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Diffstat (limited to 'Documentation/iio')
| -rw-r--r-- | Documentation/iio/ad7944.rst | 156 | ||||
| -rw-r--r-- | Documentation/iio/adis16475.rst | 403 | ||||
| -rw-r--r-- | Documentation/iio/iio_devbuf.rst | 152 | ||||
| -rw-r--r-- | Documentation/iio/index.rst | 10 |
4 files changed, 720 insertions, 1 deletions
diff --git a/Documentation/iio/ad7944.rst b/Documentation/iio/ad7944.rst new file mode 100644 index 0000000000..0d26e56aba --- /dev/null +++ b/Documentation/iio/ad7944.rst @@ -0,0 +1,156 @@ +.. SPDX-License-Identifier: GPL-2.0-only + +============= +AD7944 driver +============= + +ADC driver for Analog Devices Inc. AD7944 and similar devices. The module name +is ``ad7944``. + + +Supported devices +================= + +The following chips are supported by this driver: + +* `AD7944 <https://www.analog.com/AD7944>`_ +* `AD7985 <https://www.analog.com/AD7985>`_ +* `AD7986 <https://www.analog.com/AD7986>`_ + + +Supported features +================== + +SPI wiring modes +---------------- + +The driver currently supports three of the many possible SPI wiring configurations. + +CS mode, 3-wire, without busy indicator +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +.. code-block:: + + +-------------+ + +--------------------| CS | + v | | + VIO +--------------------+ | HOST | + | | CNV | | | + +--->| SDI AD7944 SDO |-------->| SDI | + | SCK | | | + +--------------------+ | | + ^ | | + +--------------------| SCLK | + +-------------+ + +To select this mode in the device tree, set the ``adi,spi-mode`` property to +``"single"`` and omit the ``cnv-gpios`` property. + +CS mode, 4-wire, without busy indicator +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +.. code-block:: + + +-------------+ + +-----------------------------------| CS | + | | | + | +--------------------| GPIO | + | v | | + | +--------------------+ | HOST | + | | CNV | | | + +--->| SDI AD7944 SDO |-------->| SDI | + | SCK | | | + +--------------------+ | | + ^ | | + +--------------------| SCLK | + +-------------+ + +To select this mode in the device tree, omit the ``adi,spi-mode`` property and +provide the ``cnv-gpios`` property. + +Chain mode, without busy indicator +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +.. code-block:: + + +-------------+ + +-------------------------+--------------------| CS | + v v | | + +--------------------+ +--------------------+ | HOST | + | CNV | | CNV | | | + +--->| SDI AD7944 SDO |--->| SDI AD7944 SDO |-------->| SDI | + | | SCK | | SCK | | | + GND +--------------------+ +--------------------+ | | + ^ ^ | | + +-------------------------+--------------------| SCLK | + +-------------+ + +To select this mode in the device tree, set the ``adi,spi-mode`` property to +``"chain"``, add the ``spi-cs-high`` flag, add the ``#daisy-chained-devices`` +property, and omit the ``cnv-gpios`` property. + +Reference voltage +----------------- + +All 3 possible reference voltage sources are supported: + +- Internal reference +- External 1.2V reference and internal buffer +- External reference + +The source is determined by the device tree. If ``ref-supply`` is present, then +the external reference is used. If ``refin-supply`` is present, then the internal +buffer is used. If neither is present, then the internal reference is used. + +Unimplemented features +---------------------- + +- ``BUSY`` indication +- ``TURBO`` mode + + +Device attributes +================= + +There are two types of ADCs in this family, pseudo-differential and fully +differential. The channel name is different depending on the type of ADC. + +Pseudo-differential ADCs +------------------------ + +AD7944 and AD7985 are pseudo-differential ADCs and have the following attributes: + ++---------------------------------------+--------------------------------------------------------------+ +| Attribute | Description | ++=======================================+==============================================================+ +| ``in_voltage0_raw`` | Raw ADC voltage value (*IN+* referenced to ground sense). | ++---------------------------------------+--------------------------------------------------------------+ +| ``in_voltage0_scale`` | Scale factor to convert raw value to