1. © 2000 Morgan Kaufman Overheads for Computers as Components I/O devices zI/O devices: yserial links ytimers and counters ykeyboards ydisplays yanalog I/O

2. © 2000 Morgan Kaufman Overheads for Computers as Components Timers and counters zVery similar: ya timer is incremented by a periodic signal; ya counter is incremented by an asynchronous, occasional signal. zRollover causes interrupt.

3. © 2000 Morgan Kaufman Overheads for Computers as Components Watchdog timer zWatchdog timer is periodically reset by system timer. zIf watchdog is not reset, it generates an interrupt to reset the host. host CPU watchdog timer interrupt reset

4. © 2000 Morgan Kaufman Overheads for Computers as Components Switch debouncing zA switch must be debounced to multiple contacts caused by eliminate mechanical bouncing:

5. © 2000 Morgan Kaufman Overheads for Computers as Components Encoded keyboard zAn array of switches is read by an encoder. zN-key rollover remembers multiple key depressions. row

6. © 2000 Morgan Kaufman Overheads for Computers as Components LED zMust use resistor to limit current:

7. © 2000 Morgan Kaufman Overheads for Computers as Components 7-segment LCD display zMay use parallel or multiplexed input.

8. © 2000 Morgan Kaufman Overheads for Computers as Components Types of high-resolution display zCathode ray tube (CRT) zLiquid crystal display (LCD) zPlasma, etc.

9. © 2000 Morgan Kaufman Overheads for Computers as Components Touchscreen zIncludes input and output device. zInput device is a two-dimensional voltmeter:

10. © 2000 Morgan Kaufman Overheads for Computers as Components Touchscreen position sensing ADC voltage

11. © 2000 Morgan Kaufman Overheads for Computers as Components Digital-to-analog conversion zUse resistor tree: R 2R 4R 8R bnbn b n-1 b n-2 b n-3 V out

12. © 2000 Morgan Kaufman Overheads for Computers as Components Flash A/D conversion zN-bit result requires 2 n comparators: encoder V in...

13. © 2000 Morgan Kaufman Overheads for Computers as Components Dual-slope conversion zUse counter to time required to charge/discharge capacitor. zCharging, then discharging eliminates non-linearities. V in timer

14. © 2000 Morgan Kaufman Overheads for Computers as Components Sample-and-hold zRequired in any A/D: converter V in

15. © 2000 Morgan Kaufman Overheads for Computers as Components USB 2.0 zGoals: yEasy to use. yLow cost for consumer devices. yUp to 480 Mb/s. yReal-time audio, video. yBoth isochronous and asynchronous communication.

16. © 2000 Morgan Kaufman Overheads for Computers as Components USB architecture host device interconnect Bus topology. Stack. Data flow model. Schedule.

17. © 2000 Morgan Kaufman Overheads for Computers as Components Bus tiers host function hub function Tier 1 tier 2 tier 3 tier 4 …. tier 7 Device = {hub, function}

18. © 2000 Morgan Kaufman Overheads for Computers as Components USB signaling zSpeeds: yHigh-speed is 480 Mb/s. yFull-speed is 12 Mb/s. yLow-speed is 1.5 Mb/s. zSignals: yVbus, Gnd. yD+, D-.

19. © 2000 Morgan Kaufman Overheads for Computers as Components USB power zUSB devices can pull a limited amount of power from the bus. yMay also supply their own power. zSystem may provide a power- management protocol. yIndependent of USB.

20. © 2000 Morgan Kaufman Overheads for Computers as Components USB bus protocol zPolled bus, all transfers initiated by host. zBasic transaction: yHost sends token packet: xType and direction. xUSB device number. xEndpoint number (subdevice). yData transfer packet. yAcknowledge packet.

21. © 2000 Morgan Kaufman Overheads for Computers as Components Robustness zError detection/correction. zAutomatic handling of device attach/detach. zSelf-recovery in protocol. zStreaming data management. zPipes for data management.

22. © 2000 Morgan Kaufman Overheads for Computers as Components USB pipes zFunctions are allocated to data pipes. yPipes limit interference between functions. zBandwidth is allocated among pipes. zDevices must supply buffer memory.

23. © 2000 Morgan Kaufman Overheads for Computers as Components USB data flow model zFour types of implementation: yDevice hardware. yClient software to connect to application. yUSB system software. yUSB host controller (host side system interface). hostdevice Client SW USB system SW USB host controller function USB logical device USB bus interface Physical communication

24. © 2000 Morgan Kaufman Overheads for Computers as Components Logical bus topology zBus appears to be a simple host/device system: host device

25. © 2000 Morgan Kaufman Overheads for Computers as Components Client software view zEach client sees its own function but not the whole system: function Client SW function Client SW function Client SW function Client SW

26. © 2000 Morgan Kaufman Overheads for Computers as Components Endpoints zEach logical device is a collection of endpoints. zEach endpoint is simplex (input or output). zEndpoint description: yBus frequency/latency. yBandwidth requirement. yEndpoint number. yError handling requirements. yMaximum packet size. yTransfer type. yTransfer direction.

27. © 2000 Morgan Kaufman Overheads for Computers as Components Pipes zTwo types of pipes: yStream. yMessage. zPipe description includes: yPipe type. yDirection. yBus access and bandwidth.

28. © 2000 Morgan Kaufman Overheads for Computers as Components Bus transfer types zData goes through the pipe in FIFO order. zFour types of transfers: yControl. yIsochronous—periodic data stream. yInterrupt. yBulk—non-periodic, large data transfer.