emulator: Meteor GBA
type: libretro
source: "https://github.com/libretro/meteor-libretro"
cores:
  - meteor
systems:
  - nintendo-gba

notes: |
  Meteor is a Game Boy Advance emulator by Philippe Daouadi (2009-2011).

  The libretro port does NOT load or use any external BIOS file. The core has
  a complete HLE BIOS implementation (ameteor/source/bios.cpp) that handles
  GBA SWI calls directly in C++. When no real BIOS is loaded (HasBios() returns
  false), Cpu::SoftwareInterrupt() dispatches SWI calls to the HLE handlers
  instead of executing the BIOS ROM (ameteor/source/cpu.cpp:244-311).

  The standalone frontends (GTK, text) expose LoadBios() for optional real BIOS
  loading, but the libretro port (libretro/libretro.cpp) never calls LoadBios()
  and never queries RETRO_ENVIRONMENT_GET_SYSTEM_DIRECTORY. The retro_load_game()
  function only loads the ROM via LoadRom().

  HLE SWI coverage: SoftReset (0x00), RegisterRamReset (0x01), Halt (0x02),
  IntrWait (0x04), VBlankIntrWait (0x05), Div (0x06), DivArm (0x07),
  Sqrt (0x08), ArcTan (0x09), ArcTan2 (0x0A), CpuSet (0x0B),
  CpuFastSet (0x0C), BgAffineSet (0x0E), ObjAffineSet (0x0F),
  LZ77UnCompWram (0x11), LZ77UnCompVram (0x12), HuffUnComp (0x13),
  RLUnCompWram (0x14), RLUnCompVram (0x15).

  Missing from HLE: Stop (0x03), BitUnPack (0x10), Diff8bitUnFilter (0x16-0x17),
  Diff16bitUnFilter (0x18), SoundBias (0x19), SoundDriverInit (0x1A-0x1F),
  MidiKey2Freq (0x1F), SoundDriverVSyncOff/On (0x28-0x29), GetBiosChecksum (0x0D).

  The BIOS memory region (0x00000000-0x00003FFF, 16 KB) is allocated only if
  LoadBios() is called. Memory reads to this region return BIOS protection values
  (0x0E for 8-bit, 0xF00E for 16-bit, 0xE1B0F00E for 32-bit) when no BIOS is
  loaded and PC is outside the BIOS area.

  Bios000h() (entry point) initializes stack pointers and jumps to 0x08000004,
  matching real GBA hardware boot sequence. In the libretro port, retro_reset()
  resets all units except BIOS and ROM memory.

files: []

platform_details:
  gba:
    bios_size: 16384  # 0x4000
    hle_bios: true
    source_ref: "ameteor/source/bios.cpp, ameteor/source/cpu.cpp:244-311"
    notes: |
      Full HLE BIOS. The libretro port never loads an external BIOS file.
      Cpu::SoftwareInterrupt() checks HasBios() -- if false (always in libretro),
      SWI calls are routed to C++ reimplementations. If a real BIOS were loaded
      (standalone only), execution would go through the actual BIOS ROM code via
      SoftwareInterrupt() -> branch to 0x08.