lis3lv02d.rst (4356B)
1======================= 2Kernel driver lis3lv02d 3======================= 4 5Supported chips: 6 7 * STMicroelectronics LIS3LV02DL, LIS3LV02DQ (12 bits precision) 8 * STMicroelectronics LIS302DL, LIS3L02DQ, LIS331DL (8 bits) and 9 LIS331DLH (16 bits) 10 11Authors: 12 - Yan Burman <burman.yan@gmail.com> 13 - Eric Piel <eric.piel@tremplin-utc.net> 14 15 16Description 17----------- 18 19This driver provides support for the accelerometer found in various HP laptops 20sporting the feature officially called "HP Mobile Data Protection System 3D" or 21"HP 3D DriveGuard". It detects automatically laptops with this sensor. Known 22models (full list can be found in drivers/platform/x86/hp_accel.c) will have 23their axis automatically oriented on standard way (eg: you can directly play 24neverball). The accelerometer data is readable via 25/sys/devices/platform/lis3lv02d. Reported values are scaled 26to mg values (1/1000th of earth gravity). 27 28Sysfs attributes under /sys/devices/platform/lis3lv02d/: 29 30position 31 - 3D position that the accelerometer reports. Format: "(x,y,z)" 32rate 33 - read reports the sampling rate of the accelerometer device in HZ. 34 write changes sampling rate of the accelerometer device. 35 Only values which are supported by HW are accepted. 36selftest 37 - performs selftest for the chip as specified by chip manufacturer. 38 39This driver also provides an absolute input class device, allowing 40the laptop to act as a pinball machine-esque joystick. Joystick device can be 41calibrated. Joystick device can be in two different modes. 42By default output values are scaled between -32768 .. 32767. In joystick raw 43mode, joystick and sysfs position entry have the same scale. There can be 44small difference due to input system fuzziness feature. 45Events are also available as input event device. 46 47Selftest is meant only for hardware diagnostic purposes. It is not meant to be 48used during normal operations. Position data is not corrupted during selftest 49but interrupt behaviour is not guaranteed to work reliably. In test mode, the 50sensing element is internally moved little bit. Selftest measures difference 51between normal mode and test mode. Chip specifications tell the acceptance 52limit for each type of the chip. Limits are provided via platform data 53to allow adjustment of the limits without a change to the actual driver. 54Seltest returns either "OK x y z" or "FAIL x y z" where x, y and z are 55measured difference between modes. Axes are not remapped in selftest mode. 56Measurement values are provided to help HW diagnostic applications to make 57final decision. 58 59On HP laptops, if the led infrastructure is activated, support for a led 60indicating disk protection will be provided as /sys/class/leds/hp::hddprotect. 61 62Another feature of the driver is misc device called "freefall" that 63acts similar to /dev/rtc and reacts on free-fall interrupts received 64from the device. It supports blocking operations, poll/select and 65fasync operation modes. You must read 1 bytes from the device. The 66result is number of free-fall interrupts since the last successful 67read (or 255 if number of interrupts would not fit). See the freefall.c 68file for an example on using the device. 69 70 71Axes orientation 72---------------- 73 74For better compatibility between the various laptops. The values reported by 75the accelerometer are converted into a "standard" organisation of the axes 76(aka "can play neverball out of the box"): 77 78 * When the laptop is horizontal the position reported is about 0 for X and Y 79 and a positive value for Z 80 * If the left side is elevated, X increases (becomes positive) 81 * If the front side (where the touchpad is) is elevated, Y decreases 82 (becomes negative) 83 * If the laptop is put upside-down, Z becomes negative 84 85If your laptop model is not recognized (cf "dmesg"), you can send an 86email to the maintainer to add it to the database. When reporting a new 87laptop, please include the output of "dmidecode" plus the value of 88/sys/devices/platform/lis3lv02d/position in these four cases. 89 90Q&A 91--- 92 93Q: How do I safely simulate freefall? I have an HP "portable 94workstation" which has about 3.5kg and a plastic case, so letting it 95fall to the ground is out of question... 96 97A: The sensor is pretty sensitive, so your hands can do it. Lift it 98into free space, follow the fall with your hands for like 10 99centimeters. That should be enough to trigger the detection.