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Documentation / hid / hidraw.txt




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Based on kernel version 3.16. Page generated on 2014-08-06 21:39 EST.

1	      HIDRAW - Raw Access to USB and Bluetooth Human Interface Devices
2	     ==================================================================
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	
9	Hidraw should be used if the userspace application knows exactly how to
10	communicate with the hardware device, and is able to construct the HID
11	reports manually.  This is often the case when making userspace drivers for
12	custom HID devices.
13	
14	Hidraw is also useful for communicating with non-conformant HID devices
15	which send and receive data in a way that is inconsistent with their report
16	descriptors.  Because hiddev parses reports which are sent and received
17	through it, checking them against the device's report descriptor, such
18	communication with these non-conformant devices is impossible using hiddev.
19	Hidraw is the only alternative, short of writing a custom kernel driver, for
20	these non-conformant devices.
21	
22	A benefit of hidraw is that its use by userspace applications is independent
23	of the underlying hardware type.  Currently, Hidraw is implemented for USB
24	and Bluetooth.  In the future, as new hardware bus types are developed which
25	use the HID specification, hidraw will be expanded to add support for these
26	new bus types.
27	
28	Hidraw uses a dynamic major number, meaning that udev should be relied on to
29	create hidraw device nodes.  Udev will typically create the device nodes
30	directly under /dev (eg: /dev/hidraw0).  As this location is distribution-
31	and udev rule-dependent, applications should use libudev to locate hidraw
32	devices attached to the system.  There is a tutorial on libudev with a
33	working example at:
34		http://www.signal11.us/oss/udev/
35	
36	The HIDRAW API
37	---------------
38	
39	read()
40	-------
41	read() will read a queued report received from the HID device. On USB
42	devices, the reports read using read() are the reports sent from the device
43	on the INTERRUPT IN endpoint.  By default, read() will block until there is
44	a report available to be read.  read() can be made non-blocking, by passing
45	the O_NONBLOCK flag to open(), or by setting the O_NONBLOCK flag using
46	fcntl().
47	
48	On a device which uses numbered reports, the first byte of the returned data
49	will be the report number; the report data follows, beginning in the second
50	byte.  For devices which do not use numbered reports, the report data
51	will begin at the first byte.
52	
53	write()
54	--------
55	The write() function will write a report to the device. For USB devices, if
56	the device has an INTERRUPT OUT endpoint, the report will be sent on that
57	endpoint. If it does not, the report will be sent over the control endpoint,
58	using a SET_REPORT transfer.
59	
60	The first byte of the buffer passed to write() should be set to the report
61	number.  If the device does not use numbered reports, the first byte should
62	be set to 0. The report data itself should begin at the second byte.
63	
64	ioctl()
65	--------
66	Hidraw supports the following ioctls:
67	
68	HIDIOCGRDESCSIZE: Get Report Descriptor Size
69	This ioctl will get the size of the device's report descriptor.
70	
71	HIDIOCGRDESC: Get Report Descriptor
72	This ioctl returns the device's report descriptor using a
73	hidraw_report_descriptor struct.  Make sure to set the size field of the
74	hidraw_report_descriptor struct to the size returned from HIDIOCGRDESCSIZE.
75	
76	HIDIOCGRAWINFO: Get Raw Info
77	This ioctl will return a hidraw_devinfo struct containing the bus type, the
78	vendor ID (VID), and product ID (PID) of the device. The bus type can be one
79	of:
80		BUS_USB
81		BUS_HIL
82		BUS_BLUETOOTH
83		BUS_VIRTUAL
84	which are defined in linux/input.h.
85	
86	HIDIOCGRAWNAME(len): Get Raw Name
87	This ioctl returns a string containing the vendor and product strings of
88	the device.  The returned string is Unicode, UTF-8 encoded.
89	
90	HIDIOCGRAWPHYS(len): Get Physical Address
91	This ioctl returns a string representing the physical address of the device.
92	For USB devices, the string contains the physical path to the device (the
93	USB controller, hubs, ports, etc).  For Bluetooth devices, the string
94	contains the hardware (MAC) address of the device.
95	
96	HIDIOCSFEATURE(len): Send a Feature Report
97	This ioctl will send a feature report to the device.  Per the HID
98	specification, feature reports are always sent using the control endpoint.
99	Set the first byte of the supplied buffer to the report number.  For devices
100	which do not use numbered reports, set the first byte to 0. The report data
101	begins in the second byte. Make sure to set len accordingly, to one more
102	than the length of the report (to account for the report number).
103	
104	HIDIOCGFEATURE(len): Get a Feature Report
105	This ioctl will request a feature report from the device using the control
106	endpoint.  The first byte of the supplied buffer should be set to the report
107	number of the requested report.  For devices which do not use numbered
108	reports, set the first byte to 0.  The report will be returned starting at
109	the first byte of the buffer (ie: the report number is not returned).
110	
111	Example
112	---------
113	In samples/, find hid-example.c, which shows examples of read(), write(),
114	and all the ioctls for hidraw.  The code may be used by anyone for any
115	purpose, and can serve as a starting point for developing applications using
116	hidraw.
117	
118	Document by:
119		Alan Ott <alan@signal11.us>, Signal 11 Software
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