Project64 Debugger


Most of Project64’s debugging tools are relatively new, so they are not available in a stable release at this time. To get a version of the emulator with debugging features included, you can download the latest nightly build or build it yourself from source:

Unfinished features that are not yet integrated may be found on this Github fork:

Bug Reports & Suggestions

If you have a bug report please post it to the issue tracker:

You can post feature suggestions to the discussion thread:

Debugger Setup

A few settings must be applied to enable Project64’s debugging tools.

Enabling the “Always use interpreter core” option will negatively impact game performance, but it is required for some of the debugging features to function.

External Memory Scanner Setup

Project64’s debugger includes a built-in memory scanning tool, but if you would like to use a 3rd-party memory scanner like Cheat Engine, Project64’s “Fixed Rdram Address” setting may be used to make address resolution simpler.

To enable it, open Config/Project64.cfg in a text editor and add Fixed Rdram Address=536870912 under [default]. This setting will force Project64 to always allocate RDRAM at 0x20000000 in process memory.

Note that for optimization reasons Project64 uses little-endian byte ordering for RDRAM, so string data may not appear in the correct order when viewed from an external application.

Breakpoints Overview

Project64's debugger provides the following breakpoint types:

Program Counter Breakpoints

Program counter (PC) breakpoints pause the CPU when an instruction at a specified address is about to be executed. PC breakpoints may be set or cleared by double-clicking instructions in the Commands window.

Memory Read & Write Breakpoints

Memory read & write breakpoints pause the CPU when an instruction is about to read or write to a specified address in memory. Memory write breakpoints also pause on PI DMA transfers from cartridge ROM to RDRAM. Memory read & write breakpoints may be set or cleared by right clicking bytes in the Memory window.

Register Read & Write Breakpoints

Register read & write breakpoints pause the CPU when an instruction is about to read or write to a specified register. Register read & write breakpoints may be set by clicking or right clicking the labels for the general-purpose registers (GPR) in the Commands window.

Exception Breakpoints

Exception breakpoints pause the CPU at an exception vector when a specified exception or interrupt is asserted. CPU Exception breakpoints may be set or cleared via the checkboxes in the CPU Exception Breakpoints window.

Conditional Breakpoints

Conditional breakpoints pause the CPU when a user-defined condition is met. Conditional breakpoints may be set via the scripting API using events interface callbacks and the debug.breakhere() function.


(Debugger > Commands...)

The Commands tool is used to read, edit, and debug assembly code, monitor CPU and memory-mapped registers, and manage program counter (PC) and register breakpoints.

PC Breakpoints

PC breakpoints may be toggled by double-clicking addresses or by clicking the "Toggle breakpoint" option in the context menu. The "Run to line" option may be used to set a temporary breakpoint.

Register breakpoints

Register read and write breakpoints may be toggled by clicking or right clicking the register labels.

Currently, only general purpose registers are supported. If you wish to set a breakpoint on a memory-mapped register, it can be done from the memory viewer window.

Editing code

Code may be edited by clicking the "Edit code" option in the context menu. Edited code will appear magenta in the command list. Note that edits are temporary; they are not saved to the ROM file.

Command list color legend

Register color legend

Shortcut keys

Memory Viewer

(Debugger > View Memory...)

The memory viewer is used to monitor and edit memory. Breakpoints and locks may be placed on addresses by right-clicking the displayed bytes or using the shortcut keys described below.

Editor keyboard and mouse commands

    Ctrl+C                 Copy selection to the clipboard
    Ctrl+X                 Copy selection to the clipboard and zero-fill
    Ctrl+V                 Paste data from the clipboard
    Ctrl+B                 Paste data from the clipboard without advancing caret position
    Ctrl+T                 Duplicate current tab
    Ctrl+F4                Close current tab
    Ctrl+Tab               Switch tabs
    Ctrl+G                 Set base address to caret position or beginning of selection
    Ctrl+Space             Follow pointer
    Ctrl+A                 Select all visible bytes
    Ctrl+E                 Set memory lock at the caret position
    Ctrl+R                 Set memory read breakpoint at the caret position
    Ctrl+W                 Set memory write breakpoint at the caret position
    Ctrl+Q                 Clear all memory breakpoints and locks
    Ctrl+F                 Open search tool
    Ctrl+S                 Open memory dump tool
    