[PATCH v4 14/14] docs: iio: add documentation for adxl345 driver

[Lothar Rubusch <l.rubusch@gmail.com>]

The documentation describes the ADXL345 driver, IIO interface,
interface usage and configuration.

Signed-off-by: Lothar Rubusch <l.rubusch@gmail.com>
---
 Documentation/iio/adxl345.rst | 416 ++++++++++++++++++++++++++++++++++
 1 file changed, 416 insertions(+)
 create mode 100644 Documentation/iio/adxl345.rst

diff --git a/Documentation/iio/adxl345.rst b/Documentation/iio/adxl345.rst
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+.. SPDX-License-Identifier: GPL-2.0
+
+===============
+ADXL345 driver
+===============
+
+This driver supports Analog Device's ADXL345/375 on SPI/I2C bus.
+
+1. Supported devices
+====================
+
+* `ADXL345 <https://www.analog.com/ADXL345>`_
+* `ADXL375 <https://www.analog.com/ADXL375>`_
+
+The ADXL345 is a generic purpose low power, 3-axis accelerometer with selectable
+measurement ranges. The ADXL345 supports the ±2 g, ±4 g, ±8 g, and ±16 g ranges.
+
+2. Device attributes
+====================
+
+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 table shows the ADXL345 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_sampling_frequency               | Currently selected sample rate.                          |
++-------------------------------------------+----------------------------------------------------------+
+| in_accel_sampling_frequency_available     | Available sampling frequency configurations.             |
++-------------------------------------------+----------------------------------------------------------+
+| in_accel_scale                            | Scale/range for the accelerometer channels.              |
++-------------------------------------------+----------------------------------------------------------+
+| in_accel_scale_available                  | Available scale ranges for the accelerometer channel.    |
++-------------------------------------------+----------------------------------------------------------+
+| 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                      | y-axis acceleration offset correction                    |
++-------------------------------------------+----------------------------------------------------------+
+| 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.                  |
++-------------------------------------------+----------------------------------------------------------+
+
+Channel 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.
+
++-------------------------------------+---------------------------+
+| Channel type                        | Measurement unit          |
++-------------------------------------+---------------------------+
+| Acceleration on X, Y, and Z axis    | Meters per second squared |
++-------------------------------------+---------------------------+
+
+Sensor events
+-------------
+
+Particular IIO events will be triggered by the corresponding interrupts. The
+sensor driver supports no or one active INT line, where the sensor has two
+possible INT IOs. Configure the used INT line in the devicetree. If no INT line
+is configured, the sensor falls back to FIFO bypass mode and no events are
+possible, only X, Y and Z axis measurements are possible.
+
+The following table shows the ADXL345 related device files, found in the
+specific device folder path ``/sys/bus/iio/devices/iio:deviceX/events``.
+
++---------------------------------------------+-----------------------------------------+
+| Event handle                                | Description                             |
++---------------------------------------------+-----------------------------------------+
+| in_accel_gesture_doubletap_en               | Enable double tap detection on all axis |
++---------------------------------------------+-----------------------------------------+
+| in_accel_gesture_doubletap_reset_timeout    | Double tap window in [us]               |
++---------------------------------------------+-----------------------------------------+
+| in_accel_gesture_doubletap_tap2_min_delay   | Double tap latent in [us]               |
++---------------------------------------------+-----------------------------------------+
+| in_accel_gesture_singletap_timeout          | Single tap duration in [us]             |
++---------------------------------------------+-----------------------------------------+
+| in_accel_gesture_singletap_value            | Single tap threshold value in 62.5/LSB  |
++---------------------------------------------+-----------------------------------------+
+| in_accel_mag_falling_en                     | Enable free fall detection              |
++---------------------------------------------+-----------------------------------------+
+| in_accel_mag_falling_period                 | Free fall time in [us]                  |
++---------------------------------------------+-----------------------------------------+
+| in_accel_mag_falling_value                  | Free fall threshold value in 62.5/LSB   |
++---------------------------------------------+-----------------------------------------+
+| in_accel_mag_referenced_falling_en          | Set 1 to AC-coupled inactivity, 0 for DC|
++---------------------------------------------+-----------------------------------------+
+| in_accel_mag_referenced_rising_en           | Set 1 to AC-coupled activity, 0 for DC  |
++---------------------------------------------+-----------------------------------------+
+| in_accel_x_thresh_falling_en                | Enable inactivity detection on X axis   |
++---------------------------------------------+-----------------------------------------+
+| in_accel_y_thresh_falling_en                | Enable inactivity detection on Y axis   |
++---------------------------------------------+-----------------------------------------+
+| in_accel_z_thresh_falling_en                | Enable inactivity detection on Z axis   |
++---------------------------------------------+-----------------------------------------+
+| in_accel_thresh_falling_period              | Inactivity time in seconds              |
++---------------------------------------------+-----------------------------------------+
+| in_accel_thresh_falling_value               | Inactivity threshold value in 62.5/LSB  |
++---------------------------------------------+-----------------------------------------+
+| in_accel_x_thresh_rising_en                 | Enable activity detection on X axis     |
++---------------------------------------------+-----------------------------------------+
+| in_accel_y_thresh_rising_en                 | Enable activity detection on Y axis     |
++---------------------------------------------+-----------------------------------------+
+| in_accel_z_thresh_rising_en                 | Enable activity detection on Z axis     |
++---------------------------------------------+-----------------------------------------+
+| in_accel_thresh_rising_value                | Activity threshold value in 62.5/LSB    |
++---------------------------------------------+-----------------------------------------+
+| in_accel_x_gesture_singletap_en             | Enable single tap detection on X axis   |
++---------------------------------------------+-----------------------------------------+
+| in_accel_y_gesture_singletap_en             | Enable single tap detection on Y axis   |
++---------------------------------------------+-----------------------------------------+
+| in_accel_z_gesture_singletap_en             | Enable single tap detection on Z axis   |
++---------------------------------------------+-----------------------------------------+
+
+Find a detailed description of a particular functionality in the sensor
+datasheet.
