jgenesis - RetroBIOS

Type	standalone
Classification	Other
Source	https://github.com/jsgroth/jgenesis
Version	0.14.0
Profiled	2026-08-08
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

Technical 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:172-186).

No path is hardcoded. Every BIOS, boot ROM and coprocessor ROM is an Option 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 (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:233-262, frontend/jgenesis-native-config/src/genesis.rs:115). 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).

16 files | 11 required, 5 optional | 9 in repo, 7 missing

bios_CD_U.bin required in repo standalone north-america
Sega CD BIOS (US)

• System: sega-megacd
• Size: 128.0 KB
• Validation: size
• Source: frontend/jgenesis-native-driver/src/mainloop/genesis.rs:41-51, frontend/jgenesis-native-driver/src/mainloop/genesis.rs:256-262, backend/segacd-core/src/api.rs:77-79
• Platforms: batocera, emudeck, lakka, recalbox, retroarch, retrobat, retrodeck, retropie, rocknix, romm
• Selected when the disc region is Americas, and for every region when per_region_bios is off.

bios_CD_E.bin required in repo standalone europe
Mega CD BIOS (Europe)

• System: sega-megacd
• Size: 128.0 KB
• Validation: size
• Source: frontend/jgenesis-native-driver/src/mainloop/genesis.rs:256-262, backend/segacd-core/src/api.rs:77-79
• Platforms: batocera, emudeck, lakka, recalbox, retroarch, retrobat, retrodeck, retropie, rocknix, romm

bios_CD_J.bin required in repo standalone japan
Mega CD BIOS (Japan)

• System: sega-megacd
• Size: 128.0 KB
• Validation: size
• Source: frontend/jgenesis-native-driver/src/mainloop/genesis.rs:256-262, backend/segacd-core/src/api.rs:77-79
• Platforms: batocera, emudeck, lakka, recalbox, retroarch, retrobat, retrodeck, retropie, rocknix, romm

gba_bios.bin required in repo standalone
Game Boy Advance BIOS

• System: nintendo-gba
• Size: 16.0 KB
• Validation: size
• Source: frontend/jgenesis-native-driver/src/mainloop/gba.rs:29-33, backend/gba-core/src/memory.rs:10, backend/gba-core/src/memory.rs:102-107
• Platforms: batocera, lakka, recalbox, retroarch, retrobat, retrodeck, retropie, rocknix, romm
• Every GBA load fails without it. skip_bios_animation only skips the intro, the BIOS is still mapped and read for SWI calls.

dsp1.rom required missing standalone
NEC uPD77C25 firmware for DSP-1

• System: nintendo-snes
• Size: 8.0 KB
• Aliases: SNES_dsp1.rom
• Source: backend/snes-core/src/memory/cartridge.rs:336-353, backend/snes-coprocessors/src/upd77c25.rs:28-31, backend/snes-coprocessors/src/upd77c25.rs:35-38, backend/snes-coprocessors/src/upd77c25.rs:382-390
• 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.

dsp2.rom required missing standalone
NEC uPD77C25 firmware for DSP-2

• System: nintendo-snes
• Size: 8.0 KB
• Aliases: SNES_dsp2.rom
• Source: backend/snes-core/src/memory/cartridge.rs:340-342, backend/snes-core/src/memory/cartridge.rs:929, backend/snes-coprocessors/src/upd77c25.rs:382-390

dsp3.rom required missing standalone
NEC uPD77C25 firmware for DSP-3

• System: nintendo-snes
• Size: 8.0 KB
• Aliases: SNES_dsp3.rom
• Source: backend/snes-core/src/memory/cartridge.rs:343-345, backend/snes-core/src/memory/cartridge.rs:931, backend/snes-coprocessors/src/upd77c25.rs:382-390

dsp4.rom required missing standalone
NEC uPD77C25 firmware for DSP-4

• System: nintendo-snes
• Size: 8.0 KB
• Aliases: SNES_dsp4.rom
• Source: backend/snes-core/src/memory/cartridge.rs:346-348, backend/snes-core/src/memory/cartridge.rs:933, backend/snes-coprocessors/src/upd77c25.rs:382-390

st010.rom required missing standalone
NEC uPD96050 firmware for ST010

• System: nintendo-snes
• Size: 52.0 KB
• Aliases: SNES_st010.rom
• Source: backend/snes-core/src/memory/cartridge.rs:294-305, backend/snes-core/src/memory/cartridge.rs:938-943, backend/snes-coprocessors/src/upd77c25.rs:28-31, backend/snes-coprocessors/src/upd77c25.rs:35-38
• 0xC000 program plus 0x1000 data. Used by F1 ROC II.

