man/man4/usb.4

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.Dd February 21, 1999
.Dt USB 4
.Os
.Sh NAME
.Nm usb
.Nd Universal Serial Bus
.Sh SYNOPSIS
.Cd "device usb"
.Pp
.In dev/usb/usb.h
.In dev/usb/usbhid.h
.Sh DESCRIPTION
.Fx
provides machine-independent bus support and drivers for
.Tn USB
devices.
.Pp
The
.Nm
driver has three layers: the controller, the bus, and the
device layer.
The controller attaches to a physical bus
(like
.Xr pci 4 ) .
The
.Tn 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
.Tn USB
bus.
.Pp
The
.Nm uhub
device will always be present as it is needed for the
root hub.
.Sh INTRODUCTION TO USB
The
.Tn USB
is a 12 Mb/s serial bus (1.5 Mb/s for low speed devices).
Each
.Tn USB
has a host controller that is the master of the bus;
all other devices on the bus only speak when spoken to.
.Pp
There can be up to 127 devices (apart from the host controller)
on a bus, each with its own address.
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
Each device located on a hub has several
.Xr config 8
locators:
.Bl -tag -compact -width xxxxxx
.It Cd port
this is the number of the port on the closest upstream hub.
.It Cd configuration
this is the configuration the device must be in for this driver to attach.
This locator does not set the configuration; it is iterated by the bus
enumeration.
.It Cd interface
this is the interface number within a device that an interface driver
attaches to.
.It Cd vendor
this is the 16 bit vendor id of the device.
.It Cd product
this is the 16 bit product id of the device.
.It Cd release
this is the 16 bit release (revision) number of the device.
.El
The first locator can be used to pin down a particular device
according to its physical position in the device tree.
The last three locators can be used to pin down a particular
device according to what device it actually is.
.Pp
The bus enumeration of the
.Tn USB
bus proceeds in several steps:
.Bl -enum
.It
Any device specific driver can attach to the device.
.It
If none is found, any device class specific driver can attach.
.It
If none is found, all configurations are iterated over.
For each configuration, all the interfaces are iterated over, and interface
drivers can attach.
If any interface driver attached in a certain
configuration, the iteration over configurations is stopped.
.It
If still no drivers have been found, the generic
.Tn USB
driver can attach.
.El
.Sh USB CONTROLLER INTERFACE
Use the following to get access to the
.Tn USB
specific structures and defines.
.Pp
.In dev/usb/usb.h
.Pp
The
.Pa /dev/usb Ns Ar N
can be opened and a few operations can be performed on it.
The
.Xr poll 2
system call will say that I/O is possible on the controller device when a
.Tn USB
device has been connected or disconnected to the bus.
.Pp
The following
.Xr ioctl 2
commands are supported on the controller device:
.Bl -tag -width xxxxxx
.It Dv USB_DISCOVER
This command will cause a complete bus discovery to be initiated.
If any devices attached or detached from the bus they will be
processed during this command.
This is the only way that new devices are found on the bus.
.It Dv USB_DEVICEINFO Vt "struct usb_device_info"
This command can be used to retrieve some information about a device
on the bus.
The
.Va addr
field should be filled before the call and the other fields will
be filled by information about the device on that address.
Should no such device exist, an error is reported.
.Bd -literal
struct usb_device_info {
        u_int8_t        bus;
        u_int8_t        addr;
        usb_event_cookie_t cookie;
        char            product[USB_MAX_STRING_LEN];
        char            vendor[USB_MAX_STRING_LEN];
        char            release[8];
        u_int16_t       productNo;
        u_int16_t       vendorNo;
        u_int16_t       releaseNo;
        u_int8_t        class;
        u_int8_t        subclass;
        u_int8_t        protocol;
        u_int8_t        config;
        u_int8_t        lowspeed;
        int             power;
        int             nports;
        char            devnames[USB_MAX_DEVNAMES][USB_MAX_DEVNAMELEN];
        u_int8_t        ports[16];
#define USB_PORT_ENABLED      0xff
#define USB_PORT_SUSPENDED    0xfe
#define USB_PORT_POWERED      0xfd
#define USB_PORT_DISABLED     0xfc
};
.Ed
.Pp
.Va bus
and
.Va addr
contain the topological information for the device.
.Va devnames
contains the device names of the connected drivers.
For example, the
third
.Tn USB
Zip drive connected will be
.Li umass2 .
The
.Va product , vendor
and
.Va release
fields contain self-explanatory descriptions of the device.
