ADIS16480

ADIS16480 IIO Inertial Measurement Unit.

Supported Devices

Evaluation Boards

ADIS16IMU1/PCBZ

Description

This is a Linux industrial I/O (Linux Industrial I/O Subsystem) subsystem driver, targeting serial interface Inertial Measurement Units (IMU). 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/iio/imu/adis16480.c

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_ADIS16480) || defined(CONFIG_ADIS16480_MODULE)
    {
        .modalias = "adis16480",
        .max_speed_hz = 2000000,     /* max spi clock (SCK) speed in HZ */
        .bus_num = 0,
        .chip_select = 1, /* CS, change it for your board */
        .platform_data = NULL, /* No spi_driver specific config */
        .mode = SPI_MODE_3,
        .irq = IRQ_PF5,
    },
#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);

Hardware configuration

The ADIS16IMU1/PCBZ is the primary breakout board for the ADIS1649x products. This breakout board simplifies the process of connecting an ADIS1649x IMU to an embedded processor system using a 16-pin, 1mm ribbon cable. For a detailed description, please see: /resources/eval/user-guides/inertial-mems/imu/adis1649x Here is an example of basic connection from the ADIS1649X interface connector to the host (microprocessor):

ADIS1649X       HOST MICROPROCESSOR
* DIO2 ———————> IRQ GPIO
* CS   <——————— SPI_SEL
* SCLK <——————— SPI_SCLK
* DIN  <——————— SPI_MOSI
* DOUT ———————> SPI_MISO

Note: IRQ GPIO can be connected to any DIOx pin. See the Devicetree section.

Adding Linux driver support

Kernel configuration

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

Note

The adis16480 driver depends on CONFIG_SPI_MASTER

Linux Kernel Configuration
    Device Drivers  --->
        <*>     Industrial I/O support --->
            --- Industrial I/O support
            [*]   Enable buffer support within IIO
            -*-     Industrial I/O buffering based on kfifo
            -*-   Enable triggered sampling support
            [--snip--]
            Inertial measurement units  --->
                [--snip--]
                <*> Analog Devices ADIS16480 and similar IMU driver
                [--snip--]

Devicetree configuration

Analog Devices ADIS16480 and similar IMUs

Required properties for the ADIS16480:

compatible: Must be one of
- adi,adis16375
- adi,adis16480
- adi,adis16485
- adi,adis16488
- adi,adis16490
- adi,adis16495-1
- adi,adis16495-2
- adi,adis16495-3
- adi,adis16497-1
- adi,adis16497-2
- adi,adis16497-3
reg: SPI chip select number for the device
spi-max-frequency: Max SPI frequency to use see: Documentation/devicetree/bindings/spi/spi-bus.txt
spi-cpha: See Documentation/devicetree/bindings/spi/spi-bus.txt
spi-cpol: See Documentation/devicetree/bindings/spi/spi-bus.txt
interrupts: Interrupt mapping for IRQ. Edge flags from <dt-bindings/interrupt-controller/irq.h> are:
- IRQ_TYPE_EDGE_RISING
- IRQ_TYPE_EDGE_FALLING

Optional properties

interrupt-names: Data-ready line selection. If absent, the driver selects DIO1 for compatibility, overriding the device’s factory default of DIO2. An explicit name selects the corresponding DIO1..DIO4 pin. Valid values are:
- DIO1
- DIO2
- DIO3
- DIO4
reset-gpios: must be the device tree identifier of the RESET pin. As the line is active low, it should be marked GPIO_ACTIVE_LOW.
clocks: phandle to the external clock. Should be set according to clock-names. If this field is left empty, the internal clock is used.
clock-names: The name of the external clock to be used. Valid values are:
- sync: In sync mode, the internal clock is disabled and the frequency of the external clock signal establishes the rate of data collection and processing. The clock-frequency must be:
  - 3000 to 4500 Hz for adis1649x devices.
  - 700 to 2400 Hz for adis1648x devices.
- pps: In Pulse Per Second (PPS) Mode, the rate of data collection and production is equal to the product of the external clock frequency and the scale factor in the SYNC_SCALE register, see Table 154 in the datasheet. The clock-frequency must be:
  - 1 to 128 Hz for adis1649x devices.
  - This mode is not supported by adis1648x devices. If this field is left empty, the internal clock is used.
adi,ext-clk-pin: The DIOx line to be used as an external clock input. Valid values are:
- DIO1
- DIO2
- DIO3
- DIO4

Each DIOx pin supports only one function at a time (data ready line selection or external clock input). When a single pin has two assignments, the enable bit for the lower priority function automatically resets to zero (disabling the lower priority function). Data ready has highest priority. If this field is left empty, DIO2 is assigned as default external clock input pin.

