6502 emulator

Please note that this is just a project for me to learn Rust and how the 6502 works. You can use this software, as-is. Feel free to submit issues and/or contribute, but don't expect too much.

Roadmap

Backend

Core

• Implement all addressing modes
• Test all addressing modes
• Implement all instructions
  • SBC
  • Handle over/underflow in branching instructions
• Test all instructions
• Interrupts
  • BRK
  • IRQ
  • NMI
• Test all opcodes
• Count cycles

IO

• Read plaintext files
• Read ROM files
  • Custom, minimal format
  • iNES
  • NES2.0

NES

• PPU
• APU
• etc.

Frontend

• TUI
  • Registers
  • Flags
  • Memory
    • View memory
    • Scroll memory
    • Edit memory
    • View stack
  • Port to ratatui
  • Display
  • Menus
  • Theming
• API

Specific system emulation

• 0xFFFA-0xFFFB: NMI interrupt vector
• 0xFFFC-0xFFFD: reset vector
• 0xFFFE-0xFFFF: IRQ interrupt vector

Nintendo Entertainment System / Famicom

See NESdev Wiki for more.

CPU memory map

• 0x0000-0x07FF: 2KB internal RAM (as used in Bus.rs)
• 0x0800-0x1FFF: mirrors of internal RAM
• 0x2000-0x2007: PPU registers
• 0x2008-0x3FFF: mirrors of PPU registers
• 0x4000-0x4017: APU and I/O registers
  • 0x4016 and 0x4017 read controller 1 and 2 (respectively), bit by bit
• 0x4018-0x401F: normally disabled (APU and I/O functionality)
• 0x4020-0xFFFF: cartridge space (PRG ROM/RAM and mapper registers, incl. reset and IRQ vector)

CPU-PPU registers

8 registers from 0x2000 to 0x2007, mirrored beyond that.

• 0x2000: PPUCTRL
• 0x2001: PPUMASK
• 0x2002: PPUSTATUS
• 0x2003: OAMADDR
• 0x2004: OAMDATA
• 0x2005: PPUSCROLL
• 0x2006: PPUADDR
• 0x2007: PPUDATA
• 0x4014: OAMDMA

PPU memory map

• 0x0000-0x1FFF: pattern memory ("CHR ROM")
• 0x2000-0x3EFF: nametable memory ("VRAM")
• 0x3F00-0x3FFF: palette memory