The following patches were removed and behavior returned to normal.

0019-iio-ti_am335x_adc-Add-continuous-sampling-and-trigge.patch
0020-iio-ti_am335x_adc-Add-IIO-map-interface.patch

Once 19 was re-applied, the bug returned.

It would appear that patch19 is the problem.  On an unrelated note, the 
continuous sampling patch seems to still be missing the mode file to 
tell it to sample continuously or oneshot in the sysfs directory as 
referenced at 
http://processors.wiki.ti.com/index.php/AM335x_ADC_Driver%27s_Guide. 
Maybe this should be moved to the beta kernel until stable?

Cheers.

On 3/31/2014 12:04 AM, Rob Mosher wrote:

(sorry for the duplicate, got bounces due to HTML encoding)

The specified patch is already included.  The system was running the
latest kernel from Robert Nelson's repo.  Any suggestions?  I'll try
removing some of the patches to see if it fixes this behavior.  I have a
feeling I know which one is doing it.

Thanks.

output from running patch.sh with source pulled from
https://github.com/beagleboard/kernel/tree/3.8

/home/bbuild/comp/kernel/patches/adc/0017-IIO-ADC-ti_adc-Fix-1st-sample-read.patch:
applied

Just in case, I built and installed the kernel and the same behavior
persisted.

root@rbone:/# uname -a
Linux rbone 3.8.13-00737-g7dfad77 #1 SMP Sun Mar 30 22:11:44 EDT 2014
armv7l GNU/Linux

gpio30 is connected to AIN4 using a voltage divider

root@rbone:/# cd /sys/class/gpio/
root@rbone:/sys/class/gpio# echo 30 > export
root@rbone:/sys/class/gpio# echo BB-ADC > /sys/devices/bone_capemgr.9/slots
root@rbone:/sys/class/gpio# cd /sys/devices/ocp.3/helper.11/
root@rbone:/sys/devices/ocp.3/helper.11# echo out >
/sys/class/gpio/gpio30/direction

root@rbone:/sys/devices/ocp.3/helper.11# echo 1 >
/sys/class/gpio/gpio30/value
root@rbone:/sys/devices/ocp.3/helper.11# cat AIN4
1460

root@rbone:/sys/devices/ocp.3/helper.11# echo 0 >
/sys/class/gpio/gpio30/value
root@rbone:/sys/devices/ocp.3/helper.11# cat AIN4
0

root@rbone:/sys/devices/ocp.3/helper.11# grep . AIN[0-3] AIN[5-7]
AIN0:1550
AIN1:1213
AIN2:1485
AIN3:795
AIN5:513
AIN6:744
AIN7:1698

root@rbone:/sys/devices/ocp.3/helper.11# echo 1 >
/sys/class/gpio/gpio30/value
root@rbone:/sys/devices/ocp.3/helper.11# cat AIN4
0
root@rbone:/sys/devices/ocp.3/helper.11# cat AIN4
0
root@rbone:/sys/devices/ocp.3/helper.11# cat AIN4
0
root@rbone:/sys/devices/ocp.3/helper.11# cat AIN4
0
root@rbone:/sys/devices/ocp.3/helper.11# cat AIN4
0
root@rbone:/sys/devices/ocp.3/helper.11# cat AIN4
0
root@rbone:/sys/devices/ocp.3/helper.11# cat AIN4
1460

On 3/30/2014 9:16 AM, Zubair Lutfullah wrote:

quoted

https://github.com/beagleboard/kernel/blob/3.8/patches/adc/0017-IIO-ADC-ti_adc-Fix-1st-sample-read.patch

IIRC, this patch fixes this issue

Can you compile the kernel from the sources and check?
https://github.com/beagleboard/kernel/tree/3.8

Regards
ZubairLK

On Sun, Mar 30, 2014 at 7:04 AM, Rob Mosher <nyt@countercultured.net
<mailto:nyt@countercultured.net>> wrote:

    Just a note, the same behavior persists with BB-ADC dtb and
    reading from in_voltage4_raw


    On 3/30/2014 12:30 AM, Rob Mosher wrote:

        Hello fine developers,

        It seems I've stumbled upon a problem while developing a full
        featured Ruby gem for the Beaglebone.

