gearlynx-romhacking

name	gearlynx-romhacking
description	Hack, modify, and translate Atari Lynx ROMs using the Gearlynx emulator MCP server. Provides workflows for memory searching, value discovery, cheat creation, data modification, sprite/text finding, and translation patching. Use when the user wants to create cheats, find game values in memory, modify ROM data, translate a Lynx game, patch game behavior, create ROM hacks, discover hidden content, change sprites or graphics, find text strings, apply Game Genie style codes, do infinite lives or health hacks, search for score or item counters, or reverse engineer data structures in Atari Lynx games. Also use for any ROM hacking, memory poking, or game modification task involving Gearlynx.
compatibility	Requires the Gearlynx MCP server. Direct tool mode is the default. Before installing or configuring, call debug_get_status to check if the server is already connected. If --mcp-router is enabled, use get_tool_info and execute_tool for routed tools.
metadata	{"author":"drhelius","version":"1.0"}

Atari Lynx ROM Hacking with Gearlynx

Overview

Hack, modify, and translate Atari Lynx ROMs using the Gearlynx emulator as an MCP server. Search memory for game variables, create cheats, find text strings for translation, locate sprite data, and reverse engineer data structures — all through MCP tool calls. Use save states as checkpoints and fast forward to reach specific game states.

MCP Server Prerequisite

IMPORTANT — Check before installing: Before attempting any installation or configuration, you MUST first verify if the Gearlynx MCP server is already connected in your current session. In the default mode, call debug_get_status directly. If Gearlynx was intentionally started with --mcp-router, call get_tool_info with {"name":"debug_get_status"}, then call execute_tool with {"name":"debug_get_status","arguments":{}}. A valid response from either workflow means the server is active and ready.

Only if neither workflow is available or the call fails, you need to help install and configure the Gearlynx MCP server:

Installing Gearlynx

Run the bundled install script (macOS/Linux):

bash scripts/install.sh

This installs Gearlynx via Homebrew on macOS or downloads the latest release on Linux. It prints the binary path on completion. You can also set INSTALL_DIR to control where the binary goes (default: ~/.local/bin).

Alternatively, download from GitHub Releases or install with brew install --cask drhelius/geardome/gearlynx on macOS.

Connecting as MCP Server

Configure your AI client to run Gearlynx as an MCP server via STDIO transport. Example for Claude Desktop (~/Library/Application Support/Claude/claude_desktop_config.json):

{
  "mcpServers": {
    "gearlynx": {
      "command": "/path/to/gearlynx",
      "args": ["--mcp-stdio"]
    }
  }
}

Replace /path/to/gearlynx with the actual binary path from the install script. Add --headless before --mcp-stdio on headless machines.

Hardware Documentation (References)

Atari Lynx hardware documentation is available in the references/ directory. Load them into your context when you need data formats, memory layout, or hardware details.

Reference	File	Load when...
General Overview	references/lynx1_general_overview.md	System specs, feature set, overall architecture
Hardware Overview	references/lynx2_hardware_overview.md	System block diagram: CPU, Mikey, Suzy, RAM, cart
Hardware Quirks	references/lynx3_software_hardware_perniciousness.md	Unsafe register operations, hardware gotchas to avoid when patching
CPU/ROM	references/lynx4_cpu_rom.md	65C02 cycle timing, CPU sleep, ROM mapping, opcode reference
Display	references/lynx5_display.md	Frame rate, pen/palette colors, display buffer addresses
Sprite/Collision	references/lynx6_sprite_collision.md	SCB format, sprite types, collision depository, sprite data layout
Audio/ROM Cart	references/lynx7_audio_tape_romcart.md	4 audio channels, ROM cart banking (BANK0/BANK1, AUDIN)
Timers/Interrupts	references/lynx8_timers_interrupts.md	8 timer channels, linking, reload, IRQ sources
UART	references/lynx8a_uart.md	ComLynx serial port, UART registers, baud rate
Other Hardware	references/lynx9_other_hardware.md	Hardware multiply/divide, parallel port
System Reset	references/lynx10_system_reset.md	Reset/power-up sequence, savegame EEPROM, NVRAM
System Bus Interplay	references/lynx11_system_bus_interplay.md	Bus masters, page mode, DMA timing
Hardware Addresses	references/hardware_addresses.md	64K memory map, Mikey/Suzy register addresses ($FC00-$FCFF, $FD00-$FDFF)

