Pipelined RISC Processor

This repository contains the design and implementation of a cycle-accurate, 5-stage pipelined RISC processor written in VHDL. The processor follows a MIPS-style architecture and is built entirely at the RTL level using structural design principles.

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Table of Contents

• Overview
• Features
• Architecture
• Pipeline Hazards
• Verification
• Timing Analysis
• Directory Structure
• Usage
• References

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Overview

The processor is designed to execute instructions across five stages:

1. Instruction Fetch (IF)
2. Instruction Decode (ID)
3. Execution / Address Calculation (EX)
4. Memory Access (MEM)
5. Write Back (WB)

Pipeline registers carry both data and control signals between stages, allowing instruction-level parallelism.

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Features

• Full 5-stage MIPS-style pipeline
• Instruction decode and control logic supporting:
  • R-type instructions
  • Load / store
  • Branch and jump
• Hazard detection unit to handle load-use stalls
• Forwarding unit for RAW dependency resolution
• Modular, RTL-level design for easy extension
• Cycle-level simulation and verification with benchmark programs
• Timing analysis for critical path and maximum safe clock frequency

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Architecture

Figure 1: High-level 5-stage pipelined processor datapath.

Components

• Register file (8 registers, 8-bit)
• ALU with control signals
• Pipeline registers storing data and control between stages
• Multiplexers for data selection
• Hazard detection and forwarding logic

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Pipeline Hazards

Three main types of hazards are addressed:

Data Hazards

• Detected using the hazard detection unit
• Forwarded via the forwarding unit to prevent stalls where possible

Control Hazards

• Managed using stalling or branch resolution mechanisms

Structural Hazards

• Not present due to single shared datapath

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Verification

Benchmark programs were run to validate correct instruction execution:

• Load-use dependencies
• Branch instructions
• Arithmetic operations (add, sub, or)

Simulations show that instructions execute correctly in a pipelined manner while resolving hazards.

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Timing Analysis

• Critical path determined using gate-level timing analysis
• Maximum clock frequency calculated and verified
• Comparison made against single-cycle processor design to show throughput improvements

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Directory Structure