| HIDRAW - Raw Access to USB and Bluetooth Human Interface Devices
|The hidraw driver provides a raw interface to USB and Bluetooth Human
|Interface Devices (HIDs). It differs from hiddev in that reports sent and
|received are not parsed by the HID parser, but are sent to and received from
|the device unmodified.
|Hidraw should be used if the userspace application knows exactly how to
|communicate with the hardware device, and is able to construct the HID
|reports manually. This is often the case when making userspace drivers for
|custom HID devices.
|Hidraw is also useful for communicating with non-conformant HID devices
|which send and receive data in a way that is inconsistent with their report
|descriptors. Because hiddev parses reports which are sent and received
|through it, checking them against the device's report descriptor, such
|communication with these non-conformant devices is impossible using hiddev.
|Hidraw is the only alternative, short of writing a custom kernel driver, for
|these non-conformant devices.
|A benefit of hidraw is that its use by userspace applications is independent
|of the underlying hardware type. Currently, Hidraw is implemented for USB
|and Bluetooth. In the future, as new hardware bus types are developed which
|use the HID specification, hidraw will be expanded to add support for these
|new bus types.
|Hidraw uses a dynamic major number, meaning that udev should be relied on to
|create hidraw device nodes. Udev will typically create the device nodes
|directly under /dev (eg: /dev/hidraw0). As this location is distribution-
|and udev rule-dependent, applications should use libudev to locate hidraw
|devices attached to the system. There is a tutorial on libudev with a
|working example at:
|The HIDRAW API
|read() will read a queued report received from the HID device. On USB
|devices, the reports read using read() are the reports sent from the device
|on the INTERRUPT IN endpoint. By default, read() will block until there is
|a report available to be read. read() can be made non-blocking, by passing
|the O_NONBLOCK flag to open(), or by setting the O_NONBLOCK flag using
|On a device which uses numbered reports, the first byte of the returned data
|will be the report number; the report data follows, beginning in the second
|byte. For devices which do not use numbered reports, the report data
|will begin at the first byte.
|The write() function will write a report to the device. For USB devices, if
|the device has an INTERRUPT OUT endpoint, the report will be sent on that
|endpoint. If it does not, the report will be sent over the control endpoint,
|using a SET_REPORT transfer.
|The first byte of the buffer passed to write() should be set to the report
|number. If the device does not use numbered reports, the first byte should
|be set to 0. The report data itself should begin at the second byte.
|Hidraw supports the following ioctls:
|HIDIOCGRDESCSIZE: Get Report Descriptor Size
|This ioctl will get the size of the device's report descriptor.
|HIDIOCGRDESC: Get Report Descriptor
|This ioctl returns the device's report descriptor using a
|hidraw_report_descriptor struct. Make sure to set the size field of the
|hidraw_report_descriptor struct to the size returned from HIDIOCGRDESCSIZE.
|HIDIOCGRAWINFO: Get Raw Info
|This ioctl will return a hidraw_devinfo struct containing the bus type, the
|vendor ID (VID), and product ID (PID) of the device. The bus type can be one
|which are defined in linux/input.h.
|HIDIOCGRAWNAME(len): Get Raw Name
|This ioctl returns a string containing the vendor and product strings of
|the device. The returned string is Unicode, UTF-8 encoded.
|HIDIOCGRAWPHYS(len): Get Physical Address
|This ioctl returns a string representing the physical address of the device.
|For USB devices, the string contains the physical path to the device (the
|USB controller, hubs, ports, etc). For Bluetooth devices, the string
|contains the hardware (MAC) address of the device.
|HIDIOCSFEATURE(len): Send a Feature Report
|This ioctl will send a feature report to the device. Per the HID
|specification, feature reports are always sent using the control endpoint.
|Set the first byte of the supplied buffer to the report number. For devices
|which do not use numbered reports, set the first byte to 0. The report data
|begins in the second byte. Make sure to set len accordingly, to one more
|than the length of the report (to account for the report number).
|HIDIOCGFEATURE(len): Get a Feature Report
|This ioctl will request a feature report from the device using the control
|endpoint. The first byte of the supplied buffer should be set to the report
|number of the requested report. For devices which do not use numbered
|reports, set the first byte to 0. The report will be returned starting at
|the first byte of the buffer (ie: the report number is not returned).
|In samples/, find hid-example.c, which shows examples of read(), write(),
|and all the ioctls for hidraw. The code may be used by anyone for any
|purpose, and can serve as a starting point for developing applications using
| Alan Ott <email@example.com>, Signal 11 Software