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Genesis Plus GX - RetroBIOS
Type libretro
Classification community_fork
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
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 - notes: 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
- notes: 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
- notes: 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
- notes: 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

bios_CD_E.bin -required

bios_CD_J.bin -required

bios_U.sms -optional

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

bios_E.sms -optional

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

bios_J.sms -optional

bios.gg -optional

bios_MD.bin -optional

ggenie.bin -optional

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

areplay.bin -optional

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

sk.bin -optional

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

sk2chip.bin -optional

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

Generated on 2026-03-25T14:56:43Z