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.

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Supported games

The core supports all 70 ST-V titles in the database (64 from Mednafen 1.32.1 + 6 additions), including games that require the optional protection/encryption chips. See COMPATIBILITY.md for the per-title status and special-hardware details (315-5881/5838, RAX audio, touchscreen, trackball/medal).

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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-19854.ic8	Asia / Taiwan	a2a13f306c1ce85dc5751ab1210697f9f331f384bcd18662ff85f30c6c41b97b
epr-17952a.ic8	North America	bac5a52794cf424271f073df228e0b0eb042dede6a3b829eb49abf155e7e0137
epr-17954a.ic8	Europe	3e6f91506031badc4ebdf7fe5b4f33180222a369b575522861688d3b27322a68

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Save states & rewind

Save states and RetroArch rewind are fully supported. The state size is computed automatically at first use (typically 5–7 MB depending on the game), so no manual size tuning is required.

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Input mapping

Gamepad (3-button / 6-button games)

Action buttons are mapped ergonomically to face buttons:

RetroArch button	3-button games	6-button games
B	SW1	SW1
A	SW2	SW2
Y	SW3	SW3
X	—	SW4
L1	—	SW5
R1	—	SW6
Start	Start	Start
Select	Insert Coin	Insert Coin
L3 (P1)	Test Button	Test Button
R3 (P1)	Service Button	Service Button
R3 (P2)	Pause Button	Pause Button

Batman Forever (3-button with non-standard wiring): Jump → B, Punch → A, Kick → Y.

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

Tate (vertical cabinet) games are detected automatically from the game database and reported to the frontend via SET_ROTATION. The mednafen_stv_rotation option overrides this for special setups (e.g. a physically-rotated screen).

Touchscreen (Critter Crusher)

Critter Crusher is controlled entirely via RETRO_DEVICE_POINTER:

Input	Action
Pointer move	Move cursor over target
Pointer press / click	Hit
Select	Insert Coin
L3	Test Button
R3	Service Button

Works with mouse (desktop), touchscreen (Android / mobile), or any pointer device the frontend exposes. An optional crosshair overlay shows the current pointer position (see Input options).

Trackball

Trackball games (Hashire Patrol Car, Sky Challenger, Nerae! Super Goal, Technical Bowling) accept three input methods at once — use whichever your controller exposes:

Input	Action
Mouse / real trackball	Roll trackball (1:1, unaffected by sensitivity)
Left or right analog stick	Roll trackball (speed set by sensitivity option)
D-pad	Roll trackball (fallback, speed set by sensitivity option)
B / A / R1	SW1 (A) / SW2 (B) / SW3 (C)
Start	Start
Select	Insert Coin
L3	Test Button
R3	Service Button

Both analog stick indices are read, so the stick works regardless of which index your frontend maps the physical stick to. Roll speed for the analog/D-pad methods is set by mednafen_stv_trackball_sensitivity (see Input options); mouse/real-trackball input is always 1:1.

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Core options

System

Option	Default	Description
mednafen_stv_region	auto	BIOS region: Auto / Japan / North America / Europe / Asia
mednafen_stv_cart	auto	Expansion cart: Auto / None / Backup RAM / 4M RAM / 8M RAM
mednafen_stv_skip_bios	disabled	Skip BIOS boot animation. Restart required.
mednafen_stv_autortc	enabled	Auto-set Real Time Clock from host

Input

Option	Default	Description
mednafen_stv_crosshair	enabled	Show crosshair overlay for touchscreen games (Critter Crusher)
mednafen_stv_crosshair_color	white	Crosshair colour: White / Red / Green / Blue / Yellow / Cyan
mednafen_stv_trackball_sensitivity	100	Roll speed of the analog stick / D-pad for trackball games (25–400%). Higher rolls faster at full deflection. Does not affect mouse / real-trackball input.

Video

Option	Default	Description
mednafen_stv_correct_aspect	enabled	Correct pixel aspect ratio
mednafen_stv_h_overscan	enabled	Show horizontal overscan pixels
mednafen_stv_h_blend	disabled	Horizontal blend filter (anti-dithering)
mednafen_stv_mesh_transparency	disabled	Replace VDP1 stipple (checkerboard) with 50% blend for smoke/shadow/fade effects. 16-bit framebuffer only.
mednafen_stv_deinterlacer	blend	480i handling: Blend (smooth, recommended) / Off (renderer bob) / Weave / Bob / Bob with offset / Blend gamma-correct
mednafen_stv_slstart	8	First displayed NTSC scanline (0 / 2 / 4 / 8)
mednafen_stv_slend	231	Last displayed NTSC scanline (224 / 231 / 234 / 239)
mednafen_stv_rotation	auto	Display rotation. auto follows the game database (TATE games rotated 90°, yoko games unrotated). Force 0 / 90 / 180 / 270 for special setups (e.g. 0 on a physically-rotated screen).

Audio

Option	Default	Description
mednafen_stv_volume	100	Output volume (50–200%). 100 is unchanged; raise it for quiet titles. Above 100% may clip on loud scenes. Applied live, no restart.

Performance

Option	Default	Description
mednafen_stv_frameskip	disabled	Frameskip: disabled / auto / 1–5
mednafen_stv_cpu_cache	data_cb	SH-2 cache emulation: Fast (recommended) / Full (accurate, slow). Restart required.

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Build

CMake (local / x86_64)

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

Cross-compile (e.g. aarch64 / Raspberry Pi)

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

Android (arm64-v8a)

make -f libretro/Makefile.libretro platform=android_arm64

Note on zstd linking: cross-compile uses dynamic libzstd.so; native builds link static libzstd.a to avoid a runtime dependency.

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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)
• Aaron Giles — ADSP-2181 CPU core (MAME adsp2100.cpp, BSD-3-Clause)
• Beetle Saturn authors — libretro wrapper reference
• Beetle PCE Fast authors — geometry / input reference