marlin-host

A host-side Python library for the Marlin firmware serial protocol — the PC/host end of the line-numbered, checksummed, ok-acknowledged G-code conversation that hosts like OctoPrint and Pronterface speak to a printer or CNC running Marlin. Neutral and standalone; not tied to any one application.

Status: MVP. Connect, M115 negotiation, reliable framed send, streaming, queries, and out-of-band e-stop are implemented and validated against real hardware (RAMPS 1.4 / Marlin bugfix-2.1.x, logic level — motion/thermal validation under power is ongoing). Developed against the Marlin firmware source and official docs. Licensed Apache-2.0.

Repository conventions

A few top-level directories are gitignored (local-only) and used while developing — they are intentionally not version-controlled:

• working/ — scratch material we generate: protocol references, design notes, research write-ups. Local working files, not shipped.
• _reference/ — external material pulled in to build against: Marlin firmware source, docs, and other technical references. Third-party, large, and in flux, so kept out of the repo.
• planning/ — planning notes and task breakdowns.

Anything intended to ship — the library, its tests, and curated docs — lives in tracked directories, never in working/, _reference/, or planning/.

Develop

Requires uv and just.

just setup        # uv sync
just check        # ruff format-check + lint + pyright (CI-equivalent)
just test         # pytest

Usage

Parse a single response line:

from marlin_host import parse_response

resp = parse_response("ok N12 P15 B3")
resp.is_ack          # True
resp.fields          # {'N': 12.0, 'P': 15.0, 'B': 3.0}

parse_response("Resend: 13").resend_line     # 13
parse_response("echo:busy: processing").is_keepalive   # True

Drive a real controller (pip install 'marlin-host[serial]'):

from marlin_host import MarlinHost, SerialTransport

host = MarlinHost(SerialTransport("/dev/ttyUSB0", 250000), reliable=True)
host.connect()                       # resets the board, drains the startup banner
print(host.capabilities().firmware)

host.send("G28")                     # homes; returns when the controller acks `ok`
for progress in host.stream(open("part.gcode")):
    print(f"{progress.commands_sent}/{progress.total_commands}")

host.emergency_stop()                # M112, out-of-band

Develop and test against FakeTransport — no hardware required.

Console

An interactive console for hands-on bring-up:

marlin-host --port /dev/ttyUSB0 --reliable --log session.trace
# then type G-code, or :caps  :stream part.gcode  :estop  :quit

--log records every TX/RX line (via TracingTransport) — a captured session that can seed the conformance corpus.