Chapter 9: Input/Output

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Chapter 9: Input/Output

The Architecture of Computer Hardware and Systems Software:

An Information Technology Approach 3rd Edition, Irv Englander

John Wiley and Sons 2003

Wilson Wong, Bentley College

Linda Senne, Bentley College

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Chapter 9 Input / Output 9-2

Basic Model

 Processing speed or program execution

 determined primarily by ability of I/O operations to stay ahead of processor.

Input Process Output

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I/O Considerations

Speed Issues

 CPU operates at speeds much faster than the fastest I/O device

 Devices operate at different speeds

 Bursts of data

 Block data transfer required for some devices

Coordination

 Several devices perform I/O simultaneously

 Unexpected input

 Various input formats

 Status information needed for each device

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I/O Device Interface Issues

 Different formats

 parallel interface

 serial interface

 Buffering of data

 Burst vs. stream

 Different control requirements

 electromechanical

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Examples of I/O Devices

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Simple I/O Configuration

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I/O Modules Functions

 Recognizes messages from device(s) addressed to it and accepts commands from the CPU

 Provides a buffer where the data from memory can be held until it can be transferred to the disk

 Provides the necessary registers and controls to perform a direct memory transfer

 Physically controls the device

 Copies data from its buffer to the device/from the CPU to its buffer

 Notifies with interrupts

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Input/Output Modules

 Programmed I/O

 CPU controlled I/O

 Interrupt Driven I/O

 External input controls

 Direct Memory Access Controllers

 Method for transferring data between main

memory and a device that bypasses the

CPU

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Programmed I/O

 I/O data and address registers in CPU

 One word transfers

 Address information for each I/O device

 LMC I/O capability for 100 devices

 Full instruction fetch/execute cycle

 Primary use:

 keyboards

 communication with I/O modules (see DMA)

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Programmed I/O

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Programmed I/O Example

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Programmed I/O Example

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Interrupts

 Signal that causes the CPU to alter its normal flow on instruction execution

 frees CPU from waiting for events

 provides control for external input

 Examples

 unexpected input

 abnormal situation

 illegal instructions

 multitasking, multiprocessing

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The CPU - The Interrupt Cycle

 Fetch / Execute cycle

 Interrupt cycle

HALT

START

Fetch Next Instruction

Execute Instruction

Check/Process Interrupt

Interrupts Disabled

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Interrupt Terminology

 Interrupt lines (hardware)

 Interrupt request

 Interrupt handlers

 Program that services the interrupt

 Also known as an interrupt routine

 Process Control Block (PCB)

 Located in a part of memory known as the stack area

 All registers of a program are saved here before

control is transferred to the interrupt handler

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Interrupt Terminology

 Servicing the interrupt

 suspends program in progress

 saves pertinent information including last instruction executed and data values in registers in the PCB (process control block)

 branches to interrupt handler

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Servicing an Interrupt

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Use of Interrupts

 Notify that an external event has occurred

 real-time or time-sensitive

 Signal completion

 printer ready or buffer full

 Allocate CPU time

 time sharing

 Indicate abnormal event (CPU originates for notification and recovery)

 illegal operation, hardware error

 Software interrupts

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Multiple Interrupts

 Identifying devices

 Polling (checking for input in rotation)

 Vectored interrupts (include address of interrupting device)

 Interrupt priorities

 Loss of data vs. task completion

 Maskable (disabled) interrupts

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Vectored Interrupts

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Polled Interrupts

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Multiple Interrupts Example

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Direct Memory Access

 Transferring large blocks of data

 Direct transfer to and from memory

 CPU not actively involved in transfer itself

 Required conditions for DMA

 The I/O interface and memory must be connected

 The I/O module must be capable of reading and writing to memory

 Conflicts between the CPU and the I/O module

must be avoided

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DMA Instruction Set

 Application program requests I/O service from operating system

 privileged instructions

 To initiate DMA, programmed I/O is used to send the following information:

1. location of data on I/O device 2. the starting location in memory 3. the size of the block

4. read/write

 Interrupt to CPU upon completion

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DMA Initiation and Control

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Basic CPU-Memory-I/O Pathway*

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Bus Configuration

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Bus Characteristics

 Data width in bits carried simultaneously

 Throughput, i.e., data transfer rate in bits per second

 Point-to-Point vs. Multipoint

 Parallel vs. Serial

 Use

 Distance

 Protocol

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Bus Hierarchy

 Processor bus: on-chip

 Cache bus (backside bus)

 Memory bus (front-side bus)

 connects the memory subsystem and processor

 Local I/O bus

 high-speed bus used to connect performance critical peripherals to memory and processor

 Examples: PCI, VESA Local Bus

 Standard I/O bus

 connects slower peripherals (ISA) to Local I/O bus

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Wintel Bus Systems

 ISA: Industry Standard Architecture

 MCA: Micro Channel Architecture

 EISA: Extended Industry Standard Architecture

 Local Bus

 PCI: Peripheral Component Interconnect (also Apple, Sun, Compaq Alpha Server)

 VLB: VESA (Video Electronics Standards Association) Local Bus

 AGP: Accelerated Graphics Port

 Point-to-point channel from graphics controller to main memory

 Co-exists with PCI

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Compaq 7000 and 10000

System Architecture

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External Interface Buses and Ports

 Parallel port

 Serial port

 RS-232C and RS-422 buses

 SCSI

 Small Computer System Interface

 USB, USB-2

 Universal Serial Bus

 IEEE 1394

 Firewire

 i.link

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SCSI Bus

 ANSI standard but multiple variations

 Really an I/O bus rather than simple interface

 Supports multiple devices from a single SCSI port

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Root Hub

Hub Hub

USB

 Multipoint bus

 Hubs provide

multiple connection points for I/O devices

 Supports 127 devices

Hub

Topology Example

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USB and FireWire (IEEE 1394)

 Both serial, multipoint bus specifications

 Add/remove devices w/o powering down

 Packet protocol for isochronous data transfer

 Isochronous: delivery at regular time intervals

 Guarantee specified throughput

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USB vs. FireWire

 USB: slow to medium speed data transfer applications, i.e., storage devices

 12 Mbits/sec

 USB-2: high-speed data transfer

 480Mbits/sec

 FireWire: high-speed data transfer, i.e., full motion video with sound

 400 Mbits/sec to 3.2 Gbits/sec

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Typical FireWire Configuration

 Network-like characteristics

 Device controllers independent

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Channel Architecture

 Used in IBM mainframe computers

 Channel subsystem

 Separate I/O processor that serves as a CPU for I/O operations

 Channel control words

 Programs that transfer data between memory and an I/O device using DMA

 Subchannels

 Connected to a control unit module through one or more channel paths

 Similar role to a device controller

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I/O Channel Architecture

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