Instruction Sets: Characteristics and Functions

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1 Instruction Sets: Characteristics and Functions Chapter 10 Lesson 15 Slide 1/22

2 Machine instruction set Computer designer: The machine instruction set provides the functional requirements for the CPU. Computer programmer: The user who chooses to program in machine language becomes aware of the register and memory structure, the types of data directly supported by the machine, and the functioning of the ALU. Lesson 15 Slide 2/22

3 What is an instruction set? The complete collection of instructions that are understood by a CPU Machine Code Binary Usually represented by assembly codes Lesson 15 Slide 3/22

4 Elements of an Instruction Operation code (Op code) Do this Source Operand reference To this Result Operand reference Put the answer here Next Instruction Reference When you have done that, do this... Lesson 15 Slide 4/22

5 Instruction Cycle State Diagram Lesson 15 Slide 5/22

6 Where have all the Operands gone? Main or virtual memory CPU register I/O device Lesson 15 Slide 6/22

7 Instruction Representation In machine code each instruction has a unique bit pattern For human consumption (well, programmers anyway) a symbolic representation is used. Opcodes are represented by abbreviations called mnemonics e.g. ADD, SUB, LOAD, STOR, DIV, MPY Operands can also be represented in this way ADD A,B Lesson 15 Slide 7/22

8 Simple Instruction Format Lesson 15 Slide 8/22

9 Instruction Types X = X + Y (X = 513, Y = 514) Register <= $513 from memory Register <= register + $514 from memory $513 of memory <= register Data processing: arithmetic and logic Data storage: memory Data movement: I/O Control: test and branch Lesson 15 Slide 9/22

10 3 addresses Operand 1, Operand 2, Result a = b + c; May be a forth - next instruction (usually implicit) Not common Number of Addresses (1) Needs very long words to hold everything Lesson 15 Slide 10/22

11 Number of Addresses (2) 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 Lesson 15 Slide 11/22

12 Number of Addresses (c) 1 address Implicit second address Usually a register (accumulator) Common on early machines Lesson 15 Slide 12/22

13 Number of Addresses (d) 0 (zero) addresses All addresses implicit Uses a stack Lesson 15 Slide 13/22

14 Number of Addresses (e) Lesson 15 Slide 14/22

15 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 Lesson 15 Slide 15/22

16 Operation repertoire 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 (1) Lesson 15 Slide 16/22

17 Design Decisions (2) Registers Number of CPU registers available Which operations can be performed on which registers? Addressing modes RISC v CISC Lesson 15 Slide 17/22

18 Types of Operand Addresses Numbers Integer or fixed point / floating point / decimal Characters ASCII Logical Data Bits or flags Lesson 15 Slide 18/22

19 Pentium Data Types 8 bit Byte 16 bit word => odd-numbered addresses 32 bit double word 64 bit quad word Addressing is by 8 bit unit A 32 bit double word is read at addresses divisible by 4 Lesson 15 Slide 19/22

20 Specific Data Types General - arbitrary binary contents Integer - single binary value Ordinal - unsigned integer Unpacked BCD - One digit per byte Packed BCD - 2 BCD digits per byte Near Pointer - 32 bit offset within segment Bit field Byte String Floating Point Lesson 15 Slide 20/22

21 Pentium numeric data formats Lesson 15 Slide 21/22

22 PowerPC Data Types 8 (byte), 16 (halfword), 32 (word) and 64 (doubleword) length data types Some instructions need operand aligned on 32 bit boundary Can be big- or little-endian Fixed point processor recognises: Unsigned byte, unsigned halfword, signed halfword, unsigned word, signed word, unsigned doubleword, byte string (<128 bytes) Floating point IEEE 754 Single or double precision Lesson 15 Slide 22/22

17. Instruction Sets: Characteristics and Functions

17. Instruction Sets: Characteristics and Functions Chapter 12 Spring 2016 CS430 - Computer Architecture 1 Introduction Section 12.1, 12.2, and 12.3 pp. 406-418 Computer Designer: Machine instruction set