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 | 443 ++++++++++++++++++++++++++++++++++
 Documentation/iio/index.rst   |   1 +
 2 files changed, 444 insertions(+)
 create mode 100644 Documentation/iio/adxl345.rst

diff --git a/Documentation/iio/adxl345.rst b/Documentation/iio/adxl345.rst
new file mode 100644
index 000000000000..c5525267ea12
--- /dev/null
+++ b/Documentation/iio/adxl345.rst
@@ -0,0 +1,443 @@
+.. 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
+-------------
+
+Specific IIO events are triggered by their corresponding interrupts. The sensor
+driver supports either none or a single active interrupt (INT) line, selectable
+from the two available options: INT1 or INT2. The active INT line should be
+specified in the device tree. If no INT line is configured, the sensor defaults
+to FIFO bypass mode, where event detection is disabled and only X, Y, and Z axis
+measurements are available.
+
+The table below lists the ADXL345-related device files located in the
+device-specific path: ``/sys/bus/iio/devices/iio:deviceX/events``.
+Note that activity and inactivity detection are DC-coupled by default;
+therefore, only the AC-coupled activity and inactivity events are explicitly
+listed.
+
++---------------------------------------------+---------------------------------------------+
+| 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_period                 | Inactivity time in seconds                  |
++---------------------------------------------+---------------------------------------------+
+| in_accel_mag_falling_value                  | Inactivity threshold value in 62.5/LSB      |
++---------------------------------------------+---------------------------------------------+
+| in_accel_mag_adaptive_rising_en             | Enable AC coupled activity on X axis        |
++---------------------------------------------+---------------------------------------------+
+| in_accel_mag_adaptive_falling_period        | AC coupled inactivity time in seconds       |
++---------------------------------------------+---------------------------------------------+
+| in_accel_mag_adaptive_falling_value         | AC coupled inactivity threshold in 62.5/LSB |
++---------------------------------------------+---------------------------------------------+
+| in_accel_mag_adaptive_rising_value          | AC coupled activity threshold in 62.5/LSB   |
++---------------------------------------------+---------------------------------------------+
+| in_accel_mag_rising_en                      | Enable activity detection on X axis         |
++---------------------------------------------+---------------------------------------------+
+| in_accel_mag_rising_value                   | Activity threshold value in 62.5/LSB        |
++---------------------------------------------+---------------------------------------------+
+| in_accel_x_gesture_singletap_en             | Enable single tap detection on X axis       |
++---------------------------------------------+---------------------------------------------+
+| in_accel_x&y&z_mag_falling_en               | Enable inactivity detection on all axis     |
++---------------------------------------------+---------------------------------------------+
+| in_accel_x&y&z_mag_adaptive_falling_en      | Enable AC coupled inactivity on all 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       |
++---------------------------------------------+---------------------------------------------+
+
+Please refer to the sensor's datasheet for a detailed description of this
+functionality.
+
+Manually setting the **ODR** will cause the driver to estimate default values
+for inactivity detection timing, where higher ODR values correspond to longer
+default wait times, and lower ODR values to shorter ones. If these defaults do
+not meet your application’s needs, you can explicitly configure the inactivity
+wait time. Setting this value to 0 will revert to the default behavior.
+
+When changing the **g range** configuration, the driver attempts to estimate
+appropriate activity and inactivity thresholds by scaling the default values
+based on the ratio of the previous range to the new one. The resulting threshold
+will never be zero and will always fall between 1 and 255, corresponding to up
+to 62.5 g/LSB as specified in the datasheet. However, you can override these
+estimated thresholds by setting explicit values.
+
+When **activity** and **inactivity** events are enabled, the driver
+automatically manages hysteresis behavior by setting the **link** and
+**auto-sleep** bits. The link bit connects the activity and inactivity
+functions, so that one follows the other. The auto-sleep function puts the
+sensor into sleep mode when inactivity is detected, reducing power consumption
+to the sub-12.5 Hz rate.
+
+The inactivity time is configurable between 1 and 255 seconds. In addition to
+inactivity detection, the sensor also supports free-fall detection, which, from
+the IIO perspective, is treated as a fall in magnitude across all axes. In
+sensor terms, free-fall is defined using an inactivity period ranging from 0.000
+to 1.000 seconds.
+
+The driver behaves as follows:
+* If the configured inactivity period is 1 second or more, the driver uses the
+  sensor's inactivity register. This allows the event to be linked with
+  activity detection, use auto-sleep, and be either AC- or DC-coupled.
+
+* If the inactivity period is less than 1 second, the event is treated as plain
+  inactivity or free-fall detection. In this case, auto-sleep and coupling
+  (AC/DC) are not applied.
+
+* If an inactivity time of 0 seconds is configured, the driver selects a
+  heuristically determined default period (greater than 1 second) to optimize
+  power consumption. This also uses the inactivity register.
+
+Note: It is recommended to use the activity, inactivity, or free-fall registers
+when operating with an ODR between 12.5 Hz and 400 Hz. According to the
+datasheet, the recommended free-fall threshold is between 300 mg and 600 mg
+(register values 0x05 to 0x09), and the suggested free-fall time ranges from
+100 ms to 350 ms (register values 0x14 to 0x46).
+
+In DC-coupled mode, the current acceleration magnitude is directly compared to
+the values in the THRESH_ACT and THRESH_INACT registers to determine activity or