---

Core Technique: Memory Search

Memory search is the primary tool for ROM hacking. It uses a capture → change → compare cycle to isolate memory addresses holding game values.

The Search Loop

1. memory_search_capture    → snapshot current memory state
2. (change the value in-game using controller_button, fast forward, etc.)
3. memory_search            → compare against snapshot to find changed addresses
4. Repeat 2-3 until only a few candidates remain
5. read_memory / write_memory → verify and modify the found addresses

Search Operators and Types

memory_search supports these operators: <, >, ==, !=, <=, >=

Compare types:

• previous — compare current value to last captured snapshot (most common)
• value — compare current value to a specific number
• address — compare current value to value at another address

Data types: hex, signed, unsigned

Example: Finding the Lives Counter

1. memory_search_capture                         → snapshot with 3 lives
2. Lose a life in-game (play or use controller_button)
3. memory_search (operator: <, compare: previous) → values that decreased
4. memory_search_capture                         → snapshot with 2 lives
5. Lose another life
6. memory_search (operator: <, compare: previous) → narrow further
7. Or use: memory_search (operator: ==, compare: value, value: 1)
   → find addresses holding exactly 1
8. write_memory on the candidate address to set lives to 99
9. get_screenshot to verify the change took effect

Example: Finding a Score Counter

Score values are often stored as multi-byte (16-bit little-endian on 6502):

1. memory_search_capture                                → snapshot at score 0
2. Score some points in-game
3. memory_search (operator: >, compare: previous)       → values that increased
4. memory_search_capture
5. Score more points
6. memory_search (operator: >, compare: previous)       → narrow down
7. read_memory on candidates — look for values matching current score
8. write_memory to set a custom score

For 16-bit values: the low byte is at address N, high byte at N+1 (6502 is little-endian).

---

Fast Forward for Efficiency

Use fast forward to speed through gameplay when you need to trigger in-game changes:

set_fast_forward_speed (4 = unlimited)
toggle_fast_forward              → enable
(play through the game section)
toggle_fast_forward              → disable

This is essential when you need to reach specific game states without waiting in real-time.

---

Save States as Checkpoints

Save states are critical for ROM hacking — they let you save your position and retry modifications:

select_save_state_slot (1-5)     → pick a slot
save_state                       → save current state
(try modifications)
load_state                       → revert if something breaks

Use different slots for different game states (e.g., slot 1 = start, slot 2 = boss fight, slot 3 = specific level).

list_save_state_slots shows all slots with ROM name, timestamp, and screenshot availability.

Rewind as an Alternative

The emulator also records continuous snapshots into a rewind ring buffer. Use get_rewind_status to check availability, then rewind_seek to jump to any recorded point without manual save/load. This is especially useful for quickly reverting after a failed memory write — pause, seek back a few snapshots, and retry.

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Finding and Modifying Game Data

Text and String Discovery

To find text strings for translation or modification:

1. Determine the character encoding — Lynx games often use custom character maps, not ASCII
2. read_memory across ROM banks (Bank 0, Bank 0A, Bank 1, Bank 1A) scanning for known byte patterns
3. Use memory_find_bytes to search for specific byte sequences across memory
4. Set read breakpoints on suspected text addresses with set_breakpoint (type: read) to confirm they're used for rendering
5. get_screenshot to correlate displayed text with memory contents

Sprite and Graphics Data

1. get_frame_buffer to capture the current visual state (VIDBAS or DISPADR)
2. get_suzy_registers to find sprite control block (SCB) addresses, VIDBAS pointer
3. Set read breakpoints on sprite data addresses to find the rendering code
4. read_memory on the sprite data area to analyze the packed pixel format
5. get_screenshot before/after modifications to see visual changes

Reference the Sprite/Collision hardware docs (references/lynx6_sprite_collision.md) for SCB structure details.

