chip8

Chip8 is a small emulator for the CHIP-8 interpreter language used in the COSMAC VIP and Telmac 1800 system.

This implementation uses C++ for the core functionality and a SDL2 backend completes the emulator with sound, keyboard input and GL display.

To install the SDL2 library, use sudo apt-get install libsdl2-dev (for Ubuntu).

To use the emulator:

• Run the make file using make (first time only)

• ./chip8 <rom> to load the ROM specified. (see the roms folder)

Introduction

• Chip-8 is more of a virtual machine than a physical one.

• It interprets the instructions and replicates the functionality of the original machine.

• Commonly interpreted on 4K systems such as Cosmac VIP in mid 1970s

• It was made to allow video games more easily programable for these machines as games written in chip8 language could easily run using the chip8 emulator.

Description

• 16 8bit registers labeled from V0 to VF, VF is special as it is used as flag.

• 4K bytes memory i.e 0.000 to 0xFFF

• Address space is divided into 3 sections:

  • 0x000 to 0x1FF - (first 512 bytes)reserved for the interpreter
  • 0x050 to 0x0A0 - for characters 0 through F
  • 0x200 to 0xFFF - for ROMS

• 16 bit index register for storing the memory address used in operations

• 16 bit Program Counter which holds the address of next instruction to be excecuted.

• 16 level stack to keep track of the order of excecution.

• 8 bit stack pointer (top) for using the stack.

• 8 bit delay timer for timing, decrements at rate of 60Hz.

• 8 bit sound timer for sound, similar behaviour as the delay timer.

• 16 input keys which match the first 16 hex values (0 through F).

Instructions

• 34/35 instructions in total. Eg: '00E0: CLS' to clear the display.

• 3 cycles: fetch, decode and execute.

Display

• Used SDL to render and get input in a multiplatfrom way.

ROMS

• INVADERS:

  • start the game using W
  • left: Q
  • right: E
  • W: shoot

• BRIX:

  • Q to move left
  • E to move right

• PONG: 2 player game

  • Player1: 1 and Q to move up and down
  • Player2: 4 and R to move up and down

• TANK:

  • 2 to move down
  • Q to turn left
  • E to turn right
  • S to move up
  • W to fire

• TETRIS:

  • W to move left
  • E to move right
  • Q to rotate piece