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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.
| Function | File |
|---|---|
| driver | drivers/iio/gyro/adis16136.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: Documentation/spi/spi-summary
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);
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
...
...
...
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.
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>
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. |
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
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
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:
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
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
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.
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.
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.
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.
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