What is Chip-8 Programming Language?

CHIP-8 is an interpreted programming language, developed by Joseph Weisbecker. It was initially used on the COSMAC VIP and Telmac 1800 8-bit microcomputers in the mid-1970s. CHIP-8 programs are run on a CHIP-8 virtual machine. It was made to allow video games to be more easily programmed for these computers.

What is Emulator?

I think it is very important to first understand what is an emulator. An emulator is a computer program that mimics the interior design and functionality of a computer system. Almost people confuse a simulator with an emulator and vice versa. Note that this word is not synonymous.

Pong is a 2D tennis game that was developed by Atari and ran on their hardware. However, the game wasn’t just available on Atari systems, but also on rival platforms such as Amstrad, Amiga, and the C64.

How to write an Emulator?

This guide will give you ideas about simulation programs. It will also teach you how to write the program yourself from the beginning. Personally, I have been excited about emulators software since the late 90’s. As I didn’t own a console back in the days (only had a C64), I was pleasantly surprised when I learned that you could use an emulator to run console games on the PC.

Although this guide expects you to have some basic knowledge of computer systems and assumes that you know a programming language, it should also be an interesting lesson for people who are interested in imitation in general.

Game Loop

#include 
#include   // OpenGL graphics and inputConnect Now
#include "chip8.h" // Your cpu core implementation
 
chip8 myChip8;
 
int main(int argc, char **argv) 
{
  // Set up render system and register input callbacks
  setupGraphics();
  setupInput();
 
  // Initialize the Chip8 system and load the game into the memory  
  myChip8.initialize();
  myChip8.loadGame("pong");
 
  // Emulation loop
  for(;;)
  {
    // Emulate one cycle
    myChip8.emulateCycle();
 
    // If the draw flag is set, update the screen
    if(myChip8.drawFlag)
      drawGraphics();
 
    // Store key press state (Press and Release)
    myChip8.setKeys();	
  }
 
  return 0;
}

Emulation cycle

void chip8::initialize()
{
  // Initialize registers and memory once
}
 
void chip8::emulateCycle()
{
  // Fetch Opcode
  // Decode Opcode
  // Execute Opcode
 
  // Update timers
}

CHIP-8 Opcode table

CHIP-8 has 35 opcodes, which are all two bytes long and stored big-endian. The opcodes are listed below, in hexadecimal and with the following symbols:

• NNN: address
• NN: 8-bit constant
• N: 4-bit constant
• X and Y: 4-bit register identifier
• PC: Program Counter
• I: 16bit register (For memory address) (Similar to void pointer);
• VN: One of the 16 available variables. N may be 0 to F (hexadecimal);

set_BCD(Vx)
*(I+0)=BCD(3);
*(I+1)=BCD(2);
*(I+2)=BCD(1);

CHIP-8 Fontset

unsigned char chip8_fontset[80] =
{ 
  0xF0, 0x90, 0x90, 0x90, 0xF0, // 0
  0x20, 0x60, 0x20, 0x20, 0x70, // 1
  0xF0, 0x10, 0xF0, 0x80, 0xF0, // 2
  0xF0, 0x10, 0xF0, 0x10, 0xF0, // 3
  0x90, 0x90, 0xF0, 0x10, 0x10, // 4
  0xF0, 0x80, 0xF0, 0x10, 0xF0, // 5
  0xF0, 0x80, 0xF0, 0x90, 0xF0, // 6
  0xF0, 0x10, 0x20, 0x40, 0x40, // 7
  0xF0, 0x90, 0xF0, 0x90, 0xF0, // 8
  0xF0, 0x90, 0xF0, 0x10, 0xF0, // 9
  0xF0, 0x90, 0xF0, 0x90, 0x90, // A
  0xE0, 0x90, 0xE0, 0x90, 0xE0, // B
  0xF0, 0x80, 0x80, 0x80, 0xF0, // C
  0xE0, 0x90, 0x90, 0x90, 0xE0, // D
  0xF0, 0x80, 0xF0, 0x80, 0xF0, // E
  0xF0, 0x80, 0xF0, 0x80, 0x80  // F
};

Installation

Go install github.com/bradford-hamilton/chippy