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Mednafen STV — libretro core

A libretro core for Sega ST-V (Sega Titan Video) arcade hardware, wrapping Mednafen 1.32.1's Saturn/ST-V emulation module.


Supported games

The core supports all 64 ST-V titles in the Mednafen 1.32.1 database, including games that require the optional protection/encryption chips:

315-5881 encryption chip

Game Status
Astra SuperStars `Boot, Imperfect
Final Fight Revenge `Boot, Imperfect
Steep Slope Sliders `Unknown
Tecmo World Cup '98 No Boot
Touryuu Densetsu Elan Doree Unknown

315-5838 compression + encryption chip

Game
Decathlete (V1.000)
Decathlete (V1.001)

The 315-5838 combines Decathlete-specific 16-bit decryption (decipher()) with a 12-level Huffman decompressor. The game uploads tree and dictionary tables at startup via the chip's register interface.

Status: Decathlete graphics are currently not decompressed correctly.

Batman Forever

Status: No sound, because this game use a extra Qsound card


BIOS files

Individual files in the RetroArch system directory, or a single stvbios.zip containing them (TORRENTZIPPED format supported):

File Region SHA-256
epr-20091.ic8 Japan ac778ec04aaa4df296d30743536da3de31281f8ae5c94d7be433dcc84e25d85b
epr-17952a.ic8 North America bac5a52794cf424271f073df228e0b0eb042dede6a3b829eb49abf155e7e0137
epr-17954a.ic8 Europe 3e6f91506031badc4ebdf7fe5b4f33180222a369b575522861688d3b27322a68

Input mapping

The core follows the same button mapping as Beetle Saturn (beetle-saturn-libretro):

RetroArch button Saturn button ST-V function
B A SW1
A B SW2
R1 C SW3
Y X SW4
X Y SW5
L1 Z SW6
L2 L (Left Shoulder)
R2 R (Right Shoulder)
Start Start Start
Select Insert Coin
L3 (P1) Test Button
R3 (P1) Service Button
R3 (P2) Pause Button

Coin insertion uses MDFN_QSimpleCommand(MDFN_MSC_INSERT_COIN) with edge detection (one press = one coin).


Core options

Option Default Description
mednafen_stv_region jp BIOS region (Japan / NA / Europe / Auto)
mednafen_stv_h_overscan enabled Show horizontal overscan pixels
mednafen_stv_h_blend disabled Horizontal blend filter (anti-dithering)
mednafen_stv_correct_aspect enabled Correct pixel aspect ratio
mednafen_stv_slstart 8 First displayed NTSC scanline (0–239)
mednafen_stv_slend 231 Last displayed NTSC scanline (0–239)
mednafen_stv_sound_quality 4 SCSP resampler quality (0=lowest, 4=highest)
mednafen_stv_cpu_cache data_cb SH-2 cache emulation: Fast (recommended) / Data cache only / Full (accurate, slow)
mednafen_stv_bios_sanity enabled Verify BIOS SHA-256 checksums at load
mednafen_stv_autortc enabled Auto-set Real Time Clock from host

Tate (vertical cabinet) games are detected automatically from the game database and reported to the frontend via SET_ROTATION — no manual option required.


Build

CMake (local / x86_64 for testing)

git clone <this-repo>
cd mednafen
cmake -B build_lr
cmake --build build_lr -j$(nproc)
# Output: build_lr/libretro/mednafen_stv_libretro.so

Cross-compile

make -f libretro/Makefile.libretro TARGET_CROSS=aarch64-buildroot-linux-gnu-

Credits

  • Mednafen Team — SS/ST-V emulation core
  • Andreas Naive, Olivier Galibert, David Haywood — 315-5881 cipher research (MAME)
  • David Haywood, Samuel Neves, Peter Wilhelmsen, Morten Shearman Kirkegaard — 315-5838 decompressor (MAME)
  • Beetle Saturn authors — libretro wrapper reference
  • Beetle PCE Fast authors — geometry / input reference

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ST-V libretro core based on Mednafen

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