AD7192

AD7192 IIO High Precision ADC Linux Driver.

Supported Devices

Evaluation Boards

Reference Circuits

Description

This is a Linux industrial I/O (Linux Industrial I/O Subsystem) subsystem driver, targeting multi 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?

git

yes

Files

Function

File

driver

drivers/staging/iio/adc/ad7192.c

include

drivers/staging/iio/adc/ad7192.h

Hardware configuration

https://wiki.analog.com/_media/resources/tools-software/linux-drivers/iio-adc/ad7192_eval_lr.jpg

Adding Linux driver support

Kernel configuration

Configure kernel with make menuconfig (alternatively use make xconfig or make qconfig)

Note

The AD7192 Driver depends on CONFIG_SPI

Linux Kernel Configuration
    Device Drivers  --->
        <*>     Industrial I/O support --->
            --- Industrial I/O support
            -*-   Enable buffer support within IIO
            -*-   Enable triggered sampling support
                  Analog to digital converters  --->
                      [--snip--]
                      <*>   Analog Devices AD7192 and similar ADC driver
                      [--snip--]

Devicetree configuration

Device tree is the new method for describing non-discoverable hardware in Linux. This replaces former structure based method. For configuring a device using this drivers please follow the example bellow:

/dts-v1/;
/plugin/;

/ {

    fragment@0 {
        target-path = "/";
        dvdd: fixedregulator@0 {
            compatible = "regulator-fixed";
            regulator-name = "fixed-supply";
            regulator-min-microvolt = <3300000>;
            regulator-max-microvolt = <3300000>;
            regulator-boot-on;
        };
    };

    fragment@1 {
        target-path = "/";
        avdd: fixedregulator@1 {
            compatible = "regulator-fixed";
            regulator-name = "fixed-supply2";
            regulator-min-microvolt = <3300000>;
            regulator-max-microvolt = <3300000>;
            regulator-boot-on;
        };
    };

    fragment@3 {
        target = <&spi0>;
            #address-cells = <1>;
            #size-cells = <0>;
            status = "okay";

        ad7190@0 {
            compatible = "adi,ad7190";
            reg = <0>;
            spi-max-frequency = <1000000>;
            spi-cpol;
            spi-cpha;
            #interrupt-cells = <2>;
            interrupts = <25 0x2>;
            interrupt-parent = <&gpio>;
            dvdd-supply = <&dvdd>;
            avdd-supply = <&avdd>;

            adi,reference-voltage-mv = /bits/ 16  <3300>;
            adi,clock-source-select = [02];
            adi,refin2-pins-enable;
            adi,rejection-60-Hz-enable;
            adi,chop-enable;
            adi,buffer-enable;
            adi,burnout-currents-enable;
            adi,sinc3-filter-enable;
            adi,unipolar-enable;
        };
    };
};

Important

Interrupt pin connection - interrupts = <25 0x2>; this line means that gpio pin 25 is used for the interrupt and it must be connect to the DOUT/RDY pin of AD7192 along with the SPI MISO.

Platform-data configuration

Example platform device initialization

For compile time configuration, it’s common Linux practice to keep board- and application-specific configuration out of the main driver file, instead putting it into the board support file.

For devices on custom boards, as typical of embedded and SoC-(system-on-chip) based hardware, Linux uses platform_data to point to board-specific structures describing devices and how they are connected to the SoC. This can include available ports, chip variants, preferred modes, default initialization, additional pin roles, and so on. This shrinks the board-support packages (BSPs) and minimizes board and application specific #ifdefs in drivers.

The driver obtains its reference voltage from vref-supply or AVDD, clocks from firmware clock properties, and configuration from the properties described by adi,ad7192.yaml.

