usbip-server

Keyboard

A HID boot keyboard. Linux binds its usbhid driver to it, and it types into your desktop like any keyboard: one second after the host has configured it, it types Who is typing....


Program	`out/usb_keyboard_device`
Source	src/usb_keyboard/
USB id	`fa00:0003`
Interface	HID (class `0x03`), boot interface subclass, keyboard protocol
Endpoint	`0x81` interrupt IN, 8 byte reports, polled every 8 ms

The text goes to whichever window has focus, a terminal included.

Try It

$ make
$ out/usb_keyboard_device &
$ sudo usbip attach -r localhost -b 1-1

Click into an empty editor window before the attach completes. A second later Who is typing... appears. The keyboard types once per attach; detach with sudo usbip detach -p 0 and attach again to type again.

What You See

USB Keyboard Device Activated
USBIPServer: Connected
USBIPProtocol: USBIP_CMD_REQ_DEV_IMPORT '1-1'
Configuration Active

Configuration Active is printed when the host sends SET_CONFIGURATION, the moment the keyboard is ready to be used.

How It Works

control_data() answers the HID GET_DESCRIPTOR request for the report descriptor, and sets configuration_active on SET_CONFIGURATION with a configuration other than 0.
The main loop waits for configuration_active, then waits one more second: the desktop starts listening to a new keyboard a moment after it is configured, and keys typed before that are lost.
Each character becomes a key down report, sent with usbip_device_transmit(), followed 20 ms later by an all zero key up report. Characters are 100 ms apart.
ascii_to_hid() turns characters into HID usage codes plus the shift modifier. Letters, digits, space, Enter, Backspace, Tab and the punctuation of a US keyboard are supported.
The server delivers at most one report per 8 ms polling interval, so the main loop can simply call usbip_device_transmit() and runs at the speed the descriptors promise.

Prototyping

Start here for keyboards, keypads, barcode scanners, foot pedals, or anything else that sends key presses. The boot protocol report (modifier byte, reserved byte, six key codes) works on every host, the BIOS included.

Troubleshooting

Wrong characters: the keyboard sends key positions, not characters, and the host’s keyboard layout decides what they mean. ascii_to_hid() assumes a US layout, so with another layout punctuation can come out differently.
Nothing is typed: check that the keyboard printed Configuration Active, and that a window that accepts text has focus.

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