Lecture 25 I/O Systems

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Lecture 25I/O Systems
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Categories of I/O Devices

• Human readable
• used to communicate with the user
• video display terminals
• keyboard
• mouse
• Printer
• From Operating Systems. Internals and Design
  Principles. W. Stallings. Prentice Hall

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Categories of I/O Devices

• Machine readable
• used to communicate with electronic equipment
• disk drives
• tape drives
• controllers
• Actuators
• From Operating Systems. Internals and Design
  Principles. W. Stallings. Prentice Hall

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Categories of I/O Devices

• Communication
• used to communicate with remote devices
• digital line drivers
• Modems
• From Operating Systems. Internals and Design
  Principles. W. Stallings. Prentice Hall

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Differences in I/O Devices

• Data Transfer Rate
• Application
• disk used to store files must have
  file-management software
• disk used to store virtual memory pages needs
  special hardware to support it
• terminal used by system administrator may have a
  higher priority
• From Operating Systems. Internals and Design
  Principles. W. Stallings. Prentice Hall

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Differences in I/O Devices

• Complexity of control
• Unit of transfer
• data may be transferred as a stream of bytes for
  a terminal or in larger blocks for a disk
• Data representation
• encoding schemes
• Error conditions
• devices respond to errors differently
• 
  
  Operating Systems. Internals and
  Design Principles
• .
  
  
  W. Stallings. Prentice Hall

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Hardware

• Device
• Port
• Bus
• Controller
• Computer System

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Hardware
monitor
processor
cache
Graphics controller
Memory controller
memory
PCI bus
IDE disk controller
disk
disk
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Techniques for Performing I/O

• Programmed I/O
• process is busy-waiting for the operation to
  complete
• Interrupt-driven I/O
• I/O command is issued
• processor continues executing instructions
• I/O module sends an interrupt when done
• From Operating Systems. Internals and Design
  Principles. W. Stallings. Prentice Hall

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Techniques for Performing I/O

• Direct Memory Access (DMA)
• DMA module controls exchange of data between main
  memory and the I/O device
• processor interrupted only after entire block has
  been transferred
• From Operating Systems. Internals and Design
  Principles. W. Stallings. Prentice Hall

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Programmed I/O Polling

• Controller
• Indicates its state through the busy bit in the
  status register.
• Sets the busy bit when it is busy working
• Clears the busy bit when it is ready to accept
  the next command

• Host
• Signals its wishes via the command-ready bit in
  the command register
• Sets the command ready bit when a command is
  available to execute

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Programmed I/O Polling

0
?
1
1
0
INFO
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Simple Interrupt Processing
From Operating Systems. Internals and Design
Principles. W. Stallings. Prentice Hall
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Interrupt Handler

• A program that determines nature of the interrupt
  and performs whatever actions are needed
• Control is transferred to this program
• Generally part of the operating system

From Operating Systems. Internals and Design
Principles. W. Stallings. Prentice Hall
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Multiple InterruptsSequential Order

• Disable interrupts so processor can complete task
• Interrupts remain pending until the processor
  enables interrupts
• After interrupt handler routine completes, the
  processor checks for additional interrupts

From Operating Systems. Internals and Design
Principles. W. Stallings. Prentice Hall
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Multiple InterruptsPriorities

• Higher priority interrupts cause lower-priority
  interrupts to wait
• Causes a lower-priority interrupt handler to be
  interrupted
• Example when input arrives from communication
  line, it needs to be absorbed quickly to make
  room for more input

From Operating Systems. Internals and Design
Principles. W. Stallings. Prentice Hall
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Direct Memory Access (DMA)

• I/O exchanges occur directly with memory
• Processor grants I/O module authority to read
  from or write to memory
• Relieves the processor from the task
• Processor is free to do other things

From Operating Systems. Internals and Design
Principles. W. Stallings. Prentice Hall
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Six step process to perform DMA transfer
From Operating System Concepts. Silberschatz
Galvin Addison Wsley