emulator: jgenesis
type: standalone
core_classification: other
source: "https://github.com/jsgroth/jgenesis"
upstream: "https://github.com/jsgroth/jgenesis"
profiled_date: "2026-08-08"
source_commit: "db1bec7392704aa0ecc2bbbb5ac751fec3c485a0"
core_version: "0.14.0"
display_name: "Multi-System (jgenesis)"
cores:
  - jgenesis
systems:
  - sega-megadrive
  - sega-megacd
  - sega-32x
  - sega-mastersystem
  - sega-gamegear
  - sega-sg1000
  - nintendo-nes
  - nintendo-snes
  - nintendo-gb
  - nintendo-gbc
  - nintendo-gba
  - nec-pc-engine
mode: standalone

notes: |
  Multi-system emulator written in Rust by James Groth. One binary covers
  thirteen hardware modes: Master System, Game Gear, SG-1000, Genesis, Sega CD,
  32X, Sega CD 32X, NES, SNES, Game Boy, Game Boy Color, Game Boy Advance and
  PC Engine (frontend/jgenesis-native-driver/src/extensions.rs:172-187).

  No path is hardcoded. Every BIOS, boot ROM and coprocessor ROM is an
  Option<PathBuf> in the config, defaulting to None and set through a file
  dialog or the TOML config file (frontend/jgenesis-native-driver/src/config.rs
  :76-78,95-99,146-159,191-193,205). The emulator identifies these files by
  size and layout, never by name or hash, so the names below are the ones the
  dumps circulate under rather than strings read from the source. RetroBat
  writes bios_CD_U/E/J.bin and gba_bios.bin into the TOML directly
  (retrobat emulatorLauncher/Generators/Jgenesis.Generator.cs:226-229,283-294).

  Sega CD selects the BIOS by disc region and per_region_bios defaults to true,
  so the US, European and Japanese images are each reachable
  (frontend/jgenesis-native-driver/src/mainloop/genesis.rs:215-244,
  frontend/jgenesis-native-config/src/genesis.rs:117). Setting "Use US BIOS for
  all regions" collapses all three onto the US slot.

  SNES coprocessor ROMs use the merged layout, program ROM followed by data ROM
  in one file, not the split .program.rom / .data.rom pair. Program ROM
  endianness is auto-detected from the first four opcodes, so either byte order
  of a given dump loads (backend/snes-coprocessors/src/upd77c25.rs:382-390,405-419).
  There is one DSP slot for DSP-1: guess_dsp_variant only returns Dsp1, Dsp2,
  Dsp3 or Dsp4, and DSP-1B titles fall through to the DSP-1 slot
  (backend/snes-core/src/memory/cartridge.rs:926-936). None of the seven chips
  has an HLE implementation, so an affected game refuses to load when its slot
  is empty.

  32X needs no user file. The two SH-2 boot ROMs and the 68000 vector table are
  compiled into the binary (backend/s32x-core/src/bootrom.rs:3-6). A Sega CD
  BIOS is only consulted when the hardware mode is Sega CD or Sega CD 32X.

  NES, SG-1000 and PC Engine need no BIOS. PC Engine has no CD-ROM² support, so
  no System Card is involved. CX4, SA-1, S-DD1, SPC7110, Super FX, OBC1 and the
  S-RTC are emulated from cartridge data alone and take no firmware file.

  Written by the emulator, not obtained: save files, save states, the per-game
  cheats TOML in its own serde format (frontend/jgenesis-native-config/src/lib.rs
  :215,244-275) and the config file itself. The GUI exports a palette to
  nespalette.pal (frontend/jgenesis-gui/src/app/nes.rs:428-430). portable.txt is
  tested for existence only, to keep the settings beside the executable
  (frontend/jgenesis-native-config/src/paths.rs:57-64).

files:
  # -------------------------------------------------------
  # Sega CD
  # -------------------------------------------------------
  - name: "bios_CD_U.bin"
    system: sega-megacd
    description: "Sega CD BIOS (US)"
    region: [north-america]
    required: true
    mode: standalone
    size: 131072
    validation: [size]
    source_ref: "frontend/jgenesis-native-driver/src/mainloop/genesis.rs:39-49 (read), frontend/jgenesis-native-driver/src/mainloop/genesis.rs:238-244 (bios_path_for_region), backend/segacd-core/src/api.rs:77-79 (BIOS_LEN check)"
    note: "Selected when the disc region is Americas, and for every region when per_region_bios is off."

