computer systems architecture historical perspective the universal serial bus was originally...

Computer Systems Architecture

Historical Perspective

The Universal Serial Bus was originally developed in 1995 by a group of industry leading companies

Compaq, Hewlett Packard, Intel, Lucent, Microsoft, NEC and Philips were involved in USB 2 developments

USB defines an external expansion bus which makes adding peripherals to a PC relatively easy

See: Wikipedia (Link) [http://en.wikipedia.org/wiki/Universal_Serial_Bus]

See: http://www.everythingusb.com/


Historical Perspective

Major goals of USB 1.0 were ease-of-use and low cost

USB version 1 was not designed to be a high speed bus – it’s for mice, keyboards, printers, scanners etc.

In 2006, Intel estimated that over 3.5 billion USB interfaces had shippedNB that may include 2-10 “interfaces” per PC!


USB Connections

The external expansion architecture of USB is shown below, which highlights:

PC host controller hardware and softwareRobust connectors and cable assemblies“Peripheral friendly” master-slave protocolsExpandable through multi-port hubs


USB host

Client

Describes all the software entities that are responsible for USB devices

USB System

Translation between the client data and USB transaction on the interconnect

Managing USB resources(bandwidth, power …)

USB Bus interface

Handles interactions for the electrical protocol layer


Role of USB h/w and s/w

Uniform view of I/O system for all application softwareHides hardware implementation details Manages the dynamic attachment and detachment of

peripherals“Enumeration” – initial communication with peripherals

to discover device and driver identityUnique “address” for each peripheralHost PC software incorporates attached peripherals

into the system power management scheme


Role of USB1.1 Hubs

Provides additional, bi-directional connectivity for USB peripherals and works as bi-directional repeater

Provides managed power to attached peripheralsRecognises dynamic attachment of a peripheralProvides power during initialisation and later (0.5W to

2.5W max)May be cascaded up to five levels deepMonitors signals and handles transactions addressed

to itselfSupports both 12Mbits/sec (so-called “full-speed”) and

1.5Mbits/sec (“low-speed”) peripherals


USB1.1 Peripherals

All USB peripherals are uniform slave devices that obey a defined protocol

Peripherals respond to control transactions whichmay request detailed information about the devicemay request device configuration informationmay allocate a device ID

Peripherals send and receive data to/from the host using a standard USB data format

Standardized data movement to/from the PC host gives USB great flexibility and simplicity


USB 2.0

Same cables, same software interfaces, full support for USB1.1 devices

Plus support for high-speed devices up to 480Mbits/secHub complexity increased to handle situations intelligentlyBecame available some time after mid-2000


USB Topology

Star- tiered topology

Supports up to 127 devices

Hot swappable

Plug and play capabilities

Host (Root Hub)

Hub 1 node node

Hub 2 node

Hub 3

Hub 4

node

node

node

node


USB devices

HUBServe to USB connectivityCan detect attach and detachHub Controller + Hub repeater

FunctionsUSB device that is able to transmit or receive data


USB Cables

D+ and D- carry data signal

The signals on these two wires are referenced to the (third) GND wire

VBUS carries a nominal 5V power supply, which may be used by a device for power – up to 2.5 Watts.


USB Cables

“A” receptacles point downstream from a Host or Hub, while "B" receptacles point upstream from a USB device or hub

A mini-B plug and receptacle-an alternative to B connector on handheld and portable devices

The mini-B has a fifth pin, named ID, but it is not connected


Wireless USB

High speed personal wireless interconnect technology

Connects up to 127 devicesUp to 480Mbps at 3 metresUp to 110Mbps at 10 metresBased on the WiMedia Alliance “ultra-

wideband common radio platform”See http://www.usb.org/developers/wusb/docs


USB 3.0 – added optical channel

Specifications released August 2008, chips by May 2009

USB 3.0 Promoters Group members:Intel, Microsoft, Hewlett-Packard, Texas Instruments, NEC and NXP Semiconductors

USB 3.0 products expected to arrive in 2009 or 2010About 5Gbps, copper connection, mostly backwards

compatible with USB2Originally intended to be part-optical, dropped due to

costsMore energy efficient than USB2


USB On-The-Go

In standard USB, communication is controlled by the PC

There is no way to connect peripherals together without the PC

The USB On-The-Go (OTG) initiative specifies some additional capabilities to USB2.0

It adds some host capabilities to USB peripherals for direct interconnection

See http://www.usb.org/developers/onthego/USB_OTG_Intro.pdf


Why USB?

