60 lines
2.8 KiB
Text
60 lines
2.8 KiB
Text
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There are two implementations of HIDAPI for Linux. One (linux/hid.c) uses the
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Linux hidraw driver, and the other (libusb/hid.c) uses libusb. Which one you
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use depends on your application. Complete functionality of the hidraw
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version depends on patches to the Linux kernel which are not currently in
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the mainline. These patches have to do with sending and receiving feature
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reports. The libusb implementation uses libusb to talk directly to the
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device, bypassing any Linux HID driver. The disadvantage of the libusb
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version is that it will only work with USB devices, while the hidraw
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implementation will work with Bluetooth devices as well.
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To use HIDAPI, simply drop either linux/hid.c or libusb/hid.c into your
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application and build using the build parameters in the Makefile.
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Libusb Implementation notes
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----------------------------
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For the libusb implementation, libusb-1.0 must be installed. Libusb 1.0 is
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different than the legacy libusb 0.1 which is installed on many systems. To
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install libusb-1.0 on Ubuntu and other Debian-based systems, run:
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sudo apt-get install libusb-1.0-0-dev
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Hidraw Implementation notes
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----------------------------
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For the hidraw implementation, libudev headers and libraries are required to
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build hidapi programs. To install libudev libraries on Ubuntu,
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and other Debian-based systems, run:
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sudo apt-get install libudev-dev
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On Redhat-based systems, run the following as root:
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yum install libudev-devel
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Unfortunately, the hidraw driver, which the linux version of hidapi is based
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on, contains bugs in kernel versions < 2.6.36, which the client application
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should be aware of.
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Bugs (hidraw implementation only):
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-----------------------------------
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On Kernel versions < 2.6.34, if your device uses numbered reports, an extra
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byte will be returned at the beginning of all reports returned from read()
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for hidraw devices. This is worked around in the libary. No action should be
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necessary in the client library.
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On Kernel versions < 2.6.35, reports will only be sent using a Set_Report
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transfer on the CONTROL endpoint. No data will ever be sent on an Interrupt
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Out endpoint if one exists. This is fixed in 2.6.35. In 2.6.35, OUTPUT
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reports will be sent to the device on the first INTERRUPT OUT endpoint if it
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exists; If it does not exist, OUTPUT reports will be sent on the CONTROL
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endpoint.
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On Kernel versions < 2.6.36, add an extra byte containing the report number
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to sent reports if numbered reports are used, and the device does not
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contain an INTERRPUT OUT endpoint for OUTPUT transfers. For example, if
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your device uses numbered reports and wants to send {0x2 0xff 0xff 0xff} to
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the device (0x2 is the report number), you must send {0x2 0x2 0xff 0xff
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0xff}. If your device has the optional Interrupt OUT endpoint, this does not
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apply (but really on 2.6.35 only, because 2.6.34 won't use the interrupt
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out endpoint).
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