st011.rom required missing standalone
NEC uPD96050 firmware for ST011

• System: nintendo-snes
• Size: 52.0 KB
• Aliases: SNES_st011.rom
• Source: backend/snes-core/src/memory/cartridge.rs:298-300, backend/snes-core/src/memory/cartridge.rs:938-943

st018.rom required missing standalone
ARM firmware for ST018

• System: nintendo-snes
• Size: min 160.0 KB
• Aliases: SNES_st018.rom
• Validation: size
• Source: backend/snes-core/src/memory/cartridge.rs:310-320, backend/snes-coprocessors/src/st018.rs:18-22, backend/snes-coprocessors/src/st018.rs:346-352
• 0x20000 program plus 0x8000 data. Used by Hayazashi Nidan Morita Shougi 2. Files larger than the expected length are accepted, shorter ones are rejected.

bios.sms optional in repo standalone
Master System BIOS

• System: sega-mastersystem
• Source: frontend/jgenesis-native-driver/src/mainloop/smsgg.rs:27-33, frontend/jgenesis-native-driver/src/mainloop/smsgg.rs:50-56, frontend/jgenesis-native-driver/src/mainloop/smsgg.rs:74-80, frontend/jgenesis-native-driver/src/mainloop/smsgg.rs:112-122, backend/smsgg-core/src/memory.rs:101-106, backend/smsgg-core/src/memory.rs:148-168
• Platforms: lakka, retroarch, retrodeck, retropie, rocknix, romm
• 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.

bios.gg optional in repo standalone
Game Gear BIOS

• System: sega-gamegear
• Source: frontend/jgenesis-native-driver/src/mainloop/smsgg.rs:27-33, frontend/jgenesis-native-driver/src/mainloop/smsgg.rs:50-56, frontend/jgenesis-native-driver/src/mainloop/smsgg.rs:74-80, frontend/jgenesis-native-driver/src/mainloop/smsgg.rs:112-122
• Platforms: lakka, recalbox, retroarch, retrodeck, retropie, rocknix, romm
• Read only when gg_boot_from_bios is enabled or the emulator runs without a cartridge, both off by default.

dmg_boot.bin optional in repo standalone
Game Boy boot ROM

• System: nintendo-gb
• Size: 256 B
• Validation: size
• Source: frontend/jgenesis-native-driver/src/mainloop/gb.rs:29-33, frontend/jgenesis-native-driver/src/mainloop/gb.rs:77-89, backend/gb-core/src/memory.rs:9, backend/gb-core/src/memory.rs:45-63
• Platforms: lakka, recalbox, retroarch, retropie, romm
• Loaded only when dmg_boot_rom is enabled, off by default. Without it the CPU starts post-boot.

cgb_boot.bin optional in repo standalone
Game Boy Color boot ROM

• System: nintendo-gbc
• Size: min 2.0 KB, max 2.2 KB
• Validation: size
• Source: frontend/jgenesis-native-driver/src/mainloop/gb.rs:34-38, frontend/jgenesis-native-driver/src/mainloop/gb.rs:77-89, backend/gb-core/src/memory.rs:10, backend/gb-core/src/memory.rs:45-63, backend/gb-core/src/memory.rs:168
• Platforms: lakka, recalbox, retroarch, retropie, romm
• 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.pal optional in repo standalone
External NES color palette

• System: nintendo-nes
• Size: min 192 B, max 1.5 KB
• Aliases: nespalette.pal
• Validation: size
• Source: config/nes-config/src/lib.rs:92-109, frontend/jgenesis-gui/src/app/nes.rs:407-417
• 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.

Generated on 2026-08-23T16:12:06Z