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Linux workflow

The Linux build is the same instrument as the Windows one: the same IPC protocol, the same scripts, the same project state, and the same rendered PCM. Only the installation paths and the sidecar executable differ.

Install and scan

  1. Close the DAW.

  2. Unpack the release and copy MicroPythonVST3.vst3 to ~/.vst3 for the current user, or /usr/lib/vst3 for all users.

  3. Run the scanner once, from Contents/x86_64-linux inside the installed bundle, so the DAW can see the library:

    ./micropython-vst-engine scan_plugins.py --write

    It writes Contents/Resources/moduleinfo.json, which is both what the host reads to list the plug-ins and what the plug-in reads to know which ones it offers. The scanner needs nothing installed - it is the engine itself, reading what each library module declares about itself. Run it again after adding or editing a script.

  4. Start the DAW and request a VST3 rescan.

  5. Insert any of them - TR-808, Minimoog, Tape Delay - and open its editor, or use the host's generic parameter editor. MicroPython Script Host runs whatever script MPVST_SCRIPT_PATH points at, which is the loop for developing one that is not in the library yet.

The bundle contains Contents/x86_64-linux/, holding the plug-in itself, the micropython-vst-engine sidecar, the bootstrap, and the default instrument. Both the sidecar and the shared object must keep their executable bit; the release archive preserves it, but a copy through a tool that drops permissions will leave the plug-in unable to start its engine.

Controls

Identical to Windows, including the plug-in's own editor: a patch selector, a Reload button, a Bypass switch, a status light, and a slider per macro under whatever labels the script declares. Click a control to focus it, then scroll or swipe - sideways adjusts it, up and down moves between controls.

The editor is a plain X11 child window driven by the host's own run loop, so a host that provides no IRunLoop gets no editor and the generic parameter editor still works: Bypass, Reload Script, Patch, Macro 01 through Macro 16, and the read-only Engine Ready and Engine Error status parameters.

Develop a script

Set MPVST_SCRIPT_PATH to an absolute .py file before starting the DAW. Each new instance reads that file, and toggling Reload Script off and on re-reads it, so an edit reaches a running instance without reopening the project. Saving the project embeds the source as it is on disk at that moment, after which the project reopens the same way even if the original file moves or changes.

export MPVST_SCRIPT_PATH=$HOME/instruments/my_synth.py
reaper &

Constraining the sidecar

MPVST_HEAP_BYTES caps the MicroPython heap for every instance started afterwards, so a script that allocates without bound fails inside its own sidecar rather than growing until it disturbs the DAW:

export MPVST_HEAP_BYTES=16777216

Security model

Unchanged from Windows: MicroPython scripts run with the full capabilities of the desktop user in a separate process per instance. They can reach files, networking, FFI, and TLS. The separate process buys stability, not a sandbox. Only load projects and scripts you trust.

Uninstall

Close the DAW, remove the installed MicroPythonVST3.vst3 bundle from ~/.vst3 or /usr/lib/vst3, then rescan. Project files are untouched.