# Source code for periphery.pwm

    import errno
    import os
    import time

    class PWMError(IOError):
        """Base class for PWM errors."""
        pass

    class PWM(object):
        # Number of retries to check for successful PWM export on open
        _PWM_STAT_RETRIES = 10
        # Delay between check for scucessful PWM export on open (100ms)
        _PWM_STAT_DELAY = 0.1

        def __init__(self, chip, channel):
            """Instantiate a PWM object and open the sysfs PWM corresponding to the
            specified chip and channel.

            Args:
                chip (int): PWM chip number.
                channel (int): PWM channel number.

            Returns:
                PWM: PWM object.

            Raises:
                PWMError: if an I/O or OS error occurs.
                TypeError: if `chip` or `channel` types are invalid.
                LookupError: if PWM chip does not exist.
                TimeoutError: if waiting for PWM export times out.

            """
            self._chip = None
            self._channel = None
            self._path = None
            self._period_ns = None
            self._open(chip, channel)

        def __del__(self):
            self.close()

        def __enter__(self):
            return self

        def __exit__(self, t, value, traceback):
            self.close()

        def _open(self, chip, channel):
            if not isinstance(chip, int):
                raise TypeError("Invalid chip type, should be integer.")
            if not isinstance(channel, int):
                raise TypeError("Invalid channel type, should be integer.")

            chip_path = "/sys/class/pwm/pwmchip{}".format(chip)
            channel_path = "/sys/class/pwm/pwmchip{}/pwm{}".format(chip, channel)

            if not os.path.isdir(chip_path):
                raise LookupError("Opening PWM: PWM chip {} not found.".format(chip))

            if not os.path.isdir(channel_path):
                # Export the PWM
                try:
                    with open(os.path.join(chip_path, "export"), "w") as f_export:
                        f_export.write("{:d}\n".format(channel))
                except IOError as e:
                    raise PWMError(e.errno, "Exporting PWM channel: " + e.strerror)

                # Loop until PWM is exported
                exported = False
                for i in range(PWM._PWM_STAT_RETRIES):
                    if os.path.isdir(channel_path):
                        exported = True
                        break

                    time.sleep(PWM._PWM_STAT_DELAY)

                if not exported:
                    raise TimeoutError("Exporting PWM: waiting for \"{:s}\" timed out".format(channel_path))

                # Loop until period is writable. This could take some time after
                # export as application of udev rules after export is asynchronous.
                for i in range(PWM._PWM_STAT_RETRIES):
                    try:
                        with open(os.path.join(channel_path, "period"), 'w'):
                            break
                    except IOError as e:
                        if e.errno != errno.EACCES or (e.errno == errno.EACCES and i == PWM._PWM_STAT_RETRIES - 1):
                            raise PWMError(e.errno, "Opening PWM period: " + e.strerror)

                    time.sleep(PWM._PWM_STAT_DELAY)

            self._chip = chip
            self._channel = channel
            self._path = channel_path

            # Cache the period for fast duty cycle updates
            self._period_ns = self._get_period_ns()

        def close(self):
            """Close the PWM."""

            if self._channel is not None:
                # Unexport the PWM channel
                try:
                    unexport_fd = os.open("/sys/class/pwm/pwmchip{}/unexport".format(self._chip), os.O_WRONLY)
                    os.write(unexport_fd, "{:d}\n".format(self._channel).encode())
                    os.close(unexport_fd)
                except OSError as e:
                    raise PWMError(e.errno, "Unexporting PWM: " + e.strerror)

            self._chip = None
            self._channel = None

        def _write_channel_attr(self, attr, value):
            with open(os.path.join(self._path, attr), 'w') as f_attr:
                f_attr.write(value + "\n")

        def _read_channel_attr(self, attr):
            with open(os.path.join(self._path, attr), 'r') as f_attr:
                return f_attr.read().strip()

        # Methods

        def enable(self):
            """Enable the PWM output."""
            self.enabled = True

        def disable(self):
            """Disable the PWM output."""
            self.enabled = False

        # Immutable properties

        @property
        def devpath(self):
            """Get the device path of the underlying sysfs PWM device.

            :type: str
            """
            return self._path

        @property
        def chip(self):
            """Get the PWM chip number.

            :type: int
            """
            return self._chip

        @property
        def channel(self):
            """Get the PWM channel number.

            :type: int
            """
            return self._channel

        # Mutable properties

        def _get_period_ns(self):
            period_ns_str = self._read_channel_attr("period")

            try:
                period_ns = int(period_ns_str)
            except ValueError:
                raise PWMError(None, "Unknown period value: \"{:s}\"".format(period_ns_str))

            # Update our cached period
            self._period_ns = period_ns

            return period_ns

        def _set_period_ns(self, period_ns):
            if not isinstance(period_ns, int):
                raise TypeError("Invalid period type, should be int.")

            self._write_channel_attr("period", str(period_ns))

            # Update our cached period
            self._period_ns = period_ns

        period_ns = property(_get_period_ns, _set_period_ns)
        """Get or set the PWM's output period in nanoseconds.

