regenerator2000: Skill for Claude Code

Analyze Routine Workflow

Use this skill when the user asks to "analyze this routine" or "what does this function do?"

1. Determine System & Context

• Use r2000_get_binary_info to get the system, filename, description, and may_contain_undocumented_opcodes hint.
• CRITICAL: The system field tells you the target computer (e.g., Commodore 64, VIC-20). You MUST become an expert in that specific target computer's memory map, hardware registers, and KERNAL routines.
• CONTEXT: The filename and description tell you the specific software being analyzed. Use this to identify standard libraries (e.g., "Hubbard music driver", "Exomizer decompressor") and to understand the likely purpose of routines based on the game's genre (e.g., "check_collision" in a shooter).
• UNDOCUMENTED OPCODES: If may_contain_undocumented_opcodes is true, expect illegal/undocumented MOS 6502 opcodes (e.g., LAX, SAX, SLO, DCP, ISC) within routines. These are valid instructions — do not treat them as disassembly errors.

2. Identify the Bounds

• If the user provides an address, start there.
• If no address is given, call r2000_get_disassembly_cursor first — the routine starts at the cursor address.
• Look for the start (entry point or label) and end (RTS, JMP, or RTI) of the routine.
• Note: Some routines end with a JMP to a shared epilogue — that still marks the end of this routine's body. Others fall through into the next routine with no explicit return; use cross-references and logic flow to determine the boundary.

3. Read the Code

• Use r2000_read_region (with "view": "disasm") to get the instructions.
• Analyze the flow:
  • Does it loop?
  • Does it call other known routines or OS entry points?
  • Does it access hardware registers?
• Look for common routine patterns (generic 6502):
  • SEI / CLI bracketing → IRQ setup/teardown.
  • Loop with LDA/STA and DEX/DEY/BNE → Memory copy or fill.
  • Bit-shifting, ADC/SBC chains → Math or decompressor.
  • Reads a memory-mapped I/O address then branches → Hardware polling.
• Use your knowledge of the target system (from r2000_get_binary_info) to recognize system-specific patterns:
  • Calls to OS/KERNAL entry points → System service calls.
  • Reads/writes to hardware register addresses → I/O, video, sound, or input handling.
  • Writes to interrupt vector locations → IRQ/NMI setup.
  • Writes to sound chip registers → Music/SFX driver tick.
  • Reads input port registers → Joystick, keyboard, or controller polling.