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Message-Id: <20250622155010.164451-8-l.rubusch@gmail.com>
Date: Sun, 22 Jun 2025 15:50:10 +0000
From: Lothar Rubusch <l.rubusch@...il.com>
To: lars@...afoo.de,
Michael.Hennerich@...log.com,
jic23@...nel.org,
dlechner@...libre.com,
nuno.sa@...log.com,
andy@...nel.org,
corbet@....net
Cc: linux-iio@...r.kernel.org,
linux-kernel@...r.kernel.org,
linux-doc@...r.kernel.org,
eraretuya@...il.com,
l.rubusch@...il.com
Subject: [PATCH v10 7/7] docs: iio: add documentation for adxl345 driver
The documentation describes the ADXL345 driver, IIO interface,
interface usage and configuration.
Signed-off-by: Lothar Rubusch <l.rubusch@...il.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
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