import errno
import os
import time
[docs]class PWMError(IOError):
"""Base class for PWM errors."""
pass
[docs]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()
[docs] 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
[docs] def enable(self):
"""Enable the PWM output."""
self.enabled = True
[docs] 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))