Htykuut

I'm working on a Raspberry Pi project where I have an OLED display that is continuously updated with information in a Python while True-loop. However, whenever I press a button (GPIO 5) I would like to display some other static information (e.g. system info) for as long as the button is depressed, or possibly for a predefined period of time. When the button is released, the "main loop" may take over again.
I have tried to implement this using RPi.GPIO and a callback function for the display of system info, but the problem is of course that even during the callback function execution, the main loop continues writing to the OLED, creating garbage on the OLED if GPIO 5 is depressed: Both "threads" are writing simultaneously to the OLED...

I assume I need a way to pause the execution of the main loop during the callback function and I have experimented with Semaphore and aquire/release but with no luck. I have also considered the possibility of having two callback functions in combination with Semaphore, but since the info displayed in the main loop should be continuously updated (e.g. not interrupt-driven) I'm not so sure that is a solution for me.

At this point I am not even sure what to google next. Perhaps someone in here can enlighten me? Is this perhaps a totally wrong way of doing this kind of thing? (Limited experience with Python...)

Below is a simplified code example that simulates what I would like to do.

import time

import Adafruit_GPIO.SPI as SPI

import RPi.GPIO as GPIO

import Adafruit_SSD1306

from PIL import Image

from PIL import ImageDraw

from PIL import ImageFont



# Initialize

disp = Adafruit_SSD1306.SSD1306_128_64(rst=None)

disp.begin()

disp.clear()

disp.display()

image = Image.new('1', (disp.width, disp.height))

draw = ImageDraw.Draw(image)

font = ImageFont.load_default()

GPIO.setmode(GPIO.BCM) 

GPIO.setup(5, GPIO.IN, pull_up_down=GPIO.PUD_UP) # Input with pull-up



def clear_display():

    draw.rectangle((0,0,disp.width,disp.height), outline=0, fill=0)

    disp.image(image)

    disp.display()



# Callback function 

def display_system_info(channel):

    draw.text((0, 0), "System info displayed",  font=font, fill=255)

    draw.text((0, 9), "for five seconds.",  font=font, fill=255)

    disp.image(image)

    disp.display()

    time.sleep(5)

    clear_display()



GPIO.add_event_detect(5, GPIO.RISING, callback=display_system_info, bouncetime=200)



try:

    while True:

        for counter in range(7):

            draw.text((0,counter*9), "Printing line {0:d}".format(counter),  font=font, fill=255)

            disp.image(image)

            disp.display()

            time.sleep(1)

        clear_display()

except KeyboardInterrupt:  

    GPIO.cleanup()       # clean up GPIO on CTRL+C exit

GPIO.cleanup()           # clean up GPIO on normal exit  

Many thanks for any help.

/N

I am solving situations like this with global varialbe - buttonPressed.
When you press button (GPIO 5), buttonPressed is set to True and main loop does nothing.
Hope it is clear for you and will help you.

import time

import Adafruit_GPIO.SPI as SPI

import RPi.GPIO as GPIO

import Adafruit_SSD1306

from PIL import Image

from PIL import ImageDraw

from PIL import ImageFont



# Initialize

disp = Adafruit_SSD1306.SSD1306_128_64(rst=None)

disp.begin()

disp.clear()

disp.display()

image = Image.new('1', (disp.width, disp.height))

draw = ImageDraw.Draw(image)

font = ImageFont.load_default()

GPIO.setmode(GPIO.BCM) 

GPIO.setup(5, GPIO.IN, pull_up_down=GPIO.PUD_UP) # Input with pull-up



buttonPressed = False



def clear_display():

    draw.rectangle((0,0,disp.width,disp.height), outline=0, fill=0)

    disp.image(image)

    disp.display()



# Callback function 

def display_system_info(channel):

    global buttonPressed

    buttonPressed = True

    draw.text((0, 0), "System info displayed",  font=font, fill=255)

    draw.text((0, 9), "for five seconds.",  font=font, fill=255)

    disp.image(image)

    disp.display()

    time.sleep(5)

    clear_display()

    buttonPressed = False



GPIO.add_event_detect(5, GPIO.RISING, callback=display_system_info, bouncetime=200)



try:

    while True:

        if(not buttonPressed):

            for counter in range(7):

                draw.text((0,counter*9), "Printing line {0:d}".format(counter),  font=font, fill=255)

                disp.image(image)

                disp.display()

                time.sleep(1)

            clear_display()

except KeyboardInterrupt:  

    GPIO.cleanup()       # clean up GPIO on CTRL+C exit

GPIO.cleanup()           # clean up GPIO on normal exit  

Try and let me know.

Depending on your application I'd avoid doing any real work inside of the callback. Instead I'd only set a flag which the main thread/loop can handle or add the events to a queue which is processed by the main thread/loop.

I realized interrupts was not a good path to walk for this particular application. Instead, I re-wrote my code so that it's only possible to push the button when the main loop is idle and waiting...which is most of the time of course. Thanks for input!