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8.3 Stack Organization. Stac k: A storage device that stores information in such a manner that the item stored last is the first item retrieved. Also called last-in first-out (LIFO) lis t. Useful for compound arithmetic operations and nested subroutine calls. 8.3 Stack Organization.

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8 3 stack organization
8.3 Stack Organization
  • Stack: A storage device that stores information in such a manner that the item stored last is the first item retrieved.
  • Also called last-in first-out (LIFO) list. Useful for compound arithmetic operations and nested subroutine calls.
8 3 stack organization2
8.3 Stack Organization
  • • Stack pointer (SP): A register that holds the address of the top item in the stack.SP always points at the top item in the stack
  • • Push: Operation to insert an item into the stack.• Pop: Operation to retrieve an item from the stack.
register stack
REGISTER STACK

• A stack can be organized as a collection of a finite number of registers.

slide4

• In a 64-word stack, the stack pointer contains 6 bits.• The one-bit register FULL is set to 1 when the stack is full; EMPTY register is 1 when the stack is empty.• The data register DR holds the data to be written into or read from the stack.

REGISTER STACK

the following are the micro operations associated with the stack
The following are the micro-operations associated with the stack

InitializationSP ¬ 0, EMPTY ¬ 1, FULL ¬ 0Push

SP ¬ SP + 1M[SP] ¬ DRIf (SP = 0) then (FULL ¬ 1) Note that SP becomes 0 after 63EMPTY ¬ 0

dr m sp sp sp 1 if sp 0 then empty 1 full 0
DR ¬ M[SP]SP ¬ SP - 1If (SP = 0) then (EMPTY ¬ 1)FULL ¬ 0

The following are the micro-operations associated with the stack

Pop

stack operations reverse polish notation postfix
STACK OPERATIONSREVERSE POLISH NOTATION (postfix)
  • Reverse polish notation :is a postfix notation (places operators after operands)
  • (Example) Infix notation A + BReverse Polish notation AB+ also called postfix.
stack operations reverse polish notation postfix8
STACK OPERATIONSREVERSE POLISH NOTATION (postfix)
  • A stack organization is very effective for evaluating arithmetic expressions
  • A * B + C * D (AB *)+(CD *) AB * CD * +
  • ( 3 * 4 ) + ( 5 * 6 )  34 * 56 * +
stack operations reverse polish notation postfix9
STACK OPERATIONSREVERSE POLISH NOTATION (postfix)
  • • Evaluation procedure:
  • 1. Scan the expression from left to right.2. When an operator is reached, perform the operation with the two operands found on the left side of the operator.3. Replace the two operands and the operator by the result obtained from the operation.
  • (Example) infix 3 * 4 + 5 * 6= 42 postfix 3 4 * 5 6 * +
  • 12 5 6 * +12 30 +42
stack operations reverse polish notation postfix10
STACK OPERATIONSREVERSE POLISH NOTATION (postfix)
  • • Reverse Polish notation evaluation with a stack. Stack is the most efficient way for evaluating arithmetic expressions.

stack evaluation:Get valueIf value is data: push dataElse if value is operation: pop, pop evaluate and push.

stack operations reverse polish notation postfix11
STACK OPERATIONSREVERSE POLISH NOTATION (postfix)
  • (Example) using stacks to do this.3 * 4 + 5 * 6 = 42

=> 3 4 * 5 6 * +

8 4 instruction formats
8.4 Instruction Formats
  • • The most common fields in instruction formats are:
  • Mode field: Specifies the way the effective address is determined
  • Operation code: Specifies the operations to be performed.
  • Address field: Designates a memory address or a processor register

Mode

Opcode

Address

8 4 instruction formats13
8.4 Instruction Formats

• Zero address instruction: Stack is used. Arithmetic operation pops two operands from the stack and pushes the result.

• One address instructions: AC and memory. Since the accumulator always provides one operand, only one memory address needs to be specified.

•Two address instructions: Two address registers or two memory locations are specified, one for the final result.

•Three address instructions: Three address registers or memory locations are specified, one for the final result. It is also called general address organization.

zero address instructions
Zero address instructions

Instruction: ADD

Push and pop operations need to specify one address involved in data transfer.

Stack-organized computer does not use an address field for the instructions ADD, and MUL

Instruction: POP XEvaluate X = ( A + B ) * ( C + D )

PUSH, and POP instructions need an address field to specify the operand

zero address instructions15
Zero address instructions

PUSH A

PUSH B

ADD

PUSH C

PUSH D

ADD

MUL

POP X

Advantages: No memory addresses needed during the operation.Disadvantages: results in longer program codes.

one address instructions
One address instructions
  • One address can be a register name or memory address.
  • SINGLE ACCUMULATOR ORGANIZATION
  • Since the accumulator always provides one operands, only one memory address needs to be specified.Instruction: ADD XMicrooperation: AC ¬ AC + M[X]
one address instructions17
One address instructions

LOAD A

ADD B

STORE T

All operations are done between the AC register and memory operand

Advantages: fewer bits are needed to specify the address.Disadvantages: results in writing long programs.

two address instructions
Two address instructions
  • • Assumes that the destination address is the same as that of the first operand. Can be a memory address or a register name.
  • Instruction: ADD R1, R2Microoperation: R1  R1 + R2
two address instructions19
Two address instructions

MOV R1, A

MOV R2, B

ADD R1, R2

MOV X, R1

  • most common in commercial computers
  • Each address fields specify either a processor register or a memory operand

Advantages: results in writing medium size programsDisadvantages: more bits are needed to specify two addresses.

three address organization
Three address organization
  • GENERAL REGISTER ORGANIZATION

• Three address instructions: Memory addresses for the two operands and one destination need to be specified.Instruction: ADD R1, R2, R3Microoperation: R1  R2 + R3

  • Advantages: results in writing short programsDisadvantages: more bits are needed to specify three addresses.

ADD R1, R2, R3

slide21

EXAMPLE: Show how can the following operation be performed using:a- three address instructionb- two address instructionc- one address instructiond- zero address instructionX = (A + B) * (C + D)

a three address instructions general register organization
a-Three-address instructions (general register organization)

ADD R1, A, B

R1  M[A] + M[B]

ADD R2, C, D

R2  M[C] + M[D]

MUL X, R1, R2

M[X]  R1 * R2

b two address instructions general register organization
b-Two-address instructions (general register organization)

MOV R1, A

R1  M[A]

ADD R1, B

R1  R1 + M[B]

MOV R2, C

R2  M[C]

ADD R2, D

R2  R2 + M[D]

MOV X, R2

M[X] R2

MUL X, R1

M[X]  R1 * M[X]

c one address instructions
c- One-address instructions

LOAD A

AC M[A]

ADD B

AC  AC + M[B]

STORE T

M[T ] AC

LOAD C

AC  M[C]

ADD D

AC  AC + M[D]

MUL T

AC  AC * M[T ]

STORE X

M[X]  AC Store

d zero address instructions stack organization
d- Zero-address instructions (stack organization)

Push value

Else If operator is encountered: Pop, pop, operation, push

Pop operand pop another operand then perform an operation and push the result back into the stack.

PUSH A TOS  A Push

PUSH B TOS  B

ADD TOS  (A+B)

PUSH C TOS  C

PUSH D TOS  D

ADD TOS  (C+D)

MUL TOS  (C+D)*(A+B)

POP X M[X]  TOS

(*TOS stands for top of stack).

Pop, pop, operation, push