29 November
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Transcript of 29 November
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11/29/2005 Comp 120 Fall 2005 1
29 November
• 4 to go!• Questions?• Interrupts and I/O devices
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Interrupts
How does the CPU manage SLOW I/O devices?1. Programmed I/O2. Interrupt Driven I/O
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Polling
Advantages
Simple
No surprises
Processor in full control
Disadvantages
Polling can waste lots of time
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Interrupt Driven I/O
Advantage
CPU only bothered when actually needed
Disadvantage
Can occur at surprising or inconvenient times
Have to save and restore state
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MIPS Exceptions• Reset • Hardware Errors (Check, Bus Error, Cache Error)• External Interrupt (6 inputs)• Address Error• Reserved Instruction• TLB Miss• System Call• Breakpoint• Trap• Integer Overflow• Floating Point Error• Timer• And a few more
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Exception Processing
1. EPC gets address of faulty instruction or of next instruction depending on type of exception
2. Switch to kernel mode3. Jump to a new location based on type of exception
• PC FFFF FFFF BFC0 0000 for Reset• PC FFFF FFFF BFC0 0300 for Hardware error• PC FFFF FFFF BFC0 0380 for external interrupts• PC FFFF FFFF BFC0 0400 for …
4. Save registers5. Examine the “cause” register to find out why you came here6. Branch to code to do the right thing
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Magnetic Disk
Long term, nonvolatile storageLarge, inexpensive, and slow
Rotating platter(s) coated with magnetic materialUse a movable read/write head to accessWhen magnetized region zips past coils in head, a tiny signal is
producedForce current through coils to generate magnetic field to magnetize
tiny regions on the diskUse feedback to keep the head in the right place
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Outside
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Inside
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Platters and Heads
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Magnetic Disk Organization
• Cylinder: All tracks under head with arm in a fixed position
• Read/Write time has 3 components
•Seek time to move the arm
•Rotational latency: wait for the desired sector to come by
•Transfer time: transfer bits
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Typical Disk Times
• Average Seek: 8ms to 12ms– Sum of all possible seek / number of possible seeks– Locality reduces this to maybe only 25% of average number
• Rotational Latency:– At 5400 RPM 11 ms– At 7200 RPM 8 ms– At 10000 RPM 6ms
• Transfer time depends on:– Transfer size (typical 512 bytes)– Rotation speed– Recording density– Diameter– Typical values: 10 to 40MBytes per second
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CD
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CRT Display
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LCD
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Graphics Cards
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Polygons to Surfaces• Numerical coordinates specify vertex positions in 3D
• Matrix multiply transforms 3D coordinates to eye coordinates
• Divide projects 3D to 2D in perspective
• Pixel processors fill polygons with appropriate colors based on lighting model
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Anti-aliasing
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Sound
Sound is variations in air pressure
A microphone converts these into an analog electrical signal
An analog-to-digital converter samples this at frequent intervals
The resulting numbers are stored in a file (.wav)
On playback a digital-to-analog converter changes these numbers into an analog electrical signal
And the moving cone of a speaker converts this into varying air pressure
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11/29/2005 Comp 120 Fall 2005 20
MP3?
• The sequence of numbers representing typical sounds is VERY redundant– The next value is closely related to the previous– Values aren’t random cause we don’t like noise
• Extract this redundancy to get compression• Lossy compression: Throw less important info away cause listener
won’t notice
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11/29/2005 Comp 120 Fall 2005 21
Cultural Highlight
• Check out these Christmas lights!
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Classes to go
3