09 Input Output

8/2/2019 09 Input Output

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Chapter 9: Input/Output

Ho Dac Phuong, Msc

Computer Networking & Telecommunication Department

College of Technology

Vietnam National University, Hanoi

[email protected]

http://www.coltech.vnu.edu.vn/courses/cour

se/view.php?id=69


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Introduction

5.1 Principles of I/O hardware5.2 Principles of I/O software

5.3 I/O software layers

5.4 Disks

5.5 Clocks5.6 Character-oriented terminals

5.7 Graphical user interfaces

5.8 Network terminals

5.9 Power management


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Principles of I/O Hardware

Some typical device, network, and data base rates


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Device Controllers

I/O devices have components:

mechanical component

electronic component

The electronic component is the device controller may be able to handle multiple devices

Controller's tasks

convert serial bit stream to block of bytes

perform error correction as necessary

make available to main memory


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Memory-Mapped I/O (1)

Separate I/O and memory space Memory-mapped I/O

Hybrid


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Memory-Mapped I/O (2)

(a) A single-bus architecture

(b) A dual-bus memory architecture


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Direct Memory Access (DMA)

Operation of a DMA transfer


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Interrupts Revisited

How interrupts happens. Connections between devices and interruptcontroller actually use interrupt lines on the bus rather than dedicatedwires


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Principles of I/O SoftwareGoals of I/O Software (1)

Device independence programs can access any I/O device

without specifying device in advance

(floppy, hard drive, or CD-ROM)

Uniform naming

name of a file or device a string or an integer

not depending on which machine

Error handling handle as close to the hardware as possible


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Goals of I/O Software (2)

Synchronous vs. asynchronous transfers blocked transfers vs. interrupt-driven

Buffering

data coming off a device cannot be stored in

final destination Sharable vs. dedicated devices

disks are sharable

tape drives would not be


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Programmed I/O (1)

Steps in printing a string


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Programmed I/O (2)

Writing a string to the printer using programmed I/O


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Interrupt-Driven I/O

Writing a string to the printer using interrupt-driven I/O

Code executed when print system call is made

Interrupt service procedure


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I/O Using DMA

Printing a string using DMA

code executed when the print system call ismade

interrupt service procedure


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I/O Software Layers

Layers of the I/O Software System


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Interrupt Handlers (1)

Interrupt handlers are best hidden have driver starting an I/O operation block until

interrupt notifies of completion

Interrupt procedure does its task then unblocks driver that started it

Steps must be performed in software afterinterrupt completed

1. Save regs not already saved by interrupt hardware

2. Set up context for interrupt service procedure


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Interrupt Handlers (2)

3. Set up stack for interrupt service procedure4. Ack interrupt controller, reenable

interrupts5. Copy registers from where saved6. Run service procedure7. Set up MMU context for process to run

next8. Load new process' registers9. Start running the new process


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Device Drivers

Logical position of device drivers is shown here

Communications between drivers and device controllers goes over

the bus


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Device-Independent I/O Software (1)

Functions of the device-independent I/O software

Uniform interfacing for device drivers

Buffering

Error reporting

Allocating and releasing dedicate devices

Providing a device-independent block size


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(a) Without a standard driver interface

(b) With a standard driver interface


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Device-Independent I/O Software (3)s

(a) Unbuffered input(b) Buffering in user space(c) Buffering in the kernel followed by copying to user

space(d) Double buffering in the kernel


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Networking may involve many copies


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User-Space I/O Software

Layers of the I/O system and the mainfunctions of each layer


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DisksDisk Hardware (1)

Disk parameters for the original IBM PC floppy disk and aWestern Digital WD 18300 hard disk


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Disk Hardware (2)

Physical geometry of a disk with two zones

A possible virtual geometry for this disk


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Disk Hardware (3)

Raid levels 0 through 2

Backup and parity drives are shaded


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Hamming code

Consider a Hamming code to detect and correct

for single-bit errors assuming each codewordcontains a seven-bit data field, e.g. an ASCIIcharacter. for example. Such a coding schemerequires four check bits since, with this scheme,

the check bits occupy all bit positions that arepowers of 2. Such a code is thus known as an (11,7) block code with a rate of 7/11 and aredundancy of . For example, the bit positions of

the value 1001101 are: Bit Position 11 10 9 8 7 6 5 4 3 2 1

Bit value 1 0 0 x 1 1 0 x 1 x x


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Hamming distance

Let x and y be two binary sequences of the same length.

The Hamming distance between these two codes is thenumber of symbols that disagree. Suppose the code x istransmitted over the channel. Due to errors, y is received.The decoder will assign to y the code x that minimises theHamming distance between x and y. For example, consider

the codewords: a = 10000

b = 01100

c = 10011

If the transmitter sends 10000 but there is a single bit errorand the receiver gets 10001, it can be seen that the "nearest"codeword is in fact 10000 and so the correct codeword isfound.


