120 lines
5.3 KiB
Plaintext
120 lines
5.3 KiB
Plaintext
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HIDRAW - Raw Access to USB and Bluetooth Human Interface Devices
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==================================================================
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The hidraw driver provides a raw interface to USB and Bluetooth Human
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Interface Devices (HIDs). It differs from hiddev in that reports sent and
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received are not parsed by the HID parser, but are sent to and received from
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the device unmodified.
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Hidraw should be used if the userspace application knows exactly how to
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communicate with the hardware device, and is able to construct the HID
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reports manually. This is often the case when making userspace drivers for
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custom HID devices.
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Hidraw is also useful for communicating with non-conformant HID devices
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which send and receive data in a way that is inconsistent with their report
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descriptors. Because hiddev parses reports which are sent and received
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through it, checking them against the device's report descriptor, such
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communication with these non-conformant devices is impossible using hiddev.
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Hidraw is the only alternative, short of writing a custom kernel driver, for
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these non-conformant devices.
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A benefit of hidraw is that its use by userspace applications is independent
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of the underlying hardware type. Currently, Hidraw is implemented for USB
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and Bluetooth. In the future, as new hardware bus types are developed which
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use the HID specification, hidraw will be expanded to add support for these
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new bus types.
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Hidraw uses a dynamic major number, meaning that udev should be relied on to
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create hidraw device nodes. Udev will typically create the device nodes
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directly under /dev (eg: /dev/hidraw0). As this location is distribution-
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and udev rule-dependent, applications should use libudev to locate hidraw
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devices attached to the system. There is a tutorial on libudev with a
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working example at:
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http://www.signal11.us/oss/udev/
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The HIDRAW API
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---------------
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read()
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-------
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read() will read a queued report received from the HID device. On USB
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devices, the reports read using read() are the reports sent from the device
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on the INTERRUPT IN endpoint. By default, read() will block until there is
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a report available to be read. read() can be made non-blocking, by passing
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the O_NONBLOCK flag to open(), or by setting the O_NONBLOCK flag using
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fcntl().
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On a device which uses numbered reports, the first byte of the returned data
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will be the report number; the report data follows, beginning in the second
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byte. For devices which do not use numbered reports, the report data
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will begin at the first byte.
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write()
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--------
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The write() function will write a report to the device. For USB devices, if
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the device has an INTERRUPT OUT endpoint, the report will be sent on that
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endpoint. If it does not, the report will be sent over the control endpoint,
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using a SET_REPORT transfer.
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The first byte of the buffer passed to write() should be set to the report
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number. If the device does not use numbered reports, the first byte should
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be set to 0. The report data itself should begin at the second byte.
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ioctl()
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--------
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Hidraw supports the following ioctls:
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HIDIOCGRDESCSIZE: Get Report Descriptor Size
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This ioctl will get the size of the device's report descriptor.
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HIDIOCGRDESC: Get Report Descriptor
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This ioctl returns the device's report descriptor using a
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hidraw_report_descriptor struct. Make sure to set the size field of the
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hidraw_report_descriptor struct to the size returned from HIDIOCGRDESCSIZE.
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HIDIOCGRAWINFO: Get Raw Info
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This ioctl will return a hidraw_devinfo struct containing the bus type, the
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vendor ID (VID), and product ID (PID) of the device. The bus type can be one
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of:
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BUS_USB
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BUS_HIL
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BUS_BLUETOOTH
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BUS_VIRTUAL
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which are defined in linux/input.h.
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HIDIOCGRAWNAME(len): Get Raw Name
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This ioctl returns a string containing the vendor and product strings of
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the device. The returned string is Unicode, UTF-8 encoded.
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HIDIOCGRAWPHYS(len): Get Physical Address
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This ioctl returns a string representing the physical address of the device.
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For USB devices, the string contains the physical path to the device (the
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USB controller, hubs, ports, etc). For Bluetooth devices, the string
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contains the hardware (MAC) address of the device.
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HIDIOCSFEATURE(len): Send a Feature Report
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This ioctl will send a feature report to the device. Per the HID
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specification, feature reports are always sent using the control endpoint.
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Set the first byte of the supplied buffer to the report number. For devices
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which do not use numbered reports, set the first byte to 0. The report data
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begins in the second byte. Make sure to set len accordingly, to one more
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than the length of the report (to account for the report number).
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HIDIOCGFEATURE(len): Get a Feature Report
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This ioctl will request a feature report from the device using the control
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endpoint. The first byte of the supplied buffer should be set to the report
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number of the requested report. For devices which do not use numbered
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reports, set the first byte to 0. The report will be returned starting at
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the first byte of the buffer (ie: the report number is not returned).
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Example
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---------
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In samples/, find hid-example.c, which shows examples of read(), write(),
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and all the ioctls for hidraw. The code may be used by anyone for any
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purpose, and can serve as a starting point for developing applications using
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hidraw.
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Document by:
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Alan Ott <alan@signal11.us>, Signal 11 Software
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