This is an implementation of the CHIP-8 interpreter / VM / "Emulator" from the 1970s. Below is an overview of its features, specifications,and the tools I used to implement it, as well as how to run it.
- Python 3.10.12
- Pygame 2.5.2
- Numpy 1.26.4
I built the emulator with this version, a greater version might work as well.
- Python 3.10.X
- pip 22.0.2
If you wish to run the emulator you can install the dependencies as follows:
pip install -r requirements.txt
Note: It's your choice whether you use a virtual environment or not.
After installing the requirements you can run the emulator as follows:
python main.py --rom-path="./roms/rom.ch8"
If you wish to specify the sprite's color, or background color run the emulator as follows:
python main.py --color=0xffffff --bgcolor=0x000000 --rom-path="./roms/rom.ch8"
Here are some demos of the emulator running some ROMs I found online:
The CHIP-8 VM has 4096 memory addresses, each containing 8 bits, totaling 4KB of space. The first 512 bytes were traditionally reserved for the interpreter, but this space is used for font data in modern implementations. The last 256 bytes are reserved for display refresh, and the preceding 96 bytes are allocated for the call stack, internal use, and other variables.
The CHIP-8 has 16 registers (V0...VF). VF is typically used as a flag for carry operations. Additionally, an address register (I) stores a 12-bit wide address.
The CHIP-8 virtual machine includes a built-in font with characters 0 through F. Here are the character sprite specifications:
 |
|---|
| Source |
The display is 64x32 pixels tall, although it's scaled to 640x360 in this implementation. Graphics are handled using the SDL wrapper for Python: Pygame.
The stack is used to store return addresses when subroutines are called. Modern implementations do not have the 12-level nesting limitation of older versions. In this implementation, I use an array outside the VM's memory.
| Opcode | Description |
|---|---|
| 00E0 | Clear the screen |
| 1NNN | Jump to address NNN |
| 6XNN | Set VX to NN |
| 7XNN | Add NN to VX |
| ANNN | Set I to NNN |
| DXYN | Display the value in memory location I at VX, VY position |
| 0NNN | Pause execution and execute the instruction at NNN |
| 2NNN | Push current PC to stack and call subroutine at NNN |
| 00EE | Return from subroutine (pop last address from stack) |
| 3XNN | Conditional skip if VX equals NN |
| 4XNN | Conditional skip if VX does not equal NN |
| 5XY0 | Conditional skip if VX equals VY |
| 9XY0 | Conditional skip if VX does not equal VY |
| 8XY0 | Set VX to the value of VY |
| 8XY1 | Set VX to VX OR VY |
| 8XY2 | Set VX to VX AND VY |
| 8XY3 | Set VX to VX XOR VY |
| 8XY4 | Add VY to VX; VF is set to 1 on carry, 0 otherwise |
| 8XY5 | Subtract VY from VX; VF is set to 0 on borrow, 1 otherwise |
| 8XY6 | Shift VX right by 1; VF is set to the least significant bit of VX before the shift |
| 8XY7 | Set VX to VY - VX; VF is set to 0 on borrow, 1 otherwise |
| 8XYE | Shift VX left by 1; VF is set to the most significant bit of VX before the shift |
| BXNN | Jump to address NNN plus V0 |
| CXNN | Set VX to a random number AND NN |
| EX9E | Skip the next instruction if the key stored in VX is pressed |
| EXA1 | Skip the next instruction if the key stored in VX is not pressed |
| FX07 | Set VX to value of delay timer |
| FX15 | Set delay timer to VX |
| FX18 | Set sound timer to VX |
| FX55 | Store V0 to VX in memory starting at the address in I |
| FX65 | Load V0 to VX from memory starting at address I |
| FX33 | Store binary-coded decimal representation of VX at addresses I, I+1, and I+2 |
| FX1E | Add VX to I; VF is set to 1 on overflow, 0 otherwise |
| FX0A | Wait for keypress, store key in VX |
| FX29 | Set I to the address of the sprite for the character in VX |
I couldn't have done this without the help of the following people and their resources:
- Tobias V. Langhoff's Chip-8 High Level Guide
- Cowgod's Chip-8 Technical Reference v1.0
- Timendu's CHIP-8 test suite
- Kripod's CHIP-8 ROM compilation