ADC (IIO) channels swapped after about 13 hours of operation

Technical Support
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1

Hi,

I’m running a program that is retrieving the raw ADC counts of ADC2 and ADC3 regularly using userspace (/sys/bus/iio/devices/iio:device0).
This seems to be working just fine for the first few hours and the files “in_voltage6_raw” and “in_voltage7_raw” nicely represent the correct values.

After about 13 hours though, it seems like the channels get swapped and when retrieving the value from “in_voltage6_raw” I am actually reading the value that I would expect from “in_voltage7_raw” and the other way around.
It seems like these channels get swapped for some reason.

After rebooting the entire OS, the problem is gone and I can retrieve the correct values from the correct files again.

Here is some serial output that visualizes this issue:

ge7_raw ibri-imx6:/sys/bus/iio/devices/iio:device0# cat in_voltage6_raw in_voltag
2047
0
ge7_raw ibri-imx6:/sys/bus/iio/devices/iio:device0# cat in_voltage6_raw in_voltag
2049
0
ge7_raw ibri-imx6:/sys/bus/iio/devices/iio:device0# cat in_voltage6_raw in_voltag
2047
0
ge7_raw ibri-imx6:/sys/bus/iio/devices/iio:device0# cat in_voltage6_raw in_voltag
2045
0
root@colibri-imx6:/sys/bus/iio/devices/iio:device0# reboot now
login as: root
Last login: Mon Apr 29 09:05:35 2019 from ##.##.##.##
root@colibri-imx6:~# cd /sys/bus/iio/devices/iio\:device0
root@colibri-imx6:/sys/bus/iio/devices/iio:device0# cat in_voltage6_raw in_voltage7_raw
0
2047
root@colibri-imx6:/sys/bus/iio/devices/iio:device0# cat in_voltage6_raw in_voltage7_raw
0
2039
root@colibri-imx6:/sys/bus/iio/devices/iio:device0# cat in_voltage6_raw in_voltage7_raw
0
2048

Does anyone have any idea what could be causing this?

Thanks in advance!

2

Hi @DemKev

This issue is known and we will try to fix this soon.

Best regards,
Jaski

3

Hi @DemKev,

Thank you for pointing this out. There is indeed an issue here. Another customer reported the same issue: STMPE811 IIO timeouts on read and confuses values - Technical Support - Toradex Community

This is planned to be fixed in Q2.

Which kernel version are you using?

4

Thanks for your reply.

I’m using the following kernel version: 4.9.144-2.8.5+g5758a8e.

Is there any workaround that we could use in the meantime to prevent this issue?

5

We don’t have any workaround yet, but the other customer mentioned the following: “With the profiler flag disabled, it also barely occurs.” So Could you try this. Thanks.

6

@DemKev could you also try if the same occurs on a mainline kernel? since 5.1-rc1 this driver is included in mainline.

7

Hi @DemKev

We have a fix for this Issue. You can get it from here.

Best regards,
Jaski

8

Hi Jaski,

This seems indeed to have fixed our issue. Thank you for the quick response!

Kind regards,
Ramon

9

Hi Roman,
Perfect, that it works. Thanks for the feedback.