#183 ChangeDutyCycle() leads to instant reboot

[Christian Weisser]

Dear Ben,

Thank your for your great work! I have been successfully using your rpi.GPIO for some time now.
Now, however, I'm seeing some strange behaviour whenever I try to change the duty cycle of a PWM output. The system crashes instantly and reboots. No error or exception is shown.
Some time ago I had no problems with the code. Unfortuately I can not tell when it startet to behave strange. I did a full update to the current releases and still the same.

Here my setup:
Raspberry Pi 3 Model B Plus Rev 1.3
Raspbian 10 BUSTER, 4.19.118-v7+
PYTHON 3.7.3
rpi.gpio 0.7.0

Find here some code I used to reproduce the behaviour:

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import RPi.GPIO as gpio
from time import sleep

if __name__ == '__main__':

    gpio.setmode(gpio.BCM)

    gpio_valve1 = 16

    # Set as output initial high for low active output
    gpio.setup(gpio_valve1, gpio.OUT, initial=gpio.HIGH)

    valve1 = gpio.PWM(gpio_valve1, 10)

    #  Init valve with 100% duty cycle
    valve1.start(100)

    #  Change duty cycle to 50
    valve1.ChangeDutyCycle(50) # <<<< freeze and reboot happens here
    sleep(1)

    #  Change frequency to 20 Hz
    valve1.ChangeFrequency(20)
    sleep(1)

    #  Change duty cycle to 80
    valve1.ChangeDutyCycle(80)

Please give me instructions which logging to perform on my side to analyse the issue.

Regards,
Chris

[Christian Weisser]

Update:
Seems it is not the packet but rather the raspi itself. As a test I plugged the sd card in another raspi 3B+ and it runs like a charm.
Still it would be interesting why only the ChangeDutyCyle() causes a reset but not the other code...

Thank you

[Ben Croston]

Sounds like you may have a borderline power problem with your circuit using close to what a GPIO pin or power supply can handle. Using too much current for GPIO can starve the SOC of power causing reboots.

[Christian Weisser]

Hmm, actually I don't think so. I'm using the output as sink with 8mA and a optocoupler as load. The optocoupler also prevents hazardous voltage spikes from the connected valves.
I assume it's some ESD issue.

[Christian Weisser]

Dear Ben,
omg, after two month of smooth operation I encouter the same problems again. The new Pi shows the same behaviour. ChangeDutyCycle(0) leads to a sudden system reboot.
I checked the pins capacitive load (30pF of optocopuler input) and the powersupply. Both look good. This device certainly has no ESD damage.
In the /var/log/syslog and .../kern I see no issues. Can you give me some hints for futher debuggin?
Cheers,
Christian

[Christian Weisser]

UPDATE: System reboots in also if any of the ouputs is used as regular GPIO.output().
I ordered new RPIs to check for spikes caused by the inductive valves - after optocoupler and driver MOSFET...

[Christian Weisser]

Found the failure. It was a defect solenoid in my load circuitry. Puhh...