Genesis Plus GX - RetroBIOS

Type	libretro
Classification	Community forks
Source	https://github.com/libretro/Genesis-Plus-GX
Upstream	https://github.com/ekeeke/Genesis-Plus-GX
Version	v1.7.4
Profiled	2026-03-23
Cores	genesis_plus_gx, genesisplusgx, genesisplusgx-expanded
Systems	sega-megadrive, sega-megacd, sega-mastersystem, sega-gamegear, sega-sg1000, sega-pico

Platform details

megacd: - bootrom_size: 131072 - source_ref: core/cd_hw/scd.h:73 - note: CD boot ROM region is auto-detected from disc image header.

Hardware model detected from boot ROM string at offset 0x120: WONDER-MEGA BOOT -> Wondermega WONDERMEGA2 BOOT -> Wondermega M2 / X'Eye CDX BOOT ROM -> CDX / Multi-Mega

**megadrive:**
- tmss_rom_size: 2048
- source_ref: libretro/libretro.c:3648-3666
- note: TMSS boot ROM validated by checking "GENESIS OS" at offset 0x120.

Only loaded when genesis_plus_gx_bios core option is enabled.

**mastersystem:**
- bios_max_size: 4194304
- source_ref: core/loadrom.c:504-527
- note: BIOS ROM loaded into cart.rom + 0x400000. SEGA mapper assumed

for ROMs larger than 48KB, otherwise no mapper. Region selected based on current region_code setting.

**gamegear:**
- bios_max_size: 4194304
- source_ref: core/loadrom.c:467-489
- note: Handles 1KB Majesco GG BIOS (mapped to $0000-$03FF) and

standard larger BIOS ROMs.

Technical notes

Genesis Plus GX is a Sega 8/16-bit emulator covering SG-1000, Master System, Game Gear, Mega Drive/Genesis, and Mega CD/Sega CD.

BIOS loading is handled by load_bios() in core/loadrom.c. The libretro port resolves filenames from the system directory in libretro/libretro.c:3516-3527.

Mega CD BIOS is required to boot CD images (load fails without it). Master System, Game Gear, and Mega Drive BIOS files are optional boot ROMs gated behind the "genesis_plus_gx_bios" core option (config.bios). Lock-on ROMs (Game Genie, Action Replay, Sonic & Knuckles) are optional and loaded only when the corresponding lock-on feature is enabled.

12 files | 3 required, 9 optional | 12 in repo, 0 missing

bios_CD_U.bin required in repo

• System: sega-megacd
• Source: core/loadrom.c:409
• Platforms: batocera, emudeck, lakka, recalbox, retroarch, retrobat, retrodeck, retropie, romm
• Sega CD (NTSC-U) boot ROM. Loaded for REGION_USA.

bios_CD_E.bin required in repo

• System: sega-megacd
• Source: core/loadrom.c:412
• Platforms: batocera, emudeck, lakka, recalbox, retroarch, retrobat, retrodeck, retropie, romm
• Mega CD (PAL) boot ROM. Loaded for REGION_EUROPE.

bios_CD_J.bin required in repo

• System: sega-megacd
• Source: core/loadrom.c:415
• Platforms: batocera, emudeck, lakka, recalbox, retroarch, retrobat, retrodeck, retropie, romm
• Mega CD (NTSC-J) boot ROM. Loaded for default/Japan region.

bios_U.sms optional in repo

• System: sega-mastersystem
• Source: core/loadrom.c:511
• Platforms: lakka, recalbox, retroarch, retropie, romm
• Master System (NTSC-U) boot ROM. Snail maze game built in.

bios_E.sms optional in repo

• System: sega-mastersystem
• Source: core/loadrom.c:514
• Platforms: lakka, recalbox, retroarch, retropie, romm
• Master System (PAL) boot ROM. Snail maze / Sonic built in.

bios_J.sms optional in repo

• System: sega-mastersystem
• Source: core/loadrom.c:517
• Platforms: lakka, recalbox, retroarch, retrodeck, retropie, romm
• Master System (NTSC-J) boot ROM.

bios.gg optional in repo

• System: sega-gamegear
• Source: core/loadrom.c:480
• Platforms: lakka, recalbox, retroarch, retrodeck, retropie, romm
• Game Gear boot ROM (Majesco 1KB or standard). Shows startup logo.

bios_MD.bin optional in repo

• System: sega-megadrive
• Source: libretro/libretro.c:3651
• Platforms: lakka, recalbox, retroarch, retrodeck, retropie, romm
• Mega Drive TMSS boot ROM. Shows 'Produced by or under license' screen.

ggenie.bin optional in repo

• System: sega-megadrive
• Source: core/cart_hw/ggenie.c:64
• Platforms: lakka, retroarch, retrodeck, retropie, romm
• Game Genie ROM. Loaded when Game Genie lock-on is enabled.

areplay.bin optional in repo

• System: sega-megadrive
• Source: core/cart_hw/areplay.c:64
• Platforms: lakka, retroarch, retrodeck, retropie, romm
• Action Replay (Pro) ROM. Loaded when Action Replay lock-on is enabled.

sk.bin optional in repo

• System: sega-megadrive
• Size: 2.0 MB
• Validation: size
• Source: core/cart_hw/md_cart.c:867
• Platforms: lakka, retroarch, retrodeck, retropie, romm
• Sonic & Knuckles ROM. Required for S&K lock-on feature.

sk2chip.bin optional in repo

• System: sega-megadrive
• Size: 256.0 KB
• Validation: size
• Source: core/cart_hw/md_cart.c:873
• Platforms: lakka, retroarch, retrodeck, retropie, romm
• Sonic & Knuckles UPMEM ROM. Used by Sonic 2 & Knuckles lock-on.

Generated on 2026-04-18T08:05:07Z