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CSC-205 Computer OrganizationLecture #012

Sections 5.2 through 5.4, Machine instructions andassemblers

Dr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck Cartledge

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Table of contents (1 of 1)

1 5.2Irritating things aboutdirect addressing

2 5.3How symbols make lifeeasier.

3 5.4Translating from LevelHOL6

4 Chap. 5 reviewAssembly language

5 Conclusion

6 References

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Irritating things about direct addressing

A simple program.

You (the human) have to know the code (hex) for everything.

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Irritating things about direct addressing

When do you stop printing a string?

What is difference between C++ string and char[] when printing??

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Irritating things about direct addressing

Terrific quote

“In all these examples, theinstruction simply grinds through thevon Neumann execution cycle. Youmust always remember that thetranslation process is different fromthe execution process and thattranslation happens before execution.After translation, when theinstructions are executing, the originof the bits is irrelevant. The onlything that matters is what the bitsare, not where they came fromduring the translation phase.”

J. Stanley Warford [3]

J. Stanley Warford

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How symbols make life easier.

Let the software worry about where things are.

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How symbols make life easier.

A truly silly program.

The symbol “this” points to memory location0000

Memory location 0000 contains the opcode forDEC0 with OprnSpec “this” and to treat thecontents as decimal

von Neumann starts at address 0000

Loads the instruction

Executes the instruction (outputs the contents atmemory location 0000)

Stops

The opcode is interpreted as data (as per theopcode) and output.

Seems silly, but von Neumann doesn’t distinguish between programand data. Powerful stuff.

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Translating from Level HOL6

We’ve “bumped” into the idea ofcompilers (nee, translators)before.

Compilers convert HOLdirectly into machine code(ones and zeros), or

Compiler convert HOL inassembler level code thatanother program has totranslate into machine code.

A compiler is a program (albeit,a complex one).

Image from [3].

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Translating from Level HOL6

Relative sizes of different compilers.

Files from Ubuntu 14.04.2

g++ ⇒ g++-4.8 ⇒775Kbytes

fortran ⇒ 14785Kbytes

javac ⇒ 7KBytes, an ELFfile

Executable and Linkable Format(ELF) tells computer where toget information and where to putit memory

Image from [2].

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Translating from Level HOL6

Some HOL statements get translated

Statements that actually dosomething get translated:

The cout statement

The return statement

return inside the main() becomesSTOP only in the Pep/8compiler.

What about the other statements??

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Translating from Level HOL6

Some HOL statements don’t get translated

The “#include <>” is acompiler directive on whereto get additional information

The “using namespace . . . ”is to make typing easier forthe human

The semicolons terminate alogical line

All HOLs have the same types of problems: scoping, brevity, lineendings, line beginings, etc.

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Translating from Level HOL6

Variables are just named places in memory

About variables:

At the ISA level, they live inmemory

At the ASL level, they are labelsfor memory location

At the HOL level, they exist

There are generally three types ofvariables:

Global – available to everyoneand “remember things”

Local – available to the currentcontext and then lost

Static – available to the currentcontext and then remembered

Other – available to lower contextand then lost

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Translating from Level HOL6

How to resolve structures and classes?

Remember at the lowest level, there areonly addresses.

“typedef” takes a “known type”and makes a new type

“enum” creates an int, limits thevalues it can assume, and givesthose values names

“struct” names a collection ofcontiguous memory locations

We can now create an array ofcontiguous memory locations of thesame type.

The compiler keeps track of variablenames, types, and locations in memory.

A class is a block of contiguous memory locations that has addresses offunctions inside of it.

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Translating from Level HOL6

A special type of variable that doesn’t vary.

C++ uses the compilerdirective “const” to tell thecompiler to cause an errorwhen the constant thing ismodified.

Pep/8 uses the “.EQUATE”directive

Usually you’ll use immutable variables for safety anddocumentation purposes.

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Assembly language

Moving up the “food chain.”

Relationship betweenassembly and machine code,

Pages 194 and 195,

Pep/8 pseudo operators,

Immediate addressing andtrap instructions,

Concept of symbols,

von Neumann, vonNeumann, von Neumann,

Translating from HOL6

Image from [1].

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What have we covered?

Immediate addressing and the trapinstructionsSymbolsTranslating from level HOL6Chapter review

Next period:

Test, Section 6.1, Assemblers and high order languages

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References (1 of 1)

[1] Wikipedia Staff,Adventures of Huckleberry Finn (1885)/Chapter 5,https://en.wikisource.org/wiki/Adventures_of_

Huckleberry_Finn_(1885)/Chapter_5, 2016.

[2] Xilin Staff, Building applications in sdk, http://www.xilinx.com/support/documentation/sw_manuals/

xilinx12_2/SDK_Doc/concepts/sdk_c_build.htm, 2015.

[3] J. Stanley Warford, Computer Systems, Jones & BartlettPublishers, 2010.