03A07F5F 2.0H NFXE Star Fox 64 (USA)
0x03A07F5F 2.0D NSWP Star Wars - Shadows of the Empire (Europe)
0x03A07F5F 2.0D NSWE Star Wars - Shadows of the Empire (USA) (Beta)
0x03A07F5F 2.0D NSWE Star Wars - Shadows of the Empire (USA) (Rev A)
0x03A07F5F 2.0D NSWE Star Wars - Shadows of the Empire (USA) (Rev B)
0x03A07F5F 2.0D NSWE Star Wars - Shadows of the Empire (USA)
0x03A07F5F 2.0D NSWJ Star Wars - Teikoku no Kage (Japan)
0x03A07F5F 2.0I NEPP Star Wars Episode I - Racer (Europe) (En,Fr,De)
0x03A07F5F 2.0I NEPJ Star Wars Episode I - Racer (Japan)
0x03A07F5F 2.0I NEPE Star Wars Episode I - Racer (USA)

Using Doom 64 as an example, 0x03A07F5F is masked to 0x03A07F50 (60,850,000), and then multiplied by 0.75 equals 0x02B85F7C (45,637,500).

Keep in mind that there is no known way for software to change the clock frequency used by either the RCP or CPU. So if/when games use the Count register divided by 46,875,000 to measure a real-time second, the calculated result will be inaccurate.

Polprzewodnikowy from the N64brew Discord, experimented with Doom 64 and Star Fox 64 on real hardware. They found that increasing this value increases the delay before the copyright screen or Nintendo logo (respectively) shows up on screen.

0x08 0x4 Boot Address Initial PC in RDRAM. IPL3 will DMA 1 MiB of ROM code from offset 0x1000 to this address when it has finished initializing the hardware, and then jump here to boot the ROM. The most common value for this field is 0x80000400.

The IPL3 for CIC 6103 behaves differently: the value stored here is subtracted by 0x100000 before the jump. For instance, Paper Mario (a game with CIC 6103) contains the value 0x80125C00 in this field, but the actual entry point is 0x80025C00.

The IPL3 for CIC 6106 also behaves differently: the value stored here is subtracted by 0x200000 before the jump.

0x0C 0x4 Libultra Version These 4 bytes are meant to indicate the version of the libultra SDK the ROM was compiled with.
Offset Size Description
0x0 0x2 Reserved, or possibly used to store the patch version.
0x2 0x1 Major and minor version of libultra as decimal value. For instance, version "2.0" is encoded as decimal 20 (hex 0x14).
0x3 0x1 Revision version of libultra, as ASCII letter.

For instance, libultra version "2.0L" is reported as 00 00 14 4C

This field is not used by IPL or anything else, it is just for information; moreover, many games report the wrong version here.

0x10 0x8 Check Code 64-bit check code calculated on 1 Mbyte of ROM contents starting from offset 0x1000 (after IPL3). This check code is computed with a custom algorithm implemented by IPL3 that verifies the integrity of the ROM before booting it. If the check code doesn't match, IPL3 refuses to boot the ROM and hangs the console.

Sometimes, these 8 bytes are referred to as "CRC HI/LO" or "CRC1/2", but the check code algorithm is not a CRC, and splitting it into two 4-byte words seem confusing when it is really a 64-bit value.

To see the exact algorithm used by IPL3, see the source code of the chksum64 tool shipped with libdragon.

0x18 0x8 Reserved This field is unused by Nintendo, but has seen usage by other developers.

For the Conker's Bad Fur Day debug ROM, this field is set to 6F 23 01 3A 2F C9 CB 36. For the Perfect Dark debug ROM, this field is set to 54 E4 D8 38 2F BD 95 36. Since both of these games were made by RAREWARE, this field could be a check code for their Security Dongle hardware, which was required to be able to boot these games on the N64.

Another ROM, the StarCraft 64 beta, also has data in this field. However, it seems to just be random, as the remaining header fields are also set to random values.

