usb(HW)

usb -- Universal Serial Bus

Description

Universal Serial Bus (USB) is a low-cost, hot-pluggable device bus that is supported by most modern motherboards and is also available through add-in cards. Any device that conforms to the protocol defined in the USB Specification should work with this implementation. Devices using proprietary protocols will not. If you have, for example, a USB touch tablet that presents itself as a conforming Human Interface Device, there is an excellent chance that it can be configured and will work like a USB mouse.

The USB interface is implemented via the Uniform Driver Interface (UDI). Three USB Host Controller Interfaces (HCI) exist and are supported by this implementation:

HCI name USB standard Speed

Universal Host Controller Interface (UHCI) USB 1.1 12Mbps

Open Host Controller Interface (OHCI) USB 1.1 12Mbps

Enhanced Host Controller Interface (EHCI) USB 2.0 480Mbps

HCI name	USB standard	Speed
Universal Host Controller Interface (UHCI)	USB 1.1	12Mbps
Open Host Controller Interface (OHCI)	USB 1.1	12Mbps
Enhanced Host Controller Interface (EHCI)	USB 2.0	480Mbps

USB 1.1 devices are typically low-cost, low-bandwidth units. USB 2.0 offers speeds up to 480 megabits per second, which is comparable to mid-range IDE and SCSI bus speeds.

USB hubs and USB devices (such as mice, keyboards, and mass storage devices) may be plugged into the host. A maximum of 128 devices may be nested up to 8 layers deep using combinations of hubs and devices. USB devices may be attached before or after the host computer starts; devices may be unplugged from the bus while the computer is running.

Mouse and keyboard devices send very little data across the USB bus. Other devices, such as mass storage, use bulk transfer mode to move data blocks over the bus, but the data rates achieved are typically less than SCSI or IDE bus devices. USB is an effective mechanism for adding devices to a host that does not already have that functionality, such as adding a mouse or trackball to a laptop or adding supplementary storage such as a Zip^® or CD-ROM drive. USB can be used for hard disk storage when top performance is not required.

Note the following when using these supported USB device types:

Hubs

Powered hubs are recommended over unpowered hubs.

Keyboards

USB keyboards work like AT and PS/2 keyboards.
The simultaneous use of multiple USB keyboards, along with one AT or PS/2 keyboard, is supported.
LEDs and shift states are synchronized across all keyboards physically attached to a system. If you press the <Caps Lock> key on one keyboard, the Caps Lock state (including the LEDs) is active on all keyboards.
If you hot-add a USB keyboard, it ``adopts'' the current LED and shift state.

Mice

USB mice work like keyboard mice (also known as PS/2 mice).
Any USB Human Interface Device that is a pointing device should work with the USB mouse driver.
Scrolling wheels are supported.
Three button mice are supported. Additional buttons are ignored by the X server.
You can have more than one USB mouse attached to the system at the same time. However, all USB mice are channeled through a single event channel. It is not possible to separately associate one USB mouse with one terminal and another USB mouse with a different terminal.
Having multiple USB mice might be useful if one of the devices is a joystick, graphics tablet, touchscreen, or other pointing device.
For multiple mice, the inputs are effectively connected together. It is possible, for example, to move the pointer with one USB mouse and click a mouse button on a different mouse; both operations are accepted as if they came from the same mouse. If you have identical mice and you move them in opposite directions at exactly the same speed, the mouse pointer remains still.

Printers

Multiple printers can be used on a system.
Printers can be attached and removed from the USB bus at any time.
In order for a printer to be supported, there must be a user-level driver/filter specific to that printer available.

CD-ROM/DVD-ROM drives and CD/DVD writers

Multiple CD-ROM and DVD-ROM drives and writers can be used on a system.
Removing an attached CD-ROM or DVD-ROM drive (especially one that is mounted) may trigger a problem elsewhere in the system.
Devices that support software media lock are locked while they are in use by the operating system. Devices with mechanical media releases (for example, a CD-ROM drive with a hinged door instead of a tray) cannot be locked. Ejecting the media while the device is in use by the operating system can cause data corruption or a system panic.

Tape drives

USB 2.0-conforming tape drives are supported.

Hardware

Root hub

The ``root hub'' refers to the USB ports configured on the motherboard. Many systems allow built-in USB ports to be disabled in BIOS setup. If USB is not working, check that it is enabled in the BIOS. Alternatively, if you do not wish to use USB, you may want to disable it in the BIOS setup since many motherboards use two to three interrupts for USB HCIs.

Connectivity options

The root hub ports may be used for either a USB device or a USB hub. Any combination of hubs and devices may be connected, up to the maximum device limit and the hub depth -- 128 devices nested 8 layers deep.