/**
 * struct ad7192_platform_data - platform/board specific information
 * @vref_mv:        the external reference voltage in millivolt
 * @ext_clk_Hz:     the external clock frequency in Hz, if not set
 *          the driver uses the internal clock (16.776 MHz)
 * @clock_source_sel:   [0..3]
 *          0 External 4.92 MHz clock connected from MCLK1 to MCLK2
 *          1 External Clock applied to MCLK2
 *          2 Internal 4.92 MHz Clock not available at the MCLK2 pin
 *          3 Internal 4.92 MHz Clock available at the MCLK2 pin
 * @refin2_en:      REFIN1/REFIN2 Reference Select (AD7190/2 only)
 * @rej60_en:       50/60Hz notch filter enable
 * @sinc3_en:       SINC3 filter enable (default SINC4)
 * @chop_en:        CHOP mode enable
 * @buf_en:     buffered input mode enable
 * @unipolar_en:    unipolar mode enable
 * @burnout_curr_en:    constant current generators on AIN(+|-) enable
 */

struct ad7192_platform_data {
    u16     vref_mv;
    u32     ext_clk_Hz;
    u8      clock_source_sel;
    bool        refin2_en;
    bool        rej60_en;
    bool        sinc3_en;
    bool        chop_en;
    bool        buf_en;
    bool        unipolar_en;
    bool        burnout_curr_en;
};

static struct ad7192_platform_data ad7192_pdata = {
    .vref_mv        = 3300,
    .clock_source_sel   = 2,
    .refin2_en      = true,
    .rej60_en       = false,
    .sinc3_en       = false,
    .chop_en        = false,
    .buf_en         = false,
    .unipolar_en        = true,
    .burnout_curr_en    = false,
};

Unlike PCI or USB devices, SPI devices are not enumerated at the hardware level. Instead, the software must know which devices are connected on each SPI bus segment, and what slave selects these devices are using. For this reason, the kernel code must instantiate SPI devices explicitly. The most common method is to declare the SPI devices by bus number.

This method is appropriate when the SPI bus is a system bus, as in many embedded systems, wherein each SPI bus has a number which is known in advance. It is thus possible to pre-declare the SPI devices that inhabit this bus. This is done with an array of struct spi_board_info, which is registered by calling spi_register_board_info().

For more information see: Overview of Linux kernel SPI support

Depending on the converter IC used, you may need to set the modalias accordingly, matching your part name. It may also required to adjust max_speed_hz. Please consult the datasheet, for maximum spi clock supported by the device in question.

static struct spi_board_info board_spi_board_info[] __initdata = {
#if defined(CONFIG_AD7192) \
    || defined(CONFIG_AD7192_MODULE)
    {
        .modalias = "ad7192",
        .max_speed_hz = 1000000,     /* max spi clock (SCK) speed in HZ */
        .bus_num = 0,
        .chip_select = GPIO_PF10 + MAX_CTRL_CS, /* CS, change it for your board */
        .platform_data = &ad7192_pdata,
        .mode = SPI_MODE_3,
        .irq = IRQ_PF6,
    },
#endif
};

static int __init board_init(void)
{
    [--snip--]

    spi_register_board_info(board_spi_board_info, ARRAY_SIZE(board_spi_board_info));

    [--snip--]

    return 0;
}
arch_initcall(board_init);

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.

root:/> cd /sys/bus/iio/devices/
root:/sys/bus/iio/devices> ls
iio:device0          trigger0

root:/sys/bus/iio/devices> cd iio:device0

root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> ls -l
-rw-r--r--    1 root     root          4096 Jan  4 16:59 bridge_switch_en
drwxr-xr-x    4 root     root             0 Jan  4 16:59 buffer
-rw-r--r--    1 root     root          4096 Jan  4 16:59 in_voltage-in_voltage_scale
-r--r--r--    1 root     root          4096 Jan  4 16:59 in_voltage-in_voltage_scale_available
-r--r--r--    1 root     root          4096 Jan  4 16:59 in_voltage1-in_voltage2_raw
-r--r--r--    1 root     root          4096 Jan  4 16:59 in_voltage1_raw
-r--r--r--    1 root     root          4096 Jan  4 16:59 in_voltage2-in_voltage2_shorted_raw
-r--r--r--    1 root     root          4096 Jan  4 16:59 in_voltage2_raw
-r--r--r--    1 root     root          4096 Jan  4 16:59 in_voltage3-in_voltage4_raw
-r--r--r--    1 root     root          4096 Jan  4 16:59 in_voltage3_raw
-r--r--r--    1 root     root          4096 Jan  4 16:59 in_voltage4_raw
-rw-r--r--    1 root     root          4096 Jan  4 16:59 in_voltage_scale
-r--r--r--    1 root     root          4096 Jan  4 16:59 in_voltage_scale_available
-r--r--r--    1 root     root          4096 Jan  4 16:59 name
drwxr-xr-x    2 root     root             0 Jan  4 16:59 power
-rw-r--r--    1 root     root          4096 Jan  5 11:38 sampling_frequency
lrwxrwxrwx    1 root     root             0 Jan  4 16:59 subsystem -> ../../../../../bus/iio
-r--r--r--    1 root     root          4096 Jan  4 16:59 in_temp0_raw
-rw-r--r--    1 root     root          4096 Jan  4 16:59 in_temp0_scale
drwxr-xr-x    2 root     root             0 Jan  4 16:59 trigger
-rw-r--r--    1 root     root          4096 Jan  4 16:59 uevent
root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0>

