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This version (05 Feb 2014 18:59) was approved by larsc.The Previously approved version (18 Feb 2013 15:28) is available.Diff

ADIS16136 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 In progress

Files

Function File
driver drivers/iio/imu/adis16136.c

Declaring SPI slave devices

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: Documentation/spi/spi-summary

21 Oct 2010 16:10 · Michael Hennerich

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 = {
	{
		.modalias = "adis16136",
		.max_speed_hz = 2000000,     /* max spi clock (SCK) speed in HZ */
		.bus_num = 0,
		.chip_select = 1, /* CS, change it for your board */
		.mode = SPI_MODE_3,
		.irq = IRQ_PF5,
	},
};
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);

Adding Linux driver support

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

The ADIS16136 driver depends on CONFIG_SPI_MASTER

Linux Kernel Configuration
    Device Drivers  --->
        ...
        <*>     Industrial I/O support --->
            --- Industrial I/O support
            ...
            Digital gyroscope sensors  ---> 
                ...
                <*>  Analog devices ADIS16136 and similar gyroscopes driver
                ...
            ...
        ...

Hardware configuration

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.

02 Mar 2011 15:16 · Michael Hennerich

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/devices/platform/bfin-spi.0/spi0.1/iio:device0> ls -l
drwxr-xr-x    2 root     root             0 Jan  1 01:03 buffer
-r--r--r--    1 root     root          4096 Jan  1 01:03 dev
-rw-r--r--    1 root     root          4096 Jan  1 01:03 in_anglvel_scale
-rw-r--r--    1 root     root          4096 Jan  1 01:03 in_anglvel_x_calibbias
-rw-r--r--    1 root     root          4096 Jan  1 01:03 in_anglvel_x_filter_low_pass_3db_frequency
-rw-r--r--    1 root     root          4096 Jan  1 01:03 in_anglvel_x_raw
-rw-r--r--    1 root     root          4096 Jan  1 01:03 in_temp0_offset
-rw-r--r--    1 root     root          4096 Jan  1 01:03 in_temp0_raw
-rw-r--r--    1 root     root          4096 Jan  1 01:03 in_temp0_scale
-r--r--r--    1 root     root          4096 Jan  1 01:03 name
drwxr-xr-x    2 root     root             0 Jan  1 01:03 power
-rw-r--r--    1 root     root          4096 Jan  1 01:03 sampling_frequency
drwxr-xr-x    2 root     root             0 Jan  1 01:03 scan_elements
lrwxrwxrwx    1 root     root             0 Jan  1 01:03 subsystem -> ../../../../../../../bus/iio
drwxr-xr-x    2 root     root             0 Jan  1 01:03 trigger
-rw-r--r--    1 root     root          4096 Jan  1 01:03 uevent
root:/sys/devices/platform/bfin-spi.0/spi0.1/iio:device0>

ADIS16136 device attributes

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

Gyroscope related device files Description
in_anglvel_filter_low_pass_3db_frequency Bandwidth for the gyroscope channel.
in_anglvel_scale Scale for the gyroscope channels.
in_anglvel_x_calibbias Calibration offset for the gyroscope channel.
in_anglvel_x_raw Raw gyroscope channel value.
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.

Show device name

The name file contains the name of the device. This will match the product id. E.g. adis16136 for the adis16136.

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.1/iio:device0> cat name
adis16136

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/devices/platform/bfin-spi.0/spi0.1/iio:device0> cat sampling_frequency
1024
root:/sys/devices/platform/bfin-spi.0/spi0.1/iio:device0> echo 500 > sampling_frequency
root:/sys/devices/platform/bfin-spi.0/spi0.1/iio:device0> cat sampling_frequency
504

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:

  • Angular velocity: Rad per second
  • Temperature: milli-degree Celsius

Example:

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.1/iio:device0> cat in_anglvel_x_raw
898102272
root:/sys/devices/platform/bfin-spi.0/spi0.1/iio:device0> cat in_anglvel_scale
0.000000278

Z-axis acceleration = in_anglvel_x_raw * in_anglvel_scale = TBD = TBD rad per second

Set channel bandwidth

The channel bandwidth can be set by writing the desired value to the channels in_anglvel_filter_low_pass_3db_frequency attribute. The driver will automatically round up to the nearest supported bandwidth.

Note that the low pass filter frequency depends on the sampling frequency, so changing the sampling frequency will scale the low pass filter frequency accordingly. E.g. reducing the sampling frequency by a factor of two will also reduce the bandwidth by a factor of two.

Example:

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.1/iio:device0> cat in_anglvel_filter_low_pass_3db_frequency
512
root:/sys/devices/platform/bfin-spi.0/spi0.1/iio:device0> echo 10 > in_anglvel_filter_low_pass_3db_frequency
root:/sys/devices/platform/bfin-spi.0/spi0.1/iio:device0> cat in_anglvel_filter_low_pass_3db_frequency
10

Trigger management

This driver only supports it's own default trigger source adis16136-dev0

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.1/iio:device0> cat trigger/current_trigger
adis16136-dev0

For the adis16133 and adis16135 the trigger will be called adis16133-dev0 and adis16135-dev0 respectively.

Buffer management

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.1/iio:device0/buffer> ls
enable           length

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.

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 · Michael Hennerich

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.1/iio:device0/scan_elements> ls
in_anglvel_x_en     in_temp0_en         in_timestamp_en
in_anglvel_x_index  in_temp0_index      in_timestamp_index
in_anglvel_x_type   in_temp0_type       in_timestamp_type
root:/sys/devices/platform/bfin-spi.0/spi0.1/iio:device0/scan_elements>

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 · Michael Hennerich

More Information

IMU Evaluation Board User Guides