mV. | ++---------------------------------------+--------------------------------------------------------------+ + +In "chain" mode, additional chips will appear as additional voltage input +channels, e.g. ``in_voltage1_raw``. + +Fully-differential ADCs +----------------------- + +AD7986 is a fully-differential ADC and has the following attributes: + ++---------------------------------------+--------------------------------------------------------------+ +| Attribute | Description | ++=======================================+==============================================================+ +| ``in_voltage0-voltage1_raw`` | Raw ADC voltage value (*IN+* - *IN-*). | ++---------------------------------------+--------------------------------------------------------------+ +| ``in_voltage0-voltage1_scale`` | Scale factor to convert raw value to mV. | ++---------------------------------------+--------------------------------------------------------------+ + +In "chain" mode, additional chips will appear as additional voltage input +channels, e.g. ``in_voltage2-voltage3_raw``. + + +Device buffers +============== + +This driver supports IIO triggered buffers. + +See :doc:`iio_devbuf` for more information. diff --git a/Documentation/iio/adis16475.rst b/Documentation/iio/adis16475.rst new file mode 100644 index 0000000000..130f9e97cc --- /dev/null +++ b/Documentation/iio/adis16475.rst @@ -0,0 +1,403 @@ +.. SPDX-License-Identifier: GPL-2.0 + +================ +ADIS16475 driver +================ + +This driver supports Analog Device's IMUs on SPI bus. + +1. Supported devices +==================== + +* `ADIS16465 <https://www.analog.com/ADIS16465>`_ +* `ADIS16467 <https://www.analog.com/ADIS16467>`_ +* `ADIS16470 <https://www.analog.com/ADIS16470>`_ +* `ADIS16475 <https://www.analog.com/ADIS16475>`_ +* `ADIS16477 <https://www.analog.com/ADIS16477>`_ +* `ADIS16500 <https://www.analog.com/ADIS16500>`_ +* `ADIS16505 <https://www.analog.com/ADIS16505>`_ +* `ADIS16507 <https://www.analog.com/ADIS16507>`_ + +Each supported device is a precision, miniature microelectromechanical system +(MEMS) inertial measurement unit (IMU) that includes a triaxial gyroscope and a +triaxial accelerometer. Each inertial sensor in the IMU device combines with +signal conditioning that optimizes dynamic performance. The factory calibration +characterizes each sensor for sensitivity, bias, alignment, linear acceleration +(gyroscope bias), and point of percussion (accelerometer location). As a result, +each sensor has dynamic compensation formulas that provide accurate sensor +measurements over a broad set of conditions. + +2. Device attributes +==================== + +Accelerometer, gyroscope measurements are always provided. Furthermore, the +driver offers the capability to retrieve the delta angle and the delta velocity +measurements computed by the device. + +The delta angle measurements represent a calculation of angular displacement +between each sample update, while the delta velocity measurements represent a +calculation of linear velocity change between each sample update. + +Finally, temperature data are provided which show a coarse measurement of +the temperature inside of the IMU device. This data is most useful for +monitoring relative changes in the thermal environment. + +The signal chain of each inertial sensor (accelerometers and gyroscopes) +includes the application of unique correction formulas, which are derived from +extensive characterization of bias, sensitivity, alignment, response to linear +acceleration (gyroscopes), and point of percussion (accelerometer location) +over a temperature range of −40°C to +85°C, for each ADIS device. These +correction formulas are not accessible, but users do have the opportunity to +adjust the bias for each sensor individually through the calibbias attribute. + +Each IIO device, has a device folder under ``/sys/bus/iio/devices/iio:deviceX``, +where X is the IIO index of the device. Under these folders reside a set of +device files, depending on the characteristics and features of the hardware +device in questions. These files are consistently generalized and documented in +the IIO ABI documentation. + +The following tables show the adis16475 related device files, found in the +specific