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This document outlines the characteristics and functions of computer architecture instruction sets, defining what an instruction set is and detailing its elements. It discusses instruction representations, types, and addresses, along with design decisions regarding operation repertoire, data types, and instruction formats. Additionally, it covers the specifics of various types of operations such as data transfer, arithmetic, logical operations, and control transfers.
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- 1. Computer Architecture Instruction Sets Characteristics and Functions
- 2. What is an instruction set? • The complete collection of instructions that are understood by a CPU • Machine Code • Binary • Usually represented by assembly codes
- 3. 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...
- 4. Where have all the Operands gone? • Long time passing…. • (If you don’t understand, you’re too young!) • Main memory (or virtual memory or cache) • CPU register • I/O device
- 5. Instruction Cycle State Diagram
- 6. 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
- 8. Instruction Types • Data processing • Data storage (main memory) • Data movement (I/O) • Program flow control
- 9. 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
- 10. 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
- 11. Number of Addresses (c) • 1 address —Implicit second address —Usually a register (accumulator) —Common on early machines
- 12. Number of Addresses (d) • 0 (zero) addresses —All addresses implicit —Uses a stack —e.g. push a — push b — add — pop c —c = a + b
- 13. 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
- 14. Design Decisions (1) • 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
- 15. Design Decisions (2) • Registers —Number of CPU registers available —Which operations can be performed on which registers? • Addressing modes (later…) • RISC v CISC
- 16. Types of Operand • Addresses • Numbers —Integer/floating point • Characters —ASCII etc. • Logical Data —Bits or flags • (Aside: Is there any difference between numbers and characters? Ask a C programmer!)
- 17. 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
- 18. Types of Operation • Data Transfer • Arithmetic • Logical • Conversion • I/O • System Control • Transfer of Control
- 19. Data Transfer • Specify —Source —Destination —Amount of data • May be different instructions for different movements —e.g. IBM 370 • Or one instruction and different addresses —e.g. VAX
- 20. Arithmetic • Add, Subtract, Multiply, Divide • Signed Integer • Floating point ? • May include —Increment (a++) —Decrement (a--) —Negate (-a)
- 21. Shift and Rotate Operations
- 22. Logical • Bitwise operations • AND, OR, NOT
- 23. Conversion • E.g. Binary to Decimal
- 24. Input/Output • May be specific instructions • May be done using data movement instructions (memory mapped) • May be done by a separate controller (DMA)
- 25. Systems Control • Privileged instructions • CPU needs to be in specific state —Ring 0 on 80386+ —Kernel mode • For operating systems use
- 26. Transfer of Control • Branch —e.g. branch to x if result is zero • Skip —e.g. increment and skip if zero —ISZ Register1 —Branch xxxx —ADD A • Subroutine call —c.f. interrupt call
- 29. Use of Stack