Data Tables and Structures

1. debug_pause → get_disassembly around code that loads data
2. Look for LDA/LDX/LDY instructions with absolute or indexed addressing — these point to data tables
3. read_memory at the target addresses to dump the table contents
4. add_memory_bookmark to mark discovered data regions
5. add_symbol to label data table entry points for future reference

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Creating Cheats

Infinite Lives / Health

1. Find the address using the search loop (above)
2. Set a write breakpoint: set_breakpoint (type: write) on the address
3. debug_continue → when it hits, get_disassembly to see the decrement code
4. Note the instruction (e.g., DEC $0042 or STA $0042)
5. Option A: Periodically write_memory to reset the value (simple poke cheat)
6. Option B: Identify the decrement routine for a NOP patch

Watching Values in Real-Time

Use add_memory_watch on discovered addresses. Watches appear in the emulator's GUI memory editor, letting you monitor values as the game runs — useful for verifying cheats work across different game situations.

Write Breakpoint Technique

The most powerful cheat-finding technique:

1. Find the variable address via memory search
2. set_breakpoint (type: write) on that address
3. debug_continue — the emulator stops when the game writes to that address
4. get_6502_status + get_disassembly reveals the exact code modifying the value
5. get_call_stack shows what triggered the write
6. You now know exactly where and how the game manages that variable

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Translation Workflow

1. Identify the Font System

1. get_screenshot of a screen with text
2. Find text rendering code by setting read breakpoints on display buffer areas
3. Trace back to find the character mapping table
4. read_memory to dump the font/character table
5. add_symbol to label the font table and rendering routine

2. Find String Data

1. Look for sequential text bytes in ROM banks using read_memory with large ranges
2. Use memory_find_bytes to search for known byte patterns
3. Cross-reference with the character table to decode strings
4. add_memory_bookmark to mark each string location

3. Measure Space Constraints

ROM hacking translations must fit within existing space:

1. read_memory to determine how much space each string occupies
2. Check for string terminators (commonly $00, $FF, or length-prefixed)
3. If the translation is longer, look for unused ROM space or abbreviate

4. Apply and Test

1. write_memory to patch translated strings into memory
2. get_screenshot to verify rendering
3. save_state before each change so you can load_state if it breaks
4. Test all screens that display modified text

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Memory Map Quick Reference

Use list_memory_areas to get the full list. Common areas:

Area	CPU Address	Use
Zero Page	$0000-$00FF	Fast variables, counters, game state
Stack	$0100-$01FF	6502 stack
RAM	$0000-$FFFF	Main working memory
Bank 0	Varies	ROM bank 0
Bank 0A	Varies	ROM bank 0A
Bank 1	Varies	ROM bank 1
Bank 1A	Varies	ROM bank 1A
EEPROM	Varies	Save data, high scores

Zero Page is the most common location for game variables (lives, health, score, position) because 6502 zero page addressing is faster.

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Bookmarks and Organization

Keep your hacking session organized:

• add_memory_bookmark — mark discovered data regions, variable locations, string tables
• add_memory_watch — track values that change during gameplay
• add_symbol — label addresses in disassembly for readability
• add_disassembler_bookmark — mark code routines you've identified

Use list_memory_bookmarks, list_memory_watches, list_symbols, list_disassembler_bookmarks to review.

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Persisting Changes

Changes made via write_memory to ROM bank areas are applied to the emulator's in-memory copy only — they are not persisted to the ROM file on disk. To create a permanent patch, use command-line tools (e.g., a binary patch script) to apply the discovered modifications to the actual ROM file.