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Message-Id: <20250210110119.260858-15-l.rubusch@gmail.com> Date: Mon, 10 Feb 2025 11:01:19 +0000 From: Lothar Rubusch <l.rubusch@...il.com> To: lars@...afoo.de, Michael.Hennerich@...log.com, jic23@...nel.org Cc: linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org, eraretuya@...il.com, l.rubusch@...il.com Subject: [PATCH v2 14/14] 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 | 401 ++++++++++++++++++++++++++++++++++ 1 file changed, 401 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..52bea3e7c4ac --- /dev/null +++ b/Documentation/iio/adxl345.rst @@ -0,0 +1,401 @@ +.. 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 +==================== + +Accelerometer measurements are always provided. + +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_suppressedbit_en | Enable double tap suppress bit | ++---------------------------------------------+-----------------------------------------+ +| 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 couple inactivity AC, 0 for DC | ++---------------------------------------------+-----------------------------------------+ +| in_accel_mag_referenced_rising_en | Set 1 to couple activity AC, 0 for DC | ++---------------------------------------------+-----------------------------------------+ +| in_accel_thresh_falling_en | Enable inactivity detection | ++---------------------------------------------+-----------------------------------------+ +| in_accel_thresh_falling_period | Inactivity time in seconds | ++---------------------------------------------+-----------------------------------------+ +| in_accel_thresh_falling_value | Inactivity threshold value in 62.5/LSB | ++---------------------------------------------+-----------------------------------------+ +| in_accel_thresh_rising_en | Enable activity detection | ++---------------------------------------------+-----------------------------------------+ +| 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 enabled, the driver automatically will +set 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. + +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. + +A double tap event can be invalidated in three ways: If the suppress bit is set, +any acceleration spike above the threshold already during the latency time +invalidates the double tap detection immediately, i.e. during latence must not +occur spikes for double tap detection with suppress bit set. +A double tap event is invalidated if acceleration lies above the threshold at +the start of the window time for the double tap detection. +Additionally a double tap event can be invalidated if an acceleration exceeds +the time limit for taps, set by duration register, since also for the double +tap the same value for duration counts, i.e. when rising above threshold the +fall below threshold has to be within duration time. + +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
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