emulator: SMS Plus GX
type: libretro
source: "https://github.com/libretro/smsplus-gx"
profiled_date: "2026-03-18"
core_version: "1.8"
display_name: "Sega - MS/GG (SMS Plus GX)"
cores:
  - smsplus
systems:
  - sega-master-system
  - sega-game-gear
  - colecovision
  - sega-sg1000

notes: |
  SMS Plus GX is a Sega Master System / Game Gear emulator with additional
  support for ColecoVision, SG-1000 and Sord M5 via TMS9918 VDP emulation.

  BIOS loading happens in bios_init() (smsplus_libretro.c:203-252).
  Two BIOS files are supported:

  1. bios.sms -- Sega Master System boot ROM. Optional. Loaded for all
     console types. A core option "smsplus_sms_bios" (default: disabled)
     controls whether it is used. When set to "auto" and the file exists,
     bios.enabled is set and the SMS boot sequence plays before games.

  2. BIOS.col -- ColecoVision BIOS. Required for ColecoVision ROMs only.
     Loaded into coleco.rom (0x2000 bytes = 8 KB). Without it, ColecoVision
     games will not start and the core logs an error. The filename is
     case-sensitive (uppercase BIOS, lowercase .col).

  Both files are read from the system directory root (no subdirectory).
  Path is built as: system_dir + "/" + filename (smsplus_libretro.c:211,234).

  Console type is auto-detected from ROM file extension:
    .col -> CONSOLE_COLECO
    .sg  -> CONSOLE_SG1000
  Or forced via the "smsplus_hardware" core option.

files:
  - name: "bios.sms"
    system: sega-master-system
    description: "Sega Master System boot ROM"
    required: false
    source_ref: "smsplus_libretro.c:211-229"
    notes: |
      Loaded into bios.rom (up to 1 MB allocated). Only active when the
      core option smsplus_sms_bios is set to "auto". Displays the Sega
      Master System startup screen before game execution.

  - name: "BIOS.col"
    system: colecovision
    description: "ColecoVision BIOS ROM"
    required: true
    size: 8192
    source_ref: "smsplus_libretro.c:232-248"
    notes: |
      Required for ColecoVision games. Read as 0x2000 (8192) raw bytes
      into coleco.rom. Without this file, retro_load_game() returns false
      when loading .col files. Filename is case-sensitive on Linux.

platform_details:
  bios_mapping:
    sms:
      target: "bios.rom buffer, mapped via slot system"
      source_ref: "smsplus_libretro.c:208-229, source/memz80.c"
      notes: |
        When bios.enabled has both bits set (file present + option enabled),
        the BIOS ROM is paged into the Z80 address space at startup. The
        BIOS executes the boot animation, then hands off to the cartridge.
    coleco:
      target: "coleco.rom, mapped at 0x0000-0x1FFF"
      source_ref: "smsplus_libretro.c:245, source/memz80.c"
      notes: |
        The ColecoVision BIOS provides the interrupt handler, I/O routines
        and startup code. Mapped into the first 8 KB of Z80 address space.

  console_detection:
    source_ref: "smsplus_libretro.c:605-609, source/loadrom.c:402"
    notes: |
      File extension .col forces CONSOLE_COLECO with MAPPER_NONE.
      Extension .sg forces CONSOLE_SG1000.
      The core option smsplus_hardware can override to: master system,
      master system II, game gear, game gear (sms compatibility), coleco.