OoOVisual: Out-of-Order CPU Architecture Visualizer

1. Overview

OoOVisual is an architectural-level visualization tool for an Out-of-Order (OoO) CPU core.

It models modern superscalar mechanisms such as:

• Reorder Buffer (ROB)
• Register Renaming
• Distributed Reservation Stations
• Out-of-Order Execution
• Branch Prediction & Recovery
• Load/Store Unit

The project's goal is to make dynamic scheduling, speculative execution, and pipeline behavior observable in real time, providing clear insights into microarchitectural operation.

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2. Features

Architectural Simulation

• Tomasulo-style dynamic scheduling
• Physical register allocation and renaming
• In-order commit via Reorder Buffer
• Speculative execution with branch prediction
• Pipeline flush and recovery on misprediction
• Distributed reservation stations
• Execution units and load/store handling

Visual Architecture Layout

• Units placed in 2D space, connected with animated, orthogonal wires
• Wires pulse when control or data signals propagate
• Pulse colors indicate event types:

Color	Context	Meaning
Green	Any Execution Unit → ROB	Instruction committed successfully
Green	ROB → Register Manager	Operation completed; updates the register alias table
Green	Fetch Unit → Fetch Group → Dispatcher	Fetch successful; fetch group is on its way to be dispatched
Red	Dispatcher → Any Reservation Station	Dispatch failed due to structural hazards
Orange	Dispatcher	Dispatcher is actively dispatching instructions
Purple	ROB → Register Manager	Flushing ROB entries and restoring the alias table due to branch misprediction

Interactive Inspection

• Hover over units to view current state
• Double left click → open detailed view
• Double right click → close detailed view

Clickable units include:

• Fetch Unit
• Reorder Buffer
• Register Manager
• Load/Store Execution Unit

Camera Controls

• W / A / S / D → Move camera
• + / - → Zoom in / Zoom out

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3. GUI Demonstration

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4. Dependencies

OoOVisual is built using:

• C++20
• Dear ImGui
• GLFW
• OpenGL
• CMake

Linux (Debian/Ubuntu)

sudo apt update
sudo apt install build-essential cmake libglfw3-dev libgl1-mesa-dev

Windows (vcpkg recommended)

git clone https://github.com/microsoft/vcpkg.git
cd vcpkg
.\bootstrap-vcpkg.bat
vcpkg install glfw3

macOS (Homebrew)

brew install glfw

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5. Building the Project

Linux / macOS

git clone https://github.com/f3rhd/OoOVisual.git
cd OoOVisual
cmake -S . -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build

Windows (Visual Studio)

cmake -S . -B build -G "Visual Studio 18 2026" -A x64 -DCMAKE_TOOLCHAIN_FILE="C:/path/to/vcpkg/scripts/buildsystems/vcpkg.cmake"

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6. Usage

Run the visualizer:

./OoOVisual <input.s>

When launched:

• Architectural layout is displayed
• Wires pulse each simulation tick when signals propagate
• Hover over units to inspect state
• Double left click → open detailed window
• Double right click → close detailed window
• WASD to navigate, +/- to zoom

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7. Repository Structure

OoOVisual/
├─ OoOVisual/Core/                    # OoO core implementation 
├─ OoOVisual/Frontend/                # Frontend needed for assembly parsing
├─ OoOVisual/Visualizer/              # ImGui rendering, interactions, camera control
├─ OoOVisual/tests/                   # RISC-V Assembly tests
├─ OoOVisual/vendor/                  # Third-party libraries (GLFW, ImGui)
├─ OoOVisual/main.cpp                 # Entry point
├─ CMakeLists.txt                     # Build configuration
├─ assets/                            # Assets
└─ README.md                          # This file

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8. MMIO Register Reference

The simulated CPU exposes a software GPU via memory-mapped I/O. Writing to these addresses issues graphics commands.

Address	Name	Description
0x00	CMD_TYPE	Command type: 1=FILL_RECT, 2=LINE, 3=RECT, 4=TRIANGLE, 5=FILL_TRIANGLE
0x04	X1	Start X coordinate (or triangle point 1 X)
0x08	Y1	Start Y coordinate (or triangle point 1 Y)
0x0C	X2	End X coordinate (or triangle point 2 X)
0x10	Y2	End Y coordinate (or triangle point 2 Y)
0x14	COLOR	Draw color, packed as 0xRRGGBBAA
0x18	START	Write 1 to execute the current command
0x1C	X3	Triangle point 3 X (CMD_TYPE = 4 or 5 only)
0x20	Y3	Triangle point 3 Y (CMD_TYPE = 4 or 5 only)

To issue a command, write all parameter registers first, then write 1 to START. The GPU executes synchronously on the START write.

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9. Purpose

OoOVisual is intended for:

• Studying Out-of-Order execution
• Understanding Tomasulo-style scheduling
• Visualizing speculative execution and recovery
• Teaching modern CPU microarchitecture concepts

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10. License

This project is licensed under the MIT License.