emulator: "emux (SMS)"
type: libretro
source: "https://github.com/libretro/emux"
profiled_date: "2026-03-19"
core_version: "0.1"
display_name: "Sega - Master System (Emux SMS)"
cores:
  - emux_sms
systems:
  - sms

notes: |
  emux is a multi-system emulator by Sebastien Ronsse, supporting CHIP-8,
  Game Boy, NES, and Sega Master System as separate libretro cores.

  NOT an alias of GearSystem. Completely different codebase.

  BIOS loading in controllers/mapper/sms_mapper.c:
    static char *bios_path = "bios.sms";  (line 33)
    #define BIOS_SIZE 0x2000              (line 7, 8192 bytes)
    sms_mapper->bios = file_map(PATH_SYSTEM, bios_path, 0, BIOS_SIZE);
  If file_map returns NULL, init returns false — core cannot start.
  No HLE fallback, no skip logic.

  BIOS enable/disable via slot control register port write (lines 74-90):
    bios_disable bit in control union. Reset clears bios_disable and
    adds BIOS region to memory map. Writing bios_disable=1 removes
    the BIOS overlay, exposing cartridge ROM underneath.

  Cartridge loading delegated to sega_mapper controller:
    ROM mapped via file_map(PATH_DATA, ...), 16 KB banks (BANK_SIZE=0x4000),
    3 bank slots (NUM_BANKS=3), bank select registers at 0xFFFD-0xFFFF.

  Memory map from mach/sms.c:
    0x0000-0xBFFF  Mapper (BIOS overlay + cartridge ROM banks)
    0xC000-0xDFFF  RAM (8 KB)
    0xE000-0xFFFF  RAM mirror

  The .info declares firmware_count=1, firmware0_opt=false.
  is_experimental=true. No save states, rewind, or netplay support.
  Supported extensions: sms, bms, bin, rom.

  system_directory obtained via RETRO_ENVIRONMENT_GET_SYSTEM_DIRECTORY
  (libretro/libretro.c:23-25), passed as "system-dir" config param.
  BIOS loaded from this directory via PATH_SYSTEM.

files:
  - name: "bios.sms"
    system: sms
    description: "Sega Master System BIOS"
    required: true
    size: 8192
    md5: "840481177270d5642a14ca71ee72844c"
    source_ref: "controllers/mapper/sms_mapper.c:7 (BIOS_SIZE=0x2000), :33 (bios_path), :167-172 (file_map)"
    note: "Mapped at 0x0000, overlays cartridge ROM until bios_disable bit set in slot control register. No HLE — core fails to init without this file."