+inactivity. In contrast, AC-coupled activity detection uses the acceleration
+value at the start of detection as a reference point, and subsequent samples are
+compared against this reference. While DC-coupling is the default mode-comparing
+live values to fixed thresholds-AC-coupling relies on an internal filter
+relative to the configured threshold.
+
+AC and DC coupling modes are configured separately for activity and inactivity
+detection, but only one mode can be active at a time for each. For example, if
+AC-coupled activity detection is enabled and then DC-coupled mode is set, only
+DC-coupled activity detection will be active. In other words, only the most
+recent configuration is applied.
+
+**Single tap** detection can be configured per the datasheet by setting the
+threshold and duration parameters. When only single tap detection is enabled,
+the single tap interrupt triggers as soon as the acceleration exceeds the
+threshold (marking the start of the duration) and then falls below it, provided
+the duration limit is not exceeded. If both single tap and double tap detections
+are enabled, the single tap interrupt is triggered only after the double tap
+event has been either confirmed or dismissed.
+
+To configure **double tap** detection, you must also set the window and latency
+parameters in microseconds (µs). The latency period begins once the single tap
+signal drops below the threshold and acts as a waiting time during which any
+spikes are ignored for double tap detection. After the latency period ends, the
+detection window starts. If the acceleration rises above the threshold and then
+falls below it again within this window, a double tap event is triggered upon
+the fall below the threshold.
+
+Double tap event detection is thoroughly explained in the datasheet. After a
+single tap event is detected, a double tap event may follow, provided the signal
+meets certain criteria. However, double tap detection can be invalidated for
+three reasons:
+
+* If the **suppress bit** is set, any acceleration spike above the tap
+  threshold during the tap latency period immediately invalidates the double tap
+  detection. In other words, no spikes are allowed during latency when the
+  suppress bit is active.
+
+* The double tap event is invalid if the acceleration is above the threshold at
+  the start of the double tap window.
+
+* Double tap detection is also invalidated if the acceleration duration exceeds
+  the limit set by the duration register.
+
+For double tap detection, the same duration applies as for single tap: the
+acceleration must rise above the threshold and then fall below it within the
+specified duration. Note that the suppress bit is typically enabled when double
+tap detection is active.
+
+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 formula:
+
+.. 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
+
+        ## AC coupled activity, threshold [62.5/LSB]
+        root:/sys/bus/iio/devices/iio:device0> echo 6 > ./events/in_accel_mag_adaptive_rising_value
+
+        ## AC coupled inactivity, threshold, [62.5/LSB]
+        root:/sys/bus/iio/devices/iio:device0> echo 4 > ./events/in_accel_mag_adaptive_falling_value
+
+        ## AC coupled inactivity, time [s]
+        root:/sys/bus/iio/devices/iio:device0> echo 3 > ./events/in_accel_mag_adaptive_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
+
+        ## AC coupled activity, enable
+        root:/sys/bus/iio/devices/iio:device0> echo 1 > ./events/in_accel_mag_adaptive_rising_en
+
+        ## AC coupled inactivity, enable
+        root:/sys/bus/iio/devices/iio:device0> echo 1 > ./events/in_accel_x\&y\&z_mag_adaptive_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: mag, direction: rising
+        Event: time: 1739063415963770218, type: accel(z), channel: 0, evtype: mag, 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: mag, direction: falling
+        Event: time: 1739063436539080713, type: accel(x&y&z), channel: 0, evtype: mag, direction: falling
+        Event: time: 1739063438357970381, type: accel(z), channel: 0, evtype: mag, direction: rising
+        Event: time: 1739063446726161586, type: accel(z), channel: 0, evtype: mag, direction: rising
+        Event: time: 1739063446727892670, type: accel(z), channel: 0, evtype: mag, direction: rising
+        Event: time: 1739063446743019768, type: accel(z), channel: 0, evtype: mag, direction: rising
+        Event: time: 1739063446744650696, type: accel(z), channel: 0, evtype: mag, 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: mag, direction: falling
+        ...
+
+Activity and inactivity belong together and indicate state changes as follows
+
+.. code-block:: bash
+
+        root:# iio_event_monitor adxl345
+        Found IIO device with name adxl345 with device number 0
+        Event: time: 1744648001133946293, type: accel(x), channel: 0, evtype: mag, direction: rising
+          <after inactivity time elapsed>
+        Event: time: 1744648057724775499, type: accel(x&y&z), channel: 0, evtype: mag, 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.
diff --git a/Documentation/iio/index.rst b/Documentation/iio/index.rst
index 2d6afc5a8ed5..c333720c1c9f 100644
--- a/Documentation/iio/index.rst
+++ b/Documentation/iio/index.rst
@@ -32,6 +32,7 @@ Industrial I/O Kernel Drivers
    adis16480
    adis16550
    adxl380
+   adxl345
    bno055
    ep93xx_adc
    opt4060
-- 
2.39.5

On Sun, 22 Jun 2025 15:50:10 +0000
Lothar Rubusch <l.rubusch@gmail.com> wrote:

> The documentation describes the ADXL345 driver, IIO interface,
> interface usage and configuration.
> 
> Signed-off-by: Lothar Rubusch <l.rubusch@gmail.com>
I'd add one more patch after this to talk about inactivity vs freefall and the
restrictions around that.

Do it separately rather than integrating in here so that it is easy
to spot that potentially controversial bit.

I'm not a huge fan, but I think it is a viable way to support what we have
here.  I'd kind of like a nice bit of documentation to cover what you have
in the patch description of patch 8 just so we can remember what is going
on with out checking the git logs.

Otherwise I took a quick look through the rest of the series and didn't
have anything to add.

Thanks,

Jonathan