The usbhotkey program itself reads USB events from an opened device and calls a ruby function for press and release events. The ruby script given on the command line provides these functions along with some initialisation code to open device. A single USB keyboard can be opened by one instance of usbhotkey. It should be possible to run multiple instances.

The ruby command

UHK_connect( 0x510, 0x100b, 0x81)

seaches a USB device with vendor ID 0x510 and product ID 0x100b. If found, it reads events from end-point 0x81. Use lsusb -vvv to find the data for your keyboard.

On keypress the ruby function

UHK_USB_keydn( code)

is called. code is the USB scan code.

Only keycodes are sent. These are subject to translation by the current keymap. This calling

USK_keydn( X11::XK_bracketleft)

produces a [ on US and UK keyboards, but an u-umlaut (ü) on a German keymap. You may use this feature to generate letters that are not part of the regular keymap by generating unused keycodes and mapping them in ~/.Xmodmap.

A floating overlay can be displayed using

UHK_displayImage( fileName, x, y)

• USB HID specs
  • Device Class Definition for HID 1.11 (HID1_11.pdf)
  • HID Usage Tables 1.12 (Hut1_12.pdf)
• Ruby documentation
• X11 manual