AD4170

AD4170 24-Bit Sigma-Delta ADC with Integrated PGA Linux Driver.

Supported Devices

This driver supports the

• AD4170

Evaluation Boards

• EVAL-AD4170

Description

This is a Linux industrial I/O (Linux Industrial I/O Subsystem) subsystem driver, targeting single channel serial interface ADCs. The industrial I/O subsystem provides a unified framework for drivers for many different types of converters and sensors using a number of different physical interfaces (i2c, spi, etc). See Linux Industrial I/O Subsystem for more information.

Source Code

Status

Source	Mainlined?
drivers/iio/adc/ad4170-4.c	Yes

Files

Function	File
driver	drivers/iio/adc/ad4170-4.c
devicetree bindings	adi,ad4170-4.yaml

Adding Linux driver support

Devicetree configuration

The binding requires compatible, reg, avdd-supply, iovdd-supply, spi-cpol and spi-cpha. Each channel node uses either diff-channels for a differential pair, or single-channel with common-mode-channel for a pseudo-differential input, plus adi,reference-select to pick the reference source. Input numbers 0-8 are the AIN pins; higher numbers select internal nodes such as the temperature sensor (17), REFOUT (29) or DGND (24).

#include <dt-bindings/interrupt-controller/irq.h>
spi {
    #address-cells = <1>;
    #size-cells = <0>;

    adc@0 {
        compatible = "adi,ad4170-4";
        reg = <0>;
        spi-max-frequency = <20000000>;
        spi-cpol;
        spi-cpha;
        avdd-supply = <&avdd>;
        iovdd-supply = <&iovdd>;
        interrupts = <25 IRQ_TYPE_EDGE_FALLING>;
        interrupt-names = "dig_aux1";
        #address-cells = <1>;
        #size-cells = <0>;

        /* AIN29 (REFOUT) vs AIN24 (DGND) */
        channel@0 {
            reg = <0>;
            diff-channels = <29 24>;
            adi,reference-select = <2>;
        };

        /* AIN0 vs AIN24 (DGND) */
        channel@1 {
            reg = <1>;
            diff-channels = <0 24>;
            bipolar;
            adi,reference-select = <2>;
        };

        /* AIN3 vs AIN4 */
        channel@2 {
            reg = <2>;
            diff-channels = <3 4>;
            bipolar;
            adi,reference-select = <2>;
        };
    };
};

Sensor excitation for load cell, RTD and thermocouple setups is described with adi,sensor-type, adi,excitation-pin-N, adi,excitation-current-N-microamp and adi,excitation-ac; see the binding examples for complete weigh-scale, RTD and thermocouple channel nodes. Changing a channel’s filter_type can change the set of valid output data rates, so read back sampling_frequency after switching filters.

Driver testing

Each and every IIO device, typically a hardware chip, has a device folder under /sys/bus/iio/devices/iio:deviceX. Where X is the IIO index of the device. Under every of these directory folders reside a set of files, depending on the characteristics and features of the hardware device in question. These files are consistently generalized and documented in the IIO ABI documentation. In order to determine which IIO deviceX corresponds to which hardware device, the user can read the name file /sys/bus/iio/devices/iio:deviceX/name. In case the sequence in which the iio device drivers are loaded/registered is constant, the numbering is constant and may be known in advance.

Tip

An example program which uses the interface can be found here:

