hpgl-buddy 1.8.0

Carefree, observable plotting of HP-GL files on HP pen plotters over RS-232.

hpgl-buddy

Carefree, observable plotting of HP-GL files on HP pen plotters over RS-232.

It does not just shove a file at the plotter: it validates the file, splits it to fit the device buffer, feeds it so the buffer never overflows and an inked pen never stalls mid-stroke, watches the device for faults the whole time, and logs every exchange so a run can be understood and troubleshooted from the log alone.

Supported devices:

• HP 7475A (RS-232)

New devices are added as declarative profiles (see Extending); HP-IB is planned.

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Install

pip install hpgl-buddy

Requires Python 3.11+. pyserial is the only runtime dependency. To work on hpgl-buddy itself, see Development.

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Quick start

# 1. Generate a built-in demo to a file (no plotter needed)
hpgl-buddy demo --pens 6 --out demo.hpgl

# 2. Validate it offline (no plotter needed)
hpgl-buddy check demo.hpgl

# 3. Check the plotter is alive and interpret its status
hpgl-buddy status --port /dev/cu.usbserial-XXXX

# 4. Plot it (verbose shows every byte/ESC exchange)
hpgl-buddy -v plot demo.hpgl --port /dev/cu.usbserial-XXXX

Sample HP-GL files live in examples/.

Serial defaults: 9600 8N1, no flow control (configurable). Flow control is off by default; enable it with --xonxoff if your cabling needs it.

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Commands

Command	What it does
status	Ad-hoc healthcheck: identification, buffer, status byte, errors, limits - all interpreted.
check FILE	Offline HP-GL syntax check. No device. Exit non-zero on errors.
plot FILE	Safe, buffer-aware plotting with progress + end-of-run report.
monitor enable|disable|watch	Enable/disable monitor mode (computer port) or stream the echoed bytes (terminal port).
demo	Generate demo HP-GL: --scene card (shapes/fills/labels/colours grid) or --scene house (a one-line drawing emitted as a single giant PD instruction - the >1024-byte oversized-instruction case, streamed in sub-blocks).

Global: -v/--verbose (DEBUG, incl. raw ASCII+hex wire dumps), -V/--version.

Serial options (on status/plot/monitor): --port, --model (default hp7475a), --baud, --framing (e.g. 8N1), --timeout, --xonxoff, --rtscts.

plot options

• --on-error abort|prompt|continue - on a reported error: stop and park the pen (default), ask interactively, or auto-recover (ESC.K discard -> IN -> replay the tracked state preamble -> carry on).
• --live-hpgl-verify off|chunk|pu - optional on-device HP-GL error checking (see Verification). Default off.
• --ignore-syntax-errors - plot even if the offline check found errors.
• --stats-json PATH - write run statistics as JSON (- for stdout).

monitor (two ports)

The 7475A enables monitor mode via an ESC sequence on the computer (data) port, then echoes the bytes it receives out a separate terminal port - so it's two single-purpose commands, one per port:

hpgl-buddy monitor enable  --port /dev/cu.COMPUTER   # turn monitor mode on (data port)
hpgl-buddy monitor watch   --port /dev/cu.TERMINAL   # stream the echo (terminal port)
hpgl-buddy monitor disable --port /dev/cu.COMPUTER   # turn it off when done

There are two monitor modes (enable --mode received|parsed): received (default, mode 1 in the documentstion) echoes every byte as it arrives, including ESC device-control sequences; parsed (mode 0 in the documentation) echoes only HP-GL as the plotter parses it from the buffer. watch prints every byte as binary, hex, decimal, and ASCII/control-name.

