Faculty of Computer Science © 2006 CMPUT 229 Addressing Modes Where to load from/store to

Faculty of Computer Science

CMPUT 229 © 2006

Addressing Modes

Where to load from/store to

© 2006

Department of Computing Science

CMPUT 229

Immediate and Absolute Addressing

Immediate Addressing

• The value of the operand is contained in the instruction itself:

MOVE #1234, D0 [D0] 1234

ADD #1234, D0 [D0] [D0] + 1234

• Used to handle constants

– Value must be known when the program is written

Absolute Addressing

• The address that contain the operand is part of the instruction

MOVE 1234, D0 [D0] [1234]

ADD 1234, D0 [D0] [D0] + [1234]

• Slower than immediate addressing (requires an additional memory access)

• Value can change after the program is written

Clements, pp. 249

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CMPUT 229

Address-Register Indirect Addressing

– The location of the value is in a pointer stored in an

address register:

ADD.B (A0), D0 [D0] [D0] + [[A0]]

Clements, pp. 252

COPYRIGHT 2006 OXFORD UNIVERSITY PRESS ALL RIGHTS RESERVED

© 2006


CMPUT 229

Address-Register Indirect Addressing with Displacement– A constant is added to the value in an address register to

determine the memory location of the operand.

MOVE 4(A0), D0 [D0] [[A0]+4]

Clements, pp. 252


© 2006


CMPUT 229

Postincrementing and Predecrementing

Automatically increments/decrements the address

register

MOVE.B (A0)+, D0 [D0] [[A0]];

[A0] [A0]+1

MOVE.W -(A2), (A3)+ [A2] [A2]-2;

[[A3]] [[A2]];

[A3] [A3]+2

Clements, pp. 253


© 2006


CMPUT 229

Postincrementing and Predecrementing

Clements, pp. 253


© 2006


CMPUT 229

Indexed Addressing

The address is given by two registers and a

constant displacement

MOVE.b Offset(A0, D0), D1 [D1] [[A0]+[D0]+Offset]

Clements, pp. 258


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CMPUT 229

Indexed addressing (example)

PROBLEM: DIARY is a data structure divided into

weeks and days. The week is in D0 and the position

of a day within a week is given by a constant. Write

a program that accesses the entry for Tuesday of a

given week.

– The address of this location is given by

EntryAddress = DIARY + (WEEK-1)7+TUESDAY

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CMPUT 229

Indexed addressing (example solution)

SUNDAY EQU 0

MONDAY EQU 1

TUESDAY EQU 2

WEDNESDAY EQU 3

…..

LEA DIARY, A0 A0 points to the begin of the data structure

MOVE.L WEEK, D0 D0 contains the week number

SUB.L #1, D0 D0 WEEK - 1

MULU #7, D0 D0 (WEEK - 1) 7

MOVE.B TUESDAY(A0,D0), D1 Access the required entry

EntryAddress = DIARY + (WEEK-1)7+TUESDAY

Clements, pp. 259

© 2006


CMPUT 229

Relative Address

Same as the indirect addressing, but the register

used in the Program Counter (PC).

– Makes possible to relocate programs without changing

absolute addresses

MOVE d16(PC), D0 [D0] [[PC] + d16]

Clements, pp. 259

© 2006


CMPUT 229

Relative Address

Clements, pp. 259


© 2006


CMPUT 229

Relative Branching

The target address of most branches are also

expressed relative to the current value of the PC

© 2006


CMPUT 229

Outer Product

Given two vectors, the outer product of these two

vectors is defined as follows

© 2006


CMPUT 229

Exercise #2

Write a code whose inputs are in memory at the following addresses:

• $8000: word containing the length of vector u;

• $8002: long word with the address of the first position of u;

• $8006: word containing the length of vector v;

• $8008: long word with the address of the first position of v;

• $800C: long word with the address of the first position of matrix A;

The program has to compute the values in matrix A, where A is the outer product of u and v:

– A = u v

– A must be stored on a row-first order.

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CMPUT 229

Flow-Graph Sketch Addresses/Sizes Initialization

i 0 counter for vector u

i = size of u?

j 0 counter for vector v

j = size of v?

A(i,j) = u(i)v(j)

j = j+1

i = i+1 yes

no

no

Done yes

A = u v

© 2006


CMPUT 229

RTL Sketch

A0 L #$8000

D1 W (A0)+ length of vector u

A1 L (A0)+ address of vector u

D2 W (A0)+ length of vector v

A2 L (A0)+ address of vector v

A3 L (A0) address of matrix A

Write a code whose inputs are in memory at the following addresses:

• $8000: word containing the length of vector u;

• $8002: long word with the address of the first position of u;

• $8006: word containing the length of vector v;

• $8008: long word with the address of the first position of v;

• $800C: long word with the address of the first position of matrix A;

Address/Size Initialization

© 2006


CMPUT 229

Flow-Graph Sketch

D3 W 0 counter for vector u

LoopU CMP D3,D1

BEQ Done

D4 W 0 counter for vector v

LoopV CMP D4,D2

BEQ nextU

<loop body>

D4 W D4+1 j j+1

BRA LoopV

nextU D3 W D3+1 i i+1

BRA LoopU

Done

A0 L #$8000







Addresses/Sizes Initialization


i = size of u?


j = size of v?

A(i,j) = u(i)v(j)

j = j+1

i = i+1 yes

no

no

yesDone

© 2006


CMPUT 229

Flow-Graph Sketch


LoopU CMP D3,D1

BEQ Done


LoopV CMP D4,D2

BEQ nextU

<loop body>

D4 W D4+1 j j+1

BRA LoopV


BRA LoopU

Done

A0 L #$8000









i = size of u?


j = size of v?

A(i,j) = u(i)v(j)

j = j+1

i = i+1 yes

no

no

yesDone

© 2006


CMPUT 229

Flow-Graph Sketch


LoopU CMP D3,D1

BEQ Done


LoopV CMP D4,D2

BEQ nextU

<loop body>

D4 W D4+1 j j+1

BRA LoopV


BRA LoopU

Done

A0 L #$8000









i = size of u?


j = size of v?

A(i,j) = u(i)v(j)

j = j+1

i = i+1 yes

no

no

yesDone

© 2006


CMPUT 229

Flow-Graph Sketch


LoopU CMP D3,D1

BEQ Done


LoopV CMP D4,D2

BEQ nextU

<loop body>

D4 W D4+1 j j+1

BRA LoopV


BRA LoopU

Done

A0 L #$8000









i = size of u?


j = size of v?

A(i,j) = u(i)v(j)

j = j+1

i = i+1 yes

no

no

yesDone

© 2006


CMPUT 229

Flow-Graph Sketch


LoopU CMP D3,D1

BEQ Done


LoopV CMP D4,D2

BEQ nextU

<loop body>

D4 W D4+1 j j+1

BRA LoopV


BRA LoopU

Done

A0 L #$8000









i = size of u?


j = size of v?

A(i,j) = u(i)v(j)

j = j+1

i = i+1 yes

no

no

yesDone

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