Struct Header 

#[non_exhaustive]
pub struct Header {

    pub is_nes2: bool,
    pub mapper_id: u16,
    pub submapper: u8,
    pub prg_size: usize,
    pub chr_size: usize,
    pub mirroring: Mirroring,
    pub region: Region,
    pub console_type: ConsoleType,
    pub vs_ppu_type: VsPpuType,
    pub vs_hardware_type: Option<VsHardwareType>,
    pub extended_console_type: Option<ExtendedConsoleType>,
    pub misc_rom_count: u8,
    pub default_expansion_device: ExpansionDevice,
    pub prg_ram_size: u32,
    pub prg_nvram_size: u32,
    pub chr_ram_size: u32,
    pub chr_nvram_size: u32,
    pub has_battery: bool,
    pub has_trainer: bool,
    pub four_screen: bool,
}

Parsed header view, format-detected.

Every field a 16-byte iNES / NES 2.0 header defines is modelled (since v2.9.8): what is left over are the reserved bits (byte 12 bits 2-7, byte 13 for console types 0 and 2, byte 13 bits 4-7 for console type 3, byte 14 bits 2-7, byte 15 bit 7) and, on an iNES 1.0 header, bytes 8-15, which are not part of that format. serialize_header_preserving keeps all of those.

iNES 1.0. The NES 2.0-only fields hold a fixed value on an iNES 1.0 header, whatever its bytes 8-15 contain (old dumpers wrote signatures there): submapper 0, region NTSC, console_type NES, vs_hardware_type / extended_console_type None, vs_ppu_type VsPpuType::None, misc_rom_count 0, default_expansion_device ExpansionDevice::Unspecified, both NVRAM sizes 0, and the two RAM sizes the nominal values described on each field.

#[non_exhaustive]: outside this crate, build one with Header::default and field assignment (or parse_header), so a field added later is not an API break.

The 5 boolean flags directly mirror the iNES / NES 2.0 wire format and so are not refactorable into an enum without losing parser fidelity.

Fields (Non-exhaustive)

Non-exhaustive structs could have additional fields added in future. Therefore, non-exhaustive structs cannot be constructed in external crates using the traditional Struct { .. } syntax; cannot be matched against without a wildcard ..; and struct update syntax will not work.

is_nes2: bool

True if the file is NES 2.0 (header byte 7 bits 2-3 == 10).

mapper_id: u16

12-bit mapper id (iNES 1.0 fills only the low 8 bits).

submapper: u8

4-bit submapper id (NES 2.0 only; 0 on iNES 1.0).

prg_size: usize

PRG-ROM size in bytes.

chr_size: usize

CHR-ROM size in bytes (0 if cart uses CHR-RAM).

mirroring: Mirroring

Effective initial mirroring.

region: Region

Region from NES 2.0 byte 12; defaults to NTSC for iNES 1.0.

console_type: ConsoleType

Console type from NES 2.0 byte 7; always ConsoleType::Nes for iNES 1.0.

vs_ppu_type: VsPpuType

Vs. System PPU type from NES 2.0 byte 13 low nibble, valid only when console_type == ConsoleType::VsSystem (otherwise VsPpuType::None). Resolves to the output palette + 2C05 quirks via VsPpuType::ppu_palette / VsPpuType::is_2c05. The reserved nibbles ($1, $6, $7, $C-$F) decode as VsPpuType::Rp2C03, so they do not survive a canonical re-encode; serialize_header_preserving keeps them.

vs_hardware_type: Option<VsHardwareType>

Vs. hardware type from NES 2.0 byte 13 high nibble: Some exactly when the header is NES 2.0 and console_type == ConsoleType::VsSystem. Types 5 and 6 are the Vs. DualSystem boards; see Header::is_vs_dual_system.

extended_console_type: Option<ExtendedConsoleType>

Extended console type from NES 2.0 byte 13 low nibble: Some exactly when the header is NES 2.0 and console_type == ConsoleType::Extended.

misc_rom_count: u8

Number of miscellaneous ROMs present (NES 2.0 byte 14 bits 0-1, so 0..=3; 0 on iNES 1.0). The miscellaneous ROM area itself is whatever follows CHR-ROM in the file.

default_expansion_device: ExpansionDevice

Default expansion device (NES 2.0 byte 15 bits 0-6; ExpansionDevice::Unspecified on iNES 1.0).

prg_ram_size: u32

Volatile PRG-RAM size in bytes: NES 2.0 byte 10 low nibble. iNES 1.0 has no size field, so it reports a nominal 8 KiB.

Until v2.9.8 this field held the volatile and non-volatile sizes summed; that total is now Header::prg_ram_window.

prg_nvram_size: u32

Non-volatile (battery-backed) PRG-RAM / EEPROM size in bytes: NES 2.0 byte 10 high nibble. 0 on iNES 1.0, which has no NVRAM split (whether its nominal RAM is battery-backed is Header::has_battery).

chr_ram_size: u32

Volatile CHR-RAM size in bytes: NES 2.0 byte 11 low nibble. iNES 1.0 reports a nominal 8 KiB when there is no CHR-ROM, otherwise 0.

chr_nvram_size: u32

Non-volatile CHR-RAM size in bytes: NES 2.0 byte 11 high nibble. 0 on iNES 1.0. No board in this crate allocates CHR-NVRAM from it.

has_battery: bool

True when battery-backed PRG-RAM is present (header[6] bit 1).

has_trainer: bool

True when a 512-byte trainer follows the header (header[6] bit 2).

four_screen: bool

True when bit 3 of header[6] forces four-screen mode.

Implementations

impl Header

pub const fn prg_ram_window(&self) -> u32

The whole PRG-RAM window a board allocates at $6000-$7FFF: the volatile and non-volatile sizes together. Some carts (StarTropics / MMC6) declare their save RAM only in the NVRAM nibble, so reading the volatile size alone would leave them with none.

pub const fn is_vs_dual_system(&self) -> bool

True when the header names a Vs. DualSystem board (Vs. hardware type 5 or 6). Drives DUAL-system detection; see docs/cartridge-format.md.

Trait Implementations

impl Clone for Header

fn clone(&self) -> Header

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for Header

impl Debug for Header

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for Header

fn default() -> Self

An iNES 1.0 header for mapper 0 with no ROM, horizontal mirroring, and every other field at the value parse_header gives an iNES 1.0 file with all-zero bytes 4-15, so parse_header(&canonical(default)) is the default again.

impl Eq for Header

impl PartialEq for Header

fn eq(&self, other: &Header) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for Header