        Raises:
            PWMError: if an I/O or OS error occurs.
            TypeError: if value type is not int.

        :type: int
        """

        def _get_duty_cycle_ns(self):
            duty_cycle_ns_str = self._read_channel_attr("duty_cycle")

            try:
                duty_cycle_ns = int(duty_cycle_ns_str)
            except ValueError:
                raise PWMError(None, "Unknown duty cycle value: \"{:s}\"".format(duty_cycle_ns_str))

            return duty_cycle_ns

        def _set_duty_cycle_ns(self, duty_cycle_ns):
            if not isinstance(duty_cycle_ns, int):
                raise TypeError("Invalid duty cycle type, should be int.")

            self._write_channel_attr("duty_cycle", str(duty_cycle_ns))

        duty_cycle_ns = property(_get_duty_cycle_ns, _set_duty_cycle_ns)
        """Get or set the PWM's output duty cycle in nanoseconds.

        Raises:
            PWMError: if an I/O or OS error occurs.
            TypeError: if value type is not int.

        :type: int
        """

        def _get_period(self):
            return float(self.period_ns) / 1e9

        def _set_period(self, period):
            if not isinstance(period, (int, float)):
                raise TypeError("Invalid period type, should be int or float.")

            # Convert period from seconds to integer nanoseconds
            self.period_ns = int(period * 1e9)

        period = property(_get_period, _set_period)
        """Get or set the PWM's output period in seconds.

        Raises:
            PWMError: if an I/O or OS error occurs.
            TypeError: if value type is not int or float.

        :type: int, float
        """

        def _get_duty_cycle(self):
            return float(self.duty_cycle_ns) / self._period_ns

        def _set_duty_cycle(self, duty_cycle):
            if not isinstance(duty_cycle, (int, float)):
                raise TypeError("Invalid duty cycle type, should be int or float.")
            elif not 0.0 <= duty_cycle <= 1.0:
                raise ValueError("Invalid duty cycle value, should be between 0.0 and 1.0.")

            # Convert duty cycle from ratio to nanoseconds
            self.duty_cycle_ns = int(duty_cycle * self._period_ns)

        duty_cycle = property(_get_duty_cycle, _set_duty_cycle)
        """Get or set the PWM's output duty cycle as a ratio from 0.0 to 1.0.

        Raises:
            PWMError: if an I/O or OS error occurs.
            TypeError: if value type is not int or float.
            ValueError: if value is out of bounds of 0.0 to 1.0.

        :type: int, float
        """

        def _get_frequency(self):
            return 1.0 / self.period

        def _set_frequency(self, frequency):
            if not isinstance(frequency, (int, float)):
                raise TypeError("Invalid frequency type, should be int or float.")

            self.period = 1.0 / frequency

        frequency = property(_get_frequency, _set_frequency)
        """Get or set the PWM's output frequency in Hertz.

        Raises:
            PWMError: if an I/O or OS error occurs.
            TypeError: if value type is not int or float.

        :type: int, float
        """

        def _get_polarity(self):
            return self._read_channel_attr("polarity")

        def _set_polarity(self, polarity):
            if not isinstance(polarity, str):
                raise TypeError("Invalid polarity type, should be str.")
            elif polarity.lower() not in ["normal", "inversed"]:
                raise ValueError("Invalid polarity, can be: \"normal\" or \"inversed\".")

            self._write_channel_attr("polarity", polarity.lower())

        polarity = property(_get_polarity, _set_polarity)
        """Get or set the PWM's output polarity. Can be "normal" or "inversed".

        Raises:
            PWMError: if an I/O or OS error occurs.
            TypeError: if value type is not str.
            ValueError: if value is invalid.

        :type: str
        """

        def _get_enabled(self):
            enabled = self._read_channel_attr("enable")

            if enabled == "1":
                return True
            elif enabled == "0":
                return False

            raise PWMError(None, "Unknown enabled value: \"{:s}\"".format(enabled))

        def _set_enabled(self, value):
            if not isinstance(value, bool):
                raise TypeError("Invalid enabled type, should be bool.")

            self._write_channel_attr("enable", "1" if value else "0")

        enabled = property(_get_enabled, _set_enabled)
        """Get or set the PWM's output enabled state.

        Raises:
            PWMError: if an I/O or OS error occurs.
            TypeError: if value type is not bool.

        :type: bool
        """

        # String representation

        def __str__(self):
            return "PWM {:d}, chip {:d} (period={:f} sec, duty_cycle={:f}%, polarity={:s}, enabled={:s})" \
                .format(self._channel, self._chip, self.period, self.duty_cycle * 100, self.polarity, str(self.enabled))