William Stallings William Stallings Computer Organization

d A hit tand Architecture

Chapter 9Instruction Sets:Instruction Sets:Characteristicsand Functionsand Functions

What is an instruction set?What is an instruction set?

aThe complete collection of instructions that are understood by a CPUaMachine CodeaBinaryaUsually represented by assembly codes

Elements of an InstructionElements of an Instruction

aOperation code (Op code)`Do this

aSource Operand reference`To this

l d faResult Operand reference`Put the answer here

aN t I t ti R faNext Instruction Reference`When you have done that, do this...

Where have all the Operands gone?gone?

aLong time passing.a(If you dont understand, youre too young!)aMain memory (or virtual memory or cache)aCPU registeraI/O device

Instruction RepresentationInstruction Representation

aIn machine code each instruction has a unique bit patternaFor human consumption (well, programmers

anyway) a symbolic representation is used` ADD SUB LOAD`e.g. ADD, SUB, LOAD

aOperands can also be represented in this way`ADD A B`ADD A,B

Instruction TypesInstruction Types

aData processingaData storage (main memory)aData movement (I/O)aProgram flow control

Number of Addresses (a)Number of Addresses (a)

a3 addresses`Operand 1, Operand 2, Result`a = b + c;`May be a forth - next instruction (usually implicit)`Not common`Not common`Needs very long words to hold everything

Number of Addresses (b)Number of Addresses (b)

a2 addresses`One address doubles as operand and result`a = a + b`Reduces length of instruction`Requires some extra work`Requires some extra workTemporary storage to hold some results

Number of Addresses (c)Number of Addresses (c)

a1 address`Implicit second address`Usually a register (accumulator)`Common on early machines

Number of Addresses (d)Number of Addresses (d)

a0 (zero) addresses`All addresses implicit`Uses a stack`e.g. push a` push b` push b` add` pop c` pop c

`c = a + b

How Many AddressesHow Many Addresses

aMore addresses`More complex (powerful?) instructions`More registersInter-register operations are quicker

`Fewer instructions per program`Fewer instructions per programaFewer addresses`Less complex (powerful?) instructions`Less complex (powerful?) instructions`More instructions per program`Faster fetch/execution of instructions

Design Decisions (1)Design Decisions (1)

aOperation repertoire`How many ops?`What can they do?`How complex are they?

aData t pesaData typesaInstruction formats`L th f d fi ld`Length of op code field`Number of addresses

Design Decisions (2)Design Decisions (2)

aRegisters`Number of CPU registers available`Which operations can be performed on which

registers?

aAddressing modes (later )aAddressing modes (later)

aRISC v CISCaRISC v CISC

Types of OperandTypes of Operand

aAddressesaNumbers`Integer/floating point

aCharacters`ASCII etc.

aLogical Data`Bits or flags

a (Aside: Is there any difference between numbers and characters? Ask a C programmer!)p g )

Pentium Data TypesPentium Data Types

a8 bit Bytea16 bit worda32 bit double worda64 bit quad wordaAddressing is by 8 bit unitaA 32 bit double word is read at addresses

divisible by 4

Specific Data TypesSpecific Data Types

a General - arbitrary binary contentsa Integer - single binary valuea O di l i d i ta Ordinal - unsigned integera Unpacked BCD - One digit per bytea Packed BCD - 2 BCD digits per bytea Packed BCD 2 BCD digits per bytea Near Pointer - 32 bit offset within segmenta Bit fielda Byte Stringa Floating Point

Pentium Floating Point Data TypesTypes

aSee Stallings p324

Types of OperationTypes of Operation

aData TransferaArithmeticaLogicalaConversionaI/OaSystem ControlyaTransfer of Control

Data TransferData Transfer

aSpecify`Source`Destination`Amount of data

aMa be diffe ent inst ctions fo diffe entaMay be different instructions for different movements`e g IBM 370`e.g. IBM 370

aOr one instruction and different addresses`e g VAX`e.g. VAX

ArithmeticArithmetic

aAdd, Subtract, Multiply, DivideaSigned IntegeraFloating point ?aMay include`Increment (a++)`Decrement (a--)`Negate (-a)

LogicalLogical

aBitwise operationsaAND, OR, NOT

ConversionConversion

aE.g. Binary to Decimal

Input/OutputInput/Output

aMay be specific instructionsaMay be done using data movement instructions

(memory mapped)aMay be done by a separate controller (DMA)

Systems ControlSystems Control

aPrivileged instructionsaCPU needs to be in specific state `Ring 0 on 80386+`Kernel mode

aFor operating systems use

Transfer of ControlTransfer of Control

aBranch`e.g. branch to x if result is zero

aSkip`e.g. increment and skip if zero`ISZ R i t 1`ISZ Register1`Branch xxxx`ADD A`ADD A

aSubroutine call`c f interrupt call`c.f. interrupt call

Foreground ReadingForeground Reading

aPentium and PowerPC operation typesaStallings p338 et. Seq.

Byte Order(A portion of chips?)(A portion of chips?)

aWhat order do we read numbers that occupy more than one byteae.g. (numbers in hex to make it easy to read)a12345678 can be stored in 4x8bit locations as

f llfollowsa

Byte Order (example)Byte Order (example)

aAddress Value (1) Value(2)a184 12 78a185 34 56a186 56 34a186 78 12

a i.e. read top down or bottom up?

Byte Order NamesByte Order Names

aThe problem is called EndianaThe system on the left has the least significant

byte in the lowest addressaThis is called big-endianaThe system on the right has the least

significant byte in the highest addressaThis is called little-endian

Standard What Standard?StandardWhat Standard?

aPentium (80x86), VAX are little-endianaIBM 370, Moterola 680x0 (Mac), and most RISC

are big-endianaInternet is big-endian`Makes writing Internet programs on PC more

awkward!`WinSock provides htoi and itoh (Host to Internet &`WinSock provides htoi and itoh (Host to Internet &

Internet to Host) functions to convert