[lm-sensors] i2cdetect running slow but not "bus inactive" slow, not sure why?

Wayne Tams wayne.tams at gmail.com
Tue Dec 20 17:26:19 CET 2011


On Tue, Dec 20, 2011 at 4:18 PM, Guenter Roeck
<guenter.roeck at ericsson.com> wrote:
> On Tue, Dec 20, 2011 at 11:00:35AM -0500, Wayne Tams wrote:
>> Hi Guenter,
>>
>> Turns out it was an I2C voltage translator had popped, thankfully all
>> my I2C devices are ok. Did not realise i2cdetect could behave in such
>> a peculiar way.
>>
> Hi Wayne,
>
> please don't top-post.

Sorry was not not thinking...end of the day
>
> Nothing to do with i2cdetect, but with the i2c bus driver. i2cdetect tries to read,
> and the bus driver ends up getting a transfer timeout for each read. Depending on
> the I2C bus chip and the driver, timeouts can be _very_ long, up to 500ms per read
> or even more.

I see, that makes sense. Once again thanks

Wayne
>
> Guenter
>
>> Thanks
>>
>> Wayne
>>
>> On Fri, Dec 16, 2011 at 4:29 PM, Guenter Roeck
>> <guenter.roeck at ericsson.com> wrote:
>> > On Fri, 2011-12-16 at 10:33 -0500, Wayne Tams wrote:
>> >> Hi,
>> >>
>> >> i2cdetect is behaving in a fashion that I have not seen before and I
>> >> just would like to know if anyone has a suggestion on what it is
>> >> telling me.
>> >>
>> >> Normally i2cdetect returns in <1s, if the bus were inactive it would
>> >> take closer to 20s. However I'm finding that the scanning is taken a
>> >> round 5s and the addresses returned appear random, except for one.
>> >> Obviously there must be a fault in my hardware, but I just wanted to
>> >> make sure that was/wasn't a common explanation for this behaviour
>> >> before I go debugging up the wrong tree.
>> >
>> > I typically see this kind of problem if there is something wrong on the
>> > i2c bus, for example if a signal is pulled high or low. I have also seen
>> > it after I managed to physically "destroy" an I2C controller by applying
>> > a reversed voltage to the i2c signal pins.
>> >
>> > If you have a logic analyzer or a scope, you might want to connect it to
>> > the clock and data lines to see what is happening on the bus.
>> >
>> > Guenter
>> >
>> >




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