Describe the inactivity detection additionally using the free-fall register. Due to the controversial discussions on the mailing list, this section of the documentation will be committed separately to allow for a more focused and detailed elaboration of the topic. Signed-off-by: Lothar Rubusch <l.rubusch@xxxxxxxxx> --- Documentation/iio/adxl345.rst | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) diff --git a/Documentation/iio/adxl345.rst b/Documentation/iio/adxl345.rst index 8ee01b8b87f4..4bd038cb4a37 100644 --- a/Documentation/iio/adxl345.rst +++ b/Documentation/iio/adxl345.rst @@ -150,6 +150,30 @@ 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: According to the datasheet, the optimal ODR for detecting activity, +or inactivity (or when operating with the free-fall register) should fall within +the range of 12.5 Hz to 400 Hz. The recommended free-fall threshold is between +300 mg and 600 mg (register values 0x05 to 0x09). + 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 -- 2.39.5
