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devel / comp.lang.python / Re: Is a Python event polled or interrupt driven?

SubjectAuthor
* Is a Python event polled or interrupt driven?Chris Green
`* Re: Is a Python event polled or interrupt driven?Chris Angelico
 `- Re: Is a Python event polled or interrupt driven?Chris Green

1
Is a Python event polled or interrupt driven?

<3dqkvj-vblf3.ln1@esprimo.zbmc.eu>

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From: cl...@isbd.net (Chris Green)
Newsgroups: comp.lang.python
Subject: Is a Python event polled or interrupt driven?
Date: Thu, 12 Oct 2023 10:21:07 +0100
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 by: Chris Green - Thu, 12 Oct 2023 09:21 UTC

In the following code is the event polled by the Python process
running the code or is there something cleverer going on such that
Python sees an interrupt when the input goes high (or low)?

import Adafruit_BBIO.GPIO as GPIO

Pin = "P8_8"
GPIO.setup(Pin, GPIO.IN) # set GPIO25 as input (button)

def my_callback(channel):
if GPIO.input(Pin):
print "Rising edge detected on 25"
else: # if port 25 != 1
print "Falling edge detected on 25"

GPIO.add_event_detect(Pin, GPIO.BOTH, my_callback, 1)

--
Chris Green
·

Re: Is a Python event polled or interrupt driven?

<mailman.4.1697123248.21446.python-list@python.org>

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From: ros...@gmail.com (Chris Angelico)
Newsgroups: comp.lang.python
Subject: Re: Is a Python event polled or interrupt driven?
Date: Fri, 13 Oct 2023 02:07:14 +1100
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 by: Chris Angelico - Thu, 12 Oct 2023 15:07 UTC

On Fri, 13 Oct 2023 at 01:48, Chris Green via Python-list
<python-list@python.org> wrote:
>
> In the following code is the event polled by the Python process
> running the code or is there something cleverer going on such that
> Python sees an interrupt when the input goes high (or low)?
>

This isn't something inherent to Python; it's the specific behaviour
of the library you're using. So I dug through that library a bit, and
ended up here:

https://github.com/adafruit/adafruit-beaglebone-io-python/blob/cf306ed7f9f24111d0949dd60ac232e81241bffe/source/event_gpio.c#L753

which starts a thread:

https://github.com/adafruit/adafruit-beaglebone-io-python/blob/cf306ed7f9f24111d0949dd60ac232e81241bffe/source/event_gpio.c#L662

which appears to make use of epoll for efficient event handling. Edge
detection itself seems to be done here:

https://github.com/adafruit/adafruit-beaglebone-io-python/blob/cf306ed7f9f24111d0949dd60ac232e81241bffe/source/event_gpio.c#L522

I don't know enough about the architecture of the BeagleBone to be
certain, but my reading of it is that most of the work of edge
detection is done by the OS kernel, which then sends the Adafruit
handler a notification via a file descriptor. The secondary thread
waits for those messages (which can be done very efficiently), and in
turn calls the Python callbacks.

In other words, the "something cleverer" is all inside the OS kernel,
and yes, in effect, it's an interrupt.

ChrisA

Re: Is a Python event polled or interrupt driven?

<3tmlvj-i0dh3.ln1@esprimo.zbmc.eu>

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From: cl...@isbd.net (Chris Green)
Newsgroups: comp.lang.python
Subject: Re: Is a Python event polled or interrupt driven?
Date: Thu, 12 Oct 2023 18:27:31 +0100
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 by: Chris Green - Thu, 12 Oct 2023 17:27 UTC

Chris Angelico <rosuav@gmail.com> wrote:
> On Fri, 13 Oct 2023 at 01:48, Chris Green via Python-list
> <python-list@python.org> wrote:
> >
> > In the following code is the event polled by the Python process
> > running the code or is there something cleverer going on such that
> > Python sees an interrupt when the input goes high (or low)?
> >
>
> This isn't something inherent to Python; it's the specific behaviour
> of the library you're using. So I dug through that library a bit, and
> ended up here:
>
> https://github.com/adafruit/adafruit-beaglebone-io-python/blob/cf306ed7f9f24111d0949dd60ac232e81241bffe/source/event_gpio.c#L753
>
>
> which starts a thread:
>
> https://github.com/adafruit/adafruit-beaglebone-io-python/blob/cf306ed7f9f24111d0949dd60ac232e81241bffe/source/event_gpio.c#L662
>
>
> which appears to make use of epoll for efficient event handling. Edge
> detection itself seems to be done here:
>
> https://github.com/adafruit/adafruit-beaglebone-io-python/blob/cf306ed7f9f24111d0949dd60ac232e81241bffe/source/event_gpio.c#L522
>
>
> I don't know enough about the architecture of the BeagleBone to be
> certain, but my reading of it is that most of the work of edge
> detection is done by the OS kernel, which then sends the Adafruit
> handler a notification via a file descriptor. The secondary thread
> waits for those messages (which can be done very efficiently), and in
> turn calls the Python callbacks.
>
> In other words, the "something cleverer" is all inside the OS kernel,
> and yes, in effect, it's an interrupt.
>
Wow! Thanks for doing all that research. It sounds as if it may be
more efficient than I thought so may be fast enough. I guess I'll
just have to try some actual code (and hardware) and see how it goes.

Thanks again!

--
Chris Green
·

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