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Hamming distance

It can be shown that to detect n bit errors, a

coding scheme requires the use of codewordswith a Hamming distance of at least n + 1. It canalso be shown that to correct n bit errors requiresa coding scheme with at least a Hamming

distnace of2n + 1 between the codewords. By designing a good code, we try to ensure that

the Hamming distance between possiblecodewords x is larger than the Hamming distance

arising from errors


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Hamming distance

11 = 1011

7 = 0111

6 = 0110

3 = 0011

1001

The transmitted codeword is thus:

Bit Position 11 10 9 8 7 6 5 4 3 2 1

Bit value 1 0 0 1 1 1 0 0 1 0 1


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Hamming distance

Similarly, at the receiver, the four-bit binary

numbers corresponding to those bit positionshaving a binary 1, including the check bits, areagain added together and, if no errors haveoccurred, the modulo 2 sum should be zero:

11= 1101 8 = 1100

7 = 0111

6 = 0110

3 = 0011

1 = 0001

0000


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Hamming distance

Now consider a single-bit error; say bit 11 is corrupted

from 1 to 0. The new modulo 2 sum would now be: 8 = 1100

7 = 0111

6 = 0110

3 = 0011 1 = 0001

1011

Firstly, the sum is non-zero, which indicates an error, andsecondly the modulo 2 sum, equivalent to decimal 11,

indicates that bit 11 is the erroneous bit. The latter wouldtherefore be inverted to obtain the corrected codeword andhence data bits.


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Disk Hardware (4)

Raid levels 3 through 5

Backup and parity drives are shaded


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Disk Hardware (5)

Recording structure of a CD or CD-ROM


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Disk Hardware (6)

Logical data layout on a CD-ROM


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Disk Hardware (7)

Cross section of a CD-R disk and laser

not to scale

Silver CD-ROM has similar structure

without dye layer

with pitted aluminum layer instead of gold


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Disk Hardware (8)

A double sided, dual layer DVD disk


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Disk Formatting (1)

A disk sector


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Disk Formatting (2)

An illustration of cylinder skew


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Disk Formatting (3)

No interleaving

Single interleaving

Double interleaving


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Disk Arm Scheduling Algorithms (1)

Time required to read or write a diskblock determined by 3 factors

1. Seek time

2. Rotational delay

3. Actual transfer time

Seek time dominates

Error checking is done by controllers


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Shortest Seek First (SSF) disk scheduling algorithm

Initialposition

Pendingrequests


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The elevator algorithm for scheduling disk requests

dli


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Error Handling

A disk track with a bad sector Substituting a spare for the bad sector

Shifting all the sectors to bypass the bad one

S bl S


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Stable Storage

Analysis of the influence of crashes on stable writes

Clocks


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ClocksClock Hardware

A programmable clock

Cl k S f (1)


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Clock Software (1)

Three ways to maintain the time of day

Cl k S f (2)


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Clock Software (2)

Simulating multiple timers with a single clock

S f Ti


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Soft Timers

A second clock available for timer interrupts specified by applications

no problems if interrupt frequency is low

Soft timers avoid interrupts

kernel checks for soft timer expirationbefore it exits to user mode

how well this works depends on rate ofkernel entries

Character Oriented Terminals


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Character Oriented TerminalsRS-232 Terminal Hardware

An RS-232 terminal communicates with computer 1 bit at a time Called a serial linebits go out in series, 1 bit at a time

Windows uses COM1 and COM2 ports, first to serial lines

Computer and terminal are completely independent

I t S ft (1)


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Central buffer pool

Dedicated buffer for each terminal

Input Software (1)

I t S ft (2)


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Input Software (2)

Characters handled specially in canonical mode

O t t S ft


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Output Software

The ANSI escape sequences accepted by terminal driver on output ESC is ASCII character (0x1B) n,m, and s are optional numeric parameters

Di l H d (1)


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Display Hardware (1)

Memory-mapped displays

driver writes directly into display's video RAM

Parallel port

Di l H d (2)


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Display Hardware (2)

A video RAM image

simple monochrome display

character mode

Corresponding screen

the xs are attribute bytes

Inp t Soft are


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Input Software

Keyboard driver delivers a number driver converts to characters

uses a ASCII table

Exceptions, adaptations needed for otherlanguages

many OS provide for loadable keymaps

or code pages

O t t S ft f Wi d (1)


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Output Software for Windows (1)

Sample window located at (200,100) on XGA display

O t t S ft f Wi d (2)


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Skeleton of a Windows main program (part 1)



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Skeleton of a Windows main program (part 2)



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An example rectangle drawn usingRectangle



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Copying bitmaps usingBitBlt.

before

after



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Examples of character outlines at different point sizes

Network Terminals


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Network TerminalsX Windows (1)

Clients and servers in the M.I.T. X Window System

X Windows (2)


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X Windows (2)

Skeleton of an X Windows application program

The SLIM Network Terminal (1)


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The architecture of the SLIM terminal system



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Messages used in the SLIM protocol from the server to the terminals

Power Management (1)


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Power consumption of various parts of a laptop computer

Power management (2)


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Power management (2)

The use of zones for backlighting the display



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Running at full clock speed

Cutting voltage by two cuts clock speed by two,

cuts power by four



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Telling the programs to use less energy

may mean poorer user experience

Examples change from color output to black and

white

speech recognition reduces vocabulary less resolution or detail in an image

Documents

09 Input Output