device folder path ``/sys/bus/iio/devices/iio:deviceX``. + ++-------------------------------------------+----------------------------------------------------------+ +| 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. | ++-------------------------------------------+----------------------------------------------------------+ +| in_deltavelocity_scale | Scale for delta velocity channels. | ++-------------------------------------------+----------------------------------------------------------+ +| in_deltavelocity_x_raw | Raw X-axis delta velocity channel value. | ++-------------------------------------------+----------------------------------------------------------+ +| in_deltavelocity_y_raw | Raw Y-axis delta velocity channel value. | ++-------------------------------------------+----------------------------------------------------------+ +| in_deltavelocity_z_raw | Raw Z-axis delta velocity channel value. | ++-------------------------------------------+----------------------------------------------------------+ + ++---------------------------------------+------------------------------------------------------+ +| 3-Axis Gyroscope 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. | ++---------------------------------------+------------------------------------------------------+ +| in_deltaangl_scale | Scale for delta angle channels. | ++---------------------------------------+------------------------------------------------------+ +| in_deltaangl_x_raw | Raw X-axis delta angle channel value. | ++---------------------------------------+------------------------------------------------------+ +| in_deltaangl_y_raw | Raw Y-axis delta angle channel value. | ++---------------------------------------+------------------------------------------------------+ +| in_deltaangl_z_raw | Raw Z-axis delta angle 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. | ++-------------------------------+---------------------------------------------------------+ + +The following table shows the adis16475 related device debug files, found in the +specific device debug folder path ``/sys/kernel/debug/iio/iio:deviceX``. + ++----------------------+-------------------------------------------------------------------------+ +| Debugfs device files | Description | ++----------------------+-------------------------------------------------------------------------+ +| serial_number | The serial number of the chip in hexadecimal format. | ++----------------------+-------------------------------------------------------------------------+ +| product_id | Chip specific product id (e.g. 16475, 16500, 16505, etc.). | ++----------------------+-------------------------------------------------------------------------+ +| flash_count | The number of flash writes performed on the device. | ++----------------------+-------------------------------------------------------------------------+ +| firmware_revision | String containing the firmware revision in the following format ##.##. | ++----------------------+-------------------------------------------------------------------------+ +| firmware_date | String containing the firmware date in the following format mm-dd-yyyy. | ++----------------------+-------------------------------------------------------------------------+ + +Channels processed values +------------------------- + +A channel value can be read from its _raw attribute. The value returned is the +raw value as reported by the devices. To get the processed value of the channel, +apply the following formula: + +.. code-block:: bash + + processed value = (_raw + _offset) * _scale + +Where _offset and _scale are device attributes. If no _offset attribute is +present, simply assume its value is 0. + +The adis16475 driver offers data for 5 types of channels, the table below shows +the measurement units for the processed value, which are defined by the IIO +framework: + ++-------------------------------------+---------------------------+ +| Channel type | Measurement unit | ++-------------------------------------+---------------------------+ +| Acceleration on X, Y, and Z axis | Meters per Second squared | ++-------------------------------------+---------------------------+ +| Angular velocity on X, Y and Z axis | Radians