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.

USB Hub Devices

• Do not cascade hubs beyond four levels on either SPARC based or x86 based systems. On SPARC systems, the OpenBoot^TM PROM cannot reliably probe beyond four levels of devices.

• Do not plug a bus-powered hub into another bus-powered hub in a cascading style. A bus-powered hub does not have its own power supply.

• Do not connect a device that requires a large amount of power to a bus-powered hub. These devices might not work well on bus-powered hubs or might drain the hub of power for other devices. An example of such a device is a USB diskette device.

• This Solaris release does not support connecting a low- or full-speed device to a USB 2.0 hub that is connected to a USB 2.0 port on SPARC-based systems.