emulator: BlastEm
type: standalone + libretro
core_classification: official_port
source: "https://github.com/libretro/blastem"
upstream: "https://www.retrodev.com/blastem/"
profiled_date: "2026-03-23"
core_version: "v0.6.3-pre"
display_name: "Sega - Mega Drive - Genesis (BlastEm)"
cores:
  - blastem
systems:
  - sega-megadrive
  - sega-mastersystem

notes: |
  BlastEm is a cycle-accurate Sega Mega Drive/Genesis emulator with basic
  Master System support. In standalone mode it supports TMSS ROM loading and
  multiple hardware models (MD1 VA0 through MD3 VA2, Teradrive). The Jaguar
  emulator (blastjag) is a separate standalone binary, not part of the
  libretro core.

  The libretro port (libblastem.c) does NOT expose any core options and
  defaults to model md1va3 which has TMSS disabled. There is no way to
  select a TMSS-enabled model through the libretro interface.

  Even if a TMSS-enabled model were forced, read_bundled_file() in the
  libretro build only serves rom.db and returns NULL for tmss.md, so TMSS
  ROM loading would fail (fatal_error at genesis.c:1923).

  Sega CD / Mega CD is not supported (only a TODO comment in system.c:16).
  No BIOS files are required or loaded by the libretro core.

files:
  # rom.db is embedded in the libretro binary (libblastem.c:532-542,
  # extern const char rom_db_data[]). The external file is an optional
  # override — .info lists it as firmware0_opt=true.
  # .info sha1 E5414FB1C4CC7D7F5101C07E4547316779BA3D97 does not match
  # the version in our repo (sha1 02c287d1...) — rom.db changes between
  # BlastEm releases.
  - name: rom.db
    system: sega-megadrive
    required: false
    hle_fallback: true
    note: "ROM feature database (game-specific mapper/save config). Embedded in core, external is optional override."
    source_ref: "libblastem.c:532-542 read_bundled_file()"

  # TMSS ROM — only used in standalone mode with tmss-enabled model
  # libretro build returns NULL for tmss.md (libblastem.c:541)
  - name: tmss.md
    system: sega-megadrive
    required: false
    mode: standalone
    size: 2048
    note: "TMSS startup ROM. Standalone only (models md1va6, md2va1+). Libretro core uses md1va3 (tmss off), no way to change."
    source_ref: "genesis.c:1910-1923"

analysis:
  tmss:
    standalone_support: true
    libretro_support: false
    default_model: md1va3
    default_tmss: "off"
    rom_filename: tmss.md
    rom_size: 2048  # 2 KB
    config_path: "system\0tmss_path\0"
    source_ref: "genesis.c:1910"
    note: |
      TMSS ROM is loaded from tmss.md (configurable via system/tmss_path).
      Models with tmss=on: md1va6, md2va1, md2va2, md3va1, md3va2.
      Models with tmss=off: md1va0, md1va3 (default), teradrive.
      The libretro build uses md1va3 (tmss off) with no option to change.

  sega_cd:
    supported: false
    source_ref: "system.c:16"
    note: "TODO comment only: 'Differentiate between vanilla Genesis and Sega CD/32X games'"

  jaguar_bios:
    libretro_relevant: false
    note: |
      blastjag (jaguar.c) is a separate standalone binary, not compiled
      into the libretro core. Requires BIOS as first CLI argument.