lis3lv02d.rst 4.3 KB

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