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Fix PWM bug when pin already exported #82

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Fix PWM bug when pin already exported #82

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20 changes: 12 additions & 8 deletions OPi/GPIO.py
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Original file line number Diff line number Diff line change
Expand Up @@ -725,15 +725,9 @@ def __init__(self, chip, pin, frequency, duty_cycle_percent, invert_polarity=Fal
self.duty_cycle_percent = duty_cycle_percent
self.invert_polarity = invert_polarity

# export pwm
try:
sysfs.PWM_Export(chip, pin) # creates the pwm sysfs object
if invert_polarity is True:
sysfs.PWM_Polarity(chip, pin, invert=True) # invert pwm i.e the duty cycle tells you how long the cycle is off
else:
sysfs.PWM_Polarity(chip, pin, invert=False) # don't invert the pwm signal. This is the normal way its used.
sysfs.PWM_Enable(chip, pin)
return sysfs.PWM_Frequency(chip, pin, frequency)

except (OSError, IOError) as e:
if e.errno == 16: # Device or resource busy
warnings.warn("Pin {0} is already in use, continuing anyway.".format(pin), stacklevel=2)
Expand All @@ -742,6 +736,16 @@ def __init__(self, chip, pin, frequency, duty_cycle_percent, invert_polarity=Fal
else:
raise e

# invert polarity if needed
if invert_polarity is True:
sysfs.PWM_Polarity(chip, pin, invert=True) # invert pwm i.e the duty cycle tells you how long the cycle is off
else:
sysfs.PWM_Polarity(chip, pin, invert=False) # don't invert the pwm signal. This is the normal way its used.

# enable pwm
sysfs.PWM_Enable(chip, pin)
sysfs.PWM_Frequency(chip, pin, frequency)

def start_pwm(self): # turn on pwm by setting the duty cycle to what the user specified
"""
Start PWM Signal.
Expand All @@ -755,7 +759,7 @@ def stop_pwm(self): # turn on pwm by setting the duty cycle to 0
return sysfs.PWM_Duty_Cycle_Percent(self.chip, self.pin, 0) # duty cycle at 0 is the equivilant of off

def change_frequency(self, new_frequency):
# Order of opperations:
# Order of operations:
# 1. convert to period
# 2. check if period is increasing or decreasing
# 3. If increasing update pwm period and then update the duty cycle period
Expand Down