computer architecture 計算機結構 1 chapter 11 instruction sets: addressing modes and formats...

Computer Architecture 計算機結構

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Chapter 11Instruction Sets:

Addressing Modesand Formats

Ren-Jie Wang 王仁傑 , Ph.D. [email protected]

資訊館 7F 辦公室上課時間 : 星期三 13:25—16:10


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Addressing Modes 定址模式 Immediate Addressing 立即定址 Direct Addressing 直接定址 Indirect Addressing 間接定址 Register Addressing 暫存器定址 Register Indirect Addressing 暫存間接器定址 Displacement Addressing 位移定址

Relative Addressing 相對定址 Base-Register Addressing 基底暫存器定址 Indexed Addressing 索引定址

Stack Addressing 堆疊定址


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Immediate Addressing

Operand is part of instruction

Operand = address field

e.g. ADD 5 Add 5 to contents of accumulator ( AC←AC ＋ 5 )

5 is operand

No memory reference to fetch data

Fast

Limited range （ why? ）


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Immediate Addressing Diagram

OperandOpcode

Instruction

運算碼( 指令 )

運算元( 資料 )


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Direct Addressing

Address field contains address of operand

Effective address （有效位址） EA = address field A

e.g. ADD A Add contents of cell A to accumulator ( AC←AC ＋ A )

Look in memory at address A for operand

Single memory reference to access data

No additional calculations to work out effective

address

Limited address space （ why? ）


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Direct Addressing Diagram

Address AOpcode

Instruction

Memory

Operand

AADD


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Indirect Addressing (1)

Memory cell pointed to by address field

contains the address of (pointer to) the

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

(A) : Content of location A or register A


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Indirect Addressing (2)

Large address space

2N where N = word length

May be nested, multilevel, cascaded e.g. EA = (((A)))

Draw the diagram yourself

Multiple memory accesses to find operand

Hence slower


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Indirect Addressing Diagram

Address AOpcode

Instruction

Memory

Operand

Pointer to operand

(A)ADD


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Indirect Addressing Diagram

Address AOpcode

Instruction

Memory

Operand

Pointer to operand

((A))ADD

Pointer to operand


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Register Addressing (1)

Operand is held in register named in

address filed

EA = R

Limited number of registers

Very small address field needed Shorter instructions

Faster instruction fetch


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Register Addressing (2)

No memory access

Very fast execution

Very limited address space

Multiple registers helps performance Requires good assembly programming or

compiler writing

C programming register int a;

c.f. Direct addressing


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Register Addressing Diagram

Register Address ROpcode

Instruction

Registers

Operand


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Register Indirect Addressing

C.f. indirect addressing

EA = (R)

Operand is in memory cell pointed to by

contents of register R

Large address space (2N)

One fewer memory access than indirect

addressing


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Register Indirect Addressing Diagram

Register Address ROpcode

Instruction

Memory

OperandPointer to Operand

Registers

(R)ADD


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Displacement Addressing

EA = A + (R)

Address field hold two values A = base value 基底 R = register that holds displacement 位移 or vice versa 反之亦然


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Displacement Addressing Diagram

Register ROpcode

Instruction

Memory

OperandPointer to Operand

Registers

Address A

+


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Relative Addressing

A version of displacement addressing

R = Program counter, PC

EA = A + (PC) PC-relative

i.e. get operand from A cells from current

location pointed to by PC

c.f locality of reference & cache usage


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Relative Addressing

Address AOpcode

Instruction

Memory

Operand+

PC

Pointer to Operand


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Base-Register Addressing

A holds displacement

R holds pointer to base address

R may be explicit or implicit 外顯或隱含 e.g. segment registers in 80x86


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Indexed Addressing

A = base

R = displacement

EA = A + (R)

Good for accessing arrays EA = A + (R)

(R) = (R) +1


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Combinations

Pre-index 前索引定址模式 ( 先更新索引 , 再存取資料 ) 基底暫存器 A 的值與偏移量先做加減運算當索引位址 , 來存取資料然後基底暫存器的值再更新成新的位址 EA = (A+(R))

ARM 指令 : LDR R0, [R1, #4]! ;R0:=[R1+4],

R1:=R1+4

Post-index 後索引定址模式 ( 先存取資料 , 後更新索引 ) 基底暫存器的值會先用來當所要存取的記憶體位址存取資料後，基底暫存器的值再更新成新的位址 EA = (A) + (R)

ARM 指令 : LDR R0, [R1], #4 ;R0:=[R1], R1:=R1+4


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Pre-index: EA = (A+(R))

Register ROpcode

Instruction

Memory

Operand

Displacement

Registers

Address A

+

Base

Pointer to Operand


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Register ROpcode

Instruction

Memory

OperandDisplacement

Registers

Address A

+

Post-index: EA = (A) + (R)

Base


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Stack Addressing

Operand is (implicitly) on top of stack

e.g. ADD Pop top two items from stack

and add

Textbook p. 398, problems #11.13


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IA-32 (Pentium 4) RegistersIA-32 (Pentium 4) Registershttp://www.intel.com/design/processor/manuals/253665.pdf

Streaming SIMD Extensions MMX: SIMD instruction set


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purposes in different


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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

12 addressing modes available Immediate

Register operand

Displacement

Base

Base with displacement

Scaled index with displacement

Base with index and displacement

Base scaled index with displacement

Relative


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Pentium Addressing Mode Calculation


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Pentium Instruction Format


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In-class exercise

Given the following memory values and a one-address machine with an accumulator, what values do the following instructions load into the accumulator? （ Textbook p. 397, problems #11.1 ） Word 20 contains 40 Word 30 contains 50 Word 40 contains 60 Word 50 contains 70

a. LOAD IMMEDIATE 20

b. LOAD DIRECT 20

c. LOAD INDIRECT 20

d. LOAD IMMEDIATE 30

e. LOAD DIRECT 30

f. LOAD INDIRECT 30

20 40

30 50

40 60

50 70

60

70


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In-class exercise

Assume a stack-oriented processor that includes the stack operations PUSH and POP. Arithmetic operations automatically involve the top one or two stack elements. Begin with an empty stack. What stack elements remain after the following instructions are executed? （ Textbook p. 398, problems #11.13 ） PUSH 4 PUSH 7 PUSH 8 ADD PUSH 10 SUB MUL

computer architecture 計算機結構 1 chapter 11 instruction sets: addressing modes and formats...

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