import os
[docs]class PWMError(IOError):
"""Base class for PWM errors."""
pass
[docs]class PWM(object):
# Sysfs paths
_sysfs_path = "/sys/class/pwm/"
_channel_path = "pwmchip{}"
# Channel paths
_export_path = "export"
_pin_path = "pwm{}"
# Pin attribute paths
_pin_period_path = "period"
_pin_duty_cycle_path = "duty_cycle"
_pin_polarity_path = "polarity"
_pin_enable_path = "enable"
def __init__(self, channel, pin):
"""Instantiate a PWM object and open the sysfs PWM corresponding to the
specified channel and pin.
Args:
channel (int): Linux channel number.
pin (int): Linux pin number.
Returns:
PWM: PWM object.
Raises:
PWMError: if an I/O or OS error occurs.
TypeError: if `channel` or `pin` types are invalid.
ValueError: if PWM channel does not exist.
"""
self._channel = None
self._pin = None
self._open(channel, pin)
def __del__(self):
self.close()
def __enter__(self):
return self
def __exit__(self, t, value, traceback):
self.close()
def _open(self, channel, pin):
if not isinstance(channel, int):
raise TypeError("Invalid channel type, should be integer.")
if not isinstance(pin, int):
raise TypeError("Invalid pin type, should be integer.")
channel_path = os.path.join(self._sysfs_path, self._channel_path.format(channel))
if not os.path.isdir(channel_path):
raise ValueError("PWM channel does not exist, check that the required modules are loaded.")
pin_path = os.path.join(channel_path, self._pin_path.format(pin))
if not os.path.isdir(pin_path):
try:
with open(os.path.join(channel_path, self._export_path), "w") as f_export:
f_export.write("%d\n" % pin)
except IOError as e:
raise PWMError(e.errno, "Exporting PWM pin: " + e.strerror)
self._channel = channel
self._pin = pin
# Look up the period, for fast duty cycle updates
self._period = self._get_period()
[docs] def close(self):
"""Close the sysfs PWM."""
self._channel = None
self._pin = None
def _write_pin_attr(self, attr, value):
path = os.path.join(
self._sysfs_path,
self._channel_path.format(self._channel),
self._pin_path.format(self._pin),
attr)
with open(path, 'w') as f_attr:
f_attr.write(value + "\n")
def _read_pin_attr(self, attr):
path = os.path.join(
self._sysfs_path,
self._channel_path.format(self._channel),
self._pin_path.format(self._pin),
attr)
with open(path, '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 channel(self):
"""Get the sysfs PWM channel number.
:type: int
"""
return self._channel
@property
def pin(self):
"""Get the sysfs PWM pin number.
:type: int
"""
return self._pin
# Mutable properties
def _get_period(self):
try:
period_ns = int(self._read_pin_attr(self._pin_period_path))
except ValueError:
raise PWMError(None, "Unknown period value: \"%s\"" % period_ns)
# Convert period from nanoseconds to seconds
period = period_ns / 1e9
# Update our cached period
self._period = period
return period
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
period_ns = int(period * 1e9)
self._write_pin_attr(self._pin_period_path, "{}".format(period_ns))
# Update our cached period
self._period = float(period)
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):
try:
duty_cycle_ns = int(self._read_pin_attr(self._pin_duty_cycle_path))
except ValueError:
raise PWMError(None, "Unknown duty cycle value: \"%s\"" % duty_cycle_ns)
# Convert duty cycle from nanoseconds to seconds
duty_cycle = duty_cycle_ns / 1e9
# Convert duty cycle to ratio from 0.0 to 1.0
duty_cycle = duty_cycle / self._period
return duty_cycle
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 seconds
duty_cycle = duty_cycle * self._period
# Convert duty cycle from seconds to integer nanoseconds
duty_cycle_ns = int(duty_cycle * 1e9)
self._write_pin_attr(self._pin_duty_cycle_path, "{}".format(duty_cycle_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_pin_attr(self._pin_polarity_path)
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_pin_attr(self._pin_polarity_path, 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_pin_attr(self._pin_enable_path)
if enabled == "1":
return True
elif enabled == "0":
return False
raise PWMError(None, "Unknown enabled value: \"%s\"" % enabled)
def _set_enabled(self, value):
if not isinstance(value, bool):
raise TypeError("Invalid enabled type, should be string.")
self._write_pin_attr(self._pin_enable_path, "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, pin %d (period=%f sec, duty_cycle=%f%%, polarity=%s, enabled=%s)" % \
(self._channel, self._pin, self.period, self.duty_cycle * 100,
self.polarity, str(self.enabled))