ADIS16201

ADIS16201 IIO Dual-Axis Digital Inclinometer and Accelerometer Linux Driver.

Supported Devices

Evaluation Boards

Description

This is a Linux industrial I/O (Linux Industrial I/O Subsystem) subsystem driver, targeting serial interface Inclinometer and Accelerometer. 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

The driver is a single source file; buffer and trigger support come from the shared ADIS library.

Function

File

driver

drivers/iio/accel/adis16201.c

ADIS library core

drivers/iio/imu/adis.c

ADIS buffer support

drivers/iio/imu/adis_buffer.c

ADIS trigger support

drivers/iio/imu/adis_trigger.c

include

include/linux/iio/imu/adis.h

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_ADIS16201) \
    || defined(CONFIG_ADIS16201_MODULE)
    {
        .modalias = "adis16201",
        .max_speed_hz = 1000000,     /* max spi clock (SCK) speed in HZ */
        .bus_num = 0,
        .chip_select = 5, /* CS, change it for your board */
        .platform_data = NULL, /* No spi_driver specific config */
        .mode = SPI_MODE_3,
        .irq = IRQ_PF4,
    },
#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);

Adding Linux driver support

Kernel configuration

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

Note

The ADIS16201 Driver depends on CONFIG_SPI

Linux Kernel Configuration
    Device Drivers  --->
        Industrial I/O support → Accelerometers → CONFIG_ADIS16201
            <*>     Industrial I/O support --->
                --- Industrial I/O support
                -*-   Enable buffer support within IIO
                -*-   Enable triggered sampling support

                      *** Accelerometers ***
                [--snip--]

                <*>   Analog Devices ADIS16201 Dual-Axis Digital Inclinometer and Accelerometer

                [--snip--]

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/spi0.5/iio:device0> ls -l
drwxr-xr-x    2 root     root             0 Jan  4 04:43 buffer
-r--r--r--    1 root     root          4096 Jan  4 04:43 dev
-rw-r--r--    1 root     root          4096 Jan  4 04:43 in_accel_x_calibbias
-r--r--r--    1 root     root          4096 Jan  4 04:43 in_accel_x_raw
-rw-r--r--    1 root     root          4096 Jan  4 04:43 in_accel_scale
-rw-r--r--    1 root     root          4096 Jan  4 04:43 in_incli_scale
-rw-r--r--    1 root     root          4096 Jan  4 04:43 in_accel_y_calibbias
-r--r--r--    1 root     root          4096 Jan  4 04:43 in_accel_y_raw
-rw-r--r--    1 root     root          4096 Jan  4 04:43 in_incli_x_calibbias
-r--r--r--    1 root     root          4096 Jan  4 04:43 in_incli_x_raw
-rw-r--r--    1 root     root          4096 Jan  4 04:43 in_incli_y_calibbias
-r--r--r--    1 root     root          4096 Jan  4 04:43 in_incli_y_raw
-rw-r--r--    1 root     root          4096 Jan  4 04:43 in_temp0_offset
-r--r--r--    1 root     root          4096 Jan  4 04:43 in_temp0_raw
-rw-r--r--    1 root     root          4096 Jan  4 04:43 in_temp0_scale
-r--r--r--    1 root     root          4096 Jan  4 04:43 in_voltage0_supply_raw
-rw-r--r--    1 root     root          4096 Jan  4 04:43 in_voltage0_supply_scale
-r--r--r--    1 root     root          4096 Jan  4 04:43 in_voltage1_raw
-rw-r--r--    1 root     root          4096 Jan  4 04:43 in_voltage1_scale
-r--r--r--    1 root     root          4096 Jan  4 04:43 name
drwxr-xr-x    2 root     root             0 Jan  4 04:43 power
drwxr-xr-x    2 root     root             0 Jan  4 04:43 scan_elements
lrwxrwxrwx    1 root     root             0 Jan  4 04:43 subsystem -> ../../../../../bus/iio
drwxr-xr-x    2 root     root             0 Jan  4 04:43 trigger
-rw-r--r--    1 root     root          4096 Jan  4 04:43 uevent

Identify the device

root:/sys/devices/platform/bfin-spi.0/spi0.5/iio:device0> cat name
adis16201

Attribute reference

ADIS16201 device attributes

For a detailed description please see: drivers/staging/iio/Documentation/sysfs-bus-iio

Device files

in_accel_x_calibbias

in_accel_x_raw

in_accel_scale

in_accel_y_calibbias

in_accel_y_raw

in_incli_x_raw

in_incli_scale

in_incli_y_raw

in_temp0_offset

in_temp0_raw

in_temp0_scale

in_voltage0_supply_raw

in_voltage0_supply_scale

in_voltage1_raw

in_voltage1_scale

name

Reset is performed internally during startup; this driver does not register a user-facing reset attribute.

Trigger management

Note

This driver only supports it’s own default trigger source adis16201-dev0

root:/sys/devices/platform/bfin-spi.0/spi0.5/iio:device0> cat trigger/current_trigger
adis16201-dev0

Buffer management

root:/sys/devices/platform/bfin-spi.0/spi0.5/iio:device0/buffer> ls
enable  length  watermark

Determine scan layout from scan_elements/*_type and *_index. The old bytes_per_datum sysfs file is not part of the current buffer attribute group.

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.

root:/sys/devices/platform/bfin-spi.0/spi0.5/iio:device0/scan_elements>ls
in_accel_x_en             in_incli_x_type           in_timestamp_index
in_accel_x_index          in_incli_y_en             in_timestamp_type
in_accel_x_type           in_incli_y_index          in_voltage0_supply_en
in_accel_y_en             in_incli_y_type           in_voltage0_supply_index
in_accel_y_index          in_temp0_en               in_voltage0_supply_type
in_accel_y_type           in_temp0_index            in_voltage1_en
in_incli_x_en             in_temp0_type             in_voltage1_index
in_incli_x_index          in_timestamp_en           in_voltage1_type
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; s or u specifies signed (two’s complement) or unsigned data. bits is the number of meaningful bits and storagebits is the storage width. The optional repeat count describes repeated elements. After interpreting byte order, shift the storage value right by shift and mask it to bits; signed values also require sign extension. For example, be:u12/16>>1 describes 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.

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