تاثیر معماری بر عملکرد USB در آداپتور سریال Impact of Architecture on Performance of USB to Serial Adapters

Introduction With the ever-increasing computing power of today’s PCs it is necessary to have supporting technology that is able to keep up and not bog down the system. Human interface devices and other peripherals that attach to a PC are usually the bottleneck when it comes to overall processor speed and data throughput.With processors working in excess of 1.5 GHz, hard disks that operate at a minimum of 7200 rpm, and CD-ROMs that read and write at upwards of 32x, it is necessary to have external I/O devices that operate faster than the 115 kbps standard parallel port. Several technologies have been developed over the past ten years that address this issue of slower external I/O devices. Two of the hottest technologies are USB and Fire Wire. Both of these technologies have been developed to increase the overall data throughput between the processor and external devices.These technologies have allowed, and will allow, higher-bandwidth peripherals to be developed and implemented for the PC, digital video cameras, broadband digital cable modems, and HDTV to name a few. The technology is quickly matching the pace of the computing power of a PC. This paper focuses on the USB technology, specifically on the new USB 2.0 specifications. Thediscussion begins with an introduction to USB technology, the physical topology, and how it operates.Following, a detailed discussion on the USB 2.0 technology will be presented covering the component parts, layered architecture, data flow types, and packetization specifics. In addition a brief discussion on an emerging compliment to USB 2.0, the USB On-the-go, will be presented.Finally a comparison between USB 2.0 and IEEE 1394 (Fire Wire) will be presented. Part 1: Overview of USB Technology Universal Serial Bus (USB) was originally created and released as a standard in 1995 with USB 1.0. It was jointly developed by Compaq, Hewlett-Packard, Intel, Lucent, Microsoft, NEC, and Phillips, which make up the USB Implementers Forum (Ziller, 2002). This same group has just released specifications for USB 2.0. The overall motivation for the development of USB stemmed from three main sources: • Connection of the PC with the telephone: The convergence of the telephony and data networks has spawned a race to develop technologies that can work to interconnect the two with ease. • Port expansion: The development of a port that supported multiple devices would lessen the confusion when working with external I/O devices. • Ease-of-use: If all of the computer’s I/O devices could connect to a single port, the fear of setting up a computer would virtually disappear (USB, 2000). With these three fundamental motivations, USB technology was developed and has become an industry standard for the interconnection of peripheral I/O devices. This section takes an elementary look at the physical characteristics, physical and logical topology, and how it all works. 1.1 Physical Characteristics and Throughput Capabilities Universal Serial Bus technology is exactly as it sounds. It is a bus, which is a mechanism for transferring data and instructions from one point to another, that transmits data bit by bit or in a serial fashion and is able to communicate universally to many different devices. The USB is simply another way of transferring information between external I/O devices and the internal processor of the computer.