freebsd-skq/share/man/man4/usb.4

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.Dd September 7, 2020
.Dt USB 4
.Os
.Sh NAME
.Nm usb
.Nd Universal Serial Bus
.Sh SYNOPSIS
To compile this driver into the kernel,
place the following line in your
kernel configuration file:
.Bd -ragged -offset indent
.Cd "device usb"
.Ed
.Pp
Alternatively, to load the driver as a
module at boot time, place the following line in
.Xr loader.conf 5 :
.Bd -literal -offset indent
usb_load="YES"
.Ed
.Sh USERLAND PROGRAMMING
USB functions can be accessed from userland through the libusb library.
See
.Xr libusb 3
for more information.
.Sh DESCRIPTION
.Fx
provides machine-independent bus support and drivers for
USB devices in host and device side mode.
.Pp
The
.Nm
driver has three layers:
.Bl -tag -width 6n -offset indent
.It USB Controller (Bus)
.It USB Device
.It USB Driver
.El
.Pp
The controller attaches to a physical bus
like
.Xr 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.
.Pp
The
.Nm uhub
device will always be present as it is needed for the root hub.
.Sh INTRODUCTION TO USB
The USB is a system where external devices can be connected to a PC.
The most common USB speeds are:
.Bl -tag -width 6n -offset indent
.It Low Speed (1.5 MBit/sec)
.It Full Speed (12 MBit/sec)
.It High Speed (480 MBit/sec)
.It SuperSpeed (5 GBit/sec)
.El
.Pp
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.
.Pp
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.
.Pp
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:
.Em control , isochronous , bulk ,
or
.Em 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.
.Pp
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.
.Pp
A device may operate in different configurations.
Depending on the configuration, the device may present different sets of
endpoints and interfaces.
.Pp
The bus enumeration of the USB bus proceeds in several steps:
.Bl -enum
.It
Any interface specific driver can attach to the device.
.It
If none is found, generic interface class drivers can attach.
.El
.Sh SYSCTL VARIABLES
The following variables are available as both
.Xr sysctl 8
variables and
.Xr loader 8
tunables:
.Bl -tag -width indent
.It Va hw.usb.debug
Debug output level, where 0 is debugging disabled and larger values increase
debug message verbosity.
Default is 0.
.El
.Sh SEE ALSO
The USB specifications can be found at:
.Pp
.D1 Pa https://www.usb.org/documents
.Pp
.Xr libusb 3 ,
.Xr aue 4 ,
.Xr axe 4 ,
.Xr axge 4 ,
.Xr cue 4 ,
.Xr ehci 4 ,
.Xr kue 4 ,
.Xr mos 4 ,
.Xr ohci 4 ,
.Xr pci 4 ,
.Xr rue 4 ,
.Xr ucom 4 ,
.Xr udav 4 ,
.Xr uhci 4 ,
.Xr uhid 4 ,
.Xr ukbd 4 ,
.Xr ulpt 4 ,
.Xr umass 4 ,
.Xr ums 4 ,
.Xr uplcom 4 ,
.Xr urio 4 ,
.Xr uvscom 4 ,
.Xr xhci 4
.Xr usbconfig 8 ,
.Xr usbdi 9
.Sh STANDARDS
The
.Nm
module complies with the USB 3.0 standard.
.Sh HISTORY
The
.Nm
module has been inspired by the
.Nx
USB stack initially written by
.An Lennart Augustsson .
The
.Nm
module was written by
.An Hans Petter Selasky Aq Mt hselasky@FreeBSD.org .