SIMPLEX Assembler and Emulator

This project implements a two-pass assembler and emulator for the SIMPLEX instruction set architecture.

The assembler reads SIMPLEX assembly programs, resolves labels, converts instructions into machine code, and generates both an object file and a human-readable listing file. The emulator loads the generated object code and executes it by simulating the SIMPLEX machine.

This project was developed as part of the CS2206 Computer Architecture Mini Project.

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Features

Two-Pass Assembler

• Reads assembly source files

• Builds a symbol table for labels

• Resolves forward and backward references

• Converts assembly instructions to machine code

• Detects common assembly errors:

  • Duplicate labels
  • Undefined labels
  • Invalid mnemonics
  • Invalid operands

Object File Generation

• Produces a binary object file
• Code starts from memory address 0
• Each instruction encoded as 32-bit machine code

Listing File Generation

Produces a readable listing showing:

• Memory address
• Machine instruction
• Corresponding mnemonic

Example:

00000000 00000111 br start
00000001 00005AB4 data 0x5ab4
00000002          start:
00000002 00006500 ldc 0x65

Emulator

The emulator simulates the SIMPLEX machine:

• Loads object files
• Executes instructions
• Maintains registers
• Handles branching and procedure calls
• Stops execution on HALT

Debug Utilities

• Memory inspection using hex dump
• Test cases for correct and incorrect programs

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Project Structure

simplex-assembler-emulator
│
├── src
│   ├── assembler.cpp
│   ├── emulator.cpp
│   └── hexdump.cpp
│
├── tests
│   ├── successful_tests
│   └── failure_tests
│
├── scripts
│   └── run_tests.bat
│
├── Makefile
├── README.md
├── ARCHITECTURE.md
└── .gitignore

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Build Instructions

Compile using the Makefile:

make

This produces:

assembler
emulator

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Running the Assembler

./assembler program.asm

Output files generated:

• program.obj → machine code
• program.lst → listing file

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Running the Emulator

./emulator program.obj

The emulator loads the object file and executes the program until HALT.

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Example SIMPLEX Program

ldc 5
adc 3
HALT

Expected result:

• Loads constant 5
• Adds 3
• Program halts

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Testing

The project contains automated test cases.

tests/
    successful_tests/
    failure_tests/

Successful tests verify correct assembly and execution. Failure tests verify error detection such as:

• Invalid instruction
• Undefined label
• Duplicate label

Tests can be executed using:

scripts/run_tests.bat

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Technologies Used

• C / C++
• File I/O
• Data structures (maps / symbol tables)
• Two-pass assembler design
• Instruction decoding
• Memory simulation

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Learning Outcomes

This project demonstrates:

• Assembler design
• Instruction encoding
• Label resolution
• Symbol table construction
• Emulator implementation
• Low-level architecture concepts

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Author

Ansh Goyal Computer Science Engineering