As a learning project, I decided to write an emulator in Go. It seems like CHIP-8 is generally agreed to be the easiest starting point, so I started there.
Right now, the emulator doesn't do a lot, but if your ROM only uses the opcodes that are implemented, it should work okay. The IBM Logo ROM from the CHIP-8 pack works decently and was the first 3rd party ROM that I was able to run.
The CHIP-8 pack can be found here: https://web.archive.org/web/20130903155600/http://chip8.com/?page=109
| Implemented | Opcode | Description |
|---|---|---|
| ❌ | 0x0NNN |
Calls RCA 1802 program at address 0xNNN. |
| ✅ | 0x00E0 |
Clear the screen |
| ✅ | 0x00EE |
Return from subroutine |
| ✅ | 0x1NNN |
Jump to 0xNNN |
| ✅ | 0x2NNN |
Call subroutine at 0xNNN |
| ✅ | 0x3XNN |
Skip next instruction if VX == NN |
| ✅ | 0x4XNN |
Skip next instruction if VX != NN |
| ✅ | 0x5XY0 |
Skip next instruction if VX == VY |
| ✅ | 0x6XNN |
Set VX to NN |
| ✅ | 0x7XNN |
Add NN to VX (carry flag is not changed) |
| ✅ | 0x8XY0 |
Set VX to the value of VY |
| ✅ | 0x8XY1 |
Set VX to VX | VY (bitwise OR) |
| ✅ | 0x8XY2 |
Set VX to VX & VY (bitwise AND) |
| ✅ | 0x8XY3 |
Set VX to VX xor VY |
| ❌ | 0x8XY4 |
Add VY to VX. VF is set to 1 when there's a carry, and 0 when there isn't. |
| ❌ | 0x8XY5 |
Subtract VY from VX. VF is set to 0 when there's a borrow and 1 when there isn't. |
| ❌ | 0x8XY6 |
Shift VY right by one and copy the result to VX. VF is set to the value of the least significant bit of VY before the shift. |
| ❌ | 0x8XY7 |
Set VX to VY - VX. VF is set to 0 when there's a borrow and 1 when there isn't. |
| ❌ | 0x8XYE |
Shift VY left by one and copy the result to VX. VF is set to the value of the least significant bit of VY before the shift. |
| ✅ | 0x9XY0 |
Skip the next instruction if VX doesn't equal VY. |
| ✅ | 0xANNN |
Set index register to 0xNNN |
| ❌ | 0xBNNN |
Jump to the address NNN plus V0 |
| ✅ | 0xCXNN |
Set VX to the result of a bitwise and operation on a random number and NN |
| ✅ (partial) | 0xDXYN |
Draw a sprite at coordinate (VX, VY) that has a width of 8 pixels and a height of N pixels. Each row is read as bit-coded starting from the index register, I. I doesn't change after the execution of this instruction. VF is set to 1 if any screen pixels are flipped from set to unset when the sprite is drawn, and to 0 if that doesn't happen. |
| ❌ | 0xEX9E |
Skip the next instruction if the key stored in VX is pressed. |
| ❌ | 0xEXA1 |
Skip the next instruction if the key stored in VX is not pressed. |
| ❌ | 0xFX07 |
Set VX to the value of the delay timer. |
| ❌ | 0xFX0A |
A key press is awaited and then stored in VX (blocking operation - all instructions are halted until the next key event) |
| ✅ | 0xFX15 |
Set the delay timer to the value of VX |
| ✅ | 0xFX18 |
Set the sound timer to the value of VX |
| ❌ | 0xFX1E |
Add the value of VX to the index register |
| ❌ | 0xFX29 |
Set I to the location of the sprite for the character in VX. Characters 0-F (in hex) are represented by a 4x5 font. |
| ❌ | 0xFX33 |
Stores the binary-coded decimal representation of VX, with the most significant of three digits at the address in I, the middle digit at I plus 1, and the least significant digit at I plus 2. (In other words, take the decimal representation of VX, place the hundreds digit in memory at location in I, the tens digit at location I+1, and the ones digit at location I+2.) |
| ❌ | 0xFX55 |
Stores V0 to VX (including VX) in memory starting at address I. I is increased by 1 for each value written. |
| ❌ | 0xFX65 |
Fills V0 to VX (including VX) with values from memory starting at address I. I is increased by 1 for each value written. |