CHIP-8 Interpreter

This is an interpreter for the CHIP-8 programming language which was initially used on the COSMAC VIP and TELMAC 1800 which were 8-bit microcomputers made in mid 1970s

The interpreter currently implements 34 of the 35 opcodes of chip 8 and passes all test cases in the CHIP-8 test suite developed by Timendus

Screenshots

Usage

• Install SDL3

• Clone the repository

git clone https://github.com/nishantHolla/chip8-interpreter
cd chip8-interpreter

• Build the interpreter

make release

• Run the run.sh script and select one of the ROMs to run

./run.sh

Implementation details

Process

Process is a higher-level abstraction of a running CHIP-8 program. Each process has its own memory, CPU and IO devices. This means the interpreter can run multiple chip 8 programs concurrently if the host device can support it.

Memory

The memory in the CHIP-8 interpreter is 4KB. Each CHIP-8 instruction is 16 bits wide and is stored in memory in big-endian way. The program is loaded starting from address `0x200`. Memory address `0x00` to `0x1FF` are reserved for the interpreter to store font data, screen pixel data, keyboard inputs, and timers.

CPU

The CPU of the CHIP-8 interpreter has sixteen general-purpose purpose data registers, one for each hexadecimal digit: V0 to VF. Each data register is eight bits in length. VF register is often used as a flag register and is modified by some instructions.

A 16-bit address register I is used with operations related to reading and writing memory.
A 16-bit program counter pc is used to keep track of the next instruction to be executed.

Timers

The CHIP-8 interpreter has two programmable timers, the delay timer and the sound timer. Both timers decrement to 0 at a rate of 60 times per second (60Hzl). The sound timer emits a tone when its value is non-zero.

IO Devices

Keyboard

The CHIP-8 accepts input from a 16-key keypad from 0 to F. These keys have been mapped to a standard QWERTY keyboard as shown above.

Screen

The CHIP-8 interpreter has access to a 64X32 pixel wide screen. The top left corner of the screen is assigned the coordinates (0x00, 0x00) and the bottom right corner is assigned the coordinates(0x3F, 0x1f). A pixel is drawn to be white if its corresponding value is set to be anything other than 0x00 else it is drawn to be black.

Speaker

A 300Hz sine wave is played when required by the interpreter.

Test ROMs

The Test ROMs included in this repository have been taken from these sources

• https://github.com/Timendus/chip8-test-suite/
• https://github.com/kripod/chip8-roms
• https://johnearnest.github.io/chip8Archive/