Example

#include <dt-bindings/interrupt-controller/irq.h>

imu@0 {
    compatible = "adi,adis16495-1";
    reg = <0>;
    spi-max-frequency = <3200000>;
    spi-cpol;
    spi-cpha;
    interrupts = <25 IRQ_TYPE_EDGE_FALLING>;
    interrupt-parent = <&gpio>;
    interrupt-names = "DIO2";
    clocks = <&adis16495_sync>;
    clock-names = "sync";
    adi,ext-clk-pin = "DIO1";
   };

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:/> 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/spi0.1/iio:device0> ls -l
drwxr-xr-x    2 root     root             0 Jan  4 00:03 buffer
-r--r--r--    1 root     root          4096 Jan  4 00:03 dev
-rw-r--r--    1 root     root          4096 Jan  4 00:03 in_accel_x_filter_low_pass_3db_frequency
-rw-r--r--    1 root     root          4096 Jan  4 00:03 in_accel_scale
-rw-r--r--    1 root     root          4096 Jan  4 00:03 in_accel_x_calibbias
-r--r--r--    1 root     root          4096 Jan  4 00:03 in_accel_x_raw
-rw-r--r--    1 root     root          4096 Jan  4 00:03 in_accel_y_calibbias
-r--r--r--    1 root     root          4096 Jan  4 00:03 in_accel_y_raw
-rw-r--r--    1 root     root          4096 Jan  4 00:03 in_accel_z_calibbias
-r--r--r--    1 root     root          4096 Jan  4 00:03 in_accel_z_raw
-rw-r--r--    1 root     root          4096 Jan  4 00:03 in_anglvel_x_filter_low_pass_3db_frequency
-rw-r--r--    1 root     root          4096 Jan  4 00:03 in_anglvel_scale
-rw-r--r--    1 root     root          4096 Jan  4 00:03 in_anglvel_x_calibbias
-r--r--r--    1 root     root          4096 Jan  4 00:03 in_anglvel_x_raw
-rw-r--r--    1 root     root          4096 Jan  4 00:03 in_anglvel_y_calibbias
-r--r--r--    1 root     root          4096 Jan  4 00:03 in_anglvel_y_raw
-rw-r--r--    1 root     root          4096 Jan  4 00:03 in_anglvel_z_calibbias
-r--r--r--    1 root     root          4096 Jan  4 00:03 in_anglvel_z_raw
-rw-r--r--    1 root     root          4096 Jan  4 00:03 in_magn_x_filter_low_pass_3db_frequency
-rw-r--r--    1 root     root          4096 Jan  4 00:03 in_magn_scale
-r--r--r--    1 root     root          4096 Jan  4 00:03 in_magn_x_raw
-r--r--r--    1 root     root          4096 Jan  4 00:03 in_magn_y_raw
-r--r--r--    1 root     root          4096 Jan  4 00:03 in_magn_z_raw
-rw-r--r--    1 root     root          4096 Jan  4 00:03 in_temp0_offset
-r--r--r--    1 root     root          4096 Jan  4 00:03 in_temp0_raw
-rw-r--r--    1 root     root          4096 Jan  4 00:03 in_temp0_scale
-r--r--r--    1 root     root          4096 Jan  4 00:03 name
drwxr-xr-x    2 root     root             0 Jan  4 00:03 power
-rw-r--r--    1 root     root          4096 Jan  4 00:03 sampling_frequency
drwxr-xr-x    2 root     root             0 Jan  4 00:03 scan_elements
lrwxrwxrwx    1 root     root             0 Jan  4 00:03 subsystem -> ../../../../../bus/iio
drwxr-xr-x    2 root     root             0 Jan  4 00:03 trigger
-rw-r--r--    1 root     root          4096 Jan  4 00:03 uevent
root:/sys/devices/platform/bfin-spi.0/spi0.1/iio:device0>

Use the corresponding y/z attributes when selecting another axis.

Identify the device

root:/sys/devices/platform/bfin-spi.0/spi0.1/iio:device0> cat name
adis16480

Attribute reference

ADIS16480 device attributes

For a detailed description please see: Documentation/ABI/testing/sysfs-bus-iio

3-Axis Accelerometer related device files	Description
in_accel_filter_low_pass_3db_frequency	Bandwidth for the accelerometer channels.
in_accel_scale	Scale for the accelerometer channels.
in_accel_x_calibbias	Calibration offset for the X-axis accelerometer channel.
in_accel_x_raw	Raw X-axis accelerometer channel value.
in_accel_y_calibbias	Calibration offset for the Y-axis accelerometer channel.
in_accel_y_raw	Raw Y-axis accelerometer channel value.
in_accel_z_calibbias	Calibration offset for the Z-axis accelerometer channel.
in_accel_z_raw	Raw Z-axis accelerometer channel value.
3-Axis Gyro related device files	Description
in_anglvel_filter_low_pass_3db_frequency	Bandwidth for the gyroscope channels.
in_anglvel_scale	Scale for the gyroscope channels.
in_anglvel_x_calibbias	Calibration offset for the X-axis gyroscope channel.
in_anglvel_x_raw	Raw X-axis gyroscope channel value.
in_anglvel_y_calibbias	Calibration offset for the Y-axis gyroscope channel.
in_anglvel_y_raw	Raw Y-axis gyroscope channel value.
in_anglvel_z_calibbias	Calibration offset for the Z-axis gyroscope channel.
in_anglvel_z_raw	Raw Z-axis gyroscope channel value.
3-Axis Magnetometer related device files	Description
in_magn_filter_low_pass_3db_frequency	Bandwidth for the magnetometer channels.
in_magn_scale	Scale for the magnetometer channels.
in_magn_x_raw	Raw X-axis magnetometer channel value.
in_magn_y_raw	Raw Y-axis magnetometer channel value.
in_magn_z_raw	Raw Z-axis magnetometer channel value.
Barometric pressure sensor related files	Description
in_pressure_raw	Raw barometric pressure sensor channel value.
in_pressure_scale	Scale for the barometric pressure sensor channel.
Temperature sensor related files	Description
in_temp0_offset	Offset for temperature sensor channel.
in_temp0_raw	Raw temperature channel value.
in_temp0_scale	Scale for the temperature sensor channel.
Miscellaneous device files	Description
name	Name of the IIO device.
sampling_frequency	Currently selected sample rate.

