Computer Organization and Architecture - Instruction Sets

Machine Instruction Characteristics

  • The processor's operation is dictated by the instructions it executes, known as machine or computer instructions.
  • The instruction set is the collection of different instructions a processor can execute.
  • Each instruction provides the processor with necessary execution information.

Elements of a Machine Instruction

  • Operation Code (Opcode):
    • Specifies the operation. Specified by a binary code.
  • Source Operand Reference:
    • Input operands for the operation.
  • Result Operand Reference:
    • The operation's output.
  • Next Instruction Reference:
    • Tells the processor where to fetch the next instruction after completing the current one.

Instruction Cycle State Diagram

  • The instruction cycle includes stages like instruction address calculation, instruction fetch, operand address calculation, operand fetch, data operation, operand store, and instruction complete.

Source and Result Operands

  • Location of Operands:
    • Main or virtual memory: The instruction supplies the memory address.
    • I/O device: The instruction specifies the I/O module and device (or memory-mapped address).
    • Processor register: Instruction contains the register number or name.
    • Immediate: The operand value is within the instruction itself.

Instruction Representation

  • Instructions are represented by bit sequences, divided into fields.

  • Fields correspond to the instruction's constituent elements (opcode, operands).

    Example: A simple instruction format:

    • Opcode (e.g., 4 bits)
    • Operand Reference 1 (e.g., 6 bits)
    • Operand Reference 2 (e.g., 6 bits)
    • Other data/address information (e.g., 16 bits)

Mnemonics

  • Opcodes are represented by abbreviations called mnemonics (e.g., ADD, SUB, MUL, DIV, LOAD, STOR).
  • Operands are also represented symbolically.
  • Programmers specify the location of each symbolic operand.

Instruction Types

  • Data Processing: Arithmetic and Logic instructions.
    • Arithmetic instructions: Computational capabilities for processing numeric data.
    • Logic (Boolean) instructions: Operate on bits of a word, processing any data type.
  • Data Storage: Movement of data into/out of registers/memory.
  • Data Movement: I/O instructions for transferring programs/data into memory and results to the user.
  • Control: Test and Branch instructions.
    • Test instructions: Test value of data or computation status.
    • Branch instructions: Branch to different instruction sets based on decisions.

Instruction Address Examples

  • Different address instructions impact how operations are performed.

    Examples:

    • Three-address: Y=A−B  ;  T=D×E  ;  T=T+C  ;  Y=Y/TY = A - B \; ; \; T = D \times E \; ; \; T = T + C \; ; \; Y = Y / T (Each instruction specifies two source operands and a destination)
    • Two-address: Requires overwriting one operand. MOVE instruction copies values.
    • One-address: Accumulator (AC) is implied. Requires LOAD and STOR instructions.

Utilization of Instruction Addresses (Nonbranching Instructions)

  • Table summarizing instruction address utilization:
    • OP A, B, C implies A=B  OP  CA = B \; OP \; C
    • OP A, B implies A=A  OP  BA = A \; OP \; B
    • OP A implies AC=AC  OP  AAC = AC \; OP \; A
    • OP implies T=(T−1)  OP  TT = (T - 1) \; OP \; T

Instruction Set Design

  • Fundamental design issues:
    • Operation repertoire: Types and complexity of operations.
    • Data types: Types of data operations are performed on.
    • Instruction format: Length, number of addresses, field sizes.
    • Registers: Number of processor registers and their use.
    • Addressing: Modes for specifying operand addresses.

Types of Operands

  • Addresses
  • Numbers
  • Characters
  • Logical Data

Numbers

  • Machine languages include numeric data types with magnitude and precision limits.
  • Numeric data types:
    • Binary integer or binary fixed point
    • Binary floating point
    • Decimal (Packed decimal): Each decimal digit is represented by a 4-bit code, with two digits per byte.

Characters

  • Character strings are a common data form.
  • Character codes:
    • International Reference Alphabet (IRA) / ASCII
    • Extended Binary Coded Decimal Interchange Code (EBCDIC) (used on IBM mainframes)

Logical Data

  • An n-bit unit consisting of n 1-bit items of data, each item having the value 0 or 1
  • Advantages of bit-oriented view:
    • Efficient memory use for Boolean/binary data arrays.
    • Ability to manipulate data item bits.