Ease of use – relatively simple for the userBetter than existing connectors (2S/1P…)Single standard for manufacturers

Design time will be reduced after initial learning period, broadens market

Cost to manufacturers reduced by standardisation but raised by added complexity?

Changes to PC design are reducing internal expansion capability


FireWire

Many motherboards come with IEEE1394 (a.k.a FireWire or i.Link) for DV camera connection

FireWire is a high performance, versatile LAN-style connector

Runs at about 400Mbps (similar to USB2)

Latest 800Mbps (2007)


USB and FireWire Similarities

Many people confuse IEEE 394/FireWire/i.LINK and USB

Both are modern digital data connection technologies capable of linking multiple peripherals to a computer

Both permit “hot plugging” of peripherals (adding to or disconnecting from a computer without the need to reboot)

Both use thin, flexible cables which employ simple, durable connectors


DifferencesFireWire Universal Serial Bus

Max no. of devices: 64 127 Hot-Swap: Yes YesMax cable length

between devices: 4.5 metres 5 metresData transfer rate: 200Mbps 12Mbps (1.5MB/sec)Bandwidth

Roadmap: 400Mbps [std] 480Mbps [late 2000]800Mbps [rare?] 4.8Gps (USB 3.0)1Gbps+ [never happened]

Internal peripheral connection: Yes No

Network protocol: Yes NoPower provider: Yes, >20Watts Yes, just 2.5Watts


Original Target Markets

1394/FireWire/i.Link (200/400Mbps)

DV Camcorders

Professional High-Resolution Digital Cameras

Some HDTV applications

(HDTV?) Set-Top Boxes

Hard Disks

DVD-ROM Drives

Professional-level printers

Professional-level scanners

Universal Serial Bus (v1.1)

Keyboards

Mice

Monitors

Joysticks

Consumer Digital Cameras

Low-Speed CD-ROM Drives

Modems

Speakers

Consumer-level printers

Consumer-level scanners


Different Markets and Approach• 1394 offers a data transfer rate that is many times faster

than USB1 and this was expected to continue, even with newer, faster versions of each technology

• But IEEE1394 development stalled…• Some industry commentators asked “Can IEEE1394 win

the interface war with USB?”• Most IT analysts expected IEEE1394 and USB to coexist

peacefully in modern computers• USB was expected to be reserved for lower-bandwidth

and less time-sensitive peripherals – but then came USB2• IEEE1394 is still used to connect to higher-bandwidth

electronics where guaranteed bandwidth is key


What killed FireWire?

• Still not dead - IEEE1394 flourishes in niche areas of media communication

• But why the poor market penetration in personal computers?

• IEEE1394 is a fully developed networking protocol

• It is relatively complex and expensive

• Specialist markets don’t bring huge chip sales, so prices stay high

• It is “overkill” for most current PC applications


SATA Serial Advanced Technology Attachment

• SATA is the current generation storage interface for PCs and low-end Servers

• The old Parallel ATA bus was not able to meet the increased bandwidth and performance demands of current and future PC designs

• This standard replaces the 40 pin ribbon connector with a small flexible signal cable

• SATA can be directly connected (hot plugged) to motherboards and back planes similar to current SCSI applications eliminating the need for cable completely


Serial ATA

Serial ATA overcomes the problems of parallel ATA.

The features of Serial ATA are:

• 1.5 Gbps (real speed 150MB/s)

• 3 Gbps (300 MB/s)

•6 Gbps released in May 2009

• Hot plugging

• Two power saving modes, Low voltage requirement

•7 wire cable (8 mm wide) up to 1 m long.

Serial ATAParallel ATA


eSATA Port

External Serial Advanced Technology Attachment or eSATA is an external interface for SATA technologies.

Maximum cable length of 2 metres

eSATAp is a newer standard with provision for power to be supplied through data cables

computer systems architecture historical perspective the universal serial bus was originally...

Documents

usb peripherals

usb interfaces

usb resourcesbandwidth

usb transaction

developments usb

usb great flexibility

power usb bus interface

attached peripherals