Identify the device

root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> cat name
ad7192

Basic operation

Show available scales for differential input channels

Lists all available scales for the differential input pairs:

ADC Input Pair

Channel name

AIN1(+) - AIN2(-)

in_voltage1-in_voltage2_raw

AIN3(+) - AIN4(-)

in_voltage3-in_voltage4_raw

AIN2(-) - AIN2(-)

in_voltage2-in_voltage2_shorted_raw

Setting these directly influences the ADC input range, by altering the GAIN amplifier.

root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> cat in_voltage-in_voltage_scale_available
0.000393390 0.000196690 0.000098340 0.000049170 0.000024580 0.000012290 0.000006140 0.000003070

Set sampling frequency / update rate

root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> cat sampling_frequency
10
root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> echo 50 > sampling_frequency
root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> cat sampling_frequency
50
root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0>

Bride power-down switch control

Description: /sys/bus/iio/devices/iio:deviceX/bridge_switch_en Writing 1 closes the bridge switch.

root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> echo 1 > bridge_switch_en
root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> cat bridge_switch_en
1
root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> echo 0 > bridge_switch_en

AC excitation control (AD7195 only)

Description: /sys/bus/iio/devices/iio:deviceX/ac_excitation_en Writing 1 enables AC excitation on the AD7195 ACX strobes.

root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> echo 1 > ac_excitation_en
root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> cat ac_excitation_en
1
root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> echo 0 > ac_excitation_en

Show available scales for pseudo-differential input channels

Lists all available scales for the differential input pairs:

ADC Input Pair

Channel name

AIN1 - AINCOM

in_voltage1_raw

AIN2 - AINCOM

in_voltage2_raw

AIN3 - AINCOM

in_voltage3_raw

AIN4 - AINCOM

in_voltage4_raw

Setting these directly influences the ADC input range, by altering the GAIN amplifier.

root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> cat in_voltage_scale_available
0.000393390 0.000196690 0.000098340 0.000049170 0.000024580 0.000012290 0.000006140 0.000003070

Set scale for differential input channels

Scale to be applied to in1-in2_raw, in2-in3_raw in order to obtain the measured voltage in millivolts. Allows the user to select one scale out of the available scales. If the written scale differs from the current scale. The driver performs full and zero offset calibration on all differential input channels.

root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> cat in_voltage-in_voltage_scale
0.000393390
root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> echo 0.000196690 > in_voltage-in_voltage_scale
root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> cat in_voltage-in_voltage_scale
0.000196690

Show channel in_voltage1 measurement

Description: Raw unscaled voltage measurement on channel in_voltage1

ADC Input Pair

Channel name

AIN1(+) - AIN2(-)

in_voltage1-in_voltage2_raw

AIN3(+) - AIN4(-)

in_voltage3-in_voltage4_raw

AIN2(-) - AIN2(-)

in_voltage2-in_voltage2_shorted_raw

AIN1 - AINCOM

in_voltage1_raw

AIN2 - AINCOM

in_voltage2_raw

AIN3 - AINCOM

in_voltage3_raw

AIN4 - AINCOM

in_voltage4_raw

 
root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> cat in1_raw
-1

The voltage is U_mV = (in_voltage1_raw + in_voltage_offset) × in_voltage_scale. In pseudo-differential mode, the offset also accounts for AINCOM when its voltage is supplied.

Show channel in_voltage1-in_voltage2 measurement

Description: Raw unscaled voltage measurement on channel in_voltage1-in_voltage2

root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> cat in_voltage1-in_voltage2_raw
-1

For a differential channel, U_mV = (raw + offset) × scale, using for example in_voltage1-voltage2_raw, in_voltage-voltage_offset and in_voltage-voltage_scale. In bipolar mode the raw data is offset binary and the offset is -8388608.