Single-Instruction-Multiple-Data (SIMD) Data Types

  • Introduced in x86 architecture for multimedia application performance.
  • Extensions include MMX (multimedia extensions) and SSE (streaming SIMD extensions).
  • Data types:
    • Packed byte/word/doubleword/quadword integers
    • Packed single/double-precision floating-point

Processor Actions for Various Types of Operations

  • Data Transfer: Transfer data from one location to another.
  • Arithmetic: Perform function in ALU, set condition codes/flags.
  • Logical: Similar to arithmetic.
  • Conversion: Convert data formats.
  • Transfer of Control: Update program counter, manage parameter passing for subroutines.
  • I/O: Issue command to I/O module.

Data Transfer

  • Instruction must specify source/destination locations, data length, and addressing modes.

Arithmetic

  • Basic operations (add, subtract, multiply, divide) for signed integers.
  • Often provided for floating-point and packed decimal numbers.
  • Single-operand instructions:
    • Absolute: Absolute value of operand.
    • Negate: Negate operand.
    • Increment: Add 1 to operand.
    • Decrement: Subtract 1 from operand.

Basic Logical Operations

  • Basic logical operations are NOT, AND, OR, XOR, and Equality.

    Truth Table:

    • P Q | NOT P | P AND Q | P OR Q | P XOR Q | P = Q
    • 0 0 | 1 | 0 | 0 | 0 | 1
    • 0 1 | 1 | 0 | 1 | 1 | 0
    • 1 0 | 0 | 0 | 1 | 1 | 0
    • 1 1 | 0 | 1 | 1 | 0 | 1

Shift and Rotate Operations

  • Shift and rotate operations manipulate bits within data.

    Types:

    • Logical shift (left/right): Fill with zeros.
    • Arithmetic shift (left/right): Sign extension for right shift.
    • Rotate (left/right): Wrap bits around.

Examples of Shift and Rotate Operations

  • Examples illustrating logical/arithmetic shifts and rotates.

Conversion

  • Instructions change data format.
  • Example: Decimal to binary conversion.
  • Complex Example: EAS/390 Translate (TR) instruction.

Input/Output

  • Approaches:
    • Isolated programmed I/O
    • Memory-mapped programmed I/O
    • DMA
    • Use of an I/O processor
  • Implementations provide a few I/O instructions with specific actions defined by parameters/codes.

System Control

  • Instructions executed in privileged states/memory areas.
  • Reserved for operating system use.
  • Examples:
    • Read/alter control register
    • Modify storage protection key
    • Access process control blocks

Transfer of Control

  • Reasons for transfer-of-control operations:
    • Execute instructions multiple times
    • Decision making in programs
    • Breaking tasks into smaller pieces
  • Common operations:
    • Branch
    • Skip
    • Procedure call

Branch Instructions

  • Branch instructions can be conditional or unconditional, altering the flow of execution based on conditions or addresses.

Skip Instructions

  • Skip instructions increment the program counter to skip the next instruction.
  • Example: Increment-and-skip-if-zero (ISZ).

Procedure Call Instructions

  • Self-contained programs invoked by a larger program.
  • Economy: Reuse code.
  • Modularity: Break down tasks.
  • Involves:
    • Call instruction: Branches to procedure.
    • Return instruction: Returns from procedure.

Nested Procedures

  • Nested procedures involve calls to procedures within procedures.

Use of Stack to Implement Nested Procedures

  • Stack is used to manage return addresses and parameters during nested procedure calls.

Stack Frame Growth

  • Stack frames are used to store return points, old frame pointers, and local variables for procedures.

x86 Single-Instruction, Multiple-Data (SIMD) Instructions

  • Intel introduced MMX technology in 1996 for multimedia tasks.
  • MMX is a set of optimized instructions for multimedia.
  • Video/audio data are composed of arrays of small data types.
  • New data types:
    • Packed byte
    • Packed word
    • Packed doubleword
  • Each data type is 64 bits long and consists of multiple smaller data fields, each of which holds a fixed-point integer.

Image Compositing on Color Plane Representation

  • Example of MMX code sequence for image compositing involves:

    *Unpacking byte R pixel components from images A and B.
    *Subtracting image B from image A.
    *Multiplying result by fade value.
    *Adding image B pixels.
    Packing new composite pixels back to bytes.