irq firing multiple times, why?

[thewifimaster]

I have two light barriers connected to two GPIO inputs and the following program code to handle the status change. What I do not understand is why the irq typically fires 8x times on a status change. I now just filter it in my code, but want to understand what is happening.

Any hints?

Code: Select all

import machine
import micropython
    
micropython.alloc_emergency_exception_buf(100) # enable debugging in IRQ handler as per https://docs.micropython.org/en/latest/reference/isr_rules.html#the-emergency-exception-buffer

LICHTSCHRANKE_1_PIN = const(9)
LICHTSCHRANKE_2_PIN = const(11)


class lichtschranke:
    
    def __init__(self, gpio):
        self.pin = machine.Pin(gpio, machine.Pin.IN, machine.Pin.PULL_DOWN)
        self.pin.irq(trigger = machine.Pin.IRQ_FALLING, handler = self.irq_handler)
        self.status = self.pin.value()
        
    def irq_handler(self, pin): # pin argument has to be set as it is sent by the IRQ
        if self.status != self.pin.value(): # for whatever reason up to 8x IRQs fire with one change, debouncing does not seem to be the isse and disabling the IRQ does not make sense, hence filter
            try:
                micropython.schedule(self.process, self.pin.value()) # detach any follow-on data processing task to the main program routine to keep the IRQ routine short
                self.status = self.pin.value()
            except RuntimeError: # schedule queue fills up very quickly, ignore - not sure if this is the right thing to do though (..)
                pass
                
    def process(self, data):
        print('%s: %s' % (self.pin, data))


l1 = lichtschranke(LICHTSCHRANKE_1_PIN)
l2 = lichtschranke(LICHTSCHRANKE_2_PIN)

while True:
    pass

I am on v1.17 on a Lolin S2 Mini (ESP32-S2).

[pythoncoder]

I would first investigate whether the hardware is generating multiple pulses. Can you get access to an oscilloscope or logic analyser?

[Roberthh]

Most likely the interrupt is firing multiple times. That happens if the input signal has a "slow" slope. The input logic of the GPIO port can create several high/low transitions, when the signal is about Vdd/2. That can be caused by noise, internal or external. That can be covered by software or hardware. Software would ignore the following interrupts for a while. Hardware would be to set up a Schmitt-Trigger input characteristic.

[thewifimaster]

Thanks Peter and Robert, guess I'll dig out that Oscilloscope at work

[thewifimaster]

Ok, as it seems it requires some debouncing.