利用中断方式控制树梅派的GPIO

淡淡的烟草味﹌ 2022-07-15 02:21 223阅读 0赞

# [Using Interrupt Driven GPIO][] #

In the previous post, a program keeps executing a while loop checking to see if a button has been pressed. This is called polling, and it's not very efficient because the program can't do anything else while waiting for the button to be pressed. It would be better if the program could do something else while it was waiting.

This can be achieved using interrupt driven IO. An interrupt is a signal generated by a peripheral device that lets the processor know that an event has happened. The RPi GPIO library makes this easy. You simply need to use the add\_event\_detect function to specify what type of event you're waiting for, and add\_event\_callback to specify what should happen when the event occurs.

In this exercise I used the same circuit as in the previous exercise, and I used the code below:

#!/usr/bin/env python
    
    import time
    import RPi.GPIO as GPIO
    
    
    # handle the button event
    def buttonEventHandler (pin):
        print "handling button event"
    
        # turn the green LED on
        GPIO.output(25,True)
    
        time.sleep(1)
    
        # turn the green LED off
        GPIO.output(25,False)
    
    
    
    # main function
    def main():
    
        # tell the GPIO module that we want to use 
        # the chip's pin numbering scheme
        GPIO.setmode(GPIO.BCM)
    
        # setup pin 23 as an input
        # and set up pins 24 and 25 as outputs
        GPIO.setup(23,GPIO.IN)
        GPIO.setup(24,GPIO.OUT)
        GPIO.setup(25,GPIO.OUT)
    
        # tell the GPIO library to look out for an 
        # event on pin 23 and deal with it by calling 
        # the buttonEventHandler function
        GPIO.add_event_detect(23,GPIO.FALLING)
        GPIO.add_event_callback(23,buttonEventHandler,100)
    
        # turn off both LEDs
        GPIO.output(25,False)
        GPIO.output(24,True)
    
        # make the red LED flash
        while True:
            GPIO.output(24,True)
            time.sleep(1)
            GPIO.output(24,False)
            time.sleep(1)
    
    
        GPIO.cleanup()
    
    
    
    if __name__=="__main__":
        main()

This program tells the GPIO library to look out for an event on pin 23 of the GPIO header. The event to look out for is a falling edge, where the voltage goes from 1 to 0. This example detects the GPIO.FALLING event, but it's also possible to detect GPIO.RISING and GPIO.BOTH. The function named buttonEventHandler is registered as the callback for the event.

The program then goes round the while loop making the red LED blink. When the button is pressed, buttonEventHandler is called, and the green LED is turned on for one second. The event is handled by a different thread, so while the green button is on, the red light continues to blink uninterrupted.

If your program doesn't need to do anything while its waiting for an event, you can call GPIO.wait\_for\_edge() which will make your program sleep until an event wakes it up. If your program no longer needs to wait for an event, you can unregister it by calling GPIO.remove\_event\_detect().

See also: [https://code.google.com/p/raspberry-gpio-python/wiki/Inputs][https_code.google.com_p_raspberry-gpio-python_wiki_Inputs]

[Using Interrupt Driven GPIO]: http://raspberrywebserver.com/gpio/using-interrupt-driven-gpio.html
[https_code.google.com_p_raspberry-gpio-python_wiki_Inputs]: https://code.google.com/p/raspberry-gpio-python/wiki/Inputs