Raspberry Pi Forums

Posted: **Thu Feb 19, 2015 2:18 pm**

I have written a program to output data to a WS2803 LED controller that is connected to GPIO17/GPIO18. The code itself runs properly, which is to say that the one LED I currently have connected does exactly what I expect, but I am getting an error when I CTRL+C the program to get it to stop. I think this pertains to my GPIO.cleanup() call which I added inside a try/except block to stop the "this channel is already in use" warnings when I run the program multiple times.

Here is my code:

Code: Select all

import RPi.GPIO as GPIO
from time import sleep

GPIO.setmode(GPIO.BCM)

clock = 17
mosi = 18
GPIO.setup(clock,GPIO.OUT)
GPIO.setup(mosi,GPIO.OUT)

GPIO.output(clock,True)
GPIO.output(mosi,False)

counter = 0

def writeByte(value):
        # do something to write the byte
        mask = 0x80

        for i in range(8):
                GPIO.output(clock,False)
                if (value & mask):
                        GPIO.output(mosi,True)
                else:
                        GPIO.output(mosi,False)
                GPIO.output(clock,True)
                mask >>= 1


while True:
        try:
                GPIO.output(clock,False)
                sleep(0.0005)

                for i in range(3):
                        writeByte(counter)

                for i in range(15):
                        writeByte(0)

                counter = counter + 1
                if (counter > 255):
                        counter = 0

        except KeyboardInterrupt:
                GPIO.cleanup()

And here is the error i get when I stop the program:

Code: Select all

 ~/spi $ sudo python test.py
^CTraceback (most recent call last):
  File "test.py", line 32, in <module>
    GPIO.output(clock,False)
RuntimeError: Please set pin numbering mode using GPIO.setmode(GPIO.BOARD) or GPIO.setmode(GPIO.BCM)

Without the GPIO.cleanup() I get the following errors when I run the program more than one time:

Code: Select all

test.py:8: RuntimeWarning: This channel is already in use, continuing anyway.  Use GPIO.setwarnings(False) to disable warnings.
  GPIO.setup(clock,GPIO.OUT)
test.py:9: RuntimeWarning: This channel is already in use, continuing anyway.  Use GPIO.setwarnings(False) to disable warnings.
  GPIO.setup(mosi,GPIO.OUT)

Clearly I am doing something wrong. I have general familiarity with embedded systems (some arduino/pic experience) but usually do my development in .NET, this is my first ever time using python. Can anybody spot my mistake? Thanks in advance for any help!

Posted: **Thu Feb 19, 2015 2:45 pm**

D'oh! I found the error. The try/except is inside the loop when it should be outside! Pushing that up one level fixes the problem. Here is the solution:

Code: Select all

import RPi.GPIO as GPIO
from time import sleep

GPIO.setmode(GPIO.BCM)

clock = 17
mosi = 18
GPIO.setup(clock,GPIO.OUT)
GPIO.setup(mosi,GPIO.OUT)

GPIO.output(clock,True)
GPIO.output(mosi,False)

counter = 0

def writeByte(value):
        # do something to write the byte
        mask = 0x80

        for i in range(8):
                GPIO.output(clock,False)
                if (value & mask):
                        GPIO.output(mosi,True)
                else:
                        GPIO.output(mosi,False)
                GPIO.output(clock,True)
                mask >>= 1


try:
        while True:
                GPIO.output(clock,False)
                sleep(0.0005)

                for i in range(3):
                        writeByte(counter)

                for i in range(15):
                        writeByte(0)

                counter = counter + 1
                if (counter > 255):
                        counter = 0

except KeyboardInterrupt:
        GPIO.cleanup()

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