hidraw.rst (7534B)
1================================================================ 2HIDRAW - Raw Access to USB and Bluetooth Human Interface Devices 3================================================================ 4 5The hidraw driver provides a raw interface to USB and Bluetooth Human 6Interface Devices (HIDs). It differs from hiddev in that reports sent and 7received are not parsed by the HID parser, but are sent to and received from 8the device unmodified. 9 10Hidraw should be used if the userspace application knows exactly how to 11communicate with the hardware device, and is able to construct the HID 12reports manually. This is often the case when making userspace drivers for 13custom HID devices. 14 15Hidraw is also useful for communicating with non-conformant HID devices 16which send and receive data in a way that is inconsistent with their report 17descriptors. Because hiddev parses reports which are sent and received 18through it, checking them against the device's report descriptor, such 19communication with these non-conformant devices is impossible using hiddev. 20Hidraw is the only alternative, short of writing a custom kernel driver, for 21these non-conformant devices. 22 23A benefit of hidraw is that its use by userspace applications is independent 24of the underlying hardware type. Currently, hidraw is implemented for USB 25and Bluetooth. In the future, as new hardware bus types are developed which 26use the HID specification, hidraw will be expanded to add support for these 27new bus types. 28 29Hidraw uses a dynamic major number, meaning that udev should be relied on to 30create hidraw device nodes. Udev will typically create the device nodes 31directly under /dev (eg: /dev/hidraw0). As this location is distribution- 32and udev rule-dependent, applications should use libudev to locate hidraw 33devices attached to the system. There is a tutorial on libudev with a 34working example at:: 35 36 http://www.signal11.us/oss/udev/ 37 https://web.archive.org/web/2019*/www.signal11.us 38 39The HIDRAW API 40--------------- 41 42read() 43------- 44read() will read a queued report received from the HID device. On USB 45devices, the reports read using read() are the reports sent from the device 46on the INTERRUPT IN endpoint. By default, read() will block until there is 47a report available to be read. read() can be made non-blocking, by passing 48the O_NONBLOCK flag to open(), or by setting the O_NONBLOCK flag using 49fcntl(). 50 51On a device which uses numbered reports, the first byte of the returned data 52will be the report number; the report data follows, beginning in the second 53byte. For devices which do not use numbered reports, the report data 54will begin at the first byte. 55 56write() 57------- 58The write() function will write a report to the device. For USB devices, if 59the device has an INTERRUPT OUT endpoint, the report will be sent on that 60endpoint. If it does not, the report will be sent over the control endpoint, 61using a SET_REPORT transfer. 62 63The first byte of the buffer passed to write() should be set to the report 64number. If the device does not use numbered reports, the first byte should 65be set to 0. The report data itself should begin at the second byte. 66 67ioctl() 68------- 69Hidraw supports the following ioctls: 70 71HIDIOCGRDESCSIZE: 72 Get Report Descriptor Size 73 74This ioctl will get the size of the device's report descriptor. 75 76HIDIOCGRDESC: 77 Get Report Descriptor 78 79This ioctl returns the device's report descriptor using a 80hidraw_report_descriptor struct. Make sure to set the size field of the 81hidraw_report_descriptor struct to the size returned from HIDIOCGRDESCSIZE. 82 83HIDIOCGRAWINFO: 84 Get Raw Info 85 86This ioctl will return a hidraw_devinfo struct containing the bus type, the 87vendor ID (VID), and product ID (PID) of the device. The bus type can be one 88of:: 89 90 - BUS_USB 91 - BUS_HIL 92 - BUS_BLUETOOTH 93 - BUS_VIRTUAL 94 95which are defined in uapi/linux/input.h. 96 97HIDIOCGRAWNAME(len): 98 Get Raw Name 99 100This ioctl returns a string containing the vendor and product strings of 101the device. The returned string is Unicode, UTF-8 encoded. 102 103HIDIOCGRAWPHYS(len): 104 Get Physical Address 105 106This ioctl returns a string representing the physical address of the device. 107For USB devices, the string contains the physical path to the device (the 108USB controller, hubs, ports, etc). For Bluetooth devices, the string 109contains the hardware (MAC) address of the device. 110 111HIDIOCSFEATURE(len): 112 Send a Feature Report 113 114This ioctl will send a feature report to the device. Per the HID 115specification, feature reports are always sent using the control endpoint. 116Set the first byte of the supplied buffer to the report number. For devices 117which do not use numbered reports, set the first byte to 0. The report data 118begins in the second byte. Make sure to set len accordingly, to one more 119than the length of the report (to account for the report number). 120 121HIDIOCGFEATURE(len): 122 Get a Feature Report 123 124This ioctl will request a feature report from the device using the control 125endpoint. The first byte of the supplied buffer should be set to the report 126number of the requested report. For devices which do not use numbered 127reports, set the first byte to 0. The returned report buffer will contain the 128report number in the first byte, followed by the report data read from the 129device. For devices which do not use numbered reports, the report data will 130begin at the first byte of the returned buffer. 131 132HIDIOCSINPUT(len): 133 Send an Input Report 134 135This ioctl will send an input report to the device, using the control endpoint. 136In most cases, setting an input HID report on a device is meaningless and has 137no effect, but some devices may choose to use this to set or reset an initial 138state of a report. The format of the buffer issued with this report is identical 139to that of HIDIOCSFEATURE. 140 141HIDIOCGINPUT(len): 142 Get an Input Report 143 144This ioctl will request an input report from the device using the control 145endpoint. This is slower on most devices where a dedicated In endpoint exists 146for regular input reports, but allows the host to request the value of a 147specific report number. Typically, this is used to request the initial states of 148an input report of a device, before an application listens for normal reports via 149the regular device read() interface. The format of the buffer issued with this report 150is identical to that of HIDIOCGFEATURE. 151 152HIDIOCSOUTPUT(len): 153 Send an Output Report 154 155This ioctl will send an output report to the device, using the control endpoint. 156This is slower on most devices where a dedicated Out endpoint exists for regular 157output reports, but is added for completeness. Typically, this is used to set 158the initial states of an output report of a device, before an application sends 159updates via the regular device write() interface. The format of the buffer issued 160with this report is identical to that of HIDIOCSFEATURE. 161 162HIDIOCGOUTPUT(len): 163 Get an Output Report 164 165This ioctl will request an output report from the device using the control 166endpoint. Typically, this is used to retrive the initial state of 167an output report of a device, before an application updates it as necessary either 168via a HIDIOCSOUTPUT request, or the regular device write() interface. The format 169of the buffer issued with this report is identical to that of HIDIOCGFEATURE. 170 171Example 172------- 173In samples/, find hid-example.c, which shows examples of read(), write(), 174and all the ioctls for hidraw. The code may be used by anyone for any 175purpose, and can serve as a starting point for developing applications using 176hidraw. 177 178Document by: 179 180 Alan Ott <alan@signal11.us>, Signal 11 Software