Difference between revisions of "I.MX6UL internal ADC"

Revision as of 15:07, 27 March 2017

Introduction

This description uses Linux kernel >= 4.8.

i.MX6UL (processor of OPOS6UL has an integrated 12 bits 16 channels Analog to Digital Converter.

Only channels 0-6 may be used to generic conversions and channels 2, 3, 4, 5 are used for the touchscreen on OPOS6ULDev.

• Channel 1 is available on J21 pin 40 of OPOS6ULDev (AIN1/YNLR: muxed with touchscreen)
• Channel 2 is available on J21 pin 38 of OPOS6ULDev (AIN2/YPLL: muxed with touchscreen)
• Channel 3 is available on J21 pin 39 of OPOS6ULDev (AIN3/XNUR: muxed with touchscreen)
• Channel 4 is available on J21 pin 37 of OPOS6ULDev (AIN4/XPUL: muxed with touchscreen)
• Channel 8 is available on J21 pin 12 of OPOS6ULDev (AIN8)
• Channel 9 is available on J21 pin 9 of OPOS6ULDev (AIN9)

Driver

Driver is by default included if you choose an OPOS6UL as target.

Otherwise, you can select it that way:

[  ] $ make linux-menuconfig

Device Drivers  --->
    ...
    <*> Industrial I/O support  --->
            ...
            Analog to digital converters
                ...
                <*> Freescale vf610 ADC driver

Then compile the distribution :

[  ] $ make linux && make

Use it

Read channels value

# cd /sys/bus/iio/devices/iio:device0
# ls
buffer                         in_voltage5_raw
current_timestamp_clock        in_voltage6_raw
dev                            in_voltage7_raw
in_conversion_mode             in_voltage8_raw
in_temp_input                  in_voltage9_raw
in_voltage0_raw                in_voltage_sampling_frequency
in_voltage10_raw               in_voltage_scale
in_voltage11_raw               name
in_voltage12_raw               of_node
in_voltage13_raw               power
in_voltage14_raw               sampling_frequency_available
in_voltage15_raw               scan_elements
in_voltage1_raw                subsystem
in_voltage2_raw                trigger
in_voltage3_raw                uevent
in_voltage4_raw

To read ADC value just «cat» the corresponding input file:

# cat in_voltage1_raw       for channel 1 (ADC1_IN1)
4095

All values are not converted (ie. directly show the register content). To have the mV value, you must do: value_mV = read_value * 3300/4095

AsDevices

• You can access this device from your C/C++ application using as_adc_xxx_iio functions from AsDevices
• target/demos/oscillo is a "good" example to start with...

Links

• http://www.at91.com/linux4sam/bin/view/Linux4SAM/IioAdcDriver