emulator: Gearsystem
type: libretro
core_classification: official_port
source: "https://github.com/drhelius/Gearsystem"
upstream: "https://github.com/drhelius/Gearsystem"
profiled_date: "2026-03-23"
core_version: "3.2.0"
display_name: "Sega - MS/GG/SG-1000 (Gearsystem)"
cores:
  - gearsystem
systems:
  - sega-mastersystem
  - sega-gamegear
  - sega-sg1000

notes: |
  Gearsystem is a Sega Master System / Game Gear / SG-1000 emulator by
  Ignacio Sanchez (drhelius). No BIOS is required for normal operation.

  The core supports optional boot ROMs for Master System and Game Gear,
  controlled by core options "gearsystem_bios_sms" and "gearsystem_bios_gg"
  (both disabled by default). Boot ROMs are loaded in load_bootroms()
  from the system directory with fixed filenames.

  SG-1000 and Game Gear in SMS mode have no BIOS support.
  IsBootromEnabled() returns false for both cases.

  When enabled, the boot ROM executes as on original hardware, which may
  cause invalid ROMs to lock or fail to boot entirely.

files:
  # --- Master System boot ROM (optional, behind gearsystem_bios_sms) ---
  - name: "bios.sms"
    system: sega-mastersystem
    required: false
    source_ref: "platforms/libretro/libretro.cpp:414,417 (load_bootroms)"

  - name: "bios.gg"
    system: sega-gamegear
    required: false
    source_ref: "platforms/libretro/libretro.cpp:415,418 (load_bootroms)"

platform_details:
  mastersystem:
    bios_filename: "bios.sms"
    source_ref: "src/Memory.cpp:223-228"
    note: |
      Boot ROM loaded via LoadBootromSMS() -> LoadBootroom(path, false).
      Raw binary read, stored in m_pBootromSMS. Bank count computed as
      Pow2Ceil(size / 0x4000). Memory mapping controlled by port 3E bit 3.

  gamegear:
    bios_filename: "bios.gg"
    source_ref: "src/Memory.cpp:230-235"
    note: |
      Boot ROM loaded via LoadBootromGG() -> LoadBootroom(path, true).
      Raw binary read, stored in m_pBootromGG. Same bank computation.
      Supports standard GG BIOS and Majesco 1KB variant.

  sg1000:
    bios_filename: null
    note: |
      No BIOS support. Memory.cpp:291 returns false from IsBootromEnabled()
      when IsSG1000() or IsGameGearInSMSMode() is true.