Instruction Sets:

Characteristics and Functions

Zhao Fang

Computer Organization & Architecture

-for the college students

Goal for Today

◼ Machine Instruction Characteristics

◼ Types of Operands(运算对象)

◼ Types of Operations

◼ Examples

Programming language

◼ Classification of programming language:

❑ Machine language

❑ Assembly language

❑ High-level language

◼ Compiler

❑ Translation program that converts high-

level/assembly language programs into machine

language

Machine Language and Assembly

Language

◼ Machine language

❑ Defined by the computer’s hardware design

❑ Consists of streams of numbers (1s and 0s) that

instruct computers how to perform elementary

operations

❑ A computer can understand only its own machine

language

Machine Language and Assembly

Language

◼ Assembly language

❑ Represents machine-language instructions using

English-like abbreviations(缩略语)

❑ Assemblers convert assembly language to

machine language

What is an Instruction Set?

◼ The complete collection of instructions that

are understood by a CPU

◼ Machine Code

◼ Binary

◼ Usually represented by assembly codes

Instruction set

Software, compiler

hardware

Instruction Cycle State Diagram

Elements of an Instruction

◼ Operation code (Op code)

❑ Do this

◼ Source Operand reference

❑ From this

◼ Result Operand reference

❑ Put the answer here

◼ Next Instruction Reference

❑ When you have done that, do this...

Instruction Representation

◼ A simple instruction format

Source and result operands can be in one of the following areas:

Memory, CPU registers, Immediate, I/O devices

Instruction Representation

◼ In machine code each instruction has a

unique bit pattern

◼ For human consumption (well, programmers

anyway) a symbolic representation is used

❑ e.g. ADD, SUB, LOAD

◼ Operands can also be represented in this

way

❑ ADD A,B

Instruction Types

◼ The instructions can be categorized into four

types:

❑ Data processing: arithmetic and logic instructions

❑ Data storage: memory instructions

❑ Data movement: I/O instructions

❑ Control: test and branch instructions

Instruction Types

◼ Arithmetic instructions

◼ Logic (Boolean) instructions

◼ Memory instructions: moving data between memory and the registers.

◼ I/O instructions

◼ Test instructions: used to test the value of a data word or the status of a computation.

◼ Branch instructions: used to branch to a different set of instructions.

Number of Addresses (a)

◼ 3 addresses

❑ Operand 1, Operand 2, Result

❑ a = b + c;

❑ May be a forth - next instruction (usually implicit)

❑ Not common

❑ Needs very long words to hold everything

Number of Addresses (b)

◼ 2 addresses

❑ One address doubles as operand and result

❑ a = a + b

❑ Reduces length of instruction

❑ Requires some extra work

◼ Temporary storage to hold some results

Number of Addresses (c)

◼ 1 address

❑ Implicit second address

❑ Usually a register (accumulator累加器)

❑ Common on early machines

◼ LOAD A ;AC ← A

◼ SUB B ;AC ← AC – B

◼ STORE Y ;Y ← AC

Number of Addresses (d)

◼ 0 (zero) addresses: All addresses implicit

❑ Usually use stack to imply the operands

◼ e.g. push a

◼ push b

◼ add

◼ pop c

◼ c = a + b

How Many Addresses

◼ More addresses

❑ More complex (powerful?) instructions

❑ More registers

◼ Inter-register operations are quicker

❑ Fewer instructions per program

◼ Fewer addresses

❑ Less complex (powerful?) instructions

❑ More instructions per program

❑ Faster fetch/execution of instructions

Instruction set design

◼ The most important of the fundamental design issues include the following:

❑ Operation repertoire: how many and which operations to provides, and how complex operations should be

❑ Data types: the operands types

❑ Instruction format: instruction length, number of addresses…

❑ Registers: how many registers can be used by the instructions

❑ Addressing: how to access a memory location, how many modes can be used

Design Decisions (1)

◼ Operation repertoire(计算机指令系统)

❑ How many ops?

❑ What can they do?

❑ How complex are they?

◼ Data types

◼ Instruction formats

❑ Length of op code field

❑ Number of addresses

Design Decisions (2)

◼ Registers

❑ Number of CPU registers available

❑ Which operations can be performed on which

registers?

◼ Addressing modes (later…)

◼ RISC v CISC

Types of Operand(操作数)

◼ Addresses

◼ Numbers

❑ Integer/floating point

◼ Characters

❑ ASCII etc.

◼ Logical Data

❑ Bits or flags

Numbers

◼ Three types of numerical data are common in

computers:

❑ Binary integer or binary fixed point

❑ Binary floating point

❑ Decimal

◼ Packed decimal

Little-, Big-, Bi- Endian

◼ The byte ordering:

❑ The memory unit: byte

❑ The data type: 8 bits, 16 bits, 32 bits …

❑ How are these data stored in memory?

