Emulator jzIntv Intellivision

jzIntv — Intellivision

The Intellivision bundle was where the shared-EJS pattern ran out: EmulatorJS doesn't ship an Intellivision core, full stop. So the Intellivision bundle is on its own — a custom emscripten loader with no EJS at all.

Where we started — and why we left EJS

The first check was whether EmulatorJS supports Intellivision. Verified 2026-05-20 against cdn.emulatorjs.org/stable/data/cores/: no freeintv, no intellivision, no intv files; the official supported-systems list confirms it. No EJS-flavoured Intellivision core exists at all. The shared-EJS pattern the VICE family + Coleco use doesn't apply here.

So we needed a standalone WASM emulator with its own loader. Joe Zbiciak's jzIntv is the Intellivision emulator, but it's distributed as a C source tree, not a browser build.

The WASM source

The jzIntv WASM build came from mholzinger/intellivision-overlay-editor — an overlay-design tool that happened to bundle a fully-working jzIntv WASM at static/wasm/. The repo has no published LICENSE file but README badges MIT for the wrapper code; the underlying jzIntv source is free-for-personal-use. We mirrored just three files: jzintv.js (127 KB), jzintv.wasm (364 KB), and jzintv.data (1.2 KB).

No separate jzintv-wasm repo exists. If the overlay-editor stops being maintained, the fallback would be building jzIntv to WASM from libretro/jzintv source via emsdk — a couple of hours of work, but not pleasant.

The launch API

jzintv.js exposes one function, Module.launchJzintv(), that does everything we need:

Module.launchJzintv(execBuffer, gromBuffer, romBuffer, cfgBuffer,
                    extraArgs, ecsBuffer, jlpData, romExt, ivoiceBuffer)

Internally it writes exec.bin, grom.bin, game.<ext> (and optional game.cfg, ecs.bin, ivoice.bin, game.jlp) into the WASM FS via Module.FS.writeFile, builds argv as ["-e", "exec.bin", "-g", "grom.bin", "-v1", "-z1", "--kbdhackfile=desk.kbd"] + extraArgs + [romFile], then calls Module.callMain(args).

play.html fetches BIOS + cart in parallel and hands the buffers off:

const [execBuf, gromBuf, romBuf] = await Promise.all([
  fetch('exec.bin').then(r => r.arrayBuffer()),
  fetch('grom.bin').then(r => r.arrayBuffer()),
  fetch(game.rom).then(r => r.arrayBuffer())
]);
window.Module = {
  canvas: document.getElementById('canvas'),
  noInitialRun: true,
  onRuntimeInitialized: function() {
    Module.launchJzintv(execBuf, gromBuf, romBuf, null, [], null, null, 'int', null);
  }
};

noInitialRun: true is mandatory. Without it, Module calls main() with no args before our launchJzintv gets a chance to set up the FS, and the emulator runs with no ROM loaded.

The desk.kbd parser landmines

jzIntv reads its keyboard map from a --kbdhackfile. The default desk.kbd shipped with mholzinger's build only has keypad and action-button mappings — no disc/D-pad bindings at all. Without disc input, no Intellivision game is playable. We had to write our own.

The parser turned out to be sensitive in three non-obvious ways:

1. No UTF-8 in comments. A → (U+2192) or — (U+2014) breaks parsing — the multi-byte sequence throws off tokenisation and the error surfaces as Unknown command '7' (or whatever digit appears next). ASCII-only mandatory.
2. No apostrophes in comments. A line like ; Names must match jzintv's SDL key tokens errors with Too many arguments in kbdhackfile. The ' is presumably being parsed as a string delimiter even inside a comment.
3. Disc bindings must come last. Putting UP/DOWN/LEFT/RIGHT → PD0L_D_* lines before LSHIFT/LCTRL/LALT → PD0L_A_* in the same MAP block causes the action-button names to be rejected with Unknown command 'LALT'. Putting the disc lines at the end (after all keypad and action-button bindings) works cleanly. Mechanism unclear — possibly a buffer-size or state-machine quirk in jzintv's binding-table allocator. Just keep disc bindings at the bottom.

The desk.kbd we ship

jzintv.data is an emscripten --preload-file package containing desk.kbd at the WASM FS root. Our expanded version (~1.2 KB, plain ASCII) adds:

• Arrow keys → disc N/S/W/E (jzintv synthesises diagonals when you hold two arrows)
• Numpad → keypad (period-correct shape: a numpad is a 12-key keypad)
• Space → top action button (alias of LShift) for one-handed play

jzintv's code-name table for the relevant subset:

• Disc: PD0L_D_N, _S, _E, _W (and _NE, _SE, _NW, _SW, plus 8 in-between)
• Action buttons: PD0L_A_T (top), PD0L_A_L (bottom-left), PD0L_A_R (bottom-right)
• Keypad: PD0L_KP1 … PD0L_KP9, PD0L_KP0, PD0L_KPC (CLR), PD0L_KPE (ENT)
• Player 2: same names with PD0R_ prefix

BIOS

exec.bin (8 KB, MD5 62e761035cb657903761800f4437b8af) + grom.bin (2 KB, MD5 0cd5946c6473e42e8e4c2137785e427f). Both Mattel copyright, bundled for emulator-only use — same legal posture as the Coleco BIOS we already ship.

Reuse caveats

This recipe — emscripten Module loader + launchJzintv API — does not generalise to other libretro WASM cores. It's specific to jzIntv's API shape. Future WASM-but-not-EJS emulators (a hypothetical px68k X68000 WASM, or a NINTV-DS port) will each have their own Module + arg conventions and need their own bespoke play.html.

Bundle layout

systems/intv/
├── play.html       ← ~80 lines, custom Module loader
├── controls.html
├── games.json
├── exec.bin        ← BIOS
├── grom.bin        ← BIOS
├── jzintv.js       ← emscripten glue, 127 KB
├── jzintv.wasm     ← emulator, 364 KB
├── jzintv.data     ← preload: custom desk.kbd
└── games/
    └── *.int       ← 10 cart images

Total bundle ~625 KB.

Related

• Emulator-XRoar-CoCo — different emscripten-loader gotchas
• Emulator-libretro-o2em-Odyssey2 — same "no EJS core exists" pattern, different solution
• Emulators — index