I'm seeing the same issue. The number of reads it takes to get the actual value seems to correspond to the number of analog pins you have read from. If you have only read from one adc pin, you will get the correct values each time. I've mailed those who were listed on the commits for ti_am33x_adc. Hopefully we will get a response.
On Friday, March 21, 2014 6:56:11 AM UTC-4, Jorgen wrote: > > I have enabled the analog inputs on a Beaglebone Black by adding BB-ADC to > optargs in uEnv.txt: > > optargs=capemgr.disable_partno=BB-BONELT-HDMI > capemgr.enable_partno=BB-SPIDEV0,BB-SPIDEV1,BB-UART1,BB-ADC > > > The basic analog input works, if I do a: > > cat /sys/bus/iio/devices/iio:device0/in_voltage3_raw > > it returns a value which is proportional to the applied voltage. > > However the value is not always up-to-date. If I change the input voltage, > I can read the old input voltage several times before I can read the > correct value. The strange part is that I am obviously not just reading a > stored value, because the LSB can change on subsequent reads, until I > finally read the correct value: > > jsa@bb00:~$ cat /sys/bus/iio/devices/iio:device0/in_voltage3_raw > 489 > > The applied voltage is now halved (from ~200mV to ~100mV). I wait for > about 1 second between each read: > > jsa@bb00:~$ cat /sys/bus/iio/devices/iio:device0/in_voltage3_raw > 489 > jsa@bb00:~$ cat /sys/bus/iio/devices/iio:device0/in_voltage3_raw > 488 > jsa@bb00:~$ cat /sys/bus/iio/devices/iio:device0/in_voltage3_raw > 489 > jsa@bb00:~$ cat /sys/bus/iio/devices/iio:device0/in_voltage3_raw > 489 > jsa@bb00:~$ cat /sys/bus/iio/devices/iio:device0/in_voltage3_raw > 489 > jsa@bb00:~$ cat /sys/bus/iio/devices/iio:device0/in_voltage3_raw > 488 > jsa@bb00:~$ cat /sys/bus/iio/devices/iio:device0/in_voltage3_raw > 489 > jsa@bb00:~$ cat /sys/bus/iio/devices/iio:device0/in_voltage3_raw > 243 > > Finally I read the correct value. What is going on? Can I force an update > (sample)? > -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to beagleboard+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
