emulator: Gearsystem
type: libretro
source: "https://github.com/drhelius/Gearsystem"
profiled_date: "2026-03-18"
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 has no BIOS support. IsBootromEnabled() in Memory.cpp explicitly
  returns false when a SG-1000 cartridge is detected.

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

  Note: gearcoleco, geargrafx, and gearlynx are separate emulators by the
  same author covering ColecoVision, PC Engine, and Atari Lynx respectively.
  They are not part of Gearsystem.

files:
  # --- Master System boot ROM (optional, behind gearsystem_bios_sms) ---
  - name: "bios.sms"
    system: sega-mastersystem
    description: "Master System boot ROM"
    required: false
    source_ref: "platforms/libretro/libretro.cpp:414 (load_bootroms)"
    notes: "Loaded from system directory. Core option gearsystem_bios_sms must be set to Enabled. No size or hash validation performed by the core."

  # --- Game Gear boot ROM (optional, behind gearsystem_bios_gg) ---
  - name: "bios.gg"
    system: sega-gamegear
    description: "Game Gear boot ROM"
    required: false
    source_ref: "platforms/libretro/libretro.cpp:415 (load_bootroms)"
    notes: "Loaded from system directory. Core option gearsystem_bios_gg must be set to Enabled. No size or hash validation performed by the core."

platform_details:
  mastersystem:
    bios_filename: "bios.sms"
    source_ref: "src/Memory.cpp:222-228"
    notes: |
      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:230-234"
    notes: |
      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
    notes: |
      No BIOS support. Memory.cpp:291 returns false from IsBootromEnabled()
      when IsSG1000() is true.