1. © 2000 Morgan Kaufman Overheads for Computers as Components Processes and operating systems zTelephone answering machine.

2. © 2000 Morgan Kaufman Overheads for Computers as Components Theory of operation zCompress audio using adaptive differential pulse code modulation (ADPCM). time analog ADPCM 321-2-3

3. © 2000 Morgan Kaufman Overheads for Computers as Components ADPCM coding zCoded in a small alphabet with positive and negative values. y{-3,-2,-1,1,2,3} zMinimize error between predicted value and actual signal value.

4. © 2000 Morgan Kaufman Overheads for Computers as Components ADPCM compression system quantizer integrator inverse quantizer  encoder inverse quantizer integrator decoder samples

5. © 2000 Morgan Kaufman Overheads for Computers as Components Telephone system terms zSubscriber line: line to phone. zCentral office: telephone switching system. zOff-hook: phone active. zOn-hook: phone inactive.

6. © 2000 Morgan Kaufman Overheads for Computers as Components Real and simulated subscriber line zReal subscriber line: y90V RMS ringing signal; ycompanded analog signals; ylightning protection, etc. zSimulated subscriber line: ymicrophone input; yspeaker output; yswitches for ring, off-hook, etc.

7. © 2000 Morgan Kaufman Overheads for Computers as Components Requirements

8. © 2000 Morgan Kaufman Overheads for Computers as Components Comments on analysis zDRAM requirement influenced by DRAM price. zDetails of user interface protocol could be tested on a PC-based prototype.

9. © 2000 Morgan Kaufman Overheads for Computers as Components Answering machine class diagram Microphone* Line-in* Line-out* Buttons* Speaker* Lights Playback ControlsRecord Outgoing- message Incoming- message 1 1 1 1 1 1 1 11 11 11 1 1 1 1 * * * *

10. © 2000 Morgan Kaufman Overheads for Computers as Components Physical interface classes Line-out* sample() pick-up() Microphone* sample() Line-in* sample() ring-indicator() Speaker* sample() Buttons* record-OGM play Lights* messages num-messages

11. © 2000 Morgan Kaufman Overheads for Computers as Components Message classes Message length start-adrs next-msg samples Incoming-message msg-time Outgoing-message length=30 sec

12. © 2000 Morgan Kaufman Overheads for Computers as Components Operational classes Controls operate() Record record-msg() Playback playback-msg()

13. © 2000 Morgan Kaufman Overheads for Computers as Components Software components zFront panel module. zSpeaker module. zTelephone line module. zTelephone input and output modules. zCompression module. zDecompression module.

14. © 2000 Morgan Kaufman Overheads for Computers as Components Controls activate behavior Compute buttons, line activations Activations? Play OGMRecord OGMPlay ICMEraseAnswer Wait for timeout Erase Play OGM Allocate ICM Record ICM

15. © 2000 Morgan Kaufman Overheads for Computers as Components Record-msg/playback-msg behaviors nextadrs = 0 msg.samples[nextadrs] = sample(source) End(source) F T record-msg nextadrs = 0 speaker.samples() = msg.samples[nextadrs]; nextadrs++ nextadrs=msg.length F T playback-msg

16. © 2000 Morgan Kaufman Overheads for Computers as Components Hardware platform zCPU. zMemory. zFront panel. z2 A/Ds: ysubscriber line, microphone. z2 D/A: ysubscriber line, speaker.

17. © 2000 Morgan Kaufman Overheads for Computers as Components Component design and testing zMust test performance as well as testing. yCompression time shouldn’t dominate other tasks. zTest for error conditions: ymemory overflow; ytry to delete empty message set, etc.

18. © 2000 Morgan Kaufman Overheads for Computers as Components System integration and testing zCan test partial integration on host platform; full testing requires integration on target platform. zSimulate phone line for tests: yit’s legal; yeasier to produce test conditions.