Usb on the go implementation trade offs
This presentation is the property of its rightful owner.
Sponsored Links
1 / 13

USB On-The-Go Implementation Trade-offs PowerPoint PPT Presentation


  • 105 Views
  • Uploaded on
  • Presentation posted in: General

USB On-The-Go Implementation Trade-offs. Zong Liang WU TransDimension. Agenda. On-The-Go device vs. Dual role device Dual role device: top level architecture Basic issues: system constraints System constraints vs. Implementation choices Compliance & interoperability Product decision.

Download Presentation

USB On-The-Go Implementation Trade-offs

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Usb on the go implementation trade offs

USB On-The-Go Implementation Trade-offs

Zong Liang WU

TransDimension


Agenda

Agenda

  • On-The-Go device vs. Dual role device

  • Dual role device: top level architecture

  • Basic issues: system constraints

  • System constraints vs. Implementation choices

  • Compliance & interoperability

  • Product decision


On the go device vs dual role device

On-The-Go Device Vs. Dual Role Device

  • Dual role device (DRD):

    • Supports master negotiation protocol

    • Acts as master or slave, after MNP

    • Capable of supplying at least 4mA

  • On-The-Go device (OTG):

    • Dual Role Device

    • Slave-only device drawing less than 4mA from Vbus


Dual role device top level architecture

Dual Role DeviceTop-Level Architecture

Charge Pump

5V @4mA

Processor

Interface

System

processor

HOST

Analog

Transceiver

Cable

Function

MNP

Registers

Top level control


Basic issues system constraints

Basic IssuesSystem Constraints

  • Microprocessors

    • Wide range of performance (uP itself or the part available for DRD)

    • Different interfaces: often DRD is not allowed to be system bus master

  • System software

    • Latency of HW interrupt processing

      • Maybe critical for Isochronous applications

    • Different RTOS


System constraints vs implementation choices

System Constraints Vs.Implementation Choices

  • Performance of the master:

    • Throughput supported: full 12mbits/s (as good as or even better than a PC) vs. Very limited bandwidth

    • Endpoint types supported: all 4 types vs. A subset

    • Number of devices and endpoints supported: capable of supporting many devices/endpoints simultaneously vs. Onlya few endpoints

  • Difficulties:

    • How to get maximum master performance with a limited uP?

    • How to do in embedded applications where DRD is not allowed to be system bus master ?

    • How to support Isochronous applications within a RTOS having a large interrupt latency (like wince)?


System constraints vs implementation choices1

System Constraints Vs.Implementation Choices

  • uP requirements vs. Master performance:

    • Desired target for portable or STB applications:

      • Optimal performance

      • Light load on uP

      • Minimum interrupt frequency

      • Loose requirement on uP’s interrupt latency

      • Keep at low cost (HW+SW)

    • Trade-off vs. Smart SW/HW partitioning

      Learn from OHCI and UHCI partitioning

      • Call for major architecture innovation


System constraints vs implementation choices2

System Constraints Vs.Implementation Choices

  • Many applications:

    • Portable (PDA, mobile phone, MP3, pocket PC, digital camera etc)and less portable (set-top-box, game machine, etc):

      • Many RTOS on the market

  • RTOS-based stack vs. Dedicated system SW

    • RTOS is not always necessary

    • Think of a dedicated microprocessor

  • RTOS-based: how to design once for all?

    • Try to comply with and reuse OHCI/UHCI stack

    • Partner with specialty system software house


  • System constraints vs implementation choices3

    System Constraints Vs.Implementation Choices

    • Power management:

      • Portable appliances require low power

      • OTG spec introduces the concept of sessionand wakeup protocol

      • Manage power at chip architecture level, by introducing appropriate power management logic


    System constraints vs implementation choices4

    System Constraints Vs.Implementation Choices

    • Single chip vs. 2-chip solution

      • OTG master needs to supply [email protected] (minimum)

      • Analog transceiver’s signaling is 3.3V

      • Standard 0.18um process has trouble to implement

        • Put the charge pump and the analog transceiverinto a separate chip

        • Define a standard interface: ongoing effort


    Compliance interoperability

    Compliance & Interoperability

    • Compliance to WHAT:

      • A DRD must be a 100% compliant USB function

      • OTG master vs. Embedded master vs. StandardPC host (OHCI/UHCI):

        • OTG: one to one: simpler master

        • Embedded: Strong sales point if the master cansupport what a standard PC host can do(endpoint types, number, sizes)

    • An OTG compliance spec is in development


    Product decision

    Product Decision

    • What do you really want:

      • Slave-only with mini-connector and draws <=4ma

      • Dual role device (master or slave depending on MNP result)

      • Simultaneous master and slave

    • Do not forget your expectation on master’s performance

    • Discrete IC or integrate an IP into your system:

      • Time to market vs. Cost vs. Risk


  • Login