topic Re: How to read ADC values in IMX6ULL sysfs userspace ? in i.MX Processors

How to read ADC values in IMX6ULL sysfs userspace ?

_ZZ_ — Tue, 19 Sep 2023 12:36:31 GMT

Hi,

How do I read the ADC values in IMX6ULL userspace?

for your information reference voltage is 3.3v

in /sys/bus/iio/devices/iio:device0/ I have the following itemssome communities say it is done as below

awk "BEGIN{printf (\"%d\n\", (in_voltage0_raw + in_voltage_offset) * in_voltage_scale)}"

but in my case, there is no in_voltage_offset

if I choose the in_voltage_offset as 0 , only one of the readings make sense

Re: How to read ADC values in IMX6ULL sysfs userspace ?

Sanket_Parekh — Thu, 21 Sep 2023 04:46:58 GMT

Hi @_ZZ_,

I hope you are doing well.

Could please please share more information regarding which channel and pin is used to read ADC values & sampling frequency?

Thanks & Regards,
Sanket Parekh

Re: How to read ADC values in IMX6ULL sysfs userspace ?

_ZZ_ — Fri, 22 Sep 2023 08:03:29 GMT

Hi @Sanket_Parekh

According to the i.MX 6ULL Applications Processor Reference Manual section 13.2

ADC1_IN0 Analog channel 1 input 0 GPIO1_IO00

Also vf610 ADC driver in my Linux firmware and 12 bit resolution is used.

in my Linux user space, it is in_voltage0_raw is the corresponding sysfs file to read the value.

in_voltage_scale is 1048.575927734 (I am not sure how it has been calculated as I have not build the firmware myself).

58098 is my default sampling frequency and available sampling frequencies are below:

206250, 58098, 29676, 15000, 7541

Reference voltage is 3.3v which is an actual regulator. however, every time after I power up my board and run "dmesg" Linux command, I see few kernel warning messages related to the ADC and the reference voltage as below:

[ 2.568224] vf610-adc 2198000.adc: 2198000.adc supply vref not found, using dummy regulator
[ 2.569165] vf610-adc 2198000.adc: Linked as a consumer to regulator.0

Thanks,

Re: How to read ADC values in IMX6ULL sysfs userspace ?

Sanket_Parekh — Mon, 25 Sep 2023 09:30:05 GMT

Hi @_ZZ_,

I hope you are doing well.

One can try adding the below property in the adc node in the device tree.

vref-supply = <&reg_vref_3v3>;

& below node in dts.

reg_vref_3v3: regulator-adc-verf {
compatible = "regulator-fixed";
regulator-name = "vref-3v3";
regulator-min-microvolt = <3300000>;
regulator-max-microvolt = <3300000>;
};

Please refer to Documentation/devicetree/bindings/iio/adc/fsl,vf610-adc.yaml

Please mention linux BSP version & share the device tree file.

Please share the actual voltage present at ADC channel pin and RAW input data for it.

Please try to measure the output of Vref regulator & make sure it is exactly around 3.3v.

Thanks & Regards,

Sanket Parekh

Re: How to read ADC values in IMX6ULL sysfs userspace ?

_ZZ_ — Wed, 18 Oct 2023 14:13:30 GMT

@Sanket_Parekh Thanks for your reply,

Modified the device tree as instructed and resolved issue.