11

USB System Architecture

22

Limited System Resources Limited System Resources

Interrupt Lines Shortage

I/O address conflicts

Non-shareable Interfaces

Shortcomings of the Original PC I/O Shortcomings of the Original PC I/O ParadigmParadigm

33

A single connector type to connect any PC peripheral Ability to attach many peripheral devices to the same connector A method of easing the system resource conflicts Hot plug supportAutomatic detection and configuration of peripheral devices

USB ParadigmUSB Paradigm

44

1.5Mb/s – Low Speed Device. [USB 1.0] 12Mb/s - Full Speed Device. [USB 1.1] 480Mb/s – High Speed Device. [USB 2.0] 4.8Gb/s - Super Speed Device. [USB 3.0]

USB Transmission RatesUSB Transmission Rates

55

U S B S y s te m in a P C I P la tfo rmU S B S y s te m in a P C I P la tfo rm

66

USB FeaturesUSB Features

77

USB 2.0 HierarchyUSB 2.0 Hierarchy

88

Interrupt-driven devices in legacy PC implementations USB keyboardMust be polled periodically to see if the device has data to transfer

Interrupt TransfersInterrupt Transfers

99

Transferring large blocks of datathat have no periodic or transfer rate requirement USB printer Delivered slowly

Bulk transferBulk transfer

1010

Transfer requires a constant delivery rate USB microphone and speaker To ensure that no frequency distortion results from transferring data across the USB

Isochronous transferIsochronous transfer

1111

During device configuration USB Automatic configuration A special transfer sequence

Control transferControl transfer

1212

USB is shared by a wide variety of devices, a mix of USB transfer types will likely be performed

during each 1ms frame.

Interrupt and Isochronous transfers must occur at fixed intervals, they have a special priority during the execution of each frame (90%) Control Transfers(10%) Bulk transfers are allocated the remainder of the available bandwidth

Frame-Based TransfersFrame-Based Transfers

1313

Endpoint DescriptorEndpoint Descriptor

1414

ConclusionConclusionEach endpoint within a given USB device has particular characteristics that dictate how it must be accessed. The transfer characteristics relate to the requirements of the application. The above discussed four transfer types have been definedby the USB specification, each of which reflects the nature of transfers that maybe required by a USB device endpoint