per second | ++-------------------------------------+---------------------------+ +| Delta velocity on X. Y, and Z axis | Meters per Second | ++-------------------------------------+---------------------------+ +| Delta angle on X, Y, and Z axis | Radians | ++-------------------------------------+---------------------------+ +| Temperature | Millidegrees Celsius | ++-------------------------------------+---------------------------+ + +Usage examples +-------------- + +Show device name: + +.. code-block:: bash + + root:/sys/bus/iio/devices/iio:device0> cat name + adis16505-2 + +Show accelerometer channels value: + +.. code-block:: bash + + root:/sys/bus/iio/devices/iio:device0> cat in_accel_x_raw + -275924 + root:/sys/bus/iio/devices/iio:device0> cat in_accel_y_raw + -30142222 + root:/sys/bus/iio/devices/iio:device0> cat in_accel_z_raw + 261265769 + root:/sys/bus/iio/devices/iio:device0> cat in_accel_scale + 0.000000037 + +- X-axis acceleration = in_accel_x_raw * in_accel_scale = −0.010209188 m/s^2 +- Y-axis acceleration = in_accel_y_raw * in_accel_scale = −1.115262214 m/s^2 +- Z-axis acceleration = in_accel_z_raw * in_accel_scale = 9.666833453 m/s^2 + +Show gyroscope channels value: + +.. code-block:: bash + + root:/sys/bus/iio/devices/iio:device0> cat in_anglvel_x_raw + -3324626 + root:/sys/bus/iio/devices/iio:device0> cat in_anglvel_y_raw + 1336980 + root:/sys/bus/iio/devices/iio:device0> cat in_anglvel_z_raw + -602983 + root:/sys/bus/iio/devices/iio:device0> cat in_anglvel_scale + 0.000000006 + +- X-axis angular velocity = in_anglvel_x_raw * in_anglvel_scale = −0.019947756 rad/s +- Y-axis angular velocity = in_anglvel_y_raw * in_anglvel_scale = 0.00802188 rad/s +- Z-axis angular velocity = in_anglvel_z_raw * in_anglvel_scale = −0.003617898 rad/s + +Set calibration offset for accelerometer channels: + +.. code-block:: bash + + root:/sys/bus/iio/devices/iio:device0> cat in_accel_x_calibbias + 0 + + root:/sys/bus/iio/devices/iio:device0> echo 5000 > in_accel_x_calibbias + root:/sys/bus/iio/devices/iio:device0> cat in_accel_x_calibbias + 5000 + +Set calibration offset for gyroscope channels: + +.. code-block:: bash + + root:/sys/bus/iio/devices/iio:device0> cat in_anglvel_y_calibbias + 0 + + root:/sys/bus/iio/devices/iio:device0> echo -5000 > in_anglvel_y_calibbias + root:/sys/bus/iio/devices/iio:device0> cat in_anglvel_y_calibbias + -5000 + +Set sampling frequency: + +.. code-block:: bash + + root:/sys/bus/iio/devices/iio:device0> cat sampling_frequency + 2000.000000 + + root:/sys/bus/iio/devices/iio:device0> echo 1000 > sampling_frequency + 1000.000000 + +Set bandwidth for accelerometer and gyroscope: + +.. code-block:: bash + + root:/sys/bus/iio/devices/iio:device0> cat filter_low_pass_3db_frequency + 720 + + 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 + +Show serial number: + +.. code-block:: bash + + root:/sys/kernel/debug/iio/iio:device0> cat serial_number + 0x04f9 + +Show product id: + +.. code-block:: bash + + root:/sys/kernel/debug/iio/iio:device0> cat product_id + 16505 + +Show flash count: + +.. code-block:: bash + + root:/sys/kernel/debug/iio/iio:device0> cat flash_count + 150 + +Show firmware revision: + +.. code-block:: bash + + root:/sys/kernel/debug/iio/iio:device0> cat firmware_revision + 1.6 + +Show firmware date: + +.. code-block:: bash + + root:/sys/kernel/debug/iio/iio:device0> cat firmware_date + 06-27-2019 + +3. Device buffers +================= + +This driver supports IIO buffers. + +All devices support retrieving the raw acceleration, gyroscope and temperature +measurements using buffers. + +The following device families also support retrieving the delta velocity, delta +angle and temperature measurements using buffers: + +- ADIS16477 +- ADIS16500 +- ADIS16505 +- ADIS16507 + +However, when retrieving acceleration or gyroscope data using buffers, delta +readings will not be available and vice versa. + +Usage examples +-------------- + +Set device trigger in current_trigger, if not already set: + +.. code-block:: bash + + root:/sys/bus/iio/devices/iio:device0> cat trigger/current_trigger + + root:/sys/bus/iio/devices/iio:device0> echo adis16505-2-dev0 > trigger/current_trigger + root:/sys/bus/iio/devices/iio:device0> cat trigger/current_trigger + adis16505-2-dev0 + +Select channels for buffer read: + +.. code-block:: bash + + root:/sys/bus/iio/devices/iio:device0> echo 1 > scan_elements/in_deltavelocity_x_en + root:/sys/bus/iio/devices/iio:device0> echo 1 > scan_elements/in_deltavelocity_y_en + root:/sys/bus/iio/devices/iio:device0> echo 1 > scan_elements/in_deltavelocity_z_en + root:/sys/bus/iio/devices/iio:device0> echo 1 > scan_elements/in_temp0_en + +Set the number of samples to be stored in the buffer: + +.. code-block:: bash + + root:/sys/bus/iio/devices/iio:device0> echo 10 > buffer/length + +Enable buffer readings: + +.. code-block:: bash + + root:/sys/bus/iio/devices/iio:device0> echo 1 > buffer/enable + +Obtain buffered data: + +.. code-block:: bash + + root:/sys/bus/iio/devices/iio:device0> hexdump -C /dev/iio\:device0 + ... + 00001680 01 1f 00 00 ff ff fe ef 00 00 47 bf 00 03 35 55 |..........G...5U| + 00001690 01 1f 00 00 ff ff ff d9 00 00 46 f1 00 03 35 35 |..........F...55| + 000016a0 01 1f 00 00 ff ff fe fc 00 00 46 cb 00 03 35 7b |..........F...5{| + 000016b0 01 1f 00 00 ff ff fe 41 00 00 47 0d 00 03 35 8b |.......A..G...5.| + 000016c0 01 1f 00 00 ff ff fe 37 00 00 46 b4 00 03 35 90 |.......7..F...5.| + 000016d0 01 1d 00 00 ff ff fe 5a 00 00 45 d7 00 03 36 08 |.......Z..E...6.| + 000016e0 01 1b 00 00 ff ff fe fb 00 00 45 e7 00 03 36 60 |..........E...6`| + 000016f0 01 1a 00 00 ff ff ff 17 00 00 46 bc 00 03 36 de |..........F...6.| + 00001700 01 1a 00 00 ff ff fe 59 00 00 46 d7 00 03 37 b8 |.......Y..F...7.| + 00001710 01 1a 00 00 ff ff fe ae 00 00 46 95 00 03 37 ba |..........F...7.| + 00001720 01 1a 00 00 ff ff fe c5 00 00 46 63 00 03 37 9f |..........Fc..7.| + 00001730 01 1a 00 00 ff ff fe 55 00 00 46 89 00 03 37 c1 |.......U..F...7.| + 00001740 01 1a 00 00 ff ff fe 31 00 00 46 aa 00 03 37 f7 |.......1..F...7.| + ... + +See ``Documentation/iio/iio_devbuf.rst`` for more information about how buffered +data is structured. + +4. IIO Interfacing Tools +======================== + +Linux Kernel Tools +------------------ + +Linux Kernel provides some userspace tools that can be used to retrieve data +from IIO sysfs: + +* lsiio: example application that provides a list of IIO devices and triggers +* iio_event_monitor: example application that reads events from an IIO device + and prints them +* iio_generic_buffer: example application that reads data from buffer +* iio_utils: set of APIs, typically used to access sysfs files. + +LibIIO +------ + +LibIIO is a C/C++ library that provides generic access to IIO devices. The +library abstracts the low-level details of the hardware, and provides a simple +yet complete programming interface that can be used for advanced projects. + +For more information about LibIIO, please see: +https://github.com/analogdevicesinc/libiio diff --git a/Documentation/iio/iio_devbuf.rst b/Documentation/iio/iio_devbuf.rst new file mode 100644 index 0000000000..9919e4792d --- /dev/null +++ b/Documentation/iio/iio_devbuf.rst @@ -0,0 +1,152 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============================= +Industrial IIO device buffers +============================= + +1. Overview +=========== + +The Industrial I/O core offers a way for continuous data capture based on a +trigger source. Multiple data channels can be read at once from +``/dev/iio:deviceX`` character device node, thus reducing the CPU load. + +Devices with buffer support feature an additional sub-directory in the +``/sys/bus/iio/devices/iio:deviceX/`` directory hierarchy, called bufferY, where +Y defaults to 0, for devices with a single buffer. + +2. Buffer attributes +==================== + +An IIO buffer has an associated attributes directory under +``/sys/bus/iio/iio:deviceX/bufferY/``. The attributes are described below. + +``length`` +---------- + +Read / Write attribute which states the total number of data samples (capacity) +that can be stored by the buffer. + +``enable`` +---------- + +Read / Write attribute which starts / stops the buffer capture. This file should +be written last, after length and selection of scan elements. Writing a non-zero +value may result in an error, such as EINVAL, if, for example, an unsupported +combination of channels is given. + +``watermark`` +------------- + +Read / Write positive integer