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     usb — Universal Serial Bus


     To compile this driver into the kernel, place the following line in your kernel
     configuration file:

           device usb

     Alternatively, to load the driver as a module at boot time, place the following line in



     USB functions can be accessed from userland through the libusb library.  See libusb(3) for
     more information.


     FreeBSD provides machine-independent bus support and drivers for USB devices in host and
     device side mode.

     The usb driver has three layers:

           USB Controller (Bus)

           USB Device

           USB Driver

     The controller attaches to a physical bus like pci(4).  The USB bus attaches to the
     controller, and the root hub attaches to the controller.  Any devices attached to the bus
     will attach to the root hub or another hub attached to the USB bus.

     The uhub device will always be present as it is needed for the root hub.


     The USB is a system where external devices can be connected to a PC.  The most common USB
     speeds are:

           Low Speed (1.5MBit/sec)

           Full Speed (12MBit/sec)

           High Speed (480MBit/sec)

     Each USB has a USB controller that is the master of the bus.  The physical communication is
     simplex which means the host controller only communicates with one USB device at a time.

     There can be up to 127 devices connected to an USB HUB tree.  The addresses are assigned
     dynamically by the host when each device is attached to the bus.

     Within each device there can be up to 16 endpoints.  Each endpoint is individually addressed
     and the addresses are static.  Each of these endpoints will communicate in one of four
     different modes: control, isochronous, bulk, or interrupt.  A device always has at least one
     endpoint.  This endpoint has address 0 and is a control endpoint and is used to give
     commands to and extract basic data, such as descriptors, from the device.  Each endpoint,
     except the control endpoint, is unidirectional.

     The endpoints in a device are grouped into interfaces.  An interface is a logical unit
     within a device, e.g., a compound device with both a keyboard and a trackball, would present
     one interface for each.  An interface can sometimes be set into different modes, called
     alternate settings, which affects how it operates.  Different alternate settings can have
     different endpoints within it.

     A device may operate in different configurations.  Depending on the configuration, the
     device may present different sets of endpoints and interfaces.

     The bus enumeration of the USB bus proceeds in several steps:

     1.   Any interface specific driver can attach to the device.

     2.   If none is found, generic interface class drivers can attach.


     The following variables are available as both sysctl(8) variables and loader(8) tunables:

             Debug output level, where 0 is debugging disabled and larger values increase debug
             message verbosity.  Default is 0.


     The USB specifications can be found at:


     libusb(3), aue(4), axe(4), axge(4), cue(4), ehci(4), kue(4), mos(4), ohci(4), pci(4),
     rue(4), ucom(4), udav(4), uhci(4), uhid(4), ukbd(4), ulpt(4), umass(4), ums(4), uplcom(4),
     urio(4), uvscom(4), xhci(4) usbconfig(8), usbdi(9),


     The usb module complies with the USB 2.0 standard.


     The usb module has been inspired by the NetBSD USB stack initially written by Lennart
     Augustsson.  The usb module was written by Hans Petter Selasky <>.