#81 Interrupts stop working after login

[François GUILLIER]

Hi,

Some time ago I discovered that my programme randomly stopped receiving interrupt from GPIOs. After investigation, it turns out that a login (user pi) under raspbian resets the GPIO devices directory and RPi.GPIO's "epoll" function doesn't cope well with this situation.

example:

import time
import RPi.GPIO as GPIO

def event_handler(pin):
    print('Event on PIN', pin)

GPIO.setmode(GPIO.BCM)
PIN = 9
GPIO.setup(PIN, GPIO.IN)
GPIO.add_event_detect(PIN, GPIO.BOTH, event_handler)
try:
    while True:
        time.sleep(1)
except KeyboardInterrupt:
    GPIO.cleanup()

works well until one tries to ssh to the Raspberry Pi or executes a

sudo su -
su - pi

At this point the handler won't be called ever again...

The only workaround I found so far is something along the lines of:

import os
import time
import RPi.GPIO as GPIO

GPIO_DEV = '/sys/devices/virtual/gpio/gpio%u'

def event_handler(pin):
    print('Event on PIN', pin)

GPIO.setmode(GPIO.BCM)
PIN = 9
GPIO.setup(PIN, GPIO.IN)
GPIO.add_event_detect(PIN, GPIO.BOTH, event_handler)
pin_export_time = time.ctime(os.path.getmtime(GPIO_DEV % PIN))
try:
    while True:
        if pin_export_time != time.ctime(os.path.getmtime(GPIO_DEV % PIN)):
            print('Reset !!!')
            GPIO.remove_event_detect(PIN)
            GPIO.add_event_detect(PIN, GPIO.BOTH, event_handler)
            try:
                pin_export_time = time.ctime(os.path.getmtime(GPIO_DEV % PIN))
            except Exception:
                pin_export_time = -1
        time.sleep(1)
except KeyboardInterrupt:
    GPIO.cleanup()

Not that this behaviour doesn't seem to happen on ArchLinux.

1) What makes the login under "pi" touching the /sys/devices/virtual/gpio/ ?
(couldn't find anything under /etc/profiles, .bashrc, etc...)
2) Is there a possibility to include the detection & reset directly in the RPi.GPIO code?

Regards,
François GUILLIER

[Ben Croston]

Possibly linked to issue 60 - sending task to the background using Ctrl-Z then bg has the same symptoms.

[Ben Croston]

Possibly related to this:
https://www.raspberrypi.org/forums/viewtopic.php?f=32&t=123305&sid=1cd26b5c521932440c0f31fdab9c266b#p829698