viii

A virtual iii interface that runs in the browser, designed to be compatible with grid and arc devices that don't natively support iii (older FTDI devices, older DIY grids, etc). The iii Lua VM, filesystem, and scripts all run right in your Chromium-based browser or Firefox browser. Communication with the grid/arc happens using the same protocol as serialosc MIDI goes to host apps or connected instruments via WebMIDI.

No hardware is technically required — scripts can run and send/receive MIDI data with no grid or arc connected.

Using viii

Go here in a browser that supports WebSerial/WebMIDI (Chromium, Chrome, Edge, Opera, and Firefox).

Connecting a device

1. Quit serialosc (or any other app using the serial port) — the browser needs exclusive access
2. Click connect and select your grid or arc from the serial port picker

All monome grids and arcs that speak the mext protocol are supported — older FTDI-based editions, Neotrellis-based DIY grids, etc.

Note on Windows you will need to have an FTDI Virtual COM Port driver for your device to appear if it uses an FTDI chip (older grids and arcs).

Firefox

Firefox 151+ and newer supports WebMIDI and WebSerial. Visit the viii site, then click "Continue to installation" and "Add" in the popup windows to allow viii to access your midi devices.

Click connect, then click "Continue to installation" and "Add" in the popup windows to allow viii to access your serial devices. Select your device's serial port in the popup window's dropdown menu, then click "Allow".

Running scripts

• Use the upload button (or drag and drop) to add .lua scripts
• Click the ▶ button next to any .lua file in the file list
• Type r in the REPL to re-upload and run the last uploaded script (useful for iterating)
• Some scripts to get you started are available at codeberg.org/tehn/iii-scripts

REPL

Type iii Lua commands directly in the input field and press Enter. A few shortcuts:

Command	Action
h	Show help
u	Open file upload picker
r	Re-upload and run last uploaded script
^^i	Restart the VM
^^c	Clean restart (no script)
help()	Print the iii API reference

MIDI

Select MIDI output and input ports from the dropdowns in the header. The panic button sends All Notes Off on all 16 channels.

Note that to send midi to other apps on your host you may need to enable some kind of virtual MIDI loopback. On MacOS you can enable the IAC Driver device in Audio MIDI Setup for this. On Windows, one option I tested is the new Windows MIDI Services that still require a manual install at the time of writing.

Arc key

The arc key button in the toolbar sends event_arc_key(1) on press and event_arc_key(0) on release, simulating the physical arc push-switch that is absent on older arc models. You can also call these commands inside a script for the same effect or even map midi events to them for external control. For example:

-- z is 1 for press, 0 for release. Define something to do when a key event is received from arc
function event_arc_key(z)
    print("arc key: " .. z)
end

-- Map MIDI note 60 (middle-c) to arc key event
local NOTE_ON = 0x90   -- note on status (channel in lower nibble)
local NOTE_OFF = 0x80  -- note off status
local STATUS_MASK = 0xF0
local TARGET_NOTE = 60

function event_midi(d1, d2, d3)
    local status = d1 & STATUS_MASK
    local note = d2
    local velocity = d3
    if note == TARGET_NOTE then
        if status == NOTE_ON and velocity > 0 then
            event_arc_key(1)
        elseif status == NOTE_OFF or (status == NOTE_ON and velocity == 0) then
            event_arc_key(0)
        end
    end
end

Offline use

viii can be installed as a progressive web app. After the first visit, it works offline — the browser caches all assets. On supported Chromium-based browsers you can install it as a standalone web app from the address bar. Note that Firefox does not support progressive web apps, though viii still works offline after the first visit.

Technical details for hacking viii

For building

viii compiles iii and lua to Web Assembly (WASM) using the Emscripten framework.

• Emscripten SDK

Building

source /path/to/emsdk/emsdk_env.sh
make

This compiles everything to web/viii.js and web/viii.wasm.

To serve locally:

make serve

Then open http://localhost:8080.

How it works

Platform-specific C modules in src/ provide browser implementations:

Module	Role
main.c	WASM entry point, main loop, init
device_web.c	Grid/arc communication — mext TX (direct byte construction) and RX (inline parser)
serial_web.c	REPL text I/O between JS and the Lua VM
midi_web.c	WebMIDI bridge
metro_web.c	Timer management via JS shim
fs_web.c	Filesystem backed by IndexedDB
flash_web.c	Flash storage shim

bridge.js ties everything together: WebSerial device connection, WebMIDI routing, REPL terminal, file management, and an AudioContext-driven timer that prevents background tab throttling.

Device protocol

Grid and arc communication uses the monome mext binary protocol directly. LED output is constructed as raw mext bytes (matching the approach used in monome's ansible firmware). Incoming key and encoder events are parsed by a lightweight inline mext message parser. All writes are padded to 64 bytes with 0xFF for USB bulk packet alignment. Originally viii used libmonome directly but I found there were issues with different hardware versions and how wasm specifically was assembling the serial packets using structs instead of flat arrays like ansible.

Timing

The main loop and metro callbacks are driven by an AudioContext ScriptProcessorNode that fires at audio rate (~5.8ms). This approach is used because it is immune to Chromium's background tab throttling, ensuring stable timing even when the tab is not focused. Before the first user interaction (required by browser autoplay policy), a brief setInterval pump handles initial setup.

Acknowledgements

viii is only possible because of the incredible ecosystem of open-source monome tooling and instrument firmware. A special thank you goes to @tehn for his encouragement and testing, for the iii framework, and for these awesome instruments! Another big thanks to @okyeron for additional encouragement and testing + his incredible work on the neotrellis based grid and firmware. Other shoutouts include:

• @jonwaterschoot and @awesomebrick for testing
• @schollz for lending me his FTDI grid so that I could sort out compatibility issues
• @philmillman for calling wasm to my attention in the first place

Important touchpoints from the monome open-source extended universe that were instrumental when making viii were:

• libmonome
• The ansible and norns firmwares
• The grid and arc iii firmwares
• The iii platform itself
• The diii tool I made for monome that works with iii-compatible devices