Instruction Set Architecture & Design CSE 241 Computer Engineering (1) هندسة الحاسبات (1) Lecture # 5 Ch. 3 Instruction Set Architecture & Design Dr. Tamer Samy Gaafar Dept. of Computer & Systems Engineering

Course Web Page http://www.tsgaafar.faculty.zu.edu.eg Email: tsgaafar@yahoo.com

Instruction Set Architecture & Design

Machine Instruction Characteristics Outline Machine Instruction Characteristics Elements of machine instructions, instruction representation, number of Addresses, … etc. Types of Operands Numbers, characters, logical data Types of Operations

Instruction Cycle State Diagram

Elements of an instruction Instructions Instruction set Complete collection of instructions that are understood by a CPU, i.e., the set of all machine instructions. Instructions are represented in a binary form (machine language), or a symbolic form (assembly language). Elements of an instruction Operation code (op code) Do this … (e.g., ADD, I/O). Source operand reference To this … Result operand reference Put the answer here … Next instruction reference When you have done that, do this next ... Usually implicit (from PC). Immediate: value. Main memory: address. CPU register: register number. Implicit if one register exists. I/O device: I/O module & device. MM address if memory-mapped I/O. 2

Instruction Representation Within computer, each Instruction is represented by a sequence of bits, divided into fields. During the execution phase, an instruction is read from the IR register. CPU extracts the data from these fields to perform the required operation. For programmers, a symbolic representation is used. Opcodes  mnemonics, e.g., ADD, SUB, LOAD. Operands  symbolic names, e.g., Y = 514. Example: ADD R1, Y 5

Instruction Types Data processing Data storage Data movement Arithmetic and logic instructions. Arithmetic: computations (processing) on numeric data. Logic: operate on the bits of a word (any data type). Data storage Memory instructions. Data movement I/O instructions. Program flow control Test and branch instructions. 6

Number of Addresses (1) What is the maximum number of addresses would be needed in an instruction? “addresses” here means “explicit operand references”. Arithmetic & logic instructions would need the most # of addresses. Arithmetic & logic operations are either unary (one operand) or binary (two operands). Two addresses are needed to reference operands. One more address to store the result. One for next instruction (usually implicit). Most instructions are one-, two-, or three-operand. 7

Program to Execute: Y = (A–B)/(C+D×E) 3-address instructions 1-address instructions 2-address instructions MPY D, E would alter D 10

Number of Addresses (2) 3 addresses 2 addresses Operand 1, Operand 2, Result a = b + c; Needs very long words to hold everything. 2 addresses One address doubles as operand and result a = a + b Reduces length of instruction 8

Number of Addresses (3) 1 address 0 (zero) addresses Implicit second address Usually a register (accumulator: AC) Common on early machines 0 (zero) addresses All addresses implicit Uses a stack Last-in-first-out set of locations. Top of stack. e.g. push a push b add pop c c = a + b push 3 pop a pop b pop c Top of stack push 5 3 Top of stack 19 Top of stack Stack (Last-in first-out) 745 5 Top of stack . . . 9

Types of Operands Addresses Numbers Characters Logical Data A form of data. Unsigned integers. Numbers Characters IRA (ASCII): 7-bit code. An 8th bit may be used for parity. Logical Data Bit-oriented view of data (true/false). Store an array of logical data, manipulate bits of a data item. 14

Transfer of Control (Sequencing) Types of Operations Data Movement Arithmetic Logical I/O Transfer of Control (Sequencing) 18

Instruction must specify: 1. Data Transfer Instruction must specify: Location of source operand. Location of destination operand. Location of operand and amount of data could be specified as part of opcode or operand fields: Memory. Register. Top of stack. 19

1. Data Transfer – Common Operations 19

1. Data Transfer – CPU Actions In terms of CPU action, data transfer operations are perhaps the simplest type. If both source and destination are registers: Issue a command to transfer data from a register to another, which is completely internal. If one or both operands are in memory: Calculate memory address(es) of operand(s). Translate adress(es) from virtual to physical. Check the cache. If miss, issue a command to the memory module. 19

Types of Operations Data Transfer Arithmetic Logical I/O Transfer of Control 18

Add, Subtract, Multiply, Divide 2. Arithmetic Add, Subtract, Multiply, Divide Signed Integer (fixed-point) numbers Floating point numbers. May include Increment (a++) Decrement (a--) Negate (-a) Absolute (if a<0 then -a else a) May involve data transfer Desired arithmetic operation is performed by ALU 20

3. Logical – Common Operations 21

3. Logical – AND, OR, NOT, XOR, … To manipulate individual bits  bit twiddling. Could be used for bit masking: Reset a specific group of bits: Operation: AND Mask: 0 for each bit to be reset and 1 otherwise. Set a specific group of bits: Operation: OR Mask: 1 for each bit to be set and 0 otherwise. Toggle a specific group of bits: Operation: XOR Mask: 1 for each bit to be inverted and 0 otherwise. 21

3. Logical – Shift and Rotate Operations Logical right shift Logical left shift Arithmetic right shift Arithmetic left shift Right rotate Left rotate

May be done using data movement instructions (memory-mapped). 4. Input/Output May be done using data movement instructions (memory-mapped). May be using specific i/o instructions. May be done by a separate controller (DMA). 23

4. Input/Output – Common Operations 23