Flashback for Game & Watch Retro-Go SD

Delphine Software's Flashback (1992), PC DOS version, running on the Nintendo Game & Watch with the Retro-Go SD firmware, as a GWHB homebrew: a single .bin dropped in /homebrews/, no firmware rebuild needed.

The game engine is REminiscence, Gregory Montoir's reimplementation of the Flashback engine (commercial-game-sources/reminiscence), used here with his permission. The project is built from retro-go-sd-templates: it talks to the firmware only through the firmware ABI.

The game data is not included. You need your own copy of the PC DOS version (floppy or CD): the DATA folder with LEVEL1.MAP, PERSO.SPR, GLOBAL.FIB, ...

Installation

Requires Retro-Go SD v2.0.0-rc1 or later (firmware ABI v2).

1. Build the game data pack (Python 3 only, nothing else to install):

   python3 fb_pack.py Flashback.fb /path/to/FLASHBACK/DATA
   

   On Windows: py fb_pack.py Flashback.fb C:\Games\Flashback\DATA
2. Copy both files to the SD card, side by side, with the same name:

   /homebrews/Flashback.bin
   /homebrews/Flashback.fb
   

3. Start it from the Homebrew tab.

The first start copies the pack to the external flash (a few minutes for a large pack); the game then uses its data in place from there.

Music and the size of the pack

The console is far too slow to emulate the AdLib (OPL3) chip of the PC in real time, so fb_pack.py pre-renders the music on your computer (with fb_render, the same engine built for Windows, macOS and Linux, shipped in fb_render/ next to the script). Every piece is rendered with its exact loop point, the console only plays the samples back.

Option	Pack size	Music
(default)	~34 MB	PCM, 11 kHz
--music-codec adpcm	~14 MB	IMA ADPCM, 11 kHz (4 times smaller, a slight hiss)
--music-rate 22050	~62 MB	PCM, 22 kHz
--no-music	~7 MB	none

The pack must fit in the external flash of the console: with a 16 MB flash, use --music-codec adpcm (or --no-music). If it does not fit, the console says "Pack too big for the flash".

Controls

In a level:

Game & Watch	Flashback (PC key)
D-pad	Move, jump (up), crouch (down)
A	Action (Shift): run, shoot, take, talk, use a lift...
B	Draw / put away the gun (Space)
TIME (SELECT on Zelda units)	Use the selected object (Return)
GAME (START on Zelda units)	Inventory (Backspace)
GAME + TIME	Game options panel: resume, abort, load / save game (Esc)
PAUSE/SET	Retro-Go menu

In the menus and the cutscenes: A = validate / skip, B = back / skip.

The Retro-Go menu adds savestates (anywhere in a level, they are much easier to use than the save stations of the game, which still work), and in Options: music, sound effects and, with the CD data, the language of the texts (English, Français...). Display "Scaling": Off shows the original 256x224 picture centered, the other modes stretch it to the whole screen ("Filtering" smooths it).

Building

Needs arm-none-eabi-gcc (hard-float, v10+), GNU Make, Python 3 + Pillow:

make            # → Flashback.bin
make docker     # same, inside the Retro-Go SD builder image

The music renderers (tools/bin/fb_render-*) are cross-built with zig:

pip install ziglang
tools/build_renderers.sh

Testing without hardware

harness/ builds the same engine and port code for Linux, headless, with a virtual clock, scripted buttons, PPM screenshots and WAV output:

make -C harness
harness/build/fb_host Flashback.fb -t 30000 -e 1000 -o /tmp/out -w /tmp/out/a.wav
harness/build/fb_host Flashback.fb -l 0 -s "2000:RIGHT:1,4000:RIGHT:0" -S 3000 -o /tmp/out

-l n starts at a level, -q file -Q ms writes a savestate at that time (like the pause menu would), -j file -J ms loads one, -L file restores one at start, -g lang / -G ms:lang set the language, -R dir renders the music (what fb_pack.py runs). The pack is mapped read-only, like the flash.

Layout

Path	Role
src/rs/	REminiscence (commercial-game-sources/reminiscence @ 947a4dc). Game & Watch changes are under #ifdef GNW. opl3.c is Nuked OPL3 (LGPL 2.1, music renderer only).
src/port/fb_core.cpp	The engine's SystemStub (display, sound, input), savestates, music playback and rendering.
src/port/fb_main.c	Retro-Go side: entry point, display, audio, buttons, pause menu.
src/port/fb_alloc.c, fb_cxx.cpp	Heap on the RAM left after the binary, new / delete.
src/port/fb_pack.c, fb_music.c	.fb pack reader, pre-rendered music player.
tools/fb_pack.py	Builds the .fb pack (sound effects decoded, music rendered).
tools/build_renderers.sh	Cross-builds fb_render for Windows, macOS and Linux.
harness/	Headless Linux test harness (also the music renderer).
sdk/	Retro-Go SD core / homebrew SDK (from retro-go-sd-templates).

See CLAUDE.md for the internals (memory, savestates, music).

License

See LICENSE. REminiscence is © Gregory Montoir and is distributed here with his permission only (it has no public license). Nuked OPL3 is LGPL 2.1 (src/rs/opl3.LICENSE). The SDK under sdk/ is MIT (sdk/LICENSE.MIT). The code written for this port (src/port/, tools/, harness/) is MIT. Flashback is a game by Delphine Software International.