Microprocessors and Datapath Concepts

Processor Components

• Assembly Language Processors:
  • Finite State Machines (FSM)
  • Arithmetic Logic Units (ALU)
  • Devices: Flip-flops, Circuits, Gates, Transistors

Microprocessors

• Definition: A digital device that processes input, stores values, and produces output based on internal instructions.
• Components in Design:
  • Adders, Counters, Registers

Datapath and Control Unit

• Datapath:
  • All data computations occur here, represented by diagrams of physical connections.
• Control Unit:
  • Orchestrates actions in the datapath; it is a finite state machine managing various tasks.

Example Datapath Components

• Registers: Fundaments for storing data
• ALU: Executes arithmetic operations and contains output signals (overflow, carry, negative, zero indicators).
• Control Signals: Direct how data flows between components (e.g., Load Reg, ALU operations).

Calculation Example: x² + 2x

• Process:
  1. Load X into RA & RB
  2. Multiply RA by RB (store in RA)
  3. Add X to RA (store results)
  4. Repeat to get final output

Control Unit Functions

• Acts as a FSM:
  • Responds to clock signals
  • Sends control signals to datapath
  • Determines when to execute operations

Microprocessor Components Overview

• Arithmetic Unit (ALU)
• Storage Unit: Register files and main memory.
• Controller Unit: Direct operation of the microprocessor.

ALU Details

• Performs:
  • Arithmetic operations (addition, subtraction)
  • Logical operations (AND, OR, NOT)
• Inputs: Include select bits and carry bits for operations.
• Outputs: Indicators such as overflow (V), carry (C), negative (N), and zero (Z).

Memory and Registers

• Registers: Quick storage for immediate data manipulation.
• Main Memory: Larger storage for ongoing data.
• Analogy:
  • Registers as a desk of books (quick access)
  • Memory as a library (slower access, larger capacity)

Register File Operations

• Reading/Writing:
  • Utilizes multiplexers for input and output selection based on addresses.
  • Write signal activates specified registers using a one-hot decoder.

Differences Between Memory and Registers

• Usage:
  • Registers for immediate operations
  • Memory for larger data sets
• Access Speed:
  • Registers: Immediate
  • Memory: Longer delays due to distance from the processor

Control Unit Signals in Action

• Control signals manage operations such as:
  • Write and read operations to/from memory
  • Selecting data sources and ALU operations

Instruction Execution Flow

1. Fetch:
   • Retrieve instruction from memory.
2. Decode:
   • Determine the actions based on instruction type.
3. Execute:
   • Perform computations or memory access operations.
4. Advance:
   • Move to the next instruction based on PC update.

Program Counter (PC)

• Tracks memory address of current instruction. Updates typically by incrementing by 4 (word-aligned).

Instruction Set Architecture (ISA)

• Defines how instructions are laid out in bits (32-bit for MIPS architecture).
• Instruction types include:
  • R-type: Operates on registers.
  • I-type: Contains immediate values.
  • J-type: Jump instructions.

Summary of Control Unit Signals for Operations

• Examples for an addi instruction include:
  • Setting PC, memory read/write, and ALU operations.

Final Note on Machine Code

• Instructions in machine code are binary sequences guiding processor operations. They can be created via compilation from higher-level languages.

Reflection Questions

• If creating a low-level language, consider operations, naming conventions, and the instruction format.