FroggySM

StepMania 3.9 for the Data Frog GB300 and SF2000.

A from-scratch C port of PSPMania's StepMania 3.9, written for low-end MIPS32 hardware. Runs as a libretro core on the Deimos/Multicore firmware.

The PSPMania original is a C++/Rage-framework port that needs the PSP SDK, DirectX, OpenGL, Lua, XML, threads and the PSP's hardware MP3 decoder. None of that exists on a 200 MHz MIPS32 chip with 32 MB of RAM, so this is a fresh, self-contained engine in plain C targeting 320x240 RGB565.

Features

• .sm / MSD chart parsing, all five difficulties
• Hold notes and jumps
• #BPMS, #STOPS, #OFFSET with correct beat↔second mapping
• ScoreKeeperMAX2 scoring, judgment windows, AAAA…D grade tiers
• Song wheel with folder (album) browsing
• Song preview, pause/resume, quit back to the wheel
• MP3 streaming (whole file in RAM, no SD I/O during gameplay)
• PNG/JPG backgrounds, banners and note skins
• Song clock driven by decoded audio samples, so notes never drift

Not implemented: online scores, chart editing, battle mode, 3D lanes.

Requirements

A Data Frog GB300 or SF2000 with the Deimos/Multicore firmware, and a FAT32 microSD card.

Installation

1. Copy the core

Download froggysm.sf2k from the releases page. The published binary targets the GB300V2 firmware. An SF2000 console needs a separate build (FROGGY_TYPE=SF2000): the game code is identical, but the BIOS syscall addresses differ, so the two payloads are not interchangeable.

cp froggysm.sf2k /media/<CARD>/system/Deimos/cores/froggysm.sf2k

2. Create the ROM folder and the game file

The launcher derives the core name from the folder name and then looks for system/Deimos/cores/<folder>.sf2k. The folder and the core file must therefore be spelled identically, including letter case — a difference in case alone is enough for the lookup to miss and the launch to fail silently.

mkdir -p /media/<CARD>/ROMS/froggysm/Songs
printf '' > /media/<CARD>/ROMS/froggysm/froggysm

That gives you:

system/Deimos/cores/froggysm.sf2k   ← core   (loaded)
ROMS/froggysm/froggysm              ← game   (passed to the core)
ROMS/froggysm/Songs/                ← songs

3. Optional: a menu stub

The stock file browser wants a .gba stub. The firmware reads its contents and parses them as

<core id>;<ROM folder>;<ROM file>.<extension>

The third field must contain a dot — the extension is stripped, and a bare filename makes the parse fail, leaving you with a STOCK screen.

printf 'froggysm;froggysm;froggysm.gba' > '/media/<CARD>/ROMS/froggysm;froggysm.gba'
sync

Under the FrogUI menu you can skip this: it builds the same parameters from the folder and file names in steps 1 and 2.

4. Launch

Boot the console, open the file browser and start FroggySM.

Two symptoms of a misconfigured install:

• STOCK screen — the stub in step 3 was rejected. Check it with cat '/media/<CARD>/ROMS/froggysm;froggysm.gba'; it must print froggysm;froggysm;froggysm.gba.
• Nothing happens at all — the core lookup missed. Verify that the folder and the core file are spelled identically: ls /media/<CARD>/ROMS/ | grep froggy and ls /media/<CARD>/system/Deimos/cores/ | grep froggy.

Adding songs

Standard StepMania layout — one folder per album, one per song:

/ROMS/froggysm/Songs/
└── <artist or pack>/
    └── <song>/
        ├── song.sm        # chart (required)
        ├── song.mp3       # referenced by #MUSIC
        ├── banner.png     # optional
        └── background.png # optional

#MUSIC: is resolved relative to the chart's folder. Charts without a #TITLE: borrow the folder name, split on the first -, ~, ( or [, the same rule StepMania uses. Sub-folders become albums — press SELECT on the select screen to cycle through [ ALL SONGS ] and each one.

Charts are re-scanned from the SD card when the game starts, so there is no separate refresh step after copying files.

Audio format

The MP3 decoder is software (minimp3) on a soft-float CPU, so bitrate directly costs frame time. A 320 kbps file will stutter; a 128 kbps file will not. Re-encode your library once:

find /ROMS/froggysm/Songs -iname '*.mp3' -print0 |
while IFS= read -r -d '' f; do
    ffmpeg -y -i "$f" -vn -ar 44100 -ac 2 -b:a 128k -c:a libmp3lame "$f.tmp.mp3" &&
    mv "$f.tmp.mp3" "$f"
done

44.1 kHz stereo 128 kbps CBR is the sweet spot: it divides evenly into the console's 22050 Hz output, so the resampler never drifts. -vn also drops embedded cover art from the ID3 tag, which costs RAM and parser time.

Controls

Nintendo Switch ABXY layout: X top, B bottom, Y left, A right.

Select screen

Action	Input
Previous / next song	D-Pad Up / Down
Previous / next difficulty	D-Pad Left / Right, or L / R
Next folder / album	SELECT
Play	A or START
Stop preview	B

Gameplay

Lane	Input
Left	D-Pad Left or Y
Down	D-Pad Down or B
Up	D-Pad Up or X
Right	D-Pad Right or A
Pause / resume	START
Quit to the wheel	SELECT (while paused)

Building from source

Host test runner

Builds and runs on Linux/macOS. The runner loads the library, decodes every chart, plays a song, auto-plays the chart and checks audio/video integrity:

make test SONGS_PATH=/path/to/Songs

It dumps PPM screenshots of each screen into the working directory, which is handy for checking layout changes without flashing a console.

Cross-compiling the core

make device produces dist/froggysm.sf2k. It needs the Frog/MTI mipsel-mti-elf toolchain and a checkout of the multicore frontend that wraps the core into a core_87000000 payload:

make device \
    MULTICORE_DIR=/path/to/sf2000_multicore \
    SONGS_PATH=/path/to/Songs

Pass FROGGY_TYPE=GB300V2 for the GB300V2 firmware; the default is SF2000. The game code is identical either way, only the BIOS syscall addresses and the LCD register value differ, so a payload built for one firmware will not start on the other.

Boot diagnostics can be enabled by creating an empty bios/enable_xlog.txt on the card. The core then writes froggysm_diag.log (scan roots, screen transitions, image loads) in the card root. With the flag absent the core writes nothing.

Install to SD

With the card mounted:

./install_to_sd.sh

It installs the core, creates the folders and the ROM entry, and copies the song library.

Credits

• StepMania — the rhythm game engine this port re-implements
• PSPMania by mafu9 — the PSP port this takes its feature set and note skin assets from
• minimp3 by lieff — CC0 MP3 decoder
• stb_image — public domain image loader
• The Frog/MTI MIPS toolchain and the Deimos/Multicore frontend by the Data Frog / SF2000 community

MIT licensed. StepMania-derived logic and the bundled PSPMania note skin keep their own terms — see LICENSE.

Links

• Source: https://github.com/Synaps33/FroggySM
• Releases: https://github.com/Synaps33/FroggySM/releases
• Issues: https://github.com/Synaps33/FroggySM/issues