Memory Mapped IO Very Good

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Computer Principles

AdvancedCompiler ResearchLaboratory

School of Computer Science & EngineeringSeoul National University

Memory Mapped I/O


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Computer Principles

Memory Mapped I/O

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To make all I/O devices look exactly the same to the

computer

Each I/O device is allocated an exclusive area in memory

Memory map

Data Memory

Screan

RAM

ScreenMemory Map

KeyboardMemory Map Keyboard


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Computer Principles

Memory Mapped I/O (contd.)

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Input device

Keyboard, mouse, etc.

The memory map continuously reflect the physical state ofthe device

Pressing a key on the keyboard makes a certain value

(code of the key) is written in the keyboards memorymap

Output device

Screen, speaker, etc.

The memory map continuously drive the physical state ofthe device

Whenever a bit is changed in the screens memory map, arespective pixel is drawn on the physical screen


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Computer Principles

Memory Mapped I/O (contd.)

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Hardware

Each I/O device need to provide an interface similar to

that of memory unitSoftware

Each I/O device is required to define an interactioncontract (protocol)

Standards play a key role in designing a computer system


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Computer Principles

American Standard Codefor Information Exchange (ASCII)

A character encoding based on the English alphabet

Developed from telegraphic codes

Its first commercial use was as a seven-bit teleprinter codepromoted by Bell data services

The common code for personal computers and workstations7-bit 128 numbers ranging from zero through 127 assigned toletters, numbers, punctuation marks, and the most commonspecial characters

The Extended ASCII Character Set128 numbers and ranges from 128 through 255 (using thefull 8-bits of the byte) representing additional special,mathematical, graphic, and foreign character

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http://en.wikipedia.org/wiki/Bithttp://en.wikipedia.org/wiki/Telegraphhttp://en.wikipedia.org/wiki/Bithttp://en.wikipedia.org/wiki/Bithttp://en.wikipedia.org/wiki/Telegraphhttp://en.wikipedia.org/wiki/Telegraphhttp://en.wikipedia.org/wiki/English_alphabethttp://en.wikipedia.org/wiki/English_alphabet


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Computer Principles

American Standard Codefor Information Exchange (contd.)

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Computer Principles

American Standard Codefor Information Exchange (contd.)

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Computer Principles

Unicode

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Fundamentally, computers just deal with numbers. They store lettersand other characters by assigning a number for each one. BeforeUnicode was invented, there were hundreds of different encodingsystems for assigning these numbers. No single encoding couldcontain enough characters: for example, the European Union alone

requires several different encodings to cover all its languages. Even fora single language like English no single encoding was adequate for allthe letters, punctuation, and technical symbols in common use.

These encoding systems also conflict with one another. That is, twoencodings can use the same number for two different characters, or

use different numbers for the same character. Any given computer(especially servers) needs to support many different encodings; yetwhenever data is passed between different encodings or platforms,that data always runs the risk of corruption. (from www.unicode.org)


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Computer Principles

Unicode (contd.)

Developed in cooperation between the UnicodeConsortium and the International Organization forStandardization (ISO)

16-bit character set, allowing up to 65,536 characters

An attempt to consolidate the alphabets and ideographs ofthe world's languages into a single, international characterset

Focuses on the characters themselves rather than onlanguages

The same Unicode character

A letter shared between English and Russian

An ideograph shared between kanji and Han script

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http://kb.iu.edu/data/aepo.htmlhttp://kb.iu.edu/data/aeoo.htmlhttp://kb.iu.edu/data/aeoo.htmlhttp://kb.iu.edu/data/aepo.htmlhttp://kb.iu.edu/data/aepo.htmlhttp://kb.iu.edu/data/aepo.htmlhttp://kb.iu.edu/data/aepo.htmlhttp://kb.iu.edu/data/aeoo.htmlhttp://kb.iu.edu/data/aeoo.htmlhttp://kb.iu.edu/data/aeoo.htmlhttp://kb.iu.edu/data/aeoo.html


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Computer Principles

Unicode (contd.)

Required by modern standards such as XML, Java,JavaScript, LDAP, CORBA 3.0, WML, etc.

Supported in many operating systems and all modernbrowsers

Makes it possible for developers to create applicationswithout having to resort to the costly, time-consuming task

of releasing localized versions for each language

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Computer Principles

Abstraction in Computer Science

Interested in what the entity does ignoring how it doesit

Every hardware and software developer is definingabstractions (a.k.a. interfaces) and then implementingthem

Abstractions are often built layer upon layer

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Computer Principles

Where Are We?

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Chips and Physical Gates Electrical Engineering

Transistors Physics

abstract interface

Computer Science and Engineering

Computer Hardware Platform

abstract interface (Boolean Logic)

Machine Language

abstract interface (ISA)

Assembly Language

abstract interface (Assembler)

Documents

Memory Mapped IO Very Good