![]() Game name field is ASCII characters only.The primary inspiration for the project's creation was the idea that Sonic 3's presentation got a lot of things right that Sonic & Knuckles changed for the worse.The first instruction at a valid reset vector is unlikely to be: brk, cop, stp, wdm, $FF (sbc long).The first instruction at a valid reset vector is likely to be: sei, clc, sec, stz, jmp, jml.A reset vector ![]() Specified ROM size is not smaller than file size.ROM-hacks or homebrews often omit it), additional heuristics may be used to estimate validity: Some flash-carts appear to use only the checksum to distinguish LoROM from HiROM. The primary way to verify a candidate header is to evaluate the checksum it contains. Store checksum ^ $FFFF in the ROM header ($FFDE).Store the checksum in the ROM header ($FFDC or equivalent). ![]() Add every pair of bytes from the prepared data to the checksum, as little-endian 16-bit.These two values will cancel each other out in the checksum process (as would any valid checksum+complement pair). It is recommended to ensure your ROM file's remainder reaches a power of 2 boundary.īecause the ROM header will be part of the computed checksum, before computing the checksum we must normally fill the header's checksum and complement values with $0000 and $FFFF. * This is outside the specification, and emulators are inconsistent about how to pad. Now that the remainder is a power of 2, duplicate it to fill 2x the larger power of 2 from the first part of the ROM.Find the smallest power of 2 greater than or equal to the remainder.Find the largest power of 2 less than or equal to the data size.a 3MB game might use a 2MB ROM and a 1MB ROM together.)īefore calculating the checksum, if the data is not already a power of 2 in size we must duplicate some of the data to fill up to a power of 2 in a way that matches how it will be mirrored in the memory map. Because of this, the data size is often the sum of 2 powers of two. The checksum is computed as if the ROM is a power of two in size, but some SNES games use multiple ROM chips together. Some early games may indicate just $00FFBF by setting $00FFD4 to zero.Įxpansion RAM size: 1 << N kilobytes - for GSU?Ĭhipset subtype, used if chipset is $F0-$FF The expanded header's presence is indicate by putting $33 in $00FFDA, which is the developer ID. When coprocessor is Custom, $FFBF selects from: $Fx - Coprocessor is Custom (specified with $FFBF).$Ex - Coprocessor is Other ( Super Game Boy/ Satellaview).$0x - Coprocessor is DSP ( DSP-1, 2, 3 or 4).$x5 - ROM + coprocessor + RAM + battery.RAM size: 1<<N kilobytes (so 1=2KB, 5=32KB, and so on)Īddress $00FFD5 indicates the ROM speed and map mode.Īddress $00FFD6 indicates what extra hardware is in the cartridge, if any. ROM size: 1<<N kilobytes, rounded up (so 8=256KB, 12=4096KB and so on) ROM speed and memory map mode (LoROM/HiROM/ExHiROM)Ĭhipset (Indicates if a cartridge contains extra RAM, a battery, and/or a coprocessor) See: ROM file formatsĬartridge title (21 bytes uppercase ASCII. This internal ROM header is to be confused with the additional 512-byte headers used by copier devices. Therefore, if it's correctly filled out, an emulator will have a higher chance of being able to figure out where the header is. This means that the location of the header within the actual ROM file will change based on the cartridge's memory map mode - with LoROM games placing it at $007Fxx, HiROM games placing it at $00FFxx, and ExHiROM games placing it at $40FFxx. The header is located at the CPU address range $00FFC0-$00FFDF, right before the interrupt vectors, with an optional second header at $00FFB0-$00FFBF. Homebrew games should also provide a valid header. ![]() However, emulators and flashcarts rely on this header to know how to emulate the game cartridge. This is not needed by the SNES hardware, though the game software can access it as ROM data. Nintendo required SNES developers to include a header in the game's data that describes what hardware the game cartridge contains. ![]()
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