attribute 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 watermark is available. + +Non-blocking read will retrieve the available samples from the buffer even if +there are less samples than the 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 +-------------- + +Read-only attribute 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. + +Scan elements +------------- + +The meta information associated with a channel data placed in a buffer is called +a scan element. The scan elements attributes are presented below. + +**_en** + +Read / Write attribute used for enabling a channel. If and only if its value +is non-zero, then a triggered capture will contain data samples for this +channel. + +**_index** + +Read-only unsigned integer attribute specifying the position of the channel in +the buffer. Note these are not dependent on what is enabled and may not be +contiguous. Thus for userspace 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. + +**_type** + +Read-only attribute containing the description of the scan element data storage +within the buffer and hence the form in which it is read from userspace. Format +is [be|le]:[s|u]bits/storagebits[Xrepeat][>>shift], where: + +- **be** or **le** specifies big or little-endian. +- **s** or **u** specifies if signed (2's complement) or unsigned. +- **bits** is the number of valid data bits. +- **storagebits** is the number of bits (after padding) that it occupies in the + buffer. +- **repeat** specifies the number of bits/storagebits repetitions. When the + repeat element is 0 or 1, then the repeat value is omitted. +- **shift** if specified, is the shift that needs to be applied prior to + masking out unused bits. + +For example, a driver for a 3-axis accelerometer with 12-bit resolution where +data is stored in two 8-bit registers is as follows:: + + 7 6 5 4 3 2 1 0 + +---+---+---+---+---+---+---+---+ + |D3 |D2 |D1 |D0 | X | X | X | X | (LOW byte, address 0x06) + +---+---+---+---+---+---+---+---+ + + 7 6 5 4 3 2 1 0 + +---+---+---+---+---+---+---+---+ + |D11|D10|D9 |D8 |D7 |D6 |D5 |D4 | (HIGH byte, address 0x07) + +---+---+---+---+---+---+---+---+ + +will have the following scan element type for each axis: + +.. code-block:: bash + + $ cat /sys/bus/iio/devices/iio:device0/buffer0/in_accel_y_type + le:s12/16>>4 + +A userspace application will interpret data samples read from the buffer as +two-byte little-endian signed data, that needs a 4 bits right shift before +masking out the 12 valid bits of data. + +It is also worth mentioning that the data in the buffer will be naturally +aligned, so the userspace application has to handle the buffers accordingly. + +Take for example, a driver with four channels with the following description: +- channel0: index: 0, type: be:u16/16>>0 +- channel1: index: 1, type: be:u32/32>>0 +- channel2: index: 2, type: be:u32/32>>0 +- channel3: index: 3, type: be:u64/64>>0 + +If all channels are enabled, the data will be aligned in the buffer as follows:: + + 0-1 2 3 4-7 8-11 12 13 14 15 16-23 -> buffer byte number + +-----+---+---+-----+-----+---+---+---+---+-----+ + |CHN_0|PAD|PAD|CHN_1|CHN_2|PAD|PAD|PAD|PAD|CHN_3| -> buffer content + +-----+---+---+-----+-----+---+---+---+---+-----+ + +If only channel0 and channel3 are enabled, the data will be aligned in the +buffer as follows:: + + 0-1 2 3 4 5 6 7 8-15 -> buffer byte number + +-----+---+---+---+---+---+---+-----+ + |CHN_0|PAD|PAD|PAD|PAD|PAD|PAD|CHN_3| -> buffer content + +-----+---+---+---+---+---+---+-----+ + +Typically the buffered data is found in raw format (unscaled with no offset +applied), however there are corner cases in which the buffered data may be found +in a processed form. Please note that these corner cases are not addressed by +this documentation. + +Please see ``Documentation/ABI/testing/sysfs-bus-iio`` for a complete +description of the attributes. diff --git a/Documentation/iio/index.rst b/Documentation/iio/index.rst index 1b7292c58c..fb6f9d7432 100644 --- a/Documentation/iio/index.rst +++ b/Documentation/iio/index.rst @@ -8,7 +8,15 @@ Industrial I/O :maxdepth: 1 iio_configfs + iio_devbuf - ep93xx_adc +Industrial I/O Kernel Drivers +============================= +.. toctree:: + :maxdepth: 1 + + ad7944 + adis16475 bno055 + ep93xx_adc |