.Va productNo , vendorNo , releaseNo , class , subclass
and
.Va protocol
contain the corresponding values from the device descriptors.
The
.Va config
field shows the current configuration of the device.
.Pp
.Va lowspeed
indicates whether the device is a full speed (0) or low speed (1)
device.
The
.Va power
field shows the power consumption in milli-amps drawn at 5 volts,
or zero if the device is self powered.
.Pp
If the device is a hub, the
.Va nports
field is non-zero, and the
.Va ports
field contains the addresses of the connected devices.
If no device is connected to a port, one of the
.Dv USB_PORT_*
values indicates its status.
.It Dv USB_DEVICESTATS Vt "struct usb_device_stats"
This command retrieves statistics about the controller.
.Bd -literal
struct usb_device_stats {
        u_long  requests[4];
};
.Ed
.Pp
The
.Va requests
field is indexed by the transfer kind, i.e.\&
.Dv UE_* ,
and indicates how many transfers of each kind that has been completed
by the controller.
.It Dv USB_REQUEST Vt "struct usb_ctl_request"
This command can be used to execute arbitrary requests on the control pipe.
This is
.Em DANGEROUS
and should be used with great care since it
can destroy the bus integrity.
.El
.Pp
The include file
.Aq Pa dev/usb/usb.h
contains definitions for the types used by the various
.Xr ioctl 2
calls.
The naming convention of the fields for the various
.Tn USB
descriptors exactly follows the naming in the
.Tn USB
specification.
Byte sized fields can be accessed directly, but word (16 bit)
sized fields must be access by the
.Fn UGETW field
and
.Fn USETW field value
macros to handle byte order and alignment properly.
.Pp
The include file
.Aq Pa dev/usb/usbhid.h
similarly contains the definitions for
Human Interface Devices
.Pq Tn HID .
.Sh USB EVENT INTERFACE
All
.Tn USB
events are reported via the
.Pa /dev/usb
device.
This devices can be opened for reading and each
.Xr read 2
will yield an event record (if something has happened).
The
.Xr poll 2
system call can be used to determine if an event record is available
for reading.
.Pp
The event record has the following definition:
.Bd -literal
struct usb_event {
        int                                 ue_type;
#define USB_EVENT_CTRLR_ATTACH 1
#define USB_EVENT_CTRLR_DETACH 2
#define USB_EVENT_DEVICE_ATTACH 3
#define USB_EVENT_DEVICE_DETACH 4
#define USB_EVENT_DRIVER_ATTACH 5
#define USB_EVENT_DRIVER_DETACH 6
        struct timespec                     ue_time;
        union {
                struct {
                        int                 ue_bus;
                } ue_ctrlr;
                struct usb_device_info      ue_device;
                struct {
                        usb_event_cookie_t  ue_cookie;
                        char                ue_devname[16];
                } ue_driver;
        } u;
};
.Ed
The
.Va ue_type
field identifies the type of event that is described.
The possible events are attach/detach of a host controller,
a device, or a device driver.
The union contains information
pertinent to the different types of events.
.Pp
The
.Va ue_bus
contains the number of the
.Tn USB
bus for host controller events.
.Pp
The
.Va ue_device
record contains information about the device in a device event event.
.Pp
The
.Va ue_cookie
is an opaque value that uniquely determines which which
device a device driver has been attached to (i.e., it equals
the cookie value in the device that the driver attached to).
.Pp
The
.Va ue_devname
contains the name of the device (driver) as seen in, e.g.,
kernel messages.
.Pp
Note that there is a separation between device and device
driver events.
A device event is generated when a physical
.Tn USB
device is attached or detached.
A single
.Tn USB
device may
have zero, one, or many device drivers associated with it.
.Sh SEE ALSO
The
.Tn USB
specifications can be found at:
.Pp
.D1 Pa http://www.usb.org/developers/docs.html
.Pp
.Xr usb 3 ,
.Xr aue 4 ,
.Xr cue 4 ,
.Xr kue 4 ,
.Xr ohci 4 ,
.Xr pci 4 ,
.Xr ugen 4 ,
.Xr uhci 4 ,
.Xr uhid 4 ,
.Xr ukbd 4 ,
.Xr umass 4 ,
.Xr ums 4 ,
.Xr urio 4 ,
.Xr uscanner 4 ,
.Xr usbd 8 ,
.Xr usbdevs 8
.Sh HISTORY
The
.Nm
driver first appeared in
.Fx 3.0 .
.Sh AUTHORS
The
.Nm
driver was written by
.An Lennart Augustsson Aq augustss@carlstedt.se
for the
.Nx
project.