+
+Setting the ODR explicitly will result in estimated adjusted default values
+for the inactivity time detection, where higher frequencies shall default to
+longer wait periods, and vice versa. It is also possible to explicetly
+configure inactivity wait times, if the defaulting approach does not match
+application requirements. Setting 0 here, will fall back to default setting.
+
+The g range configuration also tries to estimate activity and inactivity
+thresholds when switching to another g range. The default range will be
+factorized by the relation of old range divided by new range. The value never
+becomes 0 and will be at least 1 and at most 255 i.e. 62.5g/LSB according to
+the datasheet. Nevertheless activity and inactivity thresholds can be
+overwritten by explicit values.
+
+When activity and inactivity events are both enabled, the driver automatically
+will implement its hysteresis solution by setting link bit and autosleep bit.
+The link bit serially links the activity and inactivity functions. On the other
+side, the autosleep function switches the sensor to sleep mode if the
+inactivity function is enabled. This will reduce current consumption to the
+sub-12.5Hz rate.
+
+In dc-coupled operation, the current acceleration magnitude is compared
+directly with THRESH_ACT and THRESH_INACT registers to determine whether
+activity or inactivity was detected. In ac-coupled operation for activity
+detection, the acceleration value at the start of activity detection is taken
+as a reference value. New samples are then compared to this reference value.
+Note, ac-coupling and dc-coupling are individually set for activity and/or
+inactivity detection. Activity and inactivity detection are dependent on the
+direction, i.e. the x/y/z axis where this driver generally enables all
+directions. Also, the direction settings are particular to activity and
+inactivity detection, respectively.
+
+Single tap detection can be configured according to the datasheet by specifying
+threshold and duration. If only the single tap is in use, the single tap
+interrupt is triggered when the acceleration goes above threshold (i.e. DUR
+start) and below the threshold, as long as duration is not exceeded. If single
+tap and double tap are in use, the single tap is triggered when the doulbe tap
+event has been either validated or invalidated.
+
+For double tap configure additionally window and latency in [us]. Latency
+starts counting when the single tap goes below threshold and is a waiting
+period, any spikes here are ignored for double tap detection. After latency,
+the window starts. Any rise above threshold, with a consequent fall below
+threshold within window time, rises a double tap signal when going below
+threshold.
+
+Double tap event detection is best described in the datasheet. After a
+single tap event was detected, a double tap event can be detected. Therefore the
+signal must match several criteria, and detection can also considered invalid
+for three reasons:
+* If the suppress bit is set and when still in the tap latency period, any
+measurement of acceleration spike above the tap threshold invalidates double tap
+detection immediately, i.e. during latency must not occur spikes for double tap
+detection when the suppress bit is set.
+* A double tap event is considered invalid, if acceleration lies above the
+threshold at the start of the window time for double tap.
+* Additionally, double tap detection can be considered invalid, if an
+acceleration exceeds the time limit for taps, set by duration register.
+Note, since for double tap the same duration counts, i.e. when rising above
+threshold, a consequent falling below threshold has to be within duration time.
+Also note, the suppress bit is generally set when double tap is enabled.
+
+A free fall event will be detected if the signal goes below the configured
+threshold, for the configured time [us].
+
+Note, that activity/inactivy, as also freefall is recommended for 12.5 Hz ODR
+up to 400 Hz.
