why my interrupt callback got slow with tkinter

Question

I am interfacing rotary encoder with raspberry Pi using the interrupt method and want to show its value on tkinter Label. 1st I tested my interrupt callback function with main, where my rotary encoder works perfectly i.e. counter=1000 in one rotation of encoder but when I add the tkinter part it slows down i.e. counter=800 in one rotation of encoder. I think there is some issue with the way of handling tkinter function, but not able to trace the issue. Here I am providing my two different codes with output.

from RPi import GPIO
from time import sleep
import math
import Adafruit_MCP4725
dac=Adafruit_MCP4725.MCP4725(address=0x61)
a=22
b=23
GPIO.setmode(GPIO.BCM)
GPIO.setup(a,GPIO.IN)
GPIO.setup(b,GPIO.IN)

clkLastState=GPIO.input(a)

def my_callback(channel):
   global clkLastState
   global counter
   clkState=GPIO.input(a)
   if clkState != clkLastState:
           dtState=GPIO.input(b)
           if dtState != clkState:
              counter +=1
           else:
              counter -=1
           text=str(counter/2)
           print (text[0:-2])
   clkLastState=clkState
  # sleep(0.001)
   #finally:
counter=0
clkLastState=GPIO.input(a)
def main():
 global counter
 try:
#  GPIO.add_event_detect(23,GPIO.BOTH,callback=my_callback)
  while (1):
     print(counter/2)
     dac.set_voltage(int(counter/2))
     vlt=int(counter/2)/4096*5.0
     print(vlt)
     sleep(1)
 except KeyboardInterrupt:
  print("end it")
  GPIO.cleanup() 
GPIO.add_event_detect(23,GPIO.BOTH,callback=my_callback)
#input("enter anything")
if __name__=='__main__':
 # input("do") 
  main()

This is the code where it is working as per encoder specification.

955
955
956
956
957
957
958
958
959
959.0
1.170654296875

Here program with tkinter.

from RPi import GPIO
from time import sleep
import tkinter as tk
a=22
b=23
GPIO.setmode(GPIO.BCM)
GPIO.setup(a,GPIO.IN)
GPIO.setup(b,GPIO.IN)
root=tk.Tk()
clkLastState=GPIO.input(a)

def my_callback(channel):
   global clkLastState
   global counter
   clkState=GPIO.input(a)
   if clkState != clkLastState:
           dtState=GPIO.input(b)
           if dtState != clkState:
              counter +=1
           else:
              counter -=1
           text=str(counter/2)
           print (text[0:-2])
           var.set(text)
   clkLastState=clkState
  # sleep(0.001)
counter=0
clkLastState=GPIO.input(a)
GPIO.add_event_detect(23,GPIO.BOTH,callback=my_callback)
print (counter)
var=tk.IntVar()
L1=tk.Label(root,bg="orange",fg="red",textvariable=var)
L1.pack()
# var.set(counter)
# root.after(500,main)
root.geometry("100x100")
root.mainloop()
#var=tk.IntVar()
#L1=tk.Label(root,bg="orange",fg="red",textvariable=var)
#L1.pack()  
#GPIO.add_event_detect(23,GPIO.BOTH,callback=my_callback)
input("enter anything")
GPIO.cleanup()

And here is its output.

For more details, here is my encoder datasheet<http://dien-congnghiep.com/upload/ls_mecapion/encoder_ls_mecapion_s40.pdf>

You have called `dac.set_voltage(...)` repeatedly in the first program (without `tkinter`), but not in the one with `tkinter`. Is it the cause of the difference? — acw1668, Feb 13 '20 at 07:21
@acw1668,as per prog counter increment and decrements by interrupt callback function,so in both case counter should be same .only diff is in 1st prog i am putting counter value on `dac.set_voltage(...)` and in 2nd prog i am putting on `var.set(..)`.As per my application i want to show counter value on tkinter ,So am i using tkinter in wrong way? — Adee, Feb 13 '20 at 08:04
@Adee It seems concurent running `tkinter.mainloop()` and `GPIO event loop` slows down. Both are using `Thread` and have to share one cpu. Try to run either on in a own `Process`. — stovfl, Feb 13 '20 at 11:16
@stovfl,Thats what i am thinking also,but as per application i need tkinter window ,thats why i select raspberry pi as it is powerful,because my 8 bit nuvoton micro controller work perfectly with same encoder and other interrupt event. — Adee, Feb 13 '20 at 12:13
@stovfl,I am not getting your comment "Try to run either on in a own Process".Can u please give a small demonstration for it. — Adee, Feb 13 '20 at 15:58
***"not getting your comment"***: I advise about [multiprocessing-vs-threading-python](https://stackoverflow.com/questions/3044580) — stovfl, Feb 13 '20 at 16:12

why my interrupt callback got slow with tkinter

0 Answers0