Root/
1 | Kernel driver lis3lv02d |
2 | ======================= |
3 | |
4 | Supported chips: |
5 | |
6 | * STMicroelectronics LIS3LV02DL, LIS3LV02DQ (12 bits precision) |
7 | * STMicroelectronics LIS302DL, LIS3L02DQ, LIS331DL (8 bits) |
8 | |
9 | Authors: |
10 | Yan Burman <burman.yan@gmail.com> |
11 | Eric Piel <eric.piel@tremplin-utc.net> |
12 | |
13 | |
14 | Description |
15 | ----------- |
16 | |
17 | This driver provides support for the accelerometer found in various HP laptops |
18 | sporting the feature officially called "HP Mobile Data Protection System 3D" or |
19 | "HP 3D DriveGuard". It detects automatically laptops with this sensor. Known |
20 | models (full list can be found in drivers/hwmon/hp_accel.c) will have their |
21 | axis automatically oriented on standard way (eg: you can directly play |
22 | neverball). The accelerometer data is readable via |
23 | /sys/devices/platform/lis3lv02d. Reported values are scaled |
24 | to mg values (1/1000th of earth gravity). |
25 | |
26 | Sysfs attributes under /sys/devices/platform/lis3lv02d/: |
27 | position - 3D position that the accelerometer reports. Format: "(x,y,z)" |
28 | rate - read reports the sampling rate of the accelerometer device in HZ. |
29 | write changes sampling rate of the accelerometer device. |
30 | Only values which are supported by HW are accepted. |
31 | selftest - performs selftest for the chip as specified by chip manufacturer. |
32 | |
33 | This driver also provides an absolute input class device, allowing |
34 | the laptop to act as a pinball machine-esque joystick. Joystick device can be |
35 | calibrated. Joystick device can be in two different modes. |
36 | By default output values are scaled between -32768 .. 32767. In joystick raw |
37 | mode, joystick and sysfs position entry have the same scale. There can be |
38 | small difference due to input system fuzziness feature. |
39 | Events are also available as input event device. |
40 | |
41 | Selftest is meant only for hardware diagnostic purposes. It is not meant to be |
42 | used during normal operations. Position data is not corrupted during selftest |
43 | but interrupt behaviour is not guaranteed to work reliably. In test mode, the |
44 | sensing element is internally moved little bit. Selftest measures difference |
45 | between normal mode and test mode. Chip specifications tell the acceptance |
46 | limit for each type of the chip. Limits are provided via platform data |
47 | to allow adjustment of the limits without a change to the actual driver. |
48 | Seltest returns either "OK x y z" or "FAIL x y z" where x, y and z are |
49 | measured difference between modes. Axes are not remapped in selftest mode. |
50 | Measurement values are provided to help HW diagnostic applications to make |
51 | final decision. |
52 | |
53 | On HP laptops, if the led infrastructure is activated, support for a led |
54 | indicating disk protection will be provided as /sys/class/leds/hp::hddprotect. |
55 | |
56 | Another feature of the driver is misc device called "freefall" that |
57 | acts similar to /dev/rtc and reacts on free-fall interrupts received |
58 | from the device. It supports blocking operations, poll/select and |
59 | fasync operation modes. You must read 1 bytes from the device. The |
60 | result is number of free-fall interrupts since the last successful |
61 | read (or 255 if number of interrupts would not fit). See the hpfall.c |
62 | file for an example on using the device. |
63 | |
64 | |
65 | Axes orientation |
66 | ---------------- |
67 | |
68 | For better compatibility between the various laptops. The values reported by |
69 | the accelerometer are converted into a "standard" organisation of the axes |
70 | (aka "can play neverball out of the box"): |
71 | * When the laptop is horizontal the position reported is about 0 for X and Y |
72 | and a positive value for Z |
73 | * If the left side is elevated, X increases (becomes positive) |
74 | * If the front side (where the touchpad is) is elevated, Y decreases |
75 | (becomes negative) |
76 | * If the laptop is put upside-down, Z becomes negative |
77 | |
78 | If your laptop model is not recognized (cf "dmesg"), you can send an |
79 | email to the maintainer to add it to the database. When reporting a new |
80 | laptop, please include the output of "dmidecode" plus the value of |
81 | /sys/devices/platform/lis3lv02d/position in these four cases. |
82 | |
83 | Q&A |
84 | --- |
85 | |
86 | Q: How do I safely simulate freefall? I have an HP "portable |
87 | workstation" which has about 3.5kg and a plastic case, so letting it |
88 | fall to the ground is out of question... |
89 | |
90 | A: The sensor is pretty sensitive, so your hands can do it. Lift it |
91 | into free space, follow the fall with your hands for like 10 |
92 | centimeters. That should be enough to trigger the detection. |
93 |
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