+
+Usage examples
+--------------
+
+Show device name:
+
+.. code-block:: bash
+
+        root:/sys/bus/iio/devices/iio:device0> cat name
+        adxl345
+
+Show accelerometer channels value:
+
+.. code-block:: bash
+
+        root:/sys/bus/iio/devices/iio:device0> cat in_accel_x_raw
+        -1
+        root:/sys/bus/iio/devices/iio:device0> cat in_accel_y_raw
+        2
+        root:/sys/bus/iio/devices/iio:device0> cat in_accel_z_raw
+        -253
+
+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 50 > in_accel_x_calibbias
+        root:/sys/bus/iio/devices/iio:device0> cat in_accel_x_calibbias
+        50
+
+Given the 13-bit full resolution, the available ranges are calculated by the
+following forumla:
+
+.. code-block:: bash
+
+        (g * 2 * 9.80665) / (2^(resolution) - 1) * 100; for g := 2|4|8|16
+
+Scale range configuration:
+
+.. code-block:: bash
+
+        root:/sys/bus/iio/devices/iio:device0> cat ./in_accel_scale
+        0.478899
+        root:/sys/bus/iio/devices/iio:device0> cat ./in_accel_scale_available
+        0.478899 0.957798 1.915595 3.831190
+
+        root:/sys/bus/iio/devices/iio:device0> echo 1.915595 > ./in_accel_scale
+        root:/sys/bus/iio/devices/iio:device0> cat ./in_accel_scale
+        1.915595
+
+Set output data rate (ODR):
+
+.. code-block:: bash
+
+        root:/sys/bus/iio/devices/iio:device0> cat ./in_accel_sampling_frequency
+        200.000000
+
+        root:/sys/bus/iio/devices/iio:device0> cat ./in_accel_sampling_frequency_available
+        0.097000 0.195000 0.390000 0.781000 1.562000 3.125000 6.250000 12.500000 25.000000 50.000000 100.000000 200.000000 400.000000 800.000000 1600.000000 3200.000000
+
+        root:/sys/bus/iio/devices/iio:device0> echo 1.562000 > ./in_accel_sampling_frequency
+        root:/sys/bus/iio/devices/iio:device0> cat ./in_accel_sampling_frequency
+        1.562000
+
+Configure one or several events:
+
+.. code-block:: bash
+
+        root:> cd /sys/bus/iio/devices/iio:device0
+
+        root:/sys/bus/iio/devices/iio:device0> echo 1 > ./buffer0/in_accel_x_en
+        root:/sys/bus/iio/devices/iio:device0> echo 1 > ./buffer0/in_accel_y_en
+        root:/sys/bus/iio/devices/iio:device0> echo 1 > ./buffer0/in_accel_z_en
+
+        root:/sys/bus/iio/devices/iio:device0> echo 1 > ./scan_elements/in_accel_x_en
+        root:/sys/bus/iio/devices/iio:device0> echo 1 > ./scan_elements/in_accel_y_en
+        root:/sys/bus/iio/devices/iio:device0> echo 1 > ./scan_elements/in_accel_z_en
+
+        root:/sys/bus/iio/devices/iio:device0> echo 14   > ./in_accel_x_calibbias
+        root:/sys/bus/iio/devices/iio:device0> echo 2    > ./in_accel_y_calibbias
+        root:/sys/bus/iio/devices/iio:device0> echo -250 > ./in_accel_z_calibbias
+
+        root:/sys/bus/iio/devices/iio:device0> echo 24 > ./buffer0/length
+
+        ## activity, threshold [62.5/LSB]
+        root:/sys/bus/iio/devices/iio:device0> echo 6 > ./events/in_accel_thresh_rising_value
+
+        ## inactivity, threshold, [62.5/LSB]
+        root:/sys/bus/iio/devices/iio:device0> echo 4 > ./events/in_accel_thresh_falling_value
+
+        ## inactivity, time [s]
+        root:/sys/bus/iio/devices/iio:device0> echo 3 > ./events/in_accel_thresh_falling_period
+
+        ## singletap, threshold
+        root:/sys/bus/iio/devices/iio:device0> echo 35 > ./events/in_accel_gesture_singletap_value
+
+        ## singletap, duration [us]
+        root:/sys/bus/iio/devices/iio:device0> echo 0.001875  > ./events/in_accel_gesture_singletap_timeout
+
+        ## doubletap, window [us]
+        root:/sys/bus/iio/devices/iio:device0> echo 0.025 > ./events/in_accel_gesture_doubletap_reset_timeout
+
+        ## doubletap, latent [us]
+        root:/sys/bus/iio/devices/iio:device0> echo 0.025 > ./events/in_accel_gesture_doubletap_tap2_min_delay
+
+        ## freefall, threshold [62.5/LSB]
+        root:/sys/bus/iio/devices/iio:device0> echo 8 > ./events/in_accel_mag_falling_value
+
+        ## freefall, time [ms]
+        root:/sys/bus/iio/devices/iio:device0> echo 1.25 > ./events/in_accel_mag_falling_period
+
+        ## activity, enable
+        root:/sys/bus/iio/devices/iio:device0> echo 1 > ./events/in_accel_thresh_rising_en
+
+        ## inactivity, enable
+        root:/sys/bus/iio/devices/iio:device0> echo 1 > ./events/in_accel_thresh_falling_en
