ADIS16136
ADIS16136 IIO Inertial Measurement Unit.
Supported Devices
Evaluation Boards
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
Files
Function |
File |
|---|---|
driver |
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 = {
{
.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
Kernel configuration
Configure kernel with make menuconfig (alternatively use make xconfig or
make qconfig)
Note
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
...
...
...
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/spi0.1/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>
Identify the device
The name file contains the name of the device. This will match the product
id. E.g. adis16136 for the adis16136.
root:/sys/devices/platform/bfin-spi.0/spi0.1/iio:device0> cat name
adis16136
Attribute reference
ADIS16136 device attributes
For a detailed description please see: Documentation/ABI/testing/sysfs-bus-iio
Gyroscope related device files |
Description |
|---|---|
in_anglvel_x_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 |
The temperature channel exposes raw and scale only; no in_temp0_offset file is registered. |
|
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
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:
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:
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
X-axis angular velocity = in_anglvel_x_raw × in_anglvel_scale. Using the displayed rounded scale, 898102272 × 0.000000278 ≈ 249.6724 rad/s.
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:
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
Note
This driver only supports it’s own default trigger source adis16136-dev0
root:/sys/devices/platform/bfin-spi.0/spi0.1/iio:device0> cat trigger/current_trigger
adis16136-dev0
Note
For the adis16133 and adis16135 the trigger will be called adis16133-dev0 and adis16135-dev0 respectively.
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_bytesproperty.- 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/spi0.1/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 / 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;soruspecifies signed (two’s complement) or unsigned data.bitsis the number of meaningful bits andstoragebitsis the storage width. The optional repeat count describes repeated elements. After interpreting byte order, shift the storage value right byshiftand mask it tobits; signed values also require sign extension. For example,be:u12/16>>1describes 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
IIO mailing list: linux-iio@vger.kernel.org