SMBus fails in a loop for the first couple reads

[wildbiotiger]

Working on an Ubuntu system using the following

• Ubuntu 16.04
• Python 3.5.2
• I2C bus 8 w/ a smart battery at address 0xb

and encountered a weird error. When using SMBus or SMBusWrapper, for the first couple of reads, I get the following OSError exception:
[Errno 6] No such device or address
But after a half second or so, the reads begin to succeed. I've used the command-line python to try and reproduce but I am getting mixed results: some success, some failures.

Example code below (should reproduce it):

def main():
 nowork = True
    bust = smbus2.SMBus(8)
    while(nowork):
        try:
            temperature = bust.read_word_data(0xb, 0x8)
            nowork = False
        except OSError as ex:
            print("fail %s" % str(ex))
        except:
            print("fails")

if __name__ == "__main__":
    main()

By sticking it in a retry loop until successful, I'm able to bypass it, but it doesn't feel like a clean solution to me. Any suggestions?

[kplindegaard]

@wildbiotiger, I've no idea.

But I have come across devices that require a little time to process the last operation you send. For example, if you write/call something that does return a result successfully, the device isn't really ready for the next command right away. Some need time to do a little processing before they can accept a new one. Could that be part of the explanation here, you think? Or that the device need time to power up properly? Or there is some kind of other initialization that's not done right?

[wildbiotiger]

It may be that the script is processing faster than the underlying buffer fills, but I am curious if the operations are somewhat non-blocking. Would make things a little more interesting.

[kplindegaard]

@wildbiotiger It would surprise me if that's the explanation.