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buttery8/README.md
Butter b6b07c036f added my checklist
2026-04-07 10:48:11 -04:00

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The buttery chip-8

Just a personal project for me to get the hang of emulator development.

Load a .ch8 rom with buttery8 filename.ch8.

TODO

Project Setup

  • Initialize Rust project
  • Set up Cargo.toml with dependencies
  • Set up window/display library (I went with minifb)
  • Set up audio library
  • CLI ROM loading via command line argument

CPU / Core

  • Define CPU struct (registers, memory, stack, timers, PC, I)
  • Load ROM into memory at 0x200
  • Load fontset into memory at 0x050
  • Fetch / decode / execute loop
  • Proper cycle timing

Opcodes

  • 00E0 - CLS (clear display)
  • 00EE - RET (return from subroutine)
  • 1nnn - JP addr
  • 2nnn - CALL addr
  • 3xkk - SE Vx, byte
  • 4xkk - SNE Vx, byte
  • 5xy0 - SE Vx, Vy
  • 6xkk - LD Vx, byte
  • 7xkk - ADD Vx, byte
  • 8xy0 - LD Vx, Vy
  • 8xy1 - OR Vx, Vy
  • 8xy2 - AND Vx, Vy
  • 8xy3 - XOR Vx, Vy
  • 8xy4 - ADD Vx, Vy (with carry)
  • 8xy5 - SUB Vx, Vy (with borrow)
  • 8xy6 - SHR Vx
  • 8xy7 - SUBN Vx, Vy (with borrow)
  • 8xyE - SHL Vx
  • 9xy0 - SNE Vx, Vy
  • Annn - LD I, addr
  • Bnnn - JP V0, addr
  • Cxkk - RND Vx, byte
  • Dxyn - DRW Vx, Vy, nibble (draw sprite)
  • Ex9E - SKP Vx (skip if key pressed)
  • ExA1 - SKNP Vx (skip if key not pressed)
  • Fx07 - LD Vx, DT (read delay timer)
  • Fx0A - LD Vx, K (wait for key press)
  • Fx15 - LD DT, Vx (set delay timer)
  • Fx18 - LD ST, Vx (set sound timer)
  • Fx1E - ADD I, Vx
  • Fx29 - LD F, Vx (set I to font sprite)
  • Fx33 - LD B, Vx (BCD conversion)
  • Fx55 - LD [I], Vx (store registers to memory)
  • Fx65 - LD Vx, [I] (read registers from memory)

Display

  • 64x32 pixel framebuffer
  • XOR sprite drawing
  • Set VF on sprite collision
  • Render framebuffer to window
  • Correct draw timing / refresh rate

Input

  • Map keyboard to CHIP-8 hex keypad (0x0-0xF)
  • Key pressed state
  • Key released state
  • Blocking wait for keypress (Fx0A)

Timers

  • Delay timer counts down at 60hz
  • Sound timer counts down at 60hz
  • Buzzer sounds while sound timer > 0

Audio

  • Generate beep / tone while sound timer active

Testing & Compatibility

  • Pass 1-chip8-logo.ch8
  • Pass 2-ibm-logo.ch8
  • Pass 3-corax+.ch8
  • Pass 4-flags.ch8
  • Pass 5-quirks.ch8
  • Pass 6-keypad.ch8
  • Pass 7-beep.ch8
  • Pass 8-scrolling.ch8
  • Test with real ROMs / games

Polish

  • Configurable CPU speed / cycles per frame
  • Configurable color palette
  • Window scaling / resize support
  • Pause / resume
  • Reset / reload ROM
  • SUPER-CHIP / CHIP-48 quirks mode (optional)
  • XO-CHIP support (optional)