How could i read adc value in character device driver(evm335x)?

Seonghoon Yoo

I would like to read adc value in character device driver.

While i was lookiing for any information related to adc, i found http://processors.wiki.ti.com/index.php/AM335x_ADC_Driver's_Guide.

But it just shows how to use adc in user space like application.

I have tried to find it. but i think adc is composed in sysfs device driver.

I have 2 questions.

first, is there any way to call the function from sysfs?

(the location i'm gonna in is character device driver.)

second, is there other ways to read adc value in character device driver??

help me anyone who can know well.

thank you for reading long my sentences.

I hope to see anwser about my question, :)

over 12 years ago

0 Miroslav Kiradzhiyski XID over 12 years ago

TI__Mastermind 25235 points

Hi,

As far as I understand you want to read the ADC value and store/write it to a character device on your system.

If this is the case, then you can use a simple script to do this. Something like this (if your character device driver supports echoing to it):

echo `cat /sys/bus/iio/devices/iio\:device0/in_voltage4_raw` > your_character_device

The other way is to write a user-space application that opens both your character device and ADC file and reads the ADC value, then writes it to your character device file.

The implementation is up to you.

Best regards,
Miroslav

0 Seonghoon Yoo over 12 years ago in reply to Miroslav Kiradzhiyski XID

Prodigy 140 points

Actually, my curiosity was different. i couldn't find any solution.

so i changed my mind. i made a user application and i used "open and read function related to file descriptor"

i was able to read adc value in case of "oneshot mode"

But i don't know how to read adc value in case of "continuous mode".

do you know how to do??

if you know it, please let me realize it

0 Miroslav Kiradzhiyski XID over 12 years ago in reply to Seonghoon Yoo

TI__Mastermind 25235 points

Which SDK are you using? v6 (kernel 3.2) or v7 (kernel 3.12)? Please note that Continuous mode is not yet supported in the 3.12 kernel.

For kernel 3.2, the explanation about setting up and using continuous mode can be found here: http://processors.wiki.ti.com/index.php/AM335x_ADC_Driver%27s_Guide#How_to_set_it_up

If you wish to do this in a user-space application, then just open/write/close the relevant files as you did for one-shot mode.

Best regards,
Miroslav

0 Seonghoon Yoo over 12 years ago in reply to Miroslav Kiradzhiyski XID

Prodigy 140 points

i used kernel 3.2.

i also saw http://processors.wiki.ti.com/index.php/AM335x_ADC_Driver%27s_Guide#How_to_set_it_up.

but it doesn't work after i set up,

i don't know where to read.

because i read in_voltagex_raw in one shot mode.

but it doesn't work in continuous mode. guide shows /dev/iio:device0 captures the value.

when i try "cat /dev/iio:device0", it shows weird things.

also i don't know how to read adc value exactly in continuous.

0 Naven over 11 years ago in reply to Miroslav Kiradzhiyski XID

Intellectual 750 points

hi Miroslav ,

in my project we are uing v7 (kernel 3.12) ,
it is possible to continuous mode with 40k sampling rate .

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How could i read adc value in character device driver(evm335x)?