Universal Serial Bus Motivation
Device Framework or Layers
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- Navigate this page:
- USB Bus Interface Layer
- USB Device Layer
- Function Layer
- USB Peripheral Connection
- The Physical Environment
- High-speed Cables
- Cables and Cable Power
Device Framework or LayersProtocol stack supports 3 logical layers Describe relationship between Host hardware and software Corresponding view exists in each USB device Separate layers provided to Simplify understanding of USB communication Let’s examine USB Bus Interface LayerProvides for low level transfer of data over USB This is the physical layer in stack Consists of Physical connection Electrical signaling environment Packet transfer mechanism Layer represents actual transfer of data across USB cable Between host system and USB devices
Host controller and hub Client side comprises USB interface within the device USB Device LayerUSB Device layer Represents portion of USB Comprehends actual USB Communication mechanism Nature of transfers required by USB functional device
USB system software on host side Logical view of USB device on client side USB views logical device as collection of endpoints That comprise a functional interface
To interface client software with its USB function Has specific knowledge of USB transfer mechanisms Must allocate bus bandwidth to collection of USB devices Logical USB device represents collection of endpoints Through which client communicates with its function System software views endpoints via device descriptors Such descriptors parsed during configuration To obtain transfer characteristics of given device
Permit bandwidth to be reserved for each functional device When it’s configured
Device attachment and detachment detection Device configuration Bandwidth allocation Managing control flow between client and device Managing data flow between client and device Collecting status and transaction statistics Transaction scheduling Controlling electrical interface Function LayerLayer represents relationship between Client software Devices functional interface
Consists of particular class of device Class driver designed to manipulate
Such scheme contrasts with PCI, ISA, etc Result of not being mapped directly into memory or I/O space Device drivers must use USB programming interface To access associated device
Interface which they know how to manipulate USB system software must report to clients Interface type Other device characteristics
Provides single type of connector For attaching peripheral to system Supports two different speeds of device Low speed devices - 1.5 Mbyte / sec High speed devices - 12 Mbyte / sec All USB devices attach via USB hub Hub provides one or more ports
Device’s speed detected when attached to hub Each port must support High and low speed devices Unless has permanently attached device
All high speed devices and all hubs see transaction Each transaction has address field Identifies targeted device or hub Low speed devices only see low-speed transactions Preceded by high speed preamble Directs all hubs to enable low speed ports
For serial communication between root hub and USB devices Power supplied to USB devices USB cable Local power supply Associated with the device The Physical EnvironmentConnectors designed to permit any USB peripheral device To be attached to hub port Low-speed CablesIntended only for 1.5Mbyte/sec signaling Maximum cable length cannot exceed 3 meters Also referred to as Sub-channel cable As noted only intended for 1.5 Mb/sec signaling Sued in sub-channel applications where wider bandwidth not required Differential signaling pair May be non-twisted 28 AWG stranded conductors Used to reduce effects of noise Low speed cables do not require shielding High-speed CablesRequire twisted shielded pair Maximum
Cable length is 5 meters Propagation delay is 30 ns over length of cable When operating in range of 1-16 MHz If cannot be met Cable must be shortened Except for differences noted above Low and high speed cables are identical
Can be used to power peripheral devices Provides up to 500 ma May be as little as 100 ma  Directory: 475 475 -> Annual ambassadors signing day 475 -> A. Steps in the Policy Analysis Process 475 -> John p affatica 7660 W. Massey Dr. Littleton, co 80128 475 -> Project proposal 475 -> Pianist Aaron Diehl To Receive Jazz Journalists Association Award At Atlanta Jazz Festival 475 -> Northwestern nj: Appalachian Ridge & Valley and Highlands Regions 475 -> Pattern of Abnormal Pap smears in developing countries: a report from a large referral hospital in Saudi Arabia using the revised 2001 Bethesda System Dr Layla s abdullah, md, frcpc 475 -> “For all the children to whom we entrust the future.” Download 205.96 Kb. Share with your friends:
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