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I am reading a 24bit value using I2C in Raspberry Pi.
I open the /dev/i2c-1 file and then reading from it using the os.read function in python.
The transaction is being carried out correctly.

enter image description here

But the problem is even though I can access the register, when I try to store the value in a variable it doesn't work. According to the documentation of os.read(), if the EOF is reached, an empty string is returned and that's exactly my problem. How can I store the correct value?

Code below:

fd = os.open(filename,os.O_RDWR) //Opens the file           
#The reason i use os.open instead of normal python open is that I
#need to access the linux C function.
def func(fd,addr):
    os.write(fd,addr) // Sets the pointer to the register to be read. 
    x = os.read(fd,3) //Reads the value from the register. 
    print x //Prints an empty string

In order to cross check, I tried using the pigpio library. If I read using its function, it returns 2 values, count of the bytes read and the byte string itself.

What I noticed was that if I try to store the byte string, the one returned from the pigpio function, I still get an empty string when i print it on screen like this print(data).

What I think the problem is not of storing the data, but of properly formatting it .

So can anyone suggest how do I convert the byte string to an int value?

I know that there's one function for python 3. But I need to use python 2

Muhammad Usman
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  • Read [seek() function?](https://stackoverflow.com/a/11696554/7414759) – stovfl Aug 16 '17 at 15:07
  • Tried it. It tells me that seek cannot be performed. I read about it and found out that not all of the files allow seek operations – Muhammad Usman Aug 16 '17 at 15:25
  • This is what I'm doing. file = os.open(filename,os.O_RDWR) – Muhammad Usman Aug 16 '17 at 20:47
  • In order to cross check, I tried using the pigpio library. If I read using its function, it returns 2 values, count of the bytes read and the byte string itself. What I noticed was that if I try to store the byte string, the one returned from the pigpio function, I still get an empty string when i print it on screen like this print(data). What I think the problem is not of storing the data, but of properly formatting it .So can anyone suggest how do I convert the byte string to an int value? I know that there's one for python 3. But I need to use python 2. – Muhammad Usman Aug 16 '17 at 20:53
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    Do print len(x) you would expect 3. X is a string but its characters aren't printable. – DisappointedByUnaccountableMod Aug 16 '17 at 21:19
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    Relevant: [byte-to-hex-and-hex-to-byte-string-conversion](http://code.activestate.com/recipes/510399-byte-to-hex-and-hex-to-byte-string-conversion/) – stovfl Aug 16 '17 at 21:25
  • Think about using Module `smbus`. [using-python-smbus-on-a-raspberry-pi](https://stackoverflow.com/questions/17317317/using-python-smbus-on-a-raspberry-pi-confused-with-syntax) and [using-the-i2c-interface-2](http://www.raspberry-projects.com/pi/programming-in-python/i2c-programming-in-python/using-the-i2c-interface-2) – stovfl Aug 16 '17 at 21:46
  • Len(x) returns 3. Its just a formatting problem then! Thanks everyone :) – Muhammad Usman Aug 17 '17 at 08:43
  • Tried it. Works perfectly! – Muhammad Usman Aug 17 '17 at 08:52

0 Answers0