USB Bus Description

The USB specification is openly available and free of royalties. The specification defines the electrical and mechanical interfaces of the bus and the connectors.

USB employs a topology in which hubs provide attachment points for USB devices. The host controller contains the root hub, which is the origin of all USB ports in the system. For more information about hubs, see USB Host Controller and Root Hub.

Figure 29-1 USB Physical Device Hierarchy

Figure 29-1 shows a system with three active USB ports. The first USB port connects a Zip drive. The second USB port connects an external hub, which in turn, connects a cdrw device and a composite keyboard/mouse device. As a composite device, this keyboard contains a USB controller, which operates both the keyboard and an attached mouse. The keyboard and the mouse share a common USB bus address because they are directed by the same USB controller.

Figure 29-1 also shows an example of a hub and a printer as a compound device. The hub is an external hub that is enclosed in the same casing as the printer. The printer is permanently connected to the hub. The hub and printer have separate USB bus addresses.

The device tree path name for some of the devices that are displayed in Figure 29-1 are listed in this table.

USB Devices and Drivers

USB devices with similar attributes and services are grouped into device classes. Each device class has a corresponding driver, one for each framework. Devices within a class are managed by the same device driver pair. However, the USB specification also allows for vendor-specific devices that are not part of a specific class.

The Human Interface Device (HID) class contains devices that are user-controlled such as keyboards, mouse devices, and joysticks. The Communication Device class contains devices that connect to a telephone, such as modems or an ISDN interface. Other device classes include the Audio, Monitor, Printer, and Storage Device classes. Each USB device contains descriptors that reflect the class of the device. A device class specifies how its members should behave in configuration and data transfer. You can obtain additional class information from http://www.usb.org.

Solaris USB Architecture (USBA)

USB devices can be represented as two levels of device tree nodes. A device node represents the entire USB device. One or more child interface nodes represent the individual USB interfaces on the device.

Driver binding is achieved by using the compatible name properties. For more information, refer to 3.2.2.1 of the IEEE 1275 USB binding and Writing Device Drivers. A driver can either bind to the entire device and control all the interfaces, or can bind to just one interface. If no vendor or class driver claims the entire device, a generic USB multi-interface driver is bound to the device-level node. This driver attempts to bind drivers to each interface by using compatible names properties, as defined in section 3.3.2.1 of the IEEE 1275 binding specification.

The Solaris USB Architecture (USBA) adheres to the USB 1.1 and USB 2.0 specifications plus Solaris driver requirements. The USBA model is similar to Sun Common SCSI Architecture (SCSA). The USBA is a thin layer that provides a generic USB transport-layer abstraction to client drivers, providing them with services that implement core generic USB functionality.

Figure 29-2 Solaris USB Architecture (USBA)

About USB in the Solaris Environment

This section describes information you should know about USB in the Solaris environment.

USB Keyboards and Mouse Devices

Only Sun USB keyboards and mouse devices are supported. System configurations with multiple USB keyboards and mouse devices might work, but are not supported in the Solaris environment. See the following items for details.

• A USB keyboard and mouse can be connected anywhere on the bus and can be configured as the console keyboard and mouse. Booting the system is slower if the keyboard and mouse are connected to an external hub.

• Do not move the console keyboard and mouse during a reboot or at the ok prompt. You can move the console keyboard and mouse to another hub at any time after a system reboot. After you plug in a keyboard and mouse, they are fully functional again.

• SPARC - The power key on a USB keyboard behaves differently than the power key on the Sun type 5 keyboard. On a USB keyboard, you can suspend or shut down the system by using the SUSPEND/SHUTDOWN key, but you cannot use that key to power up the system.

• The keys just to the left of the keypad do not function on third-party USB keyboards.

• Multiple keyboards are not supported:

  • Multiple keyboards enumerate and are usable, but they are not plumbed as console keyboards.

  • The first keyboard that is probed at boot time becomes the console keyboard. The result of this probing might cause confusion if multiple keyboards are plugged in at boot time.

  • If you unplug the console keyboard, the next available USB keyboard does not become the console keyboard. The next hot-plugged keyboard becomes the console keyboard.

• Multiple mouse devices are not supported:

  • Multiple mouse devices enumerate and are usable, but they are not plumbed as console mouse devices.

  • The first mouse that is probed at boot time becomes the console mouse. The result of this probing might cause confusion if you have multiple mouse devices plugged in at boot time.

  • If you unplug the console mouse, the next available USB mouse does not become the console mouse. The next hot-plugged mouse becomes the console mouse.

• If you have a third-party composite keyboard with a PS/2 mouse, and the composite keyboard/mouse is the first one to be probed, it becomes the console keyboard/mouse even if the PS/2 mouse is not plugged in. Thus, another USB mouse plugged into the system cannot work because it is not configured as the console mouse.

• Only two-button and three-button mouse devices are supported. A wheel-on-wheel mouse acts like a plain-button mouse. A mouse with more than three buttons functions like a three-button mouse.

USB Host Controller and Root Hub

A USB hub is responsible for the following:

• Monitoring the insertion or removal of a device on its ports

• Power-managing individual devices on its ports

• Controlling power to its ports

The USB host controller has an embedded hub called the root hub. The ports that are visible at the system's back panel are the ports of the root hub. The USB host controller is responsible for the following:

• Directing the USB bus. Individual devices cannot arbitrate for the bus.

• Polling the devices by using a polling interval that is determined by the device. The device is assumed to have sufficient buffering to account for the time between the polls.

• Sending data between the USB host controller and its attached devices. Peer-to-peer communication is not supported.