USB device configuration

In general, to connect a USB device, do the following:

As root, enter:

# usbprobe
This displays all currently connected USB devices. Each line lists the USB device path, the device number on the bus, the device type, and a device description.
Connect the USB device to a USB port on the system, or to a port on a USB hub connected to the system.
Run usbprobe again to see the USB device.

Enable the device as shown (if necessary):

Keyboard no configuration necessary

Mouse mouseadmin(C)

CD-ROM mount /dev/cdN mount-point

Hard Disks mkdev hd

Printer Must use CUPS to configure and use a USB printer; see ``Getting Started with CUPS'' in Administering printers and usblp(HW).

Tape drives No configuration should be necessary; auto-configuration has been observed to fail in some cases. If device nodes do not appear when the tape device is connected, run sdimkdev -sfui to configure the device.

USB device IDs

When you attach a USB mass storage device, the system assigns the device a USB device ID. (USB device IDs are only assigned to USB storage devices, not to non-storage devices like mice and keyboards.) USB device IDs are determined by the order in which the system detects each device. However, the enumeration of devices depends on several factors and different circumstances may result in different device ID assignments on the same machine. For example, devices that you attach to a running system are enumerated in the order that you plug them in. At boot time, however, the entire USB hub/device tree is traversed and devices may be detected in a different order, resulting in different device ID assignments. In general, these guidelines apply:

if you attach all of your USB storage devices while the system is turned off, the enumeration order when the computer is started will likely persist between system reboots.
if you hot-add or hot-remove USB storage devices, device IDs may change when the system is rebooted.
if you add, remove, or change the order of USB storage devices on a non-running system that previously contained USB storage devices, device IDs may be different when the system is rebooted.

Device drivers in the USB protocol stack

HCI drivers

Controls I/O to the various USB host controllers found on motherboards and add-in cards. The HCI drivers include:

usb_ehci: Enhanced Host Controller Interface (hardware driver)
usb_ohci: Open Host Controller Interface (hardware driver)
usb_uhci: Universal Host Controller Interface (hardware driver)

usb_hci

Host Controller UDI meta-language Communications interface between the USB stack and the HCI drivers.

usbd

USB stack manager Communications interface between the USB stack and the HCI drivers. This driver maintains an internal representation of the ``tree'' of USB hubs and devices, and attaches/detaches device descriptors to corresponding USB class drivers as USB peripherals are added/removed.

usbdutil

USB stack utilities library Utility functions used by usbd.

opnusbdi

OpenUSBDI UDI meta-language USB ``tree'' management functions used by usbd.

usb_hub

Hub (USB class driver) Class driver for managing USB hubs.

usb_prnt

Printer (USB class driver) Class driver for managing USB printers.

usb_msto

Mass storage (USB class driver)
The pseudo Host Bust Adapter driver:

usb_hid

Human Interface Device (USB class driver)
Class driver for talking to Human Interface Devices (mice, keyboards, and so forth.)

udihidpr

Human Interface Device parser library
Functions for decoding messages from HID devices.

udi_hid

Human Interface Device UDI meta-language
Functions for controlling HID devices.

udiMkb

SCO OpenServer keyboard mapper
Connects HID keyboard type devices to the SCO OpenServer console driver.

udiMmse

SCO OpenServer mouse mapper
Connects HID ``pointing device'' type devices to the SCO OpenServer event driver.

usbprobe

USB probe tool
Displays connected devices on all USB busses.

Files

/dev/usb*: USB device nodes
/usr/lib/event/*: device files for mice

Notes

USB keyboards do not work with kdb. You must use a serial console or a PS/2 keyboard for kernel debugging.

Compatibility

Users of the USB implementation in earlier releases should note the following:

USB device names
In the previous USB subsystem, device nodes were created under /dev/usb or /etc/usb when a USB device was connected. In the new USB subsystem, device nodes are created under /dev. Use usbprobe to list currently connected USB devices.
USB floppy device names
USB floppy drives no longer use the /dev/fdXX device names that were used in previous releases, and that are still used for ISA floppy drives. USB floppy drives now use device nodes in the style of hard disk drive device nodes (e.g. /dev/rhdXX, /dev/hdXX, and so forth). Use usbprobe to list currently connected USB devices.

Standards conformance

This USB interface conforms to Release 2.0 of the USB specification. For more information, see the USB web page.

Keyboard	no configuration necessary
Mouse	mouseadmin(C)
CD-ROM	mount /dev/cdN *mount-point*
Hard Disks	mkdev hd
Printer	Must use CUPS to configure and use a USB printer; see ``Getting Started with CUPS'' in Administering printers and usblp(HW).
Tape drives	No configuration should be necessary; auto-configuration has been observed to fail in some cases. If device nodes do not appear when the tape device is connected, run sdimkdev -sfui to configure the device.