        It seems a patch included in the beaglebone kernel causes some
        issues while reading analog inputs.  Apparently the samples
        get backlogged by the number of adc pins in use.  I'm not sure
        which patch exactly as there are a number that affect adc
        buffering and I'm not currently setup for kernel building,
        however the below output should detail the problem.

        Using the official Debian image.
        Linux rbone 3.8.13-bone43 #1 SMP Wed Mar 26 14:21:39 UTC 2014
        armv7l GNU/Linux

        Distributor ID: Debian
        Description:    Debian GNU/Linux 7.4 (wheezy)
        Release:        7.4
        Codename:       wheezy

        root@rbone:~# echo cape-bone-iio >
        /sys/devices/bone_capemgr.9/slots

        This is the normal and expected behavior.

        1.8v applied to AIN4
        root@rbone:/sys/devices/ocp.3/helper.12# cat AIN4
        1798

        0v applied to AIN4
        root@rbone:/sys/devices/ocp.3/helper.12# cat AIN4
        0

        1.8v applied to AIN4
        root@rbone:/sys/devices/ocp.3/helper.12# cat AIN4
        1798

        0v applied to AIN4
        root@rbone:/sys/devices/ocp.3/helper.12# cat AIN4
        0

        So far working as intended....  Now reading from the other pins.

        root@rbone:/sys/devices/ocp.3/helper.12# grep . AIN[0-3] AIN[5-7]
        AIN0:1563
        AIN1:1221
        AIN2:1487
        AIN3:789
        AIN5:514
        AIN6:743
        AIN7:1698

        Now applying 1.8v to AIN4
        root@rbone:/sys/devices/ocp.3/helper.12# cat AIN4
        0
        root@rbone:/sys/devices/ocp.3/helper.12# cat AIN4
        0
        root@rbone:/sys/devices/ocp.3/helper.12# cat AIN4
        0
        root@rbone:/sys/devices/ocp.3/helper.12# cat AIN4
        0
        root@rbone:/sys/devices/ocp.3/helper.12# cat AIN4
        0
        root@rbone:/sys/devices/ocp.3/helper.12# cat AIN4
        0
        root@rbone:/sys/devices/ocp.3/helper.12# cat AIN4
        1798

        Now applying 0v to AIN4

        root@rbone:/sys/devices/ocp.3/helper.12# cat AIN4
        1460
        root@rbone:/sys/devices/ocp.3/helper.12# cat AIN4
        1798
        root@rbone:/sys/devices/ocp.3/helper.12# cat AIN4
        1798
        root@rbone:/sys/devices/ocp.3/helper.12# cat AIN4
        1460
        root@rbone:/sys/devices/ocp.3/helper.12# cat AIN4
        1460
        root@rbone:/sys/devices/ocp.3/helper.12# cat AIN4
        1460
        root@rbone:/sys/devices/ocp.3/helper.12# cat AIN4
        0



        And another example, showing relation to the number of pins in
        use.

        1.8v to AIN4
        root@rbone:/sys/devices/ocp.3/helper.12# cat AIN4
        1460
        root@rbone:/sys/devices/ocp.3/helper.12# grep . AIN[0-3]
        AIN0:1697
        AIN1:1298
        AIN2:1524
        AIN3:816
        root@rbone:/sys/devices/ocp.3/helper.12# cat AIN4
        1798

        0v to AIN4
        root@rbone:/sys/devices/ocp.3/helper.12# cat AIN4
        1798
        root@rbone:/sys/devices/ocp.3/helper.12# cat AIN4
        1460
        root@rbone:/sys/devices/ocp.3/helper.12# cat AIN4
        1460
        root@rbone:/sys/devices/ocp.3/helper.12# cat AIN4
        1460
        root@rbone:/sys/devices/ocp.3/helper.12# cat AIN4
        0

        1.8v to AIN4
        root@rbone:/sys/devices/ocp.3/helper.12# cat AIN4
        0
        root@rbone:/sys/devices/ocp.3/helper.12# cat AIN4
        0
        root@rbone:/sys/devices/ocp.3/helper.12# cat AIN4
        0
        root@rbone:/sys/devices/ocp.3/helper.12# cat AIN4
        0
        root@rbone:/sys/devices/ocp.3/helper.12# cat AIN4
        1798

        --         Rob Mosher
        Senior Network and Software Engineer
        Hurricane Electric / AS6939