187 lines
6.2 KiB
Python
187 lines
6.2 KiB
Python
# SPDX-FileCopyrightText: 2021 Melissa LeBlanc-Williams for Adafruit Industries
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#
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# SPDX-License-Identifier: MIT
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"""Custom PulseIn Class to read PWM signals"""
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import time
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import subprocess
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import os
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import atexit
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import random
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import struct
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import sysv_ipc
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DEBUG = False
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queues = []
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procs = []
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# The message queues live outside of python space, and must be formally cleaned!
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def final():
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"""In case the program is cancelled or quit, we need to clean up the PulseIn
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helper process and also the message queue, this is called at exit to do so"""
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if DEBUG:
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print("Cleaning up message queues", queues)
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print("Cleaning up processes", procs)
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for q in queues:
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q.remove()
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for proc in procs:
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proc.terminate()
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atexit.register(final)
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# pylint: disable=c-extension-no-member
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class PulseIn:
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"""PulseIn Class to read PWM signals"""
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def __init__(self, pin, maxlen=2, idle_state=False):
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"""Create a PulseIn object associated with the given pin.
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The object acts as a read-only sequence of pulse lengths with
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a given max length. When it is active, new pulse lengths are
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added to the end of the list. When there is no more room
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(len() == maxlen) the oldest pulse length is removed to make room."""
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self._pin = pin
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self._maxlen = maxlen
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self._idle_state = idle_state
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self._queue_key = random.randint(1, 9999)
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try:
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self._mq = sysv_ipc.MessageQueue(None, flags=sysv_ipc.IPC_CREX)
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if DEBUG:
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print("Message Queue Key: ", self._mq.key)
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queues.append(self._mq)
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except sysv_ipc.ExistentialError:
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raise RuntimeError(
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"Message queue creation failed"
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) from sysv_ipc.ExistentialError
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# Check if OS is 64-bit
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if struct.calcsize("P") * 8 == 64: # pylint: disable=no-member
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libgpiod_filename = "libgpiod_pulsein64"
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else:
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libgpiod_filename = "libgpiod_pulsein"
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dir_path = os.path.dirname(os.path.realpath(__file__))
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cmd = [
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dir_path + "/" + libgpiod_filename,
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"--pulses",
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str(maxlen),
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"--queue",
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str(self._mq.key),
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]
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if idle_state:
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cmd.append("-i")
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if isinstance(pin.id, tuple):
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cmd.append(f"gpiochip{pin.id[0]}")
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cmd.append(str(pin.id[1]))
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else:
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cmd.append("gpiochip0")
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cmd.append(str(pin))
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if DEBUG:
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print(cmd)
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self._process = subprocess.Popen(cmd) # pylint: disable=consider-using-with
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procs.append(self._process)
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# wait for it to start up
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if DEBUG:
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print("Waiting for startup success message from subprocess")
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message = self._wait_receive_msg(timeout=0.25)
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if message[0] != b"!":
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raise RuntimeError("Could not establish message queue with subprocess")
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self._paused = False
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# pylint: disable=redefined-builtin
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def _wait_receive_msg(self, timeout=0, type=2):
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"""Internal helper that will wait for new messages of a given type,
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and throw an exception on timeout"""
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if timeout > 0:
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stamp = time.monotonic()
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while (time.monotonic() - stamp) < timeout:
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try:
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message = self._mq.receive(block=False, type=type)
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return message
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except sysv_ipc.BusyError:
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time.sleep(0.001) # wait a bit then retry!
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# uh-oh timed out
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raise RuntimeError(
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"Timed out waiting for PulseIn message. Make sure libgpiod is installed."
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)
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message = self._mq.receive(block=True, type=type)
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return message
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# pylint: enable=redefined-builtin
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def deinit(self):
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"""Deinitialises the PulseIn and releases any hardware and software
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resources for reuse."""
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# Clean up after ourselves
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self._process.terminate()
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procs.remove(self._process)
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self._mq.remove()
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queues.remove(self._mq)
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def __enter__(self):
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"""No-op used by Context Managers."""
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return self
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def __exit__(self, exc_type, exc_value, tb):
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"""Automatically deinitializes the hardware when exiting a context."""
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self.deinit()
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def resume(self, trigger_duration=0):
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"""Resumes pulse capture after an optional trigger pulse."""
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if trigger_duration != 0:
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self._mq.send("t%d" % trigger_duration, True, type=1)
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else:
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self._mq.send("r", True, type=1)
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self._paused = False
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def pause(self):
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"""Pause pulse capture"""
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self._mq.send("p", True, type=1)
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self._paused = True
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@property
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def paused(self):
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"""True when pulse capture is paused as a result of pause() or
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an error during capture such as a signal that is too fast."""
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return self._paused
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@property
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def maxlen(self):
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"""The maximum length of the PulseIn. When len() is equal to maxlen,
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it is unclear which pulses are active and which are idle."""
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return self._maxlen
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def clear(self):
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"""Clears all captured pulses"""
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self._mq.send("c", True, type=1)
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def popleft(self):
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"""Removes and returns the oldest read pulse."""
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self._mq.send("^", True, type=1)
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message = self._wait_receive_msg()
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reply = int(message[0].decode("utf-8"))
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# print(reply)
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if reply == -1:
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raise IndexError("pop from empty list")
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return reply
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def __len__(self):
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"""Returns the current pulse length"""
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self._mq.send("l", True, type=1)
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message = self._wait_receive_msg()
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return int(message[0].decode("utf-8"))
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# pylint: disable=redefined-builtin
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def __getitem__(self, index, type=None):
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"""Returns the value at the given index or values in slice."""
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self._mq.send("i%d" % index, True, type=1)
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message = self._wait_receive_msg()
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ret = int(message[0].decode("utf-8"))
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if ret == -1:
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raise IndexError("list index out of range")
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return ret
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# pylint: enable=redefined-builtin
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