+
+        ## freefall, enable
+        root:/sys/bus/iio/devices/iio:device0> echo 1 > ./events/in_accel_mag_falling_en
+
+        ## singletap, enable
+        root:/sys/bus/iio/devices/iio:device0> echo 1 > ./events/in_accel_x_gesture_singletap_en
+        root:/sys/bus/iio/devices/iio:device0> echo 1 > ./events/in_accel_y_gesture_singletap_en
+        root:/sys/bus/iio/devices/iio:device0> echo 1 > ./events/in_accel_z_gesture_singletap_en
+
+        ## doubletap, enable
+        root:/sys/bus/iio/devices/iio:device0> echo 1 > ./events/in_accel_gesture_doubletap_en
+
+Verify incoming events:
+
+.. code-block:: bash
+
+        root:# iio_event_monitor adxl345
+        Found IIO device with name adxl345 with device number 0
+        Event: time: 1739063415957073383, type: accel(z), channel: 0, evtype: thresh, direction: rising
+        Event: time: 1739063415963770218, type: accel(z), channel: 0, evtype: thresh, direction: rising
+        Event: time: 1739063416002563061, type: accel(z), channel: 0, evtype: gesture, direction: singletap
+        Event: time: 1739063426271128739, type: accel(x|y|z), channel: 0, evtype: thresh, direction: falling
+        Event: time: 1739063436539080713, type: accel(x|y|z), channel: 0, evtype: thresh, direction: falling
+        Event: time: 1739063438357970381, type: accel(z), channel: 0, evtype: thresh, direction: rising
+        Event: time: 1739063446726161586, type: accel(z), channel: 0, evtype: thresh, direction: rising
+        Event: time: 1739063446727892670, type: accel(z), channel: 0, evtype: thresh, direction: rising
+        Event: time: 1739063446743019768, type: accel(z), channel: 0, evtype: thresh, direction: rising
+        Event: time: 1739063446744650696, type: accel(z), channel: 0, evtype: thresh, direction: rising
+        Event: time: 1739063446763559386, type: accel(z), channel: 0, evtype: gesture, direction: singletap
+        Event: time: 1739063448818126480, type: accel(x|y|z), channel: 0, evtype: thresh, direction: falling
+        ...
+
+3. Device buffers
+=================
+
+This driver supports IIO buffers.
+
+All devices support retrieving the raw acceleration and temperature measurements
+using buffers.
+
+Usage examples
+--------------
+
+Select channels for buffer read:
+
+.. code-block:: bash
+
+        root:/sys/bus/iio/devices/iio:device0> echo 1 > scan_elements/in_accel_x_en
+        root:/sys/bus/iio/devices/iio:device0> echo 1 > scan_elements/in_accel_y_en
+        root:/sys/bus/iio/devices/iio:device0> echo 1 > scan_elements/in_accel_z_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:> iio_readdev -b 16 -s 1024 adxl345 | hexdump -d
+        WARNING: High-speed mode not enabled
+        0000000   00003   00012   00013   00005   00010   00011   00005   00011
+        0000010   00013   00004   00012   00011   00003   00012   00014   00007
+        0000020   00011   00013   00004   00013   00014   00003   00012   00013
+        0000030   00004   00012   00013   00005   00011   00011   00005   00012
+        0000040   00014   00005   00012   00014   00004   00010   00012   00004
+        0000050   00013   00011   00003   00011   00012   00005   00011   00013
+        0000060   00003   00012   00012   00003   00012   00012   00004   00012
+        0000070   00012   00003   00013   00013   00003   00013   00012   00005
+        0000080   00012   00013   00003   00011   00012   00005   00012   00013
+        0000090   00003   00013   00011   00005   00013   00014   00003   00012
+        00000a0   00012   00003   00012   00013   00004   00012   00015   00004
+        00000b0   00014   00011   00003   00014   00013   00004   00012   00011
+        00000c0   00004   00012   00013   00004   00014   00011   00004   00013
+        00000d0   00012   00002   00014   00012   00005   00012   00013   00005
+        00000e0   00013   00013   00003   00013   00013   00005   00012   00013
+        00000f0   00004   00014   00015   00005   00012   00011   00005   00012
+        ...
+
+See ``Documentation/iio/iio_devbuf.rst`` for more information about how buffered
+data is structured.
+
+4. IIO Interfacing Tools
+========================
+
+See ``Documentation/iio/iio_tools.rst`` for the description of the available IIO
+interfacing tools.
-- 
2.39.5