Question: Example Usage with While Loop

[dhildreth]

I'm attempting to use this excellent library in a project where I'm attempting to turn on an LED when an interrupt is triggered, but I have a feeling I'm missing something basic. This is the first time I've heard of Twisted Reactor, so I'm wondering if that has something to do with my misunderstanding of what I thought was relatively straightforward.

I have a while loop which reads a light sensor every second. The light sensor (I2C device) is programmed to trigger an interrupt when the value reads below a certain threshold. I have the interrupt pin of the sensor connected to GPIO 65 of my SBC. I then have an LED hooked up to GPIO 64 of my SBC. Something like this:

import time
from twisted.internet import reactor
from sysfs.gpio import Controller, OUTPUT, INPUT, RISING

Controller.available_pins = [64, 65]
led_en = Controller.alloc_pin(64, OUTPUT)

def pin_changed(pin, state):
    print("Pin changed to %d state" % state)
    if state:
        led_en.set()   # Sets pin to high logic level
    else:
        led_en.reset()

intt = Controller.alloc_pin(65, INPUT, pin_changed, RISING)

reactor.run()

while True:

    # Enable sensor light interrupts
    # Read and store sensor light value via I2C
    # Print sensor light value to console for debugging
    print("Testing!")
    sleep(.5)

Anyways, so I'm expecting my while loop to execute, but it never does. Instead, I get "Pin changed to 0 state", from the pin_changed() callback and then nothing!

$ sudo python test-gpio-interrupt.py 
SysfsGPIO: alloc_pin(64, out, None, None, 0)
SysfsGPIO: alloc_pin(65, in, <function pin_changed at 0x76468830>, rising, 0)
Pin changed to 0 state

I then have to Ctrl + C to end the process.

I would've expected the code in the while loop to execute. I must be having a lapse of common sense and I'm hoping you can help.

[zpfvo]

the reactor.run() method does not return. It functions as your while loop. If you want to print something in while running you could try something like in this example: http://www.saltycrane.com/blog/2008/10/running-functions-periodically-using-twisteds-loopingcall/

[derekstavis]

@zpfvo is right. reactor.run() is the actual while True of your program. If you need to do a loop inside the loop reactor.run() does, you need to use LoopingCall 👍