0x20 0x14 Game Title String that contains the name of the game. The encoding is usually either ASCII or JIS X 0201 (a subset of Shift-JIS). Padding Is usually performed with 0x20 (ASCII space).
0x34 0x7 Reserved This field is unused by Nintendo, but saw accidental usage in the Tommy Thunder prototype ROM, where the first 4 bytes are set to 0x20. This is possibly due to the developers thinking that the game title field was 0x18 bytes rather than 0x14.
0x3B 0x4 Game Code The game code is 4 ASCII characters that are split up into 3 parts - the category code, the unique code and the destination code.
Offset Size Name Description
0x0 0x1 Category Code An alphanumeric character that specifies the kind of media the game is stored on.
N Game Pak
D 64DD Disk
C Expandable Game: Game Pak Part
E Expandable Game: 64DD Disk Part
Z Aleck64 Game Pak
0x1 0x2 Unique Code Two alphanumeric characters that identify the game.
0x3 0x1 Destination Code An alphanumeric character that specifies the destination the game is intended for.
A All H Netherlands S Spain
B Brazil I Italy U Australia
C China J Japan W Scandinavia
D Germany K Korea X Europe
E North America L Gateway 64 (PAL) Y Europe
F France N Canada Z Europe
G Gateway 64 (NTSC) P Europe
0x3F 0x1 ROM Version This byte is used to identify the version of the game. Normally the value is 0 for the first version, 1 for the second and so on.
0x40 0xFC0 IPL3 This area contains the IPL3 boot code. Each ROM ships its own IPL3 that is meant to work together with the CIC installed in the ROM. Before running IPL3, IPL2 checks its checksum also using a seed coming from the CIC, which binds each IPL3 code to a specific version of CIC.

Advanced Homebrew ROM Header

The Advanced Homebrew ROM Header format is a convention that has been agreed upon in the N64 homebrew community to add additional information in the header, using unused fields. The goal of this convention is to let homebrew ROMs declare the correct saveype and controllers that are expected to play the game. The format has been introduced by the EverDrive 64 flashcard and has been later enhanced by the homebrew community.

This is useful because emulators normally work using a game database which matches games using checksum to find out which savetype and controllers are expected by the game, to help gamers play the game. For instance, when a N64 emulator detects that a Perfect Dark ROM is loaded, it will automatically emulate a 16Kb EEPROM to save the game (that was the original support present in the physical cartridge for the original game), and will possibly also emulate a preinstalled Transfer PAK, as the accessory can be used with the game. This is done purely by matching the Perfect Dark ROM checksum in a database, so a homebrew game, which would probably not be present in game databases, would suffer from non-working saves and possibly wouldn't be able to use special controllers or accessories.

Instead, by using the Advanced Hombrew ROM Header, emulators can automatically configure the required emulated hardware as expected without having to keep any additional database, by simply decoding specific fields of the ROM header. In addition to emulators, also development flashcarts and loaders can use this format to automatically configure the correct savetype when the ROM is loaded.

Homebrew ROM Header special flags

Offset Bytes Name Description
0x34 1 Controller 1 This byte contains the suggested / expected controller hardware that should be attached to port 1.

Values 0x01-0x7F indicate a standard N64 controller, possibly with some installed pak.

Values 0x80-0xFE indicate a different kind of controller.

0x00 No information provided.

Emulators should follow their standard configuration for this port.

0x80 N64 mouse
0x01 N64 controller with Rumble Pak 0x81 VRU
0x02 N64 controller with Controller Pak 0x82 Gamecube controller
0x03 N64 controller with Transfer Pak 0x83 Randnet keyboard
0xFF Nothing attached to this port 0x84 Gamecube keyboard

0x35 1 Controller 2 This byte contains the suggested / expected controller hardware that should be attached to port 2. See byte 0x34 for more information.
0x36 1 Controller 3 This byte contains the suggested / expected controller hardware that should be attached to port 3. See byte 0x34 for more information.
0x37 1 Controller 4 This byte contains the suggested / expected controller hardware that should be attached to port 4. See byte 0x34 for more information.
0x3C 2 Game ID This must contain the ASCII characters "ED". It is used as an ID to identify that the Advanced Homebrew ROM header format Is being used by this ROM.
0x3F 1 Savetype This byte mostly contains information on the savetype. It must be decoded as a bitfield:
Bit Description
0 The game uses the serial RTC (via Joybus)
1 The game is region-free
2 Unused
3 Unused
4-7 Savetype expected by the game. possibile values:

0: None



3: 256K SRAM

4: 768K SRAM (banked)

5: Flash RAM

6: 1M SRAM

Support by emulators

Emulators not listed here do not support the advanced homebrew ROM header format.

Emulator Savetype Controllers
Ares Yes Yes
cen64 Yes No
Parallel Launcher Yes Yes
mupen64plus (core) Yes No
Rosalie's Mupen GUI Yes No

Support by flashcarts

Support by flashcarts can vary depending on the USB loader being used and/or the flashcart operating system. Notice that flashcarts can emulate a specific savetype but have nothing to do with controllers, so the maximum expected support is related to savetype.

Flashcart Loader Current support
64drive 64drive official C tool None
64drive menu None
g64drive Savetype supported
UNFLoader Savetype supported
Everdrive 64 Menu Savetype supported
ed64 None
UNFLoader Savetype supported
SummerCart64 N64FlashcartMenu Savetype supported
sc64deployer Savetype supported
UNFLoader Savetype supported