94 lines
4.2 KiB
Plaintext
94 lines
4.2 KiB
Plaintext
Kernel driver lis3lv02d
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=======================
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Supported chips:
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* STMicroelectronics LIS3LV02DL, LIS3LV02DQ (12 bits precision)
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* STMicroelectronics LIS302DL, LIS3L02DQ, LIS331DL (8 bits) and
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LIS331DLH (16 bits)
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Authors:
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Yan Burman <burman.yan@gmail.com>
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Eric Piel <eric.piel@tremplin-utc.net>
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Description
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-----------
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This driver provides support for the accelerometer found in various HP laptops
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sporting the feature officially called "HP Mobile Data Protection System 3D" or
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"HP 3D DriveGuard". It detects automatically laptops with this sensor. Known
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models (full list can be found in drivers/platform/x86/hp_accel.c) will have
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their axis automatically oriented on standard way (eg: you can directly play
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neverball). The accelerometer data is readable via
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/sys/devices/platform/lis3lv02d. Reported values are scaled
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to mg values (1/1000th of earth gravity).
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Sysfs attributes under /sys/devices/platform/lis3lv02d/:
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position - 3D position that the accelerometer reports. Format: "(x,y,z)"
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rate - read reports the sampling rate of the accelerometer device in HZ.
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write changes sampling rate of the accelerometer device.
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Only values which are supported by HW are accepted.
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selftest - performs selftest for the chip as specified by chip manufacturer.
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This driver also provides an absolute input class device, allowing
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the laptop to act as a pinball machine-esque joystick. Joystick device can be
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calibrated. Joystick device can be in two different modes.
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By default output values are scaled between -32768 .. 32767. In joystick raw
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mode, joystick and sysfs position entry have the same scale. There can be
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small difference due to input system fuzziness feature.
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Events are also available as input event device.
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Selftest is meant only for hardware diagnostic purposes. It is not meant to be
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used during normal operations. Position data is not corrupted during selftest
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but interrupt behaviour is not guaranteed to work reliably. In test mode, the
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sensing element is internally moved little bit. Selftest measures difference
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between normal mode and test mode. Chip specifications tell the acceptance
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limit for each type of the chip. Limits are provided via platform data
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to allow adjustment of the limits without a change to the actual driver.
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Seltest returns either "OK x y z" or "FAIL x y z" where x, y and z are
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measured difference between modes. Axes are not remapped in selftest mode.
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Measurement values are provided to help HW diagnostic applications to make
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final decision.
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On HP laptops, if the led infrastructure is activated, support for a led
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indicating disk protection will be provided as /sys/class/leds/hp::hddprotect.
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Another feature of the driver is misc device called "freefall" that
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acts similar to /dev/rtc and reacts on free-fall interrupts received
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from the device. It supports blocking operations, poll/select and
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fasync operation modes. You must read 1 bytes from the device. The
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result is number of free-fall interrupts since the last successful
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read (or 255 if number of interrupts would not fit). See the freefall.c
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file for an example on using the device.
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Axes orientation
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----------------
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For better compatibility between the various laptops. The values reported by
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the accelerometer are converted into a "standard" organisation of the axes
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(aka "can play neverball out of the box"):
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* When the laptop is horizontal the position reported is about 0 for X and Y
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and a positive value for Z
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* If the left side is elevated, X increases (becomes positive)
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* If the front side (where the touchpad is) is elevated, Y decreases
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(becomes negative)
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* If the laptop is put upside-down, Z becomes negative
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If your laptop model is not recognized (cf "dmesg"), you can send an
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email to the maintainer to add it to the database. When reporting a new
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laptop, please include the output of "dmidecode" plus the value of
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/sys/devices/platform/lis3lv02d/position in these four cases.
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Q&A
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---
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Q: How do I safely simulate freefall? I have an HP "portable
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workstation" which has about 3.5kg and a plastic case, so letting it
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fall to the ground is out of question...
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A: The sensor is pretty sensitive, so your hands can do it. Lift it
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into free space, follow the fall with your hands for like 10
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centimeters. That should be enough to trigger the detection.
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