Universal Serial Bus: Difference between revisions

 

=== USB 1.0 Host Controllers ===

Intel brought USB 1.0 to the market with its '''Universal Host Controller Interface''' ('''UHCI'''), while Compaq, Microsoft, and National Semiconductors did the same with their '''Open Host Controller Interface''' ('''OHCI'''). Naturally, the two interfaces are incompatible, and to make things worse, VIA Technologies licensed Intel's UHCI standard, thereby ensuring that both standards survived. Typically, an on-board chip set will contain a UHCI implementation, whereas a peripheral card typically implements the OHCI standard (but this is by no means a guarantee).

 

=== USB 2.0 Host Controllers ===

[[Image:PortRoutingBlockDiagram.gif|frame|Figure 1: Block Diagram of Port Routing Behavior]]

In designing USB 2.0, the USB-IF insisted on a single implementation. That single implementation is Intel's '''Enhanced Host Controller Interface''' ('''EHCI'''). However, even though the USB 2.0 specification requires that a USB 2.0 interface support USB 1.0 devices, this doesn't mean that the EHCI must support USB 1.0 devices, and in fact, it doesn't. Each EHCI host controller is accompanied by (usually several) UHCI and/or OHCI host controllers. When a USB 1.0 device is attached, the EHCI simply hands control over to a '''companion controller'''. Refer to figure 1 for a simple block diagram implementation of this behavior. Therefore, the system programmer must support all three standards in order to support USB 2.0.

 

=== USB 3.0 Host Controllers ===

In late 2008, the USB-IF released the USB 3.0 specifications. USB 3.0 host controllers are just starting to make their way into consumer devices since NEC introduced the world's first “SuperSpeed USB 3.0 host controller” in May, 2009, [http://www.techspot.com/news/34763-nec-introduces-worlds-first-usb-30-host-controller.html techspot reports].

 

 

On June 18th, 2010, Intel publicly released the xHCI specification.

 

== Basic Concepts and Nomenclature ==