hidraw.rst 5.3 KB

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  1. ================================================================
  2. HIDRAW - Raw Access to USB and Bluetooth Human Interface Devices
  3. ================================================================
  4. The hidraw driver provides a raw interface to USB and Bluetooth Human
  5. Interface Devices (HIDs). It differs from hiddev in that reports sent and
  6. received are not parsed by the HID parser, but are sent to and received from
  7. the device unmodified.
  8. Hidraw should be used if the userspace application knows exactly how to
  9. communicate with the hardware device, and is able to construct the HID
  10. reports manually. This is often the case when making userspace drivers for
  11. custom HID devices.
  12. Hidraw is also useful for communicating with non-conformant HID devices
  13. which send and receive data in a way that is inconsistent with their report
  14. descriptors. Because hiddev parses reports which are sent and received
  15. through it, checking them against the device's report descriptor, such
  16. communication with these non-conformant devices is impossible using hiddev.
  17. Hidraw is the only alternative, short of writing a custom kernel driver, for
  18. these non-conformant devices.
  19. A benefit of hidraw is that its use by userspace applications is independent
  20. of the underlying hardware type. Currently, Hidraw is implemented for USB
  21. and Bluetooth. In the future, as new hardware bus types are developed which
  22. use the HID specification, hidraw will be expanded to add support for these
  23. new bus types.
  24. Hidraw uses a dynamic major number, meaning that udev should be relied on to
  25. create hidraw device nodes. Udev will typically create the device nodes
  26. directly under /dev (eg: /dev/hidraw0). As this location is distribution-
  27. and udev rule-dependent, applications should use libudev to locate hidraw
  28. devices attached to the system. There is a tutorial on libudev with a
  29. working example at:
  30. http://www.signal11.us/oss/udev/
  31. The HIDRAW API
  32. ---------------
  33. read()
  34. -------
  35. read() will read a queued report received from the HID device. On USB
  36. devices, the reports read using read() are the reports sent from the device
  37. on the INTERRUPT IN endpoint. By default, read() will block until there is
  38. a report available to be read. read() can be made non-blocking, by passing
  39. the O_NONBLOCK flag to open(), or by setting the O_NONBLOCK flag using
  40. fcntl().
  41. On a device which uses numbered reports, the first byte of the returned data
  42. will be the report number; the report data follows, beginning in the second
  43. byte. For devices which do not use numbered reports, the report data
  44. will begin at the first byte.
  45. write()
  46. -------
  47. The write() function will write a report to the device. For USB devices, if
  48. the device has an INTERRUPT OUT endpoint, the report will be sent on that
  49. endpoint. If it does not, the report will be sent over the control endpoint,
  50. using a SET_REPORT transfer.
  51. The first byte of the buffer passed to write() should be set to the report
  52. number. If the device does not use numbered reports, the first byte should
  53. be set to 0. The report data itself should begin at the second byte.
  54. ioctl()
  55. -------
  56. Hidraw supports the following ioctls:
  57. HIDIOCGRDESCSIZE:
  58. Get Report Descriptor Size
  59. This ioctl will get the size of the device's report descriptor.
  60. HIDIOCGRDESC:
  61. Get Report Descriptor
  62. This ioctl returns the device's report descriptor using a
  63. hidraw_report_descriptor struct. Make sure to set the size field of the
  64. hidraw_report_descriptor struct to the size returned from HIDIOCGRDESCSIZE.
  65. HIDIOCGRAWINFO:
  66. Get Raw Info
  67. This ioctl will return a hidraw_devinfo struct containing the bus type, the
  68. vendor ID (VID), and product ID (PID) of the device. The bus type can be one
  69. of::
  70. - BUS_USB
  71. - BUS_HIL
  72. - BUS_BLUETOOTH
  73. - BUS_VIRTUAL
  74. which are defined in uapi/linux/input.h.
  75. HIDIOCGRAWNAME(len):
  76. Get Raw Name
  77. This ioctl returns a string containing the vendor and product strings of
  78. the device. The returned string is Unicode, UTF-8 encoded.
  79. HIDIOCGRAWPHYS(len):
  80. Get Physical Address
  81. This ioctl returns a string representing the physical address of the device.
  82. For USB devices, the string contains the physical path to the device (the
  83. USB controller, hubs, ports, etc). For Bluetooth devices, the string
  84. contains the hardware (MAC) address of the device.
  85. HIDIOCSFEATURE(len):
  86. Send a Feature Report
  87. This ioctl will send a feature report to the device. Per the HID
  88. specification, feature reports are always sent using the control endpoint.
  89. Set the first byte of the supplied buffer to the report number. For devices
  90. which do not use numbered reports, set the first byte to 0. The report data
  91. begins in the second byte. Make sure to set len accordingly, to one more
  92. than the length of the report (to account for the report number).
  93. HIDIOCGFEATURE(len):
  94. Get a Feature Report
  95. This ioctl will request a feature report from the device using the control
  96. endpoint. The first byte of the supplied buffer should be set to the report
  97. number of the requested report. For devices which do not use numbered
  98. reports, set the first byte to 0. The report will be returned starting at
  99. the first byte of the buffer (ie: the report number is not returned).
  100. Example
  101. -------
  102. In samples/, find hid-example.c, which shows examples of read(), write(),
  103. and all the ioctls for hidraw. The code may be used by anyone for any
  104. purpose, and can serve as a starting point for developing applications using
  105. hidraw.
  106. Document by:
  107. Alan Ott <alan@signal11.us>, Signal 11 Software