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This version (12 Nov 2019 16:18) was approved by nsa.

ADIS16475 IIO Inertial Measurement Unit Linux Driver

Supported Devices

Evaluation Boards

Description

This is a Linux industrial I/O (IIO) 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 IIO for more information.

Source Code

Status

Source Mainlined?
git WIP

Files

Function File
driver drivers/iio/imu/adis16475.c

Devicetree

Analog Devices ADIS16475 and similar IMUs

Required properties for the ADIS16475:

  • compatible: Must be one of
    • “adi,adis16465-1”
    • “adi,adis16465-2”
    • “adi,adis16465-3”
    • “adi,adis16467-1”
    • “adi,adis16467-2”
    • “adi,adis16467-3”
    • “adi,adis16470”
    • “adi,adis16475-1”
    • “adi,adis16475-2”
    • “adi,adis16475-3”
    • “adi,adis16477-1”
    • “adi,adis16477-2”
    • “adi,adis16477-3”
    • “adi,adis16500”
    • “adi,adis16505-1”
    • “adi,adis16505-2”
    • “adi,adis16505-3”
    • “adi,adis16507-1”
    • “adi,adis16507-2”
    • “adi,adis16507-3”
  • reg: SPI chip select number for the device
  • 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, accepted values are:
    • IRQF_TRIGGER_RISING
    • IRQF_TRIGGER_FALLING

Optional properties

  • 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.
  • spi-max-frequency: Max SPI frequency to use see: Documentation/devicetree/bindings/spi/spi-bus.txt. The maximum supported value is 2MHz.
  • 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: This mode is the same as internal clock mode with one exception, the SYNC pin pulses when the internal processor collects data from the inertial sensors. The clock-frequency must be:
      • 1900 to 2100 Hz.
    • direct-sync: In this mode, the signal of SYNC pin directly controls the sample clock. In this mode, the processor collects gyroscope data samples on the rising edge of the clock and it collects accelerometer data samples on both rising and falling edge of the clock. The clock-frequency must be:
      • 1900 to 2100 Hz.
    • scaled-sync: This mode is useful when synchronizing the data processing with a PPS signal from a global positioning system (GPS) receiver or with a synchronization signal from a video processing system. The clock-frequency must be:
      • 1 to 128 Hz.
    • pulse-sync: In this mode, the processor only collects accelerometer samples on the leading edge of the clock, which enables the use of narrow pulse width in the clock signal. The clock-frequency must be:
      • 1000 to 2100 Hz.
      • This mode is not supported by the adis1650x devices.
  • adi,scaled-output-hz: This property must be present if the clock mode is scaled-sync through clock-names property. In this mode, the input clock can have a range of 1Hz to 128HZ which must be scaled to originate an allowable sample rate. The frequency must be:
    • 1900 to 2100 Hz.
  • adi,burst32-enable: In this mode, a burst reading contains calibrated gyroscope and accelerometer data in 32-bit format. This mode is only supported by adis1650x devices!

Example

	imu@0 {
               compatible = "adi,adis16475-3";
               reg = <0>;
               spi-cpha;
               spi-cpol;
               spi-max-frequency = <2000000>;
               interrupts = <4 IRQ_TYPE_EDGE_RISING>;
               interrupt-parent = <&gpio>;
       };

For more supported devicetree properties take a look to dt-bindings.

Adding Linux driver support

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

The adis16475 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 ADIS16475 and similar IMU driver
				[--snip--]

Hardware configuration

The evaluation kits simplify the process of connecting an IMU to an embedded processor system using a 16-pin, 1mm ribbon cable. For a detailed description check the links (on the beginning of the page) for the appropriated evaluation kit. Here is an example of basic connection from one ADIS device interface connector to the host:(microprocessor):

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

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.

