28-12-2010, 12:55 PM
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INTRODUCTION
Universal Serial Bus (USB) is a serial bus standard to connect devices to a host computer. The USB 3.0 is the upcoming version of the USB. The USB 3.0 is also called super speed USB. Because the USB 3.0 support a raw throughput of 500MByte/s. As its previous versions it also supports the plug and play capability, hot swapping etc. USB was designed to allow many peripherals to be connected using a single standardized interface socket. . Other convenient features include providing power to low-consumption devices, eliminating the need for an external power supply; and allowing many devices to be used without requiring manufacturer-specific device drivers to be installed.
There are many new features included in the new Universal Serial Bus Specification. The most important one is the supers speed data transfer itself. Then the USB 3.0 can support more devices than the currently using specification which is USB 2.0. The bus power spec has been increased so that a unit load is 150mA (+50% over minimum using USB 2.0). An unconfigured device can still draw only 1 unit load, but a configured device can draw up to 6 unit loads (900mA, an 80% increase over USB 2.0 at a registered maximum of 500mA). Minimum device operating voltage is dropped from 4.4V to 4V. When operating in SuperSpeed mode, full-duplex signaling occurs over 2 differential pairs separate from the non-SuperSpeed differential pair. This result in USB 3.0 cables containing 2 wires for power and ground, 2 wires for non-SuperSpeed data, and 4 wires for SuperSpeed data, and a shield (not required in previous specifications).
HISTORY
2.1 PRERELEASES
•USB 0.7: Released in November 1994.
•USB 0.8: Released in December 1994.
•USB 0.9: Released in April 1995.
•USB 0.99: Released in August 1995.
•USB 1.0: Release Candidate: Released in November 1995.
2.2. USB 1.0
USB 1.0: Released in January 1996.Specified data rates of 1.5 Mbit/s (Low-Speed) and 12 Mbit/s (Full-Speed). Does not allow for extension cables or pass-through monitors (due to timing and power limitations). Few such devices actually made it to market.
USB 1.1: Released in September 1998.Fixed problems identified in 1.0, mostly relating to hubs. Earliest revision to be widely adopted.
2.3. USB 2.0
Released in April 2000.Added higher maximum speed of 480 Mbit/s (now called Hi-Speed). Further modifications to the USB specification have been done via Engineering Change Notices (ECN).
2.4. USB 3.0
On September 18, 2007, Pat Gel singer demonstrated USB 3.0 at the Intel Developer Forum. The USB 3.0 Promoter Group announced on November 17, 2008, that version 1.0 of the specification has been completed and is transitioned to the USB Implementers Forum (USB-IF), the managing body of USB specifications. This move effectively opens the spec to hardware developers for implementation in future products.
ARCHITECTURE
ARCHITECTURAL COMPONENTS
3.1. HUB
The hub provide electrical interface between the USB devices and the host. Hubs are directly responsible for supporting many of the attributes that make USB user friendly and hide its complexity from the user. Listed below the major aspects of USB functionality that hub support:
• Connectivity behavior
• Power management
• Device connect/disconnect detection
• Bus fault detection
• SuperSpeed and USB 2.0 (high-speed, full-speed, an low-speed) support
A USB 3.0 hub incorporates a USB 2.0 hub and a SuperSpeed hub consisting of two principal components: the SuperSpeed Hub Repeater/Forwarder and the SuperSpeed Hub controller. The hub repeater/forwarder is responsible for connectivity and setup and tear-down. It also support fault detection and recovery. The Hub controller provides the mechanism for host-hub communication. Hub-specific status and control commands permit the host to configure hub and to monitor and control its individual downstream port.
3.2. HOST
There are two hosts are incorporated in a USB 3.0 host. One is SuperSpeed host and the second one is Non-SuperSpeed host. This incorporation ensures the backward compatibility of the USB 3.0 hub. Here the SuperSpeed hub will be supporting the 500MB/sec data transfer rate with full duplex mode. Then the Non- SuperSpeed host will be supporting the old data rates such as High-Speed, Full-Speed, Low-Speed. The host here interacts with the devices by the help of a host controller. When the host is powered off, the hub does not provide power to its downstream unless the hub supports the charging application. When the host is powered on with SuperSpeed support enabled on its downstream port by default the following is the typical sequence of events.
• Hub detects VBUS SuperSpeed support and powers its down stream ports with SuperSpeed enabled.
• Hub connects both as a SuperSpeed and as a High-Speed device.
• Device detects VBUS and SuperSpeed support and connects as a SuperSpeed device.
• Host system begins hub enumeration at high-speed and SuperSpeed.
• Host system begins device enumeration at SuperSpeed.
A SuperSpeed host is a source or sink of information. It implements the required host-end, SuperSpeed. Communications layer to accomplish information exchanges over the bus. It owns the SuperSpeed data activity schedule and management of the SuperSpeed bus and all devices connected to it. The host includes an implementation number of the root downstream ports for SuperSpeed and USB 2.0. Through these ports the host:
• Detect the attachment and removal of USB device.
• Manages control flow between the host and the USB device.
• Manages data flow between the host and the USB device.
• Collect the status activity statistics
• Provide power to the attached USB device
3.3. DEVICE
SuperSpeed devices are sources or sink of information exchanges. They implement the required device-end, SuperSpeed communication layers to accomplish information exchanges between a driver on the host and a logical function on the device. All SuperSpeed devices share their base architecture with USB 2.0.They are required to carry information for self-identification and generic configuration. They are also required to demonstrate behavior consistent with the defined SuperSpeed Device States.
All devices are assigned a USB address when enumerated by the host. Each device supports one or more pipes though which the host may communicate with the device. All devices must be support a designed pipe at endpoint zero to which the device’s Default Control Pipe is attached. All devices support a common access mechanism for accessing information through this control pipe. SuperSpeed inherits the categories of information that are supported on the default pipe from the USB 2.0. The USB 3.0 connection model allows for the discovery and configuration of the USB device at the highest signaling speed supported by the device. The USB 3.0 supports an increased power supply for the devices operating at the SuperSpeed. USB 3.0 devices within a single physical package (i.e., a single peripheral) can consist of a number of functional topologies including single function , multiple functions on a single peripheral device (composite device), and permanently attached peripheral devices behind an integrated hub.
