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 (1.5MBit/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.

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:

             http://www.usb.org/developers/docs/

       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 2.0 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>.

Debian                                           April 24, 2018                                           USB(4)