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> 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