• IIO Oscilloscope

root@analog:~# cd /sys/bus/iio/devices/

root@analog:/sys/bus/iio/devices# ls

iio:device0  trigger0

root@analog:/sys/bus/iio/devices# cd iio\:device0

root@analog:/sys/bus/iio/devices/iio:device0# ls -l

total 0

drwxr-xr-x 2 root root    0 Sep 13 08:09 buffer
-r--r--r-- 1 root root 4096 Sep 13 08:09 dev
-rw-r--r-- 1 root root 4096 Sep 13 08:09 in_voltage0-voltage24_calibbias
-rw-r--r-- 1 root root 4096 Sep 13 08:09 in_voltage0-voltage24_calibscale
-rw-r--r-- 1 root root 4096 Sep 13 08:09 in_voltage0-voltage24_filter_type
-rw-r--r-- 1 root root 4096 Sep 13 08:09 in_voltage0-voltage24_offset
-rw-r--r-- 1 root root 4096 Sep 13 08:09 in_voltage0-voltage24_raw
-rw-r--r-- 1 root root 4096 Sep 13 08:09 in_voltage0-voltage24_sampling_frequency
-r--r--r-- 1 root root 4096 Sep 13 08:09 in_voltage0-voltage24_sampling_frequency_available
-rw-r--r-- 1 root root 4096 Sep 13 08:09 in_voltage0-voltage24_scale
-r--r--r-- 1 root root 4096 Sep 13 08:09 in_voltage0-voltage24_scale_available
-rw-r--r-- 1 root root 4096 Sep 13 08:09 in_voltage29-voltage24_calibbias
-rw-r--r-- 1 root root 4096 Sep 13 08:09 in_voltage29-voltage24_calibscale
-rw-r--r-- 1 root root 4096 Sep 13 08:09 in_voltage29-voltage24_filter_type
-rw-r--r-- 1 root root 4096 Sep 13 08:09 in_voltage29-voltage24_offset
-rw-r--r-- 1 root root 4096 Sep 13 08:09 in_voltage29-voltage24_raw
-rw-r--r-- 1 root root 4096 Sep 13 08:09 in_voltage29-voltage24_sampling_frequency
-r--r--r-- 1 root root 4096 Sep 13 08:09 in_voltage29-voltage24_sampling_frequency_available
-rw-r--r-- 1 root root 4096 Sep 13 08:09 in_voltage29-voltage24_scale
-r--r--r-- 1 root root 4096 Sep 13 08:09 in_voltage29-voltage24_scale_available
-rw-r--r-- 1 root root 4096 Sep 13 08:09 in_voltage3-voltage4_calibbias
-rw-r--r-- 1 root root 4096 Sep 13 08:09 in_voltage3-voltage4_calibscale
-rw-r--r-- 1 root root 4096 Sep 13 08:09 in_voltage3-voltage4_filter_type
-rw-r--r-- 1 root root 4096 Sep 13 08:09 in_voltage3-voltage4_offset
-rw-r--r-- 1 root root 4096 Sep 13 08:09 in_voltage3-voltage4_raw
-rw-r--r-- 1 root root 4096 Sep 13 08:09 in_voltage3-voltage4_sampling_frequency
-r--r--r-- 1 root root 4096 Sep 13 08:09 in_voltage3-voltage4_sampling_frequency_available
-rw-r--r-- 1 root root 4096 Sep 13 08:09 in_voltage3-voltage4_scale
-r--r--r-- 1 root root 4096 Sep 13 08:09 in_voltage3-voltage4_scale_available
-r--r--r-- 1 root root 4096 Sep 13 08:09 in_voltage-voltage_filter_type_available
-r--r--r-- 1 root root 4096 Sep 13 08:09 name
lrwxrwxrwx 1 root root    0 Sep 13 08:09 of_node -> ../../../../../../../../firmware/devicetree/base/soc/spi@7e204000/ad4170@0
drwxr-xr-x 2 root root    0 Sep 13 08:09 power
drwxr-xr-x 2 root root    0 Sep 13 08:09 scan_elements
lrwxrwxrwx 1 root root    0 Sep 13 08:09 subsystem -> ../../../../../../../../bus/iio
drwxr-xr-x 2 root root    0 Sep 13 08:09 trigger
-rw-r--r-- 1 root root 4096 Sep 13 08:09 uevent

Identify the device

root:/sys/bus/iio/devices/iio:device0> cat name
ad4170

Basic operation

Show channel scale, offset, sampling_frequency, calibbias, calibscale

Set CHAN to the differential channel name reported under the device’s sysfs directory, e.g. in_voltage29-voltage24.

DEV=/sys/bus/iio/devices/iio:deviceX
CHAN=in_voltage29-voltage24
cat "$DEV/${CHAN}_scale"
cat "$DEV/${CHAN}_offset"
cat "$DEV/${CHAN}_raw"
cat "$DEV/${CHAN}_calibbias"
cat "$DEV/${CHAN}_calibscale"
cat "$DEV/${CHAN}_sampling_frequency"

The voltage is U_mV = (raw + offset) × scale; the offset is in raw-code units. Bipolar conversion values are sign-extended by the driver.

Show channel scale_available and sampling_frequency_available

Description:
Scales and sampling rates to be applied to the channel.

root:/sys/bus/iio/devices/iio:device0> cat in_voltage29-voltage24_scale_available
0.000149011 0.000074505 0.000037252 0.000018626 0.000009313 0.000004656 0.000002328 0.000001164 0.000298023 0.000149011
root:/sys/bus/iio/devices/iio:device0> cat in_voltage29-voltage24_sampling_frequency_available
[7.629860220 15.259720441 125000.000000000]

Show filter_type_available

root:/sys/bus/iio/devices/iio:device0> cat in_voltage-voltage_filter_type_available
sinc5+avg sinc5 sinc3

More Information

• IIO mailing list: linux-iio@vger.kernel.org

• IIO Linux Kernel Documentation sysfs-bus-iio-*

• IIO Documentation

• IIO Oscilloscope

• Libiio

• About libiio

• IIO High Speed

• Software Defined Radio using the IIO framework

• libiio introduction