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

     usb - Universal Serial Bus

     device usb

     #include <dev/usb/usb.h>
     #include <dev/usb/usbhid.h>

     FreeBSD provides machine-independent bus support and drivers for USB

     The usb driver has three layers: the controller, the bus, and the device
     layer.  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 12 Mb/s serial bus (1.5 Mb/s for low speed devices).  Each
     USB has a host controller that is the master of the bus; all other
     devices on the bus only speak when spoken to.

     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.

     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

     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

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

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

     2.   If none is found, any device class specific driver can attach.

     3.   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.

     4.   If still no drivers have been found, the generic USB driver can

     Use the following to get access to the USB specific structures and


     The /dev/usbN can be opened and a few operations can be performed on it.
     The poll(2) system call will say that I/O is possible on the controller
     device when a USB device has been connected or disconnected to the bus.

     The following ioctl(2) commands are supported on the controller device:

             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.

     USB_DEVICEINFO struct usb_device_info
             This command can be used to retrieve some information about a
             device on the bus.  The 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

             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

             bus and addr contain the topological information for the device.
             devnames contains the device names of the connected drivers.  For
             example, the third USB Zip drive connected will be umass2.  The
             product, vendor and release fields contain self-explanatory
             descriptions of the device.  productNo, vendorNo, releaseNo,
             class, subclass and protocol contain the corresponding values
             from the device descriptors.  The config field shows the current
             configuration of the device.

             lowspeed indicates whether the device is a full speed (0) or low
             speed (1) device.  The power field shows the power consumption in
             milli-amps drawn at 5 volts, or zero if the device is self

             If the device is a hub, the nports field is non-zero, and the
             ports field contains the addresses of the connected devices.  If
             no device is connected to a port, one of the USB_PORT_* values
             indicates its status.

     USB_DEVICESTATS struct usb_device_stats
             This command retrieves statistics about the controller.

             struct usb_device_stats {
                     u_long  requests[4];

             The requests field is indexed by the transfer kind, i.e. UE_*,
             and indicates how many transfers of each kind that has been
             completed by the controller.

     USB_REQUEST struct usb_ctl_request
             This command can be used to execute arbitrary requests on the
             control pipe.  This is DANGEROUS and should be used with great
             care since it can destroy the bus integrity.

     The include file <dev/usb/usb.h> contains definitions for the types used
     by the various ioctl(2) calls.  The naming convention of the fields for
     the various USB descriptors exactly follows the naming in the USB
     specification.  Byte sized fields can be accessed directly, but word (16
     bit) sized fields must be access by the UGETW(field) and USETW(field,
     value) macros to handle byte order and alignment properly.

     The include file <dev/usb/usbhid.h> similarly contains the definitions
     for Human Interface Devices (HID).

     All USB events are reported via the /dev/usb device.  This devices can be
     opened for reading and each read(2) will yield an event record (if
     something has happened).  The poll(2) system call can be used to
     determine if an event record is available for reading.

     The event record has the following definition:

     struct usb_event {
             int                                 ue_type;
             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;
     The 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.

     The ue_bus contains the number of the USB bus for host controller events.

     The ue_device record contains information about the device in a device
     event event.

     The 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).

     The ue_devname contains the name of the device (driver) as seen in, e.g.,
     kernel messages.

     Note that there is a separation between device and device driver events.
     A device event is generated when a physical USB device is attached or
     detached.  A single USB device may have zero, one, or many device drivers
     associated with it.

     The USB specifications can be found at:


     usb(3), aue(4), cue(4), kue(4), ohci(4), pci(4), ucom(4), ugen(4),
     uhci(4), uhid(4), ukbd(4), umass(4), ums(4), urio(4), uscanner(4),
     usbd(8), usbdevs(8)

     The usb driver first appeared in FreeBSD 3.0.

     The usb driver was written by Lennart Augustsson <>
     for the NetBSD project.

FreeBSD 11.0-PRERELEASE        February 21, 1999       FreeBSD 11.0-PRERELEASE


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