emulator: a5200
type: libretro
source: "https://github.com/libretro/a5200"
profiled_date: "2026-03-18"
core_version: "2.0.2"
display_name: "Atari - 5200 (a5200)"
cores:
  - a5200
systems:
  - atari-5200

# a5200 is a dedicated Atari 5200 emulator forked from Atari800/Atari++ codebase.
# It loads the official 5200 OS ROM from <system_dir>/5200.rom (2048 bytes, mapped
# to memory at 0xF800-0xFFFF via MEMORY_InitialiseMachine).
#
# If 5200.rom is missing or the user selects "internal" via core option "a5200_bios",
# the core falls back to Altirra 5200 OS, an open-source replacement compiled from
# Altirra-3.20-test4 (altirra_5200_os.c). The fallback has reduced compatibility
# compared to the original Atari OS ROM.
#
# BIOS loading (libretro.c:409-500):
#   1. check_bios_variable() reads core option "a5200_bios" (official/internal)
#   2. load_bios() attempts to read <system_dir>/5200.rom (0x800 bytes)
#   3. On failure or "internal" selected: memcpy from ROM_altirra_5200_os fallback
#
# Cartridge detection (atari.c:169-236):
#   Auto-detects cart type from header bytes and size. ROM database in cartridge.c
#   maps MD5 hashes to cart types (standard 8K/16K/32K/40K, bounty bob, super cart).

files:
  - name: "5200.rom"
    path: "5200.rom"
    size: 2048
    required: false
    hle_fallback: true
    note: >
      Atari 5200 OS ROM. Provides the built-in OS routines used by all 5200
      cartridges. Without it, the core uses the Altirra open-source replacement
      which has lower compatibility with some games. Core option "a5200_bios"
      controls whether to use this file or the internal fallback.
    source_ref: "libretro/libretro.c:58-59, libretro/libretro.c:409-500, emu/memory.c:46"

notes:
  altirra_fallback: >
    The built-in Altirra 5200 OS (from altirra_5200_os.c, 0x800 bytes) is a free
    replacement that works for most games but some titles require the original ROM
    for full compatibility. The core displays a notification when falling back.
  cart_db: >
    cartridge.c contains an MD5-based ROM database for automatic cart type detection
    (standard, EE banked, bounty bob, super cart variants). Unknown ROMs are detected
    by size heuristic.