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How plotting works

file -> parse -> offline syntax check -> plan into chunks -> stream to device -> report

1. Parse the bytes into instructions, each tagged with its byte offset, source line and column, and sequence index - so any error names the exact command and can be located even in a single-line file (where the line number is always 1).
2. Syntax check offline; plot refuses a file with errors unless --ignore-syntax-errors.
3. Plan into chunks of <=256 bytes, split only at instruction boundaries (never inside a command), each tagged whether it ends with the pen up.
4. Stream: a chunk is sent only when ESC.B reports enough free buffer space. This one gate both prevents overflow and keeps the buffer fed, so a long pen-down stroke spanning several chunks never underruns (an underrun would park an inked pen and blot). An instruction larger than the buffer (e.g. a single huge PD polyline) is streamed across several ESC.B-gated sub-blocks - never split as HP-GL, since the plotter reassembles the byte stream as it parses - so it plots like any other.
5. Watch (always on, after each chunk): ESC.E for I/O faults (overflow / framing / data loss) and ESC.O for environmental faults (paper lever or pinch wheels raised -> abort; VIEW pressed -> warn). Both are immediate and never stall the pen.
6. Confirm: a final OS;OE;OI; tailgate waits for the pen to physically finish and reports the end status / any HP-GL error.
7. Report instructions/chunks/bytes sent, elapsed time, recovered errors, and warnings (and the same as JSON via --stats-json).

Verification

HP-GL/syntax errors are a property of the file (already validated offline), so on-device HP-GL error checking is optional and off by default. When enabled it never stalls the pen - it uses a one-deep tailgate: the OS;OE;OI; query is prefixed to the chunk after a pen-up, so its verdict reports the previous chunk while the current one is already drawing.

• chunk - check at pen-up chunk boundaries.
• pu - break a chunk at every pen-up so each completed stroke is checked (more, smaller chunks).

Either way you learn a chunk is clean within ~1 chunk, and a reported error names the span of chunks it could belong to with all candidate instructions.

Limits to know

• No pen sensing on the 7475A: a missing or fallen pen plots dry and is not detectable by any status query. Pre-load the pens your file uses. (plot warns about this.)
• Throughput is bound by the baud rate: a huge pen-down instruction with very short segments can outrun a 9600-baud link no matter how we feed it (the pen draws faster than bytes arrive). hpgl-buddy always feeds as fast as the buffer allows; raise the baud if a dense drawing dwells.

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Architecture

Thoroughly separated layers, each replaceable on its own:

hpgl/       parse HP-GL bytes into a Program; offline syntax check
devices/    declarative TOML profiles + abstract Device base (registry)
interface/  Transport abstraction + pyserial RS-232 implementation
status/     ESC + HP-GL command builders, response parsers, status interpretation, monitor
execution/  planner (Program -> chunks) + flow control + executor + progress/report
demo/       demo HP-GL generators

The full design rationale, with HP manual citations, lives in DESIGN.md. To embed hpgl-buddy as a library (e.g. a GUI), see INTEGRATION.md.

Extending

Add a simple device by dropping a <model>.toml into devices/profiles/ (buffer size, pen count, serial defaults, capabilities, pen_sensing). A device with unusual behavior can subclass Device and register it. The interface layer is transport-agnostic, so HP-IB can be added as another Transport without touching the rest.

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Development

pip install -e . -r requirements-dev.txt   # editable install + pinned dev tooling
tox                                         # run the test suite (your local Python)
tox -e build                                # build the sdist + wheel

To run the suite across every supported Python (3.11-3.13) without installing those interpreters yourself, use the per-version container matrix:

docker compose -f docker-compose.test.yml up --abort-on-container-exit

Dependencies follow a loose-rough -> pinned pattern, frozen in clean environments by the dependencies_update GitHub Actions workflow:

• runtime: requirements-rough.txt (hand-maintained, loose; kept in sync with [project.dependencies]) -> requirements.txt (fully pinned).
• dev / CI tooling: requirements-dev-rough.txt (loose: pytest, tox, build, twine) -> requirements-dev.txt (fully pinned), needed only in CI and dev environments.

A Dockerfile provides a reproducible build/test image (not for serial I/O - hardware is not reachable from a container).

Conventions: extensive logging (no print), ASCII-only output, descriptive names, and errors that state what happened, where, and why.

References and Attributions

• Logo is rendered out of a picture from Ed Nisley's Blog: https://softsolder.com/2015/04/21/hp-7475a-plotter-oem-pen-body-model/

Vibe-code disclosure

This library is written heavily with Claude. The design is decided upon by the initial human-author. All hands-on tests are conducted by a human-operator.

The human-conducted code review (HCCR) is an optimisation of a sort. It will be done in the right time.