LC-3 Virtual Machine (C++)

A C++ implementation of the LC-3 (Little Computer 3) virtual machine.

This project simulates the LC-3 CPU, memory, instruction execution cycle, and terminal I/O behavior needed to run LC-3 object programs such as 2048.

Features

• 16-bit LC-3 architecture simulation
• 65,536 memory locations
• Full fetch-decode-execute loop
• Implemented core instruction groups:
  • Arithmetic/logic: ADD, AND, NOT
  • Data movement: LD, ST, LDR, STR, LDI, STI, LEA
  • Control flow: BR, JMP, JSR/JSRR
  • System calls: TRAP routines (GETC, OUT, PUTS, IN, PUTSP, HALT)
• Memory-mapped keyboard registers (KBSR, KBDR)
• LC-3 object image loading with endianness conversion
• Terminal raw-mode input handling for interactive programs

Project Structure

• lc3.hpp - VM declarations, enums, and class interface
• lc3.cpp - VM implementation (instructions, memory, traps, runtime loop)
• main.cpp - CLI entry point and image loading
• Makefile - build rules (all, clean, fclean, re, run)
• programs/ - sample LC-3 object programs

Build

make

Run

Run with one LC-3 object file:

./lc3-vm programs/2048.obj

Makefile Targets

• make / make all - build executable
• make clean - remove object files
• make fclean - remove object files and executable
• make re - full rebuild (fclean then all)
• make run - run executable

Notes

• On launch of some programs (like 2048), you may be prompted with terminal capability questions.
• Controls for 2048 are typically W, A, S, D.

Reference

This implementation is based on and inspired by the LC-3 VM article:

• https://www.jmeiners.com/lc3-vm/