linux/Documentation/hid/hidraw.txt
<<
>>
Prefs
   1      HIDRAW - Raw Access to USB and Bluetooth Human Interface Devices
   2     ==================================================================
   3
   4The hidraw driver provides a raw interface to USB and Bluetooth Human
   5Interface Devices (HIDs).  It differs from hiddev in that reports sent and
   6received are not parsed by the HID parser, but are sent to and received from
   7the device unmodified.
   8
   9Hidraw should be used if the userspace application knows exactly how to
  10communicate with the hardware device, and is able to construct the HID
  11reports manually.  This is often the case when making userspace drivers for
  12custom HID devices.
  13
  14Hidraw is also useful for communicating with non-conformant HID devices
  15which send and receive data in a way that is inconsistent with their report
  16descriptors.  Because hiddev parses reports which are sent and received
  17through it, checking them against the device's report descriptor, such
  18communication with these non-conformant devices is impossible using hiddev.
  19Hidraw is the only alternative, short of writing a custom kernel driver, for
  20these non-conformant devices.
  21
  22A benefit of hidraw is that its use by userspace applications is independent
  23of the underlying hardware type.  Currently, Hidraw is implemented for USB
  24and Bluetooth.  In the future, as new hardware bus types are developed which
  25use the HID specification, hidraw will be expanded to add support for these
  26new bus types.
  27
  28Hidraw uses a dynamic major number, meaning that udev should be relied on to
  29create hidraw device nodes.  Udev will typically create the device nodes
  30directly under /dev (eg: /dev/hidraw0).  As this location is distribution-
  31and udev rule-dependent, applications should use libudev to locate hidraw
  32devices attached to the system.  There is a tutorial on libudev with a
  33working example at:
  34        http://www.signal11.us/oss/udev/
  35
  36The HIDRAW API
  37---------------
  38
  39read()
  40-------
  41read() will read a queued report received from the HID device. On USB
  42devices, the reports read using read() are the reports sent from the device
  43on the INTERRUPT IN endpoint.  By default, read() will block until there is
  44a report available to be read.  read() can be made non-blocking, by passing
  45the O_NONBLOCK flag to open(), or by setting the O_NONBLOCK flag using
  46fcntl().
  47
  48On a device which uses numbered reports, the first byte of the returned data
  49will be the report number; the report data follows, beginning in the second
  50byte.  For devices which do not use numbered reports, the report data
  51will begin at the first byte.
  52
  53write()
  54--------
  55The write() function will write a report to the device. For USB devices, if
  56the device has an INTERRUPT OUT endpoint, the report will be sent on that
  57endpoint. If it does not, the report will be sent over the control endpoint,
  58using a SET_REPORT transfer.
  59
  60The first byte of the buffer passed to write() should be set to the report
  61number.  If the device does not use numbered reports, the first byte should
  62be set to 0. The report data itself should begin at the second byte.
  63
  64ioctl()
  65--------
  66Hidraw supports the following ioctls:
  67
  68HIDIOCGRDESCSIZE: Get Report Descriptor Size
  69This ioctl will get the size of the device's report descriptor.
  70
  71HIDIOCGRDESC: Get Report Descriptor
  72This ioctl returns the device's report descriptor using a
  73hidraw_report_descriptor struct.  Make sure to set the size field of the
  74hidraw_report_descriptor struct to the size returned from HIDIOCGRDESCSIZE.
  75
  76HIDIOCGRAWINFO: Get Raw Info
  77This ioctl will return a hidraw_devinfo struct containing the bus type, the
  78vendor ID (VID), and product ID (PID) of the device. The bus type can be one
  79of:
  80        BUS_USB
  81        BUS_HIL
  82        BUS_BLUETOOTH
  83        BUS_VIRTUAL
  84which are defined in linux/input.h.
  85
  86HIDIOCGRAWNAME(len): Get Raw Name
  87This ioctl returns a string containing the vendor and product strings of
  88the device.  The returned string is Unicode, UTF-8 encoded.
  89
  90HIDIOCGRAWPHYS(len): Get Physical Address
  91This ioctl returns a string representing the physical address of the device.
  92For USB devices, the string contains the physical path to the device (the
  93USB controller, hubs, ports, etc).  For Bluetooth devices, the string
  94contains the hardware (MAC) address of the device.
  95
  96HIDIOCSFEATURE(len): Send a Feature Report
  97This ioctl will send a feature report to the device.  Per the HID
  98specification, feature reports are always sent using the control endpoint.
  99Set the first byte of the supplied buffer to the report number.  For devices
 100which do not use numbered reports, set the first byte to 0. The report data
 101begins in the second byte. Make sure to set len accordingly, to one more
 102than the length of the report (to account for the report number).
 103
 104HIDIOCGFEATURE(len): Get a Feature Report
 105This ioctl will request a feature report from the device using the control
 106endpoint.  The first byte of the supplied buffer should be set to the report
 107number of the requested report.  For devices which do not use numbered
 108reports, set the first byte to 0.  The report will be returned starting at
 109the first byte of the buffer (ie: the report number is not returned).
 110
 111Example
 112---------
 113In samples/, find hid-example.c, which shows examples of read(), write(),
 114and all the ioctls for hidraw.  The code may be used by anyone for any
 115purpose, and can serve as a starting point for developing applications using
 116hidraw.
 117
 118Document by:
 119        Alan Ott <alan@signal11.us>, Signal 11 Software
 120
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.