Linux/PROCESSOR-SDK-AM335X: Raw ADC value access from another driver

Moses Christopher Bollavarapu

Tool/software: Linux

Hi,

I am working on BeagleBone Black rev C.
I am trying to make a custom character driver where I should be able to access the raw ADC values inside my character driver.
Currently, I am reading the raw adc values using sysio (/sys/bus/iio/devices/iio\:device0/in_voltage4_raw) in my driver, But I want a proper way of accessing the ADC raw values from driver level itself, so that I dont have to go to user space to read the values.
Assume ti_am335x_adc is already loaded in the Kernel.

Kindly provide me with a sample code or using any API showing the way to access the ADC Raw Values of a particular Channel directly in my Character Driver.

Regards
Moses Christopher

over 8 years ago

0 Nick Saulnier over 8 years ago

TI__Guru** 107490 points

Hello Moses,

An overview of the drivers TI provides and how they interact can be found in the Sitara ADC/Touchscreen Overview. The Processor SDK Linux ADC wiki may also be helpful.

If you want to make a custom driver, I would suggest looking at TI's ADC driver for example code. It can be found in Processor SDK at <kernel src>/drivers/iio/adc/ti_am335x_adc.c.

Please note that TI's ADC driver interacts with the MFD driver to ensure that the ADC driver is not accessing ADC pins at the same time as the Touchscreen driver. We suggest that your driver uses the same interaction with the MFD driver.

Regards,

Nick

0 Moses Christopher Bollavarapu over 8 years ago in reply to Nick Saulnier

Intellectual 980 points

Thanks Nick,

I failed to provide more specific details in my question,
Consider I am not using Touch Screen, I have modified dts file so that all AIN pins are configured for ADC I/O .
Consider I am using ti_am335x_adc driver already, I dont want to modify ti_am335x_adc.c

My Custom driver serves some X purpose which just need ADC values. Hence I want to use any api so that if I call read_adc_chan1() or something like that, then it should provide me adc value from channel 1 in my custom driver.

PS: I have seen that in ti_am335x_adc.c there are no EXPORT_SYMBOLs, hence I posted this Question.

0 Nick Saulnier over 8 years ago in reply to Moses Christopher Bollavarapu

TI__Guru** 107490 points

Hello Moses,
The only way to access the TI adc driver is to go through userspace - we do not provide an API that exposes it to other drivers. You would need to add functionality to your driver based on the code in the adc driver. You may want to look at the tiadc_read_raw function in ti_am335x_adc.c as a template.
Regards,
Nick

0 Moses Christopher Bollavarapu over 8 years ago in reply to Nick Saulnier

Intellectual 980 points

Thanks for the information Nick. :-)

0 Nick Saulnier over 8 years ago in reply to Moses Christopher Bollavarapu

TI__Guru** 107490 points

Update: I misspoke, it looks like you can access raw adc values within the kernel by using the iio framework. Please see this post:

https://e2e.ti.com/support/arm/sitara_arm/f/791/p/403893/1517144#1517144

The consumer driver should also have

#include <linux/iio/consumer.h>

Regards,

Nick

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Linux/PROCESSOR-SDK-AM335X: Raw ADC value access from another driver