Show internal temperature

Description: /sys/bus/iio/devices/iio:deviceX/in_temp0_raw Shows raw unscaled temperature.

root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> cat in_temp0_raw
-175

Trigger management

Note

This driver only supports it’s own default trigger source ad7192-dev0

root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> cat trigger/current_trigger
ad7192-dev0

Buffer management

root:/sys/devices/platform/bfin-spi.0/spi0.18/device0/iio:buffer> ls
enable           length

The Industrial I/O subsystem supports buffered data acquisition. Buffer implementation and capabilities depend on the driver. Devices with buffer support expose each buffer at /sys/bus/iio/devices/iio:deviceX/bufferY, where Y is the buffer index, starting at 0. The first buffer is additionally exposed through the legacy buffer directory, which contains its buffer-control attributes. Its scan configuration is exposed through the legacy scan_elements directory, while multi-buffer systems expose the scan attributes in the corresponding bufferY directory. Read samples from the device character node /dev/iio:deviceX; the selected buffer is determined by the active buffer configuration.

length

Get/set the number of sample sets that may be held by the buffer.

enable

Enables/disables the buffer. This file should be written last, after length and selection of scan elements.

watermark

A single positive integer specifying the maximum number of scan elements to wait for. Poll will block until the watermark is reached. Blocking read will wait until the minimum between the requested read amount or the low water mark is available. Non-blocking read will retrieve the available samples from the buffer even if there are less samples then watermark level. This allows the application to block on poll with a timeout and read the available samples after the timeout expires and thus have a maximum delay guarantee.

data_available

A read-only value indicating the bytes of data available in the buffer. In the case of an output buffer, this indicates the amount of empty space available to write data to. In the case of an input buffer, this indicates the amount of data available for reading.

length_align_bytes

Using the high-speed interface. DMA buffers may have an alignment requirement for the buffer length. Newer versions of the kernel will report the alignment requirements associated with a device through the length_align_bytes property.

scan_elements

The scan_elements directory contains interfaces for elements that will be captured for a single triggered sample set in the buffer.

root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0/scan_elements> ls
in_voltage1-in_voltage2_en             in_voltage2_en                 in_voltage4_en
in_voltage1-in_voltage2_index          in_voltage2_index              in_voltage4_index
in_voltage1-in_voltage2_type           in_voltage2_type               in_voltage4_type
in_voltage1_en                         in_voltage3-in_voltage4_en     in_temp0_en
in_voltage1_index                      in_voltage3-in_voltage4_index  in_temp0_index
in_voltage1_type                       in_voltage3-in_voltage4_type   in_temp0_type
in_voltage2-in_voltage2_shorted_en     in_voltage3_en                 timestamp_en
in_voltage2-in_voltage2_shorted_index  in_voltage3_index              timestamp_index
in_voltage2-in_voltage2_shorted_type   in_voltage3_type               timestamp_type
root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0/scan_elements>
in_voltageX_en / in_voltageX-voltageY_en / in_timestamp_en:

Scan element control for triggered data capture. Writing 1 will enable the scan element, writing 0 will disable it

in_voltageX_type / in_voltageX-voltageY_type / in_timestamp_type:

Describes the scan element’s representation in the buffer. The format is [be|le]:[s|u]bits/storagebits[Xrepeat]>>shift. The prefix gives byte order; s or u specifies signed (two’s complement) or unsigned data. bits is the number of meaningful bits and storagebits is the storage width. The optional repeat count describes repeated elements. After interpreting byte order, shift the storage value right by shift and mask it to bits; signed values also require sign extension. For example, be:u12/16>>1 describes an unsigned 12-bit value in big-endian 16-bit storage, shifted right by one bit. Account for alignment padding when combining enabled elements into a complete scan.

in_voltageX_index / in_voltageX-voltageY_index / in_timestamp_index:

A nonnegative integer specifying the ordering of this scan element in the buffer. Note these are not dependent on what is enabled and may not be contiguous. Thus for user-space to establish the full layout these must be used in conjunction with all _en attributes to establish which channels are present, and the relevant _type attributes to establish the data storage format.

More Information