USB(4)                 FreeBSD Kernel Interfaces Manual                 USB(4)

NAME
     usb - Universal Serial Bus

SYNOPSIS
     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 loader.conf(5):

           usb_load="YES"

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

DESCRIPTION
     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.

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

           Low Speed (1.5 MBit/sec)

           Full Speed (12 MBit/sec)

           High Speed (480 MBit/sec)

           SuperSpeed (5 GBit/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.

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

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

SEE ALSO
     The USB specifications can be found at:

           https://www.usb.org/documents

     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)

STANDARDS
     The usb module complies with the USB 3.0 standard.

HISTORY
     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 <hselasky@FreeBSD.org>.

FreeBSD 13.1-RELEASE-p6        September 7, 2020       FreeBSD 13.1-RELEASE-p6