Two-Pass Assembler

Table of Contents

1. Project Overview
2. Features
3. Getting Started
   • Prerequisites
   • Installation
4. Usage
   • Running the Assembler
   • Input File Format
   • Output Files
5. Project Structure
6. Contributing
7. License
8. Acknowledgements
9. Contact

Project Overview

This project implements a two-pass assembler for a hypothetical assembly language. The assembler translates assembly language source code into machine code, performing lexical analysis, syntax analysis, and code generation in two passes.

Features

• Two-Pass Processing: Ensures accurate resolution of symbols and addresses.
• Error Handling: Detects and reports syntax and semantic errors.
• Memory and Symbol Management: Efficient handling of labels and memory.
• Output Files: Generates machine code, extern labels usage, entry labels definitions, macro-extended file

Getting Started

Prerequisites

• GCC (GNU Compiler Collection)
• Make (build automation)

Installation

1. Clone the repository:

   git clone https://github.com/Tal45/Assembler-C-Project.git
   cd Assembler-C-Project

2. Compile the assembler:

   make

Usage

Running the Assembler

To assemble a source file, run the following command for '.as' source files:

./assembler source1 source2 source3 ...

Input File Format

The assembler expects the source file to be in a specific format. Below are the details of the expected input:

Registers

The assembler supports 8 registers:

• r0, r1, r2, r3, r4, r5, r6, r7

Supported Commands and Instructions

• mov: (Move data)
• cmp: (Compare)
• add: (Addition)
• sub: (Subtraction)
• lea: (Load effective address)
• clr: (Clear register)
• inc: (Increment)
• dec: (Decrement)
• jmp: (Jump)
• bne: (Branch if not equal)
• red: (Read input)
• prn: (Print)
• jsr: (Jump to subroutine)
• rts: (Return from subroutine)
• stop: (Stop execution)

Addressing Modes

• Immediate: # (e.g., mov #5, r1)
• Direct: (e.g., mov label, r1)
• Register Direct: r<register_number> (e.g., mov r2, r1)
• Register Indirect: *r<register_number> (e.g., mov *r3, r1)

Directives

1. Data Definition:
   • .data <value1>, <value2>, ...
   • Example: .data 10, 20, -30
2. String Definition:
   • .string "<text>"
   • Example: .string "hello"
3. Entry Definition:
   • .entry <label>
   • Example: .entry LOOP
4. Extern Definition:
   • .extern <label>
   • Example: .extern GLOBAL

Memory Layout

• Addressable memory: 0 to 4095 (decimal).
• Each instruction is encoded into 15 bits:
  • Bits 14-11: Opcode.
  • Bits 10-7: Source operand addressing method.
  • Bits 6-3: Destination operand addressing method.
  • Bits 2-0: Additional flags (A, R, E).

Symbols and Labels

• Labels must start with an alphabetic character and be followed by alphanumeric characters.
• Labels end with a colon (:) and can appear before an instruction or directive.
  • Example: LOOP: mov r1, r2
• Symbols must be defined before use unless declared as .extern.

Macros

• Define macros using the syntax:

  macr <macro name>
  <command #1>
  <command #2>
  .
  .
  .
  endmacr

• To invoke the macro block in the code simply put the macro name

Output Files

• Macro-Extended File: source.am
• Machine Code File: source.ob
• Extern Labels: source.ext
• Entry Labels: source.ent

Project Structure

The project directory structure is as follows:

Assembler-C-Project/
│
├── src/
│ ├── main.c
│ ├── preprocess.c
│ ├── firstpass.c
│ ├── secondpass.c
│ ├── filehandler.c
│ ├── valdation.c
│ ├── marcohandler.c
│ ├── labelhandler.c
│ └── virtualmemory.c
│
├── headers/
│ ├── main.h
│ ├── virtualmemory.h
│ ├── validation.h
│ ├── structs.h
│ ├── labelhandler.h
│ ├── macrohandler.h
│ ├── constants.h
│ └── filehandler.h
│
├── inputfiles/
│ ├──
│ └── ...
│
├── outputfiles/
│ ├──
│ └── ...
│
├── README.md
├── makefile
└── LICENSE

Contributing

We are not accepting any contributions at the moment.

License

This project is licensed under the MIT License - see the LICENSE file for details.

Acknowledgements

• Made by Vadim Volkov and Tal Levi @ Open University as final project for C-Programming Labratory Course semester 2024b.
• Studies based on the book The C Programming Language (ANSI-C) 2nd Edition by Brian W.Kernighan and Dennis M. Ritchie.

Contact

For any questions or feedback, please reach out to [[email protected]] or [[email protected]].