Set sampling frequency

Write the desired rate in Hz to sampling_frequency. The driver chooses a nearest-integer decimation divisor and clamps it to the device’s supported range; it does not simply round the requested output rate upward. Read the attribute back to obtain the selected rate.

The ADIS16480 internal base rate is 2460 Hz; other variants and external-clock configurations use different base rates.

Run this request/readback sequence in the identified device’s sysfs directory:

cat sampling_frequency
echo 2000 > sampling_frequency
cat sampling_frequency

Show channel value

A channel value can be read from its _raw attribute. The value returned by the _raw attribute is the raw value as reported by the device. To get the processed value of the channel in a standardized unit add the channels _offset attribute to the _raw value and multiply the result by _scale attribute. If no _offset attribute is present assume 0 for the offset.

processed value = (raw + offset) * scale

The units by the IIO framework are:

Acceleration: Meter per Second squared
Angular velocity: Rad per second
Pressure: kilo Pascal
Magnetometer: gauss
Temperature: milli Degree Celsius

Example:

root:/sys/devices/platform/bfin-spi.0/spi0.1/iio:device0> cat in_accel_z_raw
265126938
root:/sys/devices/platform/bfin-spi.0/spi0.1/iio:device0> cat in_accel_scale

The driver exposes a 32-bit acceleration raw value. Read in_accel_scale from the same device and calculate acceleration in m/s² as in_accel_z_raw * in_accel_scale. Do not use a scale for a narrower raw format with this value; the scale depends on the device variant.

Set channel bandwidth

The channels bandwidth can be set by writing the desired value to the channels _filter_low_pass_3db_frequency attribute. The driver will automatically round up to the nearest supported bandwidth.

The driver reports fixed filter-bank labels per variant: 55, 63, 275 and 310 Hz for the older family, or 100 and 300 Hz for ADIS1649x. It does not rescale these sysfs values when decimation changes. Writing 0 disables the filter.

For ADIS16480, run these commands in the device’s sysfs directory to request 55 Hz and read back the selected setting:

echo 55 > in_anglvel_x_filter_low_pass_3db_frequency
cat in_anglvel_x_filter_low_pass_3db_frequency

Use the corresponding y/z attributes when selecting another axis.

Trigger management

Note

This driver only supports it’s own default trigger source adis16480-dev0

root:/sys/devices/platform/bfin-spi.0/spi0.1/iio:device0> cat trigger/current_trigger
adis16480-dev0

Tip

In case there is no trigger specified, run the following command:

root:/sys/devices/platform/bfin-spi.0/spi0.1/iio:device0> echo adis16480-dev0 > trigger/current_trigger

Buffer management

root:/sys/devices/platform/bfin-spi.0/spi0.1/iio:device0/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.

The scan layout differs between variants. Inspect it on the device (replace X with the device number identified by reading name):

DEV=/sys/bus/iio/devices/iio:deviceX
for attr in "$DEV"/scan_elements/*_index "$DEV"/scan_elements/*_type; do
    [ -f "$attr" ] || continue
    printf '%s: ' "${attr##*/}"
    cat "$attr"
done

Each enabled channel’s _index determines scan order. Its _type records endianness, signedness, valid bits, storage bits and any right shift. The buffer record also includes alignment padding and, when enabled, a software timestamp.

With the kernel iio_generic_buffer tool installed, the device idle, and its data-ready interrupt and trigger working, a bounded capture can be run as:

iio_generic_buffer -N "${DEV##*iio:device}" -a -c 10

The tool uses the device’s channel metadata and normally finds its trigger automatically. If necessary, select the actual registered trigger with -t or -T. The -a option enables available channels when none are already enabled; it does not override an existing channel selection. This command is an example to run on hardware, not a captured result.

For a physical measurement channel, use its exported scale and offset, where present, to convert the decoded raw code according to the IIO ABI. Status and CRC-failure channels are flags, not scaled physical measurements.