A simple emulator for the CHIP-8 interpreted programming language.

Overview

CHIP-8 Emulator

A simple emulator for the CHIP-8 interpreted programming language written in C (SDL for graphics).

About

This is a really basic emulator written for educational purposes, the code is meant to be readable and clear, with a lot of comments. I am a beginner in this field and this is my first attempt to emulators. I have implemented this project mainly by following the Wikipedia page and this awesome resource; I had no experience with SDL either so I have helped myself during that process with various resources online. The most important part to me was understanding the architecture itself, not the graphics.

Requirements

This project has been developed under a Linux system.

  • SDL library
  • C compiler

Run

make

./bin/emulator.out <game_rom_path>

Or you could use the test_emu script I wrote to automate the process of testing the program.

./test_emu.sh

Quick Walkthrough

By reading here:

Chip-8 is a simple, interpreted, programming language which was first used
on some do-it-yourself computer systems in the late 1970s and early 1980s.
The COSMAC VIP, DREAM 6800, and ETI 660 computers are a few examples.
These computers typically were designed to use a television as a display
had between 1 and 4K of RAM, and used a 16-key hexadecimal keypad for input.
The interpreter took up only 512 bytes of memory, and programs, which were entered into the computer in hexadecimal, were even smaller

So this emulator replicates this behaviour by creating a virtual machine with the following specs:

  • 4096 Bytes of memory
  • 16 general 8-bit purpose registers
  • A special 16-bit register
  • ProgramCounter and StackPointer pseudo registers
  • The stack (array of 16 16-bit values)
  • The keypad (adapted to modern keyboards)
  • 64x32 pixels monochrome screen
  • Delay timer
  • Sound timer

The emulator is then able to run .ch8 games. Please note that I have written only the emulator itself, not the games (freely accessible on the Internet).

The emulator logic consits of parsing and executing the instructions coming from those games.

scr_1

The default mode is debug mode, which outputs a lot of stuff to the screen, if you want to disable it you have to set the int DEBUG = 1; variable to 0 in chip8.c.

Improvements

  • Sound support
    • I was lazy and focused more on the interpreter so there's no sound here
  • Use function pointers instead of big switch statements.

References

Another good article

Improvements

Issues
  • Many bugs at main.c lines 20 and 25

    Many bugs at main.c lines 20 and 25

    At line 20 of main.c, check_rom() is called. Soon after, load_rom() is called at line 25. This causes several problems:

    check_rom() fopen()s a file and doesn't close it before returning, causing the open FILE to leak. Additionally, it unnecessarily makes any further attempt at opening the file implementation-defined behavior, although I don't know of a C implementation where opening the same file multiple times doesn't just work.

    The load_rom() call also fopen()s the same file, without any checking of return values. A non-existing file is not the only cause for an error return of fopen().

    Even if the above issues are fixed, there is an inherent TOCTTOU error in doing this. There is no guarantee that the file will still exist by the time load_rom() is called.

    The fix is to get rid of the check_rom() function and check the return value of fopen() in load_rom().

    bug fixed 
    opened by guijan 2
  • overhaul Makefile

    overhaul Makefile

    Hi again. Someone in the thread at https://www.reddit.com/r/C_Programming/comments/lcgwj3/a_simple_and_beginner_friendly_chip8_emulator/ provided an overhauled Makefile.

    I made a few small changes to their suggestion:

    • The .POSIX special target was added, now the makefile is explicitly POSIX-compliant.
    • CFLAGS, LDFLAGS, and LDLIBS are appended to MYCFLAGS, MYLDFLAGS, and MYLDLIBS respectively, these variables are then used by the C compiler. This allows appending extra compiler flags in pure POSIX make, no GNU extensions.
    • /usr/local/include is added to the list of paths to search for includes. /usr/local/lib is searched for libraries, so I thought this would match the original intent. This change also fixes the build on OpenBSD.

    Now making debug or optimized builds is easy: $ make CFLAGS='-g' Would build this program with debug symbols without touching the source code for instance.

    opened by guijan 1
  • use memcpy to copy memory

    use memcpy to copy memory

    Hi, I'm a beginner C programmer myself and I'm sending a minor patch to test the waters.

    It's a bit silly to use a for loop to copy memory when we have memcpy. This patch also gets rid of the magic number 80, the sizeof operator is the right tool for this job.

    opened by guijan 1
  • Improving load_rom()

    Improving load_rom()

    As suggested by a oh5nxo on Reddit, the function load_rom() could be improved in the following way:

    void load_rom(char* filename) {
        FILE* fp = fopen(filename, "rb");
    
        // read program size into memory
        fread(memory + 0x200, 1, sizeof(memory) - 0x200, fp);
    
        fclose(fp);
    }
    

    From a quick first test, it seems good. Waiting to update to give it a better look.

    enhancement good first issue 
    opened by f0lg0 1
Owner
Leonardo Folgoni
Trying to emulate life in C
Leonardo Folgoni
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