  - name: "bios_CD_E.bin"
    system: sega-megacd
    description: "Mega CD BIOS (Europe)"
    region: [europe]
    required: true
    mode: standalone
    size: 131072
    validation: [size]
    source_ref: "frontend/jgenesis-native-driver/src/mainloop/genesis.rs:238-244 (eu_bios_path), backend/segacd-core/src/api.rs:77-79"

  - name: "bios_CD_J.bin"
    system: sega-megacd
    description: "Mega CD BIOS (Japan)"
    region: [japan]
    required: true
    mode: standalone
    size: 131072
    validation: [size]
    source_ref: "frontend/jgenesis-native-driver/src/mainloop/genesis.rs:238-244 (jp_bios_path), backend/segacd-core/src/api.rs:77-79"

  # -------------------------------------------------------
  # Game Boy Advance
  # -------------------------------------------------------
  - name: "gba_bios.bin"
    system: nintendo-gba
    description: "Game Boy Advance BIOS"
    required: true
    mode: standalone
    size: 16384
    validation: [size]
    source_ref: "frontend/jgenesis-native-driver/src/mainloop/gba.rs:29-33 (GbaNoBios), backend/gba-core/src/memory.rs:10,102-107 (BIOS_ROM_LEN check)"
    note: "Every GBA load fails without it. skip_bios_animation only skips the intro, the BIOS is still mapped and read for SWI calls."

  # -------------------------------------------------------
  # SNES coprocessor firmware (merged program+data layout)
  # -------------------------------------------------------
  - name: "dsp1.rom"
    aliases: ["SNES_dsp1.rom"]
    system: nintendo-snes
    description: "NEC uPD77C25 firmware for DSP-1"
    required: true
    mode: standalone
    size: 8192
    source_ref: "backend/snes-core/src/memory/cartridge.rs:336-353 (MissingDsp1Rom), backend/snes-coprocessors/src/upd77c25.rs:28-31,35-38,382-390"
    note: "0x1800 program plus 0x800 data. Also used by DSP-1B titles, which have no separate slot. Layout is sliced at a fixed offset, size is not checked."

  - name: "dsp2.rom"
    aliases: ["SNES_dsp2.rom"]
    system: nintendo-snes
    description: "NEC uPD77C25 firmware for DSP-2"
    required: true
    mode: standalone
    size: 8192
    source_ref: "backend/snes-core/src/memory/cartridge.rs:340-342 (MissingDsp2Rom), :929 (Dungeon Master CRC32 match), backend/snes-coprocessors/src/upd77c25.rs:382-390"

  - name: "dsp3.rom"
    aliases: ["SNES_dsp3.rom"]
    system: nintendo-snes
    description: "NEC uPD77C25 firmware for DSP-3"
    required: true
    mode: standalone
    size: 8192
    source_ref: "backend/snes-core/src/memory/cartridge.rs:343-345 (MissingDsp3Rom), :931 (SD Gundam GX CRC32 match), backend/snes-coprocessors/src/upd77c25.rs:382-390"

  - name: "dsp4.rom"
    aliases: ["SNES_dsp4.rom"]
    system: nintendo-snes
    description: "NEC uPD77C25 firmware for DSP-4"
    required: true
    mode: standalone
    size: 8192
    source_ref: "backend/snes-core/src/memory/cartridge.rs:346-348 (MissingDsp4Rom), :933 (Top Gear 3000 CRC32 match), backend/snes-coprocessors/src/upd77c25.rs:382-390"

  - name: "st010.rom"
    aliases: ["SNES_st010.rom"]
    system: nintendo-snes
    description: "NEC uPD96050 firmware for ST010"
    required: true
    mode: standalone
    size: 53248
    source_ref: "backend/snes-core/src/memory/cartridge.rs:294-305 (MissingSt010Rom), :938-943 (variant detection), backend/snes-coprocessors/src/upd77c25.rs:28-31,35-38"
    note: "0xC000 program plus 0x1000 data. Used by F1 ROC II."

