A Chip-8 Emulator written in C with OpenGL. Chip-8 is interpreted programming language from the 1970s originally developed for the COSMAC VIP and Telmac 1800 8-bit computers.
Chip-8 VM is composed of 16 8 bit general purpose data registers V0-VF. Register VF is used as a flag for some instructions. Two other special registers exist, the 16 bit address register, I, and the 16 bit Program Counter. The VM contains 4096 1 byte memory locations. Of those, the first 512 bytes are reserved for the interpreter with the program memory starting at address 0x200. Output is via a 64x32 monochromatic display, with input from a 16 key hex keyboard. Additionally, there are two timers, the delay time and the sound timer, both of which count down at 60 Hz until they reach zero. The sound times produces a tone when it is not zero
Each instruction is 16bit length and contains some combination of registers IDs, and immediate values. The opcodes are stored big-endian.
- X and Y are 4 bit registers IDs
- I is the memory register
- N is a 4 bit immediate value
- NN is a 8 bit immediate value
- NNN is a 12 bit immediate value
| Code | Description | Status |
|---|---|---|
| 0NNN | Call RCA 1802 program at address NNN | Not implemented few ROMs depend on it |
| 00E0 | Clear display | Implemented and Tested |
| 00EE | Return from subroutine | Implemented and Tested |
| 1NNN | Jump to address NNN | Implemented and Tested |
| 2NNN | Call subroutine at NNN | Implemented and Tested |
| 3XNN | Skip next instruction if Vx = NN | Implemented and Tested |
| 4XNN | Skip next instruction if Vx != NN | Implemented and Tested |
| 5XY0 | Skip next instruction if Vx == Vy | Implemented and Tested |
| 6XNN | Sets Vx to NN | Implemented and Tested |
| 7XNN | Sets Vx to Vx plus NN | Implemented and Tested |
| 8XY0 | Sets Vx to Vy | Implemented and Tested |
| 8XY1 | Sets Vx to bitwise Vx or Vy | Implemented and Tested |
| 8XY2 | Sets Vx to bitwise Vx and Vy | Implemented and Tested |
| 8XY3 | Sets Vx to bitwise Vx xor Vy | Implemented and Tested |
| 8XY4 | Sets Vx to Vx plus Vy | Implemented and Tested |
| 8XY5 | Sets Vx to Vx minus Vy | Implemented and Tested |
| 8XY6 | Sets Vx and Vy to Vy shifted one bit to the right. Vf is set to the least significant bit of Vy from before the shift | Implemented and Tested |
| 8XY7 | Sets Vx to Vy minus Vx + Implemented and Tested | Implement and Tested |
| 8XYE | Sets Vx and Vy to Vy shifted one bit to the left. Vf is set to the most significant bit of Vy from before the shift | Implemented and Tested |
| 9XY0 | Skips the next instruction if Vx != Vy | Implemented and Tested |
| ANNN | Sets I to NNN | Implemented and Tested |
| BNNN | Jumps to Vx + NNN | Implemented and Tested |
| CXNN | Sets Vx to random [0,255] anded with NN | Implemented and Tested |
| DXYN | Draws a sprite at (Vx,Vy) with a width of 8 pixels and a height of N pixels from the memory location pointed to by I. Sprites are xor'd with the current state of the screen. Vf is set to 1 if any pixels go from set to unset | Implemented and Tested |
| EX9E | Skips the next instruction if the key code in Vx is pressed | Implemented and Tested |
| EXA1 | Skips the next instruction if the key code in Vx is not pressed | Implemented and Tested |
| FX07 | Sets Vx to the current value of the delay timer | Implemented and Tested |
| FX0A | Blocks until the next key press, and stores the key code in Vx | Implemented and Tested |
| FX15 | Sets the delay timer to Vx | Implemented and Tested |
| FX18 | Sets the sound timer to Vx | Implemented and Tested |
| FX1E | Sets I to I + Vx | Implemented and Tested |
| FX29 | Sets I to the location of the font character in Vx. For example if Vx 0xA, I will be set to the location of 'A' | Implemented and Tested |
| FX33 | Causes the BCD representation of Vx to be stored starting at I. I + 0 is set to the hundreds place of Vx, I + 1 is set to the tens place of Vx, and I + 2 is set to the ones place of Vx | Implemented and Tested |
| FX55 | Dump registers [V0, VX] to memory starting at I. I is incremented for each value written | Implemented and Tested |
| FX65 | Load registers [V0, VX] from memory starting at I. I is incremented for each value read | Implemented and Tested |
srccontains the sourcestestcontains the unit, and functionality teststestdatacontains test data used in the functionality testsromscontains public domain ROMS for the Chip-8
- Build binary
make
- Build unit Tests
make test
2. Execute Unit Tests
./tests
The unit tests for the Chip-8 core implementation are located in the test/chip8_test.c file along with additional units tests for other components. These tests are written using the Check C unit testing frame work. The goals of Chip-* core unit tests is to test the core functionality of the Chip-8 VM, by verify each instruction behaves as expected along verifying higher level functionality such as timers, drawing to the display, and program executions works as expected.
The implementation of the emulator core is complete. The display output, and keyboarad input are functioning correctly.
- Key maps 2: Instruction rate limiting
- Set a fixxed max rate of instructions per a second
- Sound timer
- Make a sound when delay timer is not 0