linux-pinenote/Documentation/hwmon/lis3lv02d

Kernel driver lis3lv02d
=======================

Supported chips:

  * STMicroelectronics LIS3LV02DL and LIS3LV02DQ

Authors:
        Yan Burman <burman.yan@gmail.com>
	Eric Piel <eric.piel@tremplin-utc.net>


Description
-----------

This driver provides support for the accelerometer found in various HP
laptops sporting the feature officially called "HP Mobile Data
Protection System 3D" or "HP 3D DriveGuard". It detects automatically
laptops with this sensor. Known models (for now the HP 2133, nc6420,
nc2510, nc8510, nc84x0, nw9440 and nx9420) will have their axis
automatically oriented on standard way (eg: you can directly play
neverball).  The accelerometer data is readable via
/sys/devices/platform/lis3lv02d.

Sysfs attributes under /sys/devices/platform/lis3lv02d/:
position - 3D position that the accelerometer reports. Format: "(x,y,z)"
calibrate - read: values (x, y, z) that are used as the base for input
		  class device operation.
            write: forces the base to be recalibrated with the current
		   position.
rate - reports the sampling rate of the accelerometer device in HZ

This driver also provides an absolute input class device, allowing
the laptop to act as a pinball machine-esque joystick.

Another feature of the driver is misc device called "freefall" that
acts similar to /dev/rtc and reacts on free-fall interrupts received
from the device. It supports blocking operations, poll/select and
fasync operation modes. You must read 1 bytes from the device.  The
result is number of free-fall interrupts since the last successful
read (or 255 if number of interrupts would not fit).


Axes orientation
----------------

For better compatibility between the various laptops. The values reported by
the accelerometer are converted into a "standard" organisation of the axes
(aka "can play neverball out of the box"):
 * When the laptop is horizontal the position reported is about 0 for X and Y
	and a positive value for Z
 * If the left side is elevated, X increases (becomes positive)
 * If the front side (where the touchpad is) is elevated, Y decreases
	(becomes negative)
 * If the laptop is put upside-down, Z becomes negative

If your laptop model is not recognized (cf "dmesg"), you can send an
email to the authors to add it to the database.  When reporting a new
laptop, please include the output of "dmidecode" plus the value of
/sys/devices/platform/lis3lv02d/position in these four cases.

Q&A
---

Q: How do I safely simulate freefall? I have an HP "portable
workstation" which has about 3.5kg and a plastic case, so letting it
fall to the ground is out of question...

A: The sensor is pretty sensitive, so your hands can do it. Lift it
into free space, follow the fall with your hands for like 10
centimeters. That should be enough to trigger the detection.