GPIO callbacks called simultaneously

Question

With Raspberry Pi, if you have

import RPi.GPIO as GPIO  
GPIO.setmode(GPIO.BCM)  

GPIO.setup(20, GPIO.IN, pull_up_down=GPIO.PUD_UP)  
GPIO.setup(17, GPIO.IN, pull_up_down=GPIO.PUD_UP)  

def my_callback(channel):  
    print "falling edge detected on ", channel  

GPIO.add_event_detect(17, GPIO.FALLING, callback=my_callback, bouncetime=300)  
GPIO.add_event_detect(20, GPIO.FALLING, callback=my_callback, bouncetime=300)  

you get the usual callback called when pin 17 falls or when pin 20 falls The callback function prints which channel was called.

My question is, what happens if both pins falls at the same time?

Unfortunately I don't have a Pi to try it right now and even if I did, the human error in -say- pressing one pin attached button before another also counts. What happens when it is done at the exact same time?

Answer 1

Both events fire in quick succession. I wired both GPIO 17 and GPIO 20 to the same button and got the following :

falling edge detected on 20
falling edge detected on 17

Edit : code added

import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)  

GPIO.setup(20, GPIO.IN, pull_up_down=GPIO.PUD_UP)  
GPIO.setup(17, GPIO.IN, pull_up_down=GPIO.PUD_UP)  

def my_callback(channel):  
    print("falling edge detected on ", channel) 

GPIO.add_event_detect(17, GPIO.FALLING, callback=my_callback, bouncetime=300)  
GPIO.add_event_detect(20, GPIO.FALLING, callback=my_callback, bouncetime=300)

while True:
    time.sleep(0.1)
    print(".")