◼ There are two ways to store the values

❑ Big endian: the most significant byte is stored in

the lowest byte address(从左到右序，西方书写模式)

❑ Little endian: the least significant byte is stored in

the lowest byte address(从右到左序，算数顺序)

Little-, Big-, Bi- Endian

◼ Suppose we want to store a 32-bit hex value

12345678 to address 184

Address Value

184 12

185 34

186 56

187 78

Address Value

184 78

185 56

186 34

187 12

Big endian Little endian

Characters

◼ A common form of data is text or character strings.

◼ The earliest common example:

❑ Morse code(摩斯码)

◼ The most commonly used:

❑ International Reference Alphabet (IRA)

◼ United States as the American Standard Code for

Information Interchange (ASCII)

◼ Extended Binary Coded Decimal Interchange Code

(EBCDIC)

❑ Used on IBM mainframes

Logical Data

◼ Boolean or binary data items

❑ Each item can take on only the values 1 (true) and

0 (false)

◼ There are occasions when we wish to

manipulate the bits of a data item

Example

Types of Operation

◼ Data Transfer

◼ Arithmetic

◼ Logical

◼ Conversion

◼ I/O

◼ System Control

◼ Transfer of Control

Data Transfer

◼ Location of source and destination must be

specified:

❑ Memory

❑ Register

❑ Top of the stack

◼ For the memory access, addressing mode

must be specified – the memory address

format

◼ The length of the operands must be specified

Common Data Transfer Instructions

Arithmetic

◼ Add, subtract, multiply, divide, absolute, negate,

increment, decrement

◼ The operands are

❑ Signed integer (fixed point) numbers

❑ Floating-point numbers

❑ Packed decimal numbers

◼ CPU actions:

Logical

◼ Bitwise operations

◼ AND, OR, NOT

Shift and Rotate(旋转) Operations

Conversion

◼ E.g. Binary to Decimal

Input/Output

◼ May be specific instructions

◼ May be done using data movement instructions

(memory mapped)

◼ May be done by a separate controller (DMA)

Systems Control

◼ Privileged instructions(特权指令)

◼ CPU needs to be in specific state

❑ Kernel mode

◼ For operating systems use

◼ Examples:

❑ Read or write a control register

❑ Read or write a storage protection key

❑ Access to process control blocks in a

multiprogramming system

Transfer of Control

Branch Instructions

◼ Also called jump instructions

◼ The operands involve the address of the next

instruction to be executed

◼ For conditional branch instructions, the

branch is made only if a certain condition is

met

❑ Otherwise, executes next instruction in sequence

◼ Usually the condition is taken as a result of

an operation (arithmetic or logic)

Branch Instruction

Skip Instructions

◼ The skip instruction includes an implied address

◼ The skip implies that one instruction be skipped

❑ The implied address equals the address of the next

instruction plus one instruction-length

301

…

309 ISZ R1

310 BR 301

311 …

ISZ: increment and skip if zero

Procedure Call Instructions

◼ A procedure is a subroutine

◼ It is invoked by a calling instruction and returned by a return instruction

❑ A procedure call can appear in a procedure – nested

❑ Each procedure call is matched by a return in the called program

◼ The CPU must save the returning address in one of the following

❑ Register

❑ Start of called procedure

❑ Top of stack

Nested Procedure Calls

The Use of Stacks

Stack Frame Growth

Passing Parameters

◼ Pass parameters is important to the

procedure call.

◼ Using registers :

❑ Must assure that the registers are used properly

◼ Using memory cells:

❑ It is difficult to exchange the variables

Passing Parameters

◼ Using stack is more flexible: when a

procedure is called

❑ Stack the return address

❑ Stack parameters to be passed to the called

procedure

❑ When return, the return parameters can also be

placed on the stack

◼ All above stacked info for the procedure is

called a stack frame.

Stack Operation

◼ A stack is an ordered set of elements, only one

of which can be accessed at a time.

◼ The point of access is called the top of the stack

◼ It is a last in first out (LIFO) list

Stack Organization

High address

Low address

Summary

◼ Machine Instruction Characteristics

◼ Types of Operands

◼ Pentium and PowerPC Data Types

◼ Types of Operations

Key Terms

Address Conditional

branch

Machine

instruction

Procedu

re return

stack

Arithmetic

shift

Instruction

set

operand Push

Bi-endian Jump Operation Reentrant

procedure

Big endian Little

endian

Pop Rotate

branch Logical

shift

Procedure

call

Skip

Assignment

◼ Review questions:

❑ 12.1 12.2 12.3 12.5 12.6 12.9 12.11 12.12

◼ Problems:

❑ 12.1 12.2 12.3 12.4 12.6 12.8 12.16 12.17 12.18

12.19