  - name: "st011.rom"
    aliases: ["SNES_st011.rom"]
    system: nintendo-snes
    description: "NEC uPD96050 firmware for ST011"
    required: true
    mode: standalone
    size: 53248
    source_ref: "backend/snes-core/src/memory/cartridge.rs:298-300 (MissingSt011Rom), :938-943 (Hayazashi Nidan Morita Shougi CRC32 match)"

  - name: "st018.rom"
    aliases: ["SNES_st018.rom"]
    system: nintendo-snes
    description: "ARM firmware for ST018"
    required: true
    mode: standalone
    min_size: 163840
    validation: [size]
    source_ref: "backend/snes-core/src/memory/cartridge.rs:310-320 (MissingSt018Rom), backend/snes-coprocessors/src/st018.rs:18-22,346-352 (TOTAL_ROM_LEN check)"
    note: "0x20000 program plus 0x8000 data. Used by Hayazashi Nidan Morita Shougi 2. Files larger than the expected length are accepted, shorter ones are rejected."

  # -------------------------------------------------------
  # Master System / Game Gear
  # -------------------------------------------------------
  - name: "bios.sms"
    system: sega-mastersystem
    description: "Master System BIOS"
    required: false
    mode: standalone
    source_ref: "frontend/jgenesis-native-driver/src/mainloop/smsgg.rs:27-33,50-56,74-80,112-122, backend/smsgg-core/src/memory.rs:101-106,148-168"
    note: "Read only when sms_boot_from_bios is enabled or the emulator runs without a cartridge, both off by default. One slot accepts any regional dump, no size or content check."

  - name: "bios.gg"
    system: sega-gamegear
    description: "Game Gear BIOS"
    required: false
    mode: standalone
    source_ref: "frontend/jgenesis-native-driver/src/mainloop/smsgg.rs:27-33,50-56,74-80,112-122"
    note: "Read only when gg_boot_from_bios is enabled or the emulator runs without a cartridge, both off by default."

  # -------------------------------------------------------
  # Game Boy / Game Boy Color
  # -------------------------------------------------------
  - name: "dmg_boot.bin"
    system: nintendo-gb
    description: "Game Boy boot ROM"
    required: false
    mode: standalone
    size: 256
    validation: [size]
    source_ref: "frontend/jgenesis-native-driver/src/mainloop/gb.rs:29-33,77-89, backend/gb-core/src/memory.rs:9,45-63 (DMG_BOOT_ROM_LEN check)"
    note: "Loaded only when dmg_boot_rom is enabled, off by default. Without it the CPU starts post-boot."

  - name: "cgb_boot.bin"
    system: nintendo-gbc
    description: "Game Boy Color boot ROM"
    required: false
    mode: standalone
    min_size: 2048
    max_size: 2304
    validation: [size]
    source_ref: "frontend/jgenesis-native-driver/src/mainloop/gb.rs:34-38, 77-89, backend/gb-core/src/memory.rs:10, 45-63, backend/gb-core/src/memory.rs:164 (CGB_BOOT_ROM_LEN check and pad_cgb_boot_rom)"
    note: "Loaded only when cgb_boot_rom is enabled, off by default. 2304 bytes is taken as is, 2048 bytes gets the filler page inserted."

  # -------------------------------------------------------
  # NES
  # -------------------------------------------------------
  - name: "nes.pal"
    aliases: ["nespalette.pal"]
    system: nintendo-nes
    description: "External NES color palette"
    required: false
    mode: standalone
    min_size: 192
    max_size: 1536
    validation: [size]
    source_ref: "config/nes-config/src/lib.rs:92-109 (NesPalette::read_from), frontend/jgenesis-gui/src/app/nes.rs:407-417"
    note: "1536 bytes gives 512 colors, 192 bytes gives 64 colors extrapolated to 512. Smaller files are rejected and the built-in palette stays in use."