src/lerobot/utils/pedal.py

# Copyright 2025 The HuggingFace Inc. team. All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
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"""Generic foot pedal listener using evdev.

Callers supply a callback receiving the pressed key code (e.g. ``"KEY_A"``)
and an optional device path.  The listener runs in a daemon thread and
silently no-ops when :mod:`evdev` is not installed or the device is
unavailable.  Strategy-specific key mapping logic lives in the caller.
"""

from __future__ import annotations

import logging
import threading
from collections.abc import Callable

logger = logging.getLogger(__name__)

DEFAULT_PEDAL_DEVICE = "/dev/input/by-id/usb-PCsensor_FootSwitch-event-kbd"


def start_pedal_listener(
    on_press: Callable[[str], None],
    device_path: str = DEFAULT_PEDAL_DEVICE,
) -> threading.Thread | None:
    """Spawn a daemon thread that forwards pedal key-press codes to ``on_press``.

    Parameters
    ----------
    on_press:
        Callback invoked with the pressed key code string (e.g. ``"KEY_A"``)
        on each pedal press event.  The callback runs in the listener thread
        and must be thread-safe.
    device_path:
        Linux input device path (e.g. ``/dev/input/by-id/...``).

    Returns
    -------
    The started daemon :class:`threading.Thread`, or ``None`` when
    :mod:`evdev` is not installed (optional dependency; silent no-op).
    """
    try:
        from evdev import InputDevice, categorize, ecodes
    except ImportError:
        return None

    def pedal_reader() -> None:
        try:
            dev = InputDevice(device_path)
            logger.info("Pedal connected: %s", dev.name)
            for ev in dev.read_loop():
                if ev.type != ecodes.EV_KEY:
                    continue
                key = categorize(ev)
                code = key.keycode
                if isinstance(code, (list, tuple)):
                    code = code[0]
                if key.keystate != 1:  # only key-down events
                    continue
                try:
                    on_press(code)
                except Exception as cb_err:  # pragma: no cover - defensive
                    logger.warning("Pedal callback error: %s", cb_err)
        except (FileNotFoundError, PermissionError):
            pass
        except Exception as e:
            logger.warning("Pedal error: %s", e)

    thread = threading.Thread(target=pedal_reader, daemon=True, name="PedalListener")
    thread.start()
    return thread