William Stallings Computer Organization and Architecture6th Edition

Chapter 11Instruction Sets:Addressing Modesand Formats

Addressing Modes

Teknik Teknik Pengalamatan (Addressing) :

• Immediate• Direct• Indirect• Register• Register Indirect• Displacement (Indexed) • Stack

Immediate Addressing

• Operand is part of instruction• Operand = address field• Address field atau operand berisi Nilai

Konstan• e.g. ADD 5

—Add 5 to contents of accumulator—5 is operand

• No memory reference to fetch data• Fast• Limited range

Immediate Addressing Diagram

OperandOpcode

Instruction

Direct Addressing

• Address field contains address of operand• EA (Effective Address) adalah alamat

aktual dari lokasi yang berisi operand • Effective address (EA) = address A• e.g. ADD A

—Add contents of cell A to accumulator—Look in memory at address A for operand

• Single memory reference to access data• Tidak ada kalkulasi tambahan selain

effective address• Limited address space

Direct Addressing Diagram

Address AOpcode

Instruction

Memory

Operand

Indirect Addressing (1)

• Pengalamatan tidak langsung• address field berisi alamat dari alamat

operand• EA = (A)

—Look in A, find address (A) and look there for operand

• e.g. ADD (A)—Add contents of cell pointed to by contents of

A to accumulator

Indirect Addressing (2)

• Large address space • May be nested, multilevel, cascaded

—e.g. EA = (((A)))

• Multiple memory accesses to find operand• slower

Indirect Addressing Diagram

Address AOpcode

Instruction

Memory

Operand

Pointer to operand

Register Addressing (1)

• Operand is held in register• EA = R• Limited number of registers• Very small address field needed (Nama

register punya kode sendiri)—Shorter instructions—Faster instruction fetch

Register Addressing (2)

• No memory access• Very fast execution• Very limited address space• Multiple registers helps performance

—Requires good assembly programming or compiler writing

—N.B. C programming – register int a;

• Hampir sama dgn Direct addressing

Register Addressing Diagram

Register Address ROpcode

Instruction

Registers

Operand

Register Indirect Addressing

• Hampir sama dengan indirect addressing• EA = (R)• Operand is in memory cell pointed to by

contents of register R• Large address space• fewer memory access than indirect

addressing

Register Indirect Addressing Diagram

Register Address ROpcode

Instruction

Memory

OperandPointer to Operand

Registers

Displacement Addressing

• EA = A + (R)• Address field hold two values

—A = base value—R = register that holds displacement—or vice versa

Displacement Addressing Diagram

Register ROpcode

Instruction

Memory

OperandPointer to Operand

Registers

Address A

+

Relative Addressing

• A version of displacement addressing• Dimana register R = Program counter, PC• EA = A + (PC)• i.e. get operand from A cells from current

location pointed to by PC• c.f locality of reference & cache usage

Base-Register Addressing

• Khusus di 80x86• A version of displacement addressing• A holds displacement• R holds pointer to base address• R may be explicit or implicit

Indexed Addressing

• A version of displacement addressing• A = base• R = displacement• EA = A + R• Good for accessing arrays

—EA = A + R—R++

Stack Addressing

• Operand is (implicitly) on top of stack• e.g.

—ADD Pop top two items from stackand add

Indexing

• Autoindexing— EA = A + (R)

(R) = (R) + 1

• Post Indexing: Indexing dilakukan setelah Indirection— EA = (A) + (R)

• PreIndexing : Indexing dilakukan sebelum Indirection—EA = (A + (R))

Pre-index addressing

LDR R0, [R1, #4] @ R0=mem[R1+4]

@ R1 unchanged

R0

R1 +

LDR R0, [R1, ]

Auto-indexing addressing

LDR R0, [R1, #4]! @ R0=mem[R1+4]

@ R1=R1+4

LDR R0, [R1, ]!

R0

R1 +

No extra time; Fast;

Post-index addressing

LDR R0, R1, #4 @ R0=mem[R1]

@ R1=R1+4

R0R1

+

LDR R0,[R1],

Example

Example

Example

Pentium Addressing Modes

• Virtual or effective address is offset into segment—Starting address plus offset gives linear address—This goes through page translation if paging enabled

• Pentium Addressing Mode— Immediate Operand = A—Register operand LA=R—Displacement LA=(SR)+A—Base LA=(SR)+(B)—Base with displacement LA=(SR)+(B)+A—Scaled index with displacement LA=(SR)+(I)xS

+ A—Base with index and displacement LA=(SR)+(B)+

(I)+A—Base scaled index with displacement LA=(SR)+(I)xS+

(B)+A—Relative LA=(PC)+A

• LA =Linear Address• (X) = Content of X• SR = segment register• PC=Program Counter• A =Content of an address field in the

instruction• R=Register• B= Base Register• I = Index Register• S = Scaling Factor

Pentium Addressing Mode Calculation

• Scaling factor 2 : Array /Data 16-bit integer

• Scaling factor 4 : Array / Data 32-bit integer atau floating point number (single precision)

• Scaling factor 8 : Array / Data double precision floating point

PowerPC Addressing Modes• PowerPC => RISC• RISC pengalamatannya lebih sederhana dari CISC• Mode Algorithm

Load/Store AlgorithmIndirect EA = (BR) + DIndirect Indexed EA = (BR) + (IR)

Branch AddressingAbsolute EA = IRelative EA = (PC) + IIndirect EA = (L / CR)

Fixed Point Computation

Register EA = GPRImmediate Operand = I

Floating PointRegister EA = FPR

PowerPC Addressing Modes

• EA = Effective Address• (X) = Content of X• BR = Base Register• IR = Index Register• L/CR = Link or Count Register• GPR = General Purpose register• FPR = Floating Point Register• D = Displacement• I = Immediate Value• PC = Program Counter

PowerPC Memory Operand Addressing Modes

Instruction Formats

• Format Instruksi mendefinisikan :— Layout of bits in an instruction— Includes opcode (Harus ada OpCode)— Includes (implicit or explicit) operand(s)— Usually more than one instruction format in

an instruction set

Instruction Length

• Panjang Instruksi mempengaruhi :— Memory size (Kapasitas memori)— Memory organization— Bus structure— CPU complexity— CPU speed

• Trade off between powerful instruction and saving space

• Programmer menginginkan lebih banyak:— Opcode— Operand— Addressing mode

Allocation of Bits

• Faktor-faktor yang menentukan penggunaan addressing bit:— Number of addressing modes— Number of operands— Register versus memory— Number of register sets— Address range— Address granularity (alamat mengacu byte,

word, dll)

PDP-8 Instruction Format

PDP-10 Instruction Format

PDP-11 Instruction Format

VAX Instruction Examples

Pentium Instruction Format

PowerPC Instruction Formats (1)

PowerPC Instruction Formats (2)