02 Mar 2011 15:16

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


This specifies any shell prompt running on the target

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/bus/iio/devices/iio:device0> ls -l
total 0
drwxr-xr-x 2 root root    0 Jul 12 10:17 buffer
-rw-r--r-- 1 root root 4096 Jul 12 10:17 burst_mode_enable
-rw-r--r-- 1 root root 4096 Jul 12 10:17 current_timestamp_clock
-r--r--r-- 1 root root 4096 Jul 12 10:17 dev
-rw-r--r-- 1 root root 4096 Jul 12 10:17 filter_low_pass_3db_frequency
-rw-r--r-- 1 root root 4096 Jul 12 10:17 in_accel_scale
-rw-r--r-- 1 root root 4096 Jul 12 10:17 in_accel_x_calibbias
-rw-r--r-- 1 root root 4096 Jul 12 10:17 in_accel_x_raw
-rw-r--r-- 1 root root 4096 Jul 12 10:17 in_accel_y_calibbias
-rw-r--r-- 1 root root 4096 Jul 12 10:17 in_accel_y_raw
-rw-r--r-- 1 root root 4096 Jul 12 10:17 in_accel_z_calibbias
-rw-r--r-- 1 root root 4096 Jul 12 10:17 in_accel_z_raw
-rw-r--r-- 1 root root 4096 Jul 12 10:17 in_anglvel_scale
-rw-r--r-- 1 root root 4096 Jul 12 10:17 in_anglvel_x_calibbias
-rw-r--r-- 1 root root 4096 Jul 12 10:17 in_anglvel_x_raw
-rw-r--r-- 1 root root 4096 Jul 12 10:17 in_anglvel_y_calibbias
-rw-r--r-- 1 root root 4096 Jul 12 10:17 in_anglvel_y_raw
-rw-r--r-- 1 root root 4096 Jul 12 10:17 in_anglvel_z_calibbias
-rw-r--r-- 1 root root 4096 Jul 12 10:17 in_anglvel_z_raw
-rw-r--r-- 1 root root 4096 Jul 12 10:17 in_temp0_raw
-rw-r--r-- 1 root root 4096 Jul 12 10:17 in_temp0_scale
-r--r--r-- 1 root root 4096 Jul 12 10:17 name
lrwxrwxrwx 1 root root    0 Jul 12 10:17 of_node -> ../../../../../../../../firmware/devicetree/base/soc/spi@7e204000/adis16475@0
drwxr-xr-x 2 root root    0 Jul 12 10:17 power
-rw-r--r-- 1 root root 4096 Jul 12 10:17 sampling_frequency
drwxr-xr-x 2 root root    0 Jul 12 10:17 scan_elements
lrwxrwxrwx 1 root root    0 Jul 12 10:17 subsystem -> ../../../../../../../../bus/iio
drwxr-xr-x 2 root root    0 Jul 12 10:17 trigger
-rw-r--r-- 1 root root 4096 Jul 12 10:17 uevent

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

ADIS16475 device attributes

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

3-Axis Accelerometer related device files Description
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_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.
Temperature sensor related files Description
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.
filter_low_pass_3db_frequency Bandwidth for the accelerometer and gyroscope channels.
burst_mode_enable Enables reading of the data with a SPI burst read.

Show device name

This specifies any shell prompt running on the target

root:/sys/bus/iio/devices/iio:device0> cat name
adis16477-1

Set sampling frequency

The sampling frequency of the device can be set by writing the desired value to the sampling_frequency file. The driver will automatically round up to the nearest supported sampling frequency.

Example:

This specifies any shell prompt running on the target

root:/sys/bus/iio/devices/iio:device0> cat sampling_frequency
2000.000000
pi@raspberrypi:/s
root:/sys/bus/iio/devices/iio:device0> echo 1000 > sampling_frequency
root:/sys/bus/iio/devices/iio:device0> cat sampling_frequency
1000.000000

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
  • Temperature: milli Degree Celsius

Example:

This specifies any shell prompt running on the target

root:/sys/bus/iio/devices/iio:device0> cat in_accel_z_raw
52612913
root:/sys/bus/iio/devices/iio:device0> cat in_accel_scale
0.000000187

Z-axis acceleration = in_accel_z_raw * in_accel_scale = 52612913 * 0.000000187 m/s^2 = 9.838 m/s^2

Set gyro and accel bandwidth

The gyro and accel bandwidth can be set by writing the desired value to the filter_low_pass_3db_frequency attribute. The driver will automatically round up to the nearest supported bandwidth.

Example:

This specifies any shell prompt running on the target

root:/sys/bus/iio/devices/iio:device0> cat filter_low_pass_3db_frequency
720.000000
root:/sys/bus/iio/devices/iio:device0> echo 360 > filter_low_pass_3db_frequency
root:/sys/bus/iio/devices/iio:device0> cat filter_low_pass_3db_frequency
360.000000

Trigger management

This driver only supports it's own default trigger source adis16477-1-dev0

This specifies any shell prompt running on the target

root:/sys/bus/iio/devices/iio:device0> cat trigger/current_trigger
adis16477-1-dev0

Buffer management

This specifies any shell prompt running on the target

root:/sys/bus/iio/devices/iio:device0/buffer> ls
data_available  enable  length  watermark

The Industrial I/O subsystem provides support for various ring buffer based data acquisition methods. Apart from device specific hardware buffer support, the user can chose between two different software ring buffer implementations. One is the IIO lock free software ring, and the other is based on Linux kfifo. Devices with buffer support feature an additional sub-folder in the /sys/bus/iio/devices/deviceX/ folder hierarchy. Called deviceX:bufferY, where Y defaults to 0, for devices with a single buffer.

