Function get_PWM_frequency() return 800Hz when hardware PWM freq is set to zero. about pigpio HOT 9 CLOSED

The above code always sets PWMduty to 500000. Does setting PWMduty to 0 when PWMfreq is 0 help? Does the call to hardware_PWM always return 0 or is an error code returned when PWMfreq is 0?

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Strange as it may seem that is actually the intended behaviour.

See http://abyz.co.uk/rpi/pigpio/python.html#get_PWM_frequency

Returns the frequency (in Hz) used for the GPIO.

For normal PWM the frequency will be that defined for the GPIO by set_PWM_frequency.

If a hardware clock is active on the GPIO the reported frequency will be that set by hardware_clock.

If hardware PWM is active on the GPIO the reported frequency will be that set by hardware_PWM.

As hardware PWM is not active (0 switches it off) the default PWM frequency (or that set by set_PWM_frequency) is returned.

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Is the intended behavior good?

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Who's to say? If the duty cycle is zero the frequency is irrelevant anyhow.

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Yes, if the duty cycle is 0 the frequency is irrelevant. However, although I haven't tested it, I'd expect get_PWM_dutycycle to return 500000 in the above code. A frequency of 800Hz and a duty cycle of 50% implies 800 pulses per second, but in this case there are 0 pulses.

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I have not opinion about what is the good behavior. I just want a proper way to check when PWM pulse are stopped.

If I initialize soft PWM with pi.set_PWM_frequency(13,0) in the above test code then get_PWM_frequency() return 10Hz (seen to be the soft PWM lower limit).

Alternative if I use dutycycle=0 to stop PWM and check it using get_PWM_dutycycle(13) the code raised a pigpio.error: 'GPIO is not in use for PWM' if freq is also set to 0...

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@nachoplus why not leave the frequency as is and set the duty cycle to 0 to turn PWM off?

The output of the following program:

import pigpio

pi=pigpio.pi()
pi.set_mode(13, pigpio.OUTPUT)

# PWM on
pi.hardware_PWM(13,1000,500000)
print "get_PWM_frequency()/get_PWM_dutycycle()",pi.get_PWM_frequency(13),"/",pi.get_PWM_dutycycle(13)

# PWM off
pi.hardware_PWM(13,1000,0)
print "get_PWM_frequency()/get_PWM_dutycycle()",pi.get_PWM_frequency(13),"/",pi.get_PWM_dutycycle(13)

is:

get_PWM_frequency()/get_PWM_dutycycle() 1000 / 500000
get_PWM_frequency()/get_PWM_dutycycle() 1000 / 0

If pi.get_PWM_dutycycle(13) returns 0, PWM pulses are stopped.

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I am reluctant to change a defined interface without a very good reason. For all I know people may be depending on the currently defined interface in their code.

@fivdi gives a solution. It seems good to me.

So I will not change the interface.

from pigpio.

OK. I have adopted the solution proposed by @fivdi . Thank you very much for supporting!

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