https://github.com/bourgeoisor/chasm
CHIP-8 emulator written in C++ using SFML.
https://github.com/bourgeoisor/chasm
asm chip8 emulator
Last synced: about 1 year ago
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CHIP-8 emulator written in C++ using SFML.
- Host: GitHub
- URL: https://github.com/bourgeoisor/chasm
- Owner: bourgeoisor
- License: mit
- Created: 2019-02-24T03:43:22.000Z (over 7 years ago)
- Default Branch: main
- Last Pushed: 2021-06-08T17:10:08.000Z (almost 5 years ago)
- Last Synced: 2025-02-07T11:35:23.706Z (over 1 year ago)
- Topics: asm, chip8, emulator
- Language: C++
- Homepage:
- Size: 26.4 KB
- Stars: 4
- Watchers: 0
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE.md
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README
# Chasm
Chasm is a CHIP-8 virtual machine emulator written in C++. CHIP-8 is an interpreted programming language developed in the mid-1970s targetting the Telmac 1800 and COSMAC VIP microcomputers to ease development of 8-bit video games.
## Screenshot
## How to Compile
This project has been written in a platform-agnostic structure through [CMake](https://cmake.org/). Most C++ IDE's such as Microsoft Visual Studio and JetBrains CLion supports CMake projects natively. If you are to compile this project outside of an IDE, the `cmake` command can generate a Makefile that you can then run using `make`.
I have used the [SFML v2.5.1](https://www.sfml-dev.org/download/sfml/2.5.1/) library to handle cross-platform windowing, graphics, and sounds. Note that you will need to have this library installed on your platform and edit `CMakeList.txt` to include its path.
## How to Run
Once the application is running, it will prompt you for the path of a program to load. Simply input an absolute or relative path to a valid CHIP-8 ROM. I have included a variety of public domain CHIP-8 ROMs in the `roms/` directory available in this repository.
## Specifications
### Memory
The CHIP-8 implementation can access up to 4KiB (4,096 bytes) of RAM. Originally, the interpreter was located within locations 0x000 0x1FF. Nowadays, that section can be used to store sprites and character sets.
+----------------+= 0xFFF (4095) End of Chip-8 RAM
| |
| |
| |
| |
| |
| 0x200 to 0xFFF |
| Chip-8 |
| Program / Data |
| Space |
| |
| |
| |
+- - - - - - - - += 0x600 (1536) Start of ETI 660 Chip-8 programs
| |
| |
| |
+----------------+= 0x200 (512) Start of most Chip-8 programs
| 0x000 to 0x1FF |
| Reserved for |
| interpreter |
+----------------+= 0x000 (0) Start of Chip-8 RAM
### Registers
There are a handful of registers made available through the CHIP-8 specification:
- 16 multi-purpose 8-bit registers, V0 through VF;
- A 16-bit register used to store addresses, I;
- Two 8-bit registers used for timing (see section on Timers);
- A 16-bit program counter (PC);
- An 8-bit stack pointer (SP);
- A 16 16-bit value stack used for subroutines;
Note: the VF register is used by some instructions to store state flags.
### Display
The original implementation of CHIP-8 uses a 64x32 monochrome display:
┌───────────────────┐
│ (0,0) (63,0) │
│ │
│ (0,31) (63,31) │
└───────────────────┘
### Input
The microcomputers that ran CHIP-8 generally had a 16-key numeric pad. For ease of convenience with modern devices, I have translated the key to fit a QWERTY (sorry, France) layout.
┌───┬───┬───┬───┐ ┌───┬───┬───┬───┐
│ 1 │ 2 │ 3 │ 4 │ │ 1 │ 2 │ 3 │ C │
└─┬─┴─┬─┴─┬─┴─┬─┴─┐ │───┼───┼───┼───┤
│ Q │ W │ E │ R │ │ 4 │ 5 │ 6 │ D │
└─┬─┴─┬─┴─┬─┴─┬─┴─┐ <-- │───┼───┼───┼───┤
│ A │ S │ D │ F │ │ 7 │ 8 │ 9 │ E │
└─┬─┴─┬─┴─┬─┴─┬─┴─┐ │───┼───┼───┼───┤
│ Z │ X │ C │ V │ │ A │ 0 │ B | F |
└───┴───┴───┴───┘ └───┴───┴───┴───┘
### Timers
There are two timers made available through opcodes:
- A delay timer which decrements by 1 every cycle;
- A sound timer which decrements by 1 every cycle and plays a tone while non-zero;
### Instructions
CHIP-8 has 35 instructions
| Opcode | Type | Description |
|--------|------|-------------|
| 0NNN | Call | Calls RCA 1802 program at address NNN. |
| 00E0 | Display | Clears the screen. |
| 00EE | Flow | Returns from a subroutine. |
| 1NNN | Flow | Jumps to address NNN. |
| 2NNN | Flow | Calls subroutine at NNN. |
| 3XNN | Cond | Skips the next instruction if VX equals NN. |
| 4XNN | Cond | Skips the next instruction if VX doesn't equal NN. |
| 5XY0 | Cond | Skips the next instruction if VX equals VY. |
| 6XNN | Const | Sets VX to NN. |
| 7XNN | Const | Adds NN to VX. |
| 8XY0 | Assign | Sets VX to the value of VY. |
| 8XY1 | BitOp | Sets VX to VX OR VY. |
| 8XY2 | BitOp | Sets VX to VX AND VY. |
| 8XY3 | BitOp | Sets VX to VX XOR VY. |
| 8XY4 | Math | Adds VY to VX. VF is set to 1 when there's a carry, and to 0 when there isn't. |
| 8XY5 | Math | VY is subtracted from VX. VF is set to 0 when there's a borrow, and 1 when there isn't. |
| 8XY6 | BitOp | Stores the least significant bit of VX in VF and then shifts VX to the right by 1. |
| 8XY7 | Math | Sets VX to VY minus VX. VF is set to 0 when there's a borrow, and 1 when there isn't. |
| 8XYE | BitOp | Stores the most significant bit of VX in VF and then shifts VX to the left by 1. |
| 9XY0 | Cond | Skips the next instruction if VX doesn't equal VY. |
| ANNN | Mem | Sets I to the address NNN. |
| BNNN | Flow | Jumps to the address NNN plus V0. |
| CXNN | Rand | Sets VX to the result of a bitwise and operation on a random number and NN. |
| DXYN | Disp | Draws a sprite at coordinate (VX, VY) that has a width of 8 pixels and a height of N pixels. |
| EX9E | KeyOp | Skips the next instruction if the key stored in VX is pressed. |
| EXA1 | KeyOp | Skips the next instruction if the key stored in VX isn't pressed. |
| FX07 | Timer | Sets VX to the value of the delay timer. |
| FX0A | KeyOp | A key press is awaited, and then stored in VX. |
| FX15 | Timer | Sets the delay timer to VX. |
| FX18 | Sound | Sets the sound timer to VX. |
| FX1E | Mem | Adds VX to I. |
| FX29 | Mem | Sets I to the location of the sprite for the character in VX. |
| FX33 | Mem | Stores the binary-coded decimal representation of VX at address I through I+2. |
| FX55 | Mem | Stores V0 to VX (including VX) in memory starting at address I. |
| FX65 | Mem | Fills V0 to VX (including VX) with values from memory starting at address I. |
## Development State
Chasm is currently fully working, but I may plan on adding a few little features here and there. For any contribution ideas or bug reports, please feel free to either message me for more information or to directly send in a pull request.