DigiAlchemy GamePack - VOL.1

A pocket arcade for the Elektron Digitone mk1 / Digitone Keys (OS 1.43). Three tiny games that run on the synth's 128×64 screen as one elekloader mod (digidoom). Press MIDI+YES for the game-select menu, pick a game, and play with the arrow keys and YES/NO — the instrument keeps running underneath, and the games get out of the way when you close the menu.

• DOOM — a compact first-person raycaster (grid walls, 4×4 ordered-dither shading, z-buffered billboard sprites, HUD, weapon, doors, chasing monsters). A from-scratch engine, not the Doom engine.
• INVADERS — a very lightweight Space Invaders (a 6×4 fleet, a ship, one player bullet, alien fire, lives and a score).
• SNAKE — a grid snake that grows and speeds up with every dot it eats.

Status: v0.21. Built, linted, patched, and verified in digiemu (boots to a live UI; the menu opens; all three games launch and play).

Download: grab the latest release — DigiAlchemy-GamePack-<ver>.zip (the .elemod + install notes) or the bare .elemod — from Releases. The .elemod is a linkable mod, not firmware; build the flashable .syx locally (see Build below).

Launch trigger is MIDI+YES → the game-select menu:

DOOM — title, play, and game over:

Space Invaders:

Snake (grown, SCORE 7):

Why this is a from-scratch engine, not a port of Doom

The reference is the RP2040 "Smallest-Doom" (a Chocolate Doom fork). A literal port is not possible on the Digitone:

So DIGIDOOM keeps the spirit of the tiny builds — a grid raycaster — and reuses the ideas (DDA wall casting, camera plane, distance shading), not the code. It fits in ~3 KB of the 128 KB budget.

How it runs on the Digitone

It is an elekloader format-2 mod (mods/digidoom/). It owns no firmware site; it only subscribes to the core hook bus, so it combines with any other mod:

Drawing with FILLRECT/VLINE (addresses 0x400DD292 / 0x400DC92C, y = 0 is the bottom row) means no knowledge of the panel's memory layout is needed. Distance shading is a 4×4 ordered dither (separable: a column term (x&3) and a row term ((row+off)&3), both under the level), drawn as short VLINE runs; near walls are solid, far ones stipple. Floor and ceiling are left black. Runs are naturally bounded because far walls are short.

Fixed point is Q15 throughout (1 world cell = 32768); there is no C library and no float. The DDA is overflow-safe at that precision.

Performance

The dominant cost is the recompose: forcing the firmware to redraw a frame also redraws every stock view underneath us. So DIGIDOOM only requests a recompose when the screen actually changes — on a fresh key press, on a slow blink cadence for the title (~7 Hz), and at ~15 Hz while a game is running. The static screens (menu, game-over) cost essentially nothing.

Measured in digiemu over a 20M-instruction window: menu ≈ 4 draws / 128 ticks; INVADERS play ≈ 69 draws / 129 ticks (i.e. half the 30 Hz tick). If you want more headroom, change the (g_ticks & 1) test in digidoom_tick to (g_ticks & 3) for ~10 Hz, or (g_ticks & 7) for ~7 Hz.

Controls

Flow: menu → (DOOM: title → play → game over) or (INVADERS: play → over).

• DOOM: YES fires (a black impact patch with an x on a hit, a * on the wall); NO opens a door.
• INVADERS: YES fires the ship's bullet; the fleet speeds up as it thins; 3 lives and a score.
• SNAKE: arrows steer; each dot makes the snake one segment longer and a little faster; hitting a wall or yourself ends it.

Key codes are the measured Digitone runtime codes (MIDI=2, YES=13, NO=14, UP=15, DOWN=16, LEFT=17, RIGHT=18). While active, DIGIDOOM swallows its keys so the stock UI does not act on them.

Build, lint, patch

$env:PATH          = "C:\SysGCC\m68k-elf\bin;" + $env:PATH
$env:ELEKLOADER_CROSS = "m68k-elf-"
$env:PYTHONPATH    = "C:\Users\benan\Music\ELEKTRON\elekloader"
$stock = "C:\Users\benan\Music\ELEKTRON\Digitone_and_Digitone_Keys_OS1.43.syx"
$core  = "C:\Users\benan\Music\ELEKTRON\elekloader\mods\core-dn1\out\core-2.0a.elemod"

python -m elekloader.sdk.build mods\digidoom --stock $stock --out elemod
python -m elekloader.lint  elemod\digidoom-0.21.elemod --stock $stock --with $core
python -m elekloader.patch --stock $stock --mod $core `
    --mod elemod\digidoom-0.21.elemod `
    --out testout\test-digidoom-0.21.syx --version 0.1L

--out elemod writes the built mod straight into elemod/. (Builds also drop a elemod\digidoom.work\ dir, which is gitignored.)

Expect BUILT, OK: links as core … > digidoom … (≈15 KB of 128 KB), and WROTE after verified: ….

Testing in digiemu (what we did)

Boot/settle and screen capture use the emulator in ..\digiemu-main with its patched-Unicorn venv:

1. python -m emu.portable --add testout\test-digidoom-0.5.syx --yes boots, reaches "USER INTERFACE IS LIVE", and saves a gui.snap.
2. Resume that snapshot, inject panel keys with emu.panelin, and read the frame with emu.panel.read(m, profile.fb_front) / panel.write_png. Two gotchas: the snapshot's build manifest pins unblock_except=(0x4137B93C,) (the frame semaphore), and emu.config needs DT2_SECTIONS pointed at the firmware's extracted sections/.

Note: the emulator's display model cannot tolerate hooking the panel-present entry points (panel_diff/panel_flush) — the proven DigiScreen overlay mod fails to reach a live UI there too. That is why DIGIDOOM renders through ev_draw instead. On hardware both approaches are the same technique.

Layout

mods/digidoom/digidoom.c   the launcher + all three games (one file)
mods/digidoom/mod.json     the elemod manifest (ev_draw/ev_tick/ev_key, no sites)
elemod/                    the latest built mod (digidoom-0.21.elemod)
testout/                   emulator screenshots (the .syx builds are gitignored)
README.md                  this overview
HANDOFF.md                 working handoff (state, environment, testing recipe)
docs/GAME-MAKING.md        how to write a game on this platform (API + optimizations)
LICENSE / NOTICE           GPL-2.0-or-later; what is (and isn't) redistributed

Releases (a packaged .zip + the .elemod) live in the repo's Releases section on GitHub.

Roadmap

Done: the game-select menu (MIDI+YES); DOOM (raycaster, 4×4 dither, sprites, HUD, weapon, fire, doors, monsters, title/game-over); INVADERS (fleet, ship, bullets, lives, score, win/lose); SNAKE (grid snake that grows and speeds up).

• Content: more DOOM levels/monsters/weapons; INVADERS shields and a UFO; SNAKE a border and high score.
• Sound: none yet (the mod is display/UI only; the FM engine is untouched).

Repository contents (and what isn't here)

This repo holds our own code and assets: the mod source (mods/digidoom/digidoom.c), the built .elemods, the docs, and screenshots. It deliberately does not contain:

• any firmware — no stock or patched Elektron .syx files. You build the flashable image yourself from your own stock OS plus the .elemods (elekloader.patch), so nothing proprietary is redistributed;
• the third-party RP2040 "Smallest-Doom" reference tree (Chocolate Doom / id shareware) — it is only a local reference, not part of this pack.

See .gitignore. The .elemod files reference firmware bytes by address and hash, never by value (the elekloader format's rule), so they carry no firmware.

Licence

GPL-2.0-or-later for our own code. Not affiliated with or endorsed by Elektron or id Software.