Every buffer implementation features a set of files:

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.

02 Mar 2011 15:16

This specifies any shell prompt running on the target

root:/sys/bus/iio/devices/iio:device0/scan_elements> ls -l
total 0
-rw-r--r-- 1 root root 4096 Jul 12 10:17 in_accel_x_en
-r--r--r-- 1 root root 4096 Jul 12 10:17 in_accel_x_index
-r--r--r-- 1 root root 4096 Jul 12 10:17 in_accel_x_type
-rw-r--r-- 1 root root 4096 Jul 12 10:17 in_accel_y_en
-r--r--r-- 1 root root 4096 Jul 12 10:17 in_accel_y_index
-r--r--r-- 1 root root 4096 Jul 12 10:17 in_accel_y_type
-rw-r--r-- 1 root root 4096 Jul 12 10:17 in_accel_z_en
-r--r--r-- 1 root root 4096 Jul 12 10:17 in_accel_z_index
-r--r--r-- 1 root root 4096 Jul 12 10:17 in_accel_z_type
-rw-r--r-- 1 root root 4096 Jul 12 10:17 in_anglvel_x_en
-r--r--r-- 1 root root 4096 Jul 12 10:17 in_anglvel_x_index
-r--r--r-- 1 root root 4096 Jul 12 10:17 in_anglvel_x_type
-rw-r--r-- 1 root root 4096 Jul 12 10:17 in_anglvel_y_en
-r--r--r-- 1 root root 4096 Jul 12 10:17 in_anglvel_y_index
-r--r--r-- 1 root root 4096 Jul 12 10:17 in_anglvel_y_type
-rw-r--r-- 1 root root 4096 Jul 12 10:17 in_anglvel_z_en
-r--r--r-- 1 root root 4096 Jul 12 10:17 in_anglvel_z_index
-r--r--r-- 1 root root 4096 Jul 12 10:17 in_anglvel_z_type
-rw-r--r-- 1 root root 4096 Jul 12 10:17 in_flags0_en
-r--r--r-- 1 root root 4096 Jul 12 10:17 in_flags0_index
-r--r--r-- 1 root root 4096 Jul 12 10:17 in_flags0_type
-rw-r--r-- 1 root root 4096 Jul 12 10:17 in_flags1_crc_en
-r--r--r-- 1 root root 4096 Jul 12 10:17 in_flags1_crc_index
-r--r--r-- 1 root root 4096 Jul 12 10:17 in_flags1_crc_type
-rw-r--r-- 1 root root 4096 Jul 12 10:17 in_temp0_en
-r--r--r-- 1 root root 4096 Jul 12 10:17 in_temp0_index
-r--r--r-- 1 root root 4096 Jul 12 10:17 in_temp0_type
-rw-r--r-- 1 root root 4096 Jul 12 10:17 in_timestamp_en
-r--r--r-- 1 root root 4096 Jul 12 10:17 in_timestamp_index
-r--r--r-- 1 root root 4096 Jul 12 10:17 in_timestamp_type
root:/sys/bus/iio/devices/iio:device0/scan_elements>

From the above list, note the following 2 elements:

  • in_flags0_*: This element refers to diagnostics data (register DIAG_STAT) related to the device.
  • in_flags1_crc_*: This element refers to crc validation of the received burst data. When set to 1, the data is likely invalid.
Both this elements are relevant only when burst_mode_enable is set

in_voltageX_en / in_voltageX-voltageY_en / 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 / timestamp_type:
Description of the scan element data storage within the buffer and therefore in the form in which it is read from user-space. Form is [s|u]bits/storage-bits. s or u specifies if signed (2's complement) or unsigned. bits is the number of bits of data and storage-bits is the space (after padding) that it occupies in the buffer. Note that some devices will have additional information in the unused bits so to get a clean value, the bits value must be used to mask the buffer output value appropriately. The storage-bits value also specifies the data alignment. So u12/16 will be a unsigned 12 bit integer stored in a 16 bit location aligned to a 16 bit boundary. For other storage combinations this attribute will be extended appropriately.

in_voltageX_index / in_voltageX-voltageY_index / timestamp_index:
A single positive integer specifying the position 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.

02 Mar 2011 15:16

More Information

resources/tools-software/linux-drivers/iio-inertial-measurement-units/adis16475.txt · Last modified: 12 Nov 2019 16:18 by nsa