Assembly Simulator

Overview

This project is a two-pass assembler and simulator. It reads assembly code from a text file, processes it, converts it into machine code, and simulates its execution.

It is designed for educational purposes to demonstrate how assemblers and simple CPUs work.

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Prerequisites

• C compiler (GCC recommended)
• Basic understanding of command-line usage

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File Structure

├── src
│   ├── emulator
│   │   ├── handle_instruction.c
│   │   ├── handle_instruction.h
│   │   ├── main.c
│   │   ├── memory.c
│   │   ├── memory.h
│   │   └── opcode_table.h
│   ├── parser
│   │   ├── isa.c
│   │   ├── isa.h
│   │   ├── lexer.c
│   │   ├── lexer.h
│   │   ├── main.c
│   │   ├── parser.c
│   │   ├── parser.h
│   │   ├── symbol.c
│   │   ├── symbol.h
│   │   └── token.h
│   ├── error.c
│   ├── error.h
│   ├── instruction.c
│   ├── instruction.h
│   ├── main.c
│   ├── main.h
│   └── type.h
└── Makefile

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Instruction Set Architecture (ISA)

Opcode	Instruction	Description
0	or rd, rn, S	Bitwise OR between rn and S, stored in rd
1	and rd, rn, S	Bitwise AND between rn and S, stored in rd
2	xor rd, rn, S	Bitwise XOR between rn and S, stored in rd
3	add rd, rn, S	Adds rn and S, stored in rd
4	sub rd, rn, S	Subtracts S from rn, stored in rd
5	mul rd, rn, S	Multiplies lower 16 bits of rn and S, stored in rd
6	div rd, rn, S	Integer division of rn by S, stored in rd
7	shr rd, rn, S	Shifts rn right by S bits (left if S < 0)
12	ldb rd, (rn)S	Load 1 byte from memory at rn + S into rd
13	ldh rd, (rn)S	Load 2 bytes from memory at rn + S into rd
14	ldw rd, (rn)S	Load 4 bytes from memory at rn + S into rd
15	stb (rd)S, rn	Store 1 byte from rn into memory at rd + S
16	sth (rd)S, rn	Store 2 bytes from rn into memory at rd + S
17	stw (rd)S, rn	Store 4 bytes from rn into memory at rd + S
21	jmp S	Unconditional jump to address S
22	jzs S	Jump to S if Zero flag is set
23	jzc S	Jump to S if Zero flag is clear
24	jcs S	Jump to S if Carry flag is set
25	jcc S	Jump to S if Carry flag is clear
26	jns S	Jump to S if Negative flag is set
27	jnc S	Jump to S if Negative flag is clear
28	in rd	Reads an integer from input and stores it in rd
29	out rd	Outputs the decimal value of rd
30	rnd rd, rn, S	Random integer in [rn, S-1] stored in rd
31	hlt	Stops program execution

Operand Rules

• For all instructions except jumps, S can be:

  • A register
  • An immediate value

• For jump instructions, S can be:

  • A register
  • An immediate value
  • A label

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Labels

• Labels are identifiers followed by a colon (:)
• Must start with a letter or underscore
• Can contain letters, digits, and underscores

Examples

main:
_loop1:

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Registers

• Registers are named r0 through r31
• Case-insensitive (r0 or R0)
• Valid range: 0–31

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Numbers

• Decimal: #42
• Hexadecimal: #h2A

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Syntax Rules

• Tokens can be separated by spaces, tabs, or commas
• Parentheses () are used for memory addressing
• Colon : is used for labels
• Comments are not supported in this version
• Each instruction must be on its own line

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Usage Example

Example Program

The following program reads a value from input, increments it by 1, and outputs the result:

main:
    in r1
    add r1, r1, #1
    out r1
    hlt

Note: Comments are shown here for explanation but are not supported by the assembler.

Save this program in a file, for example: example.txt.

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Build and Run

Compile

make

Run the Simulator

./simulator example.txt