Based on kernel version 3.19. Page generated on 2015-02-13 21:21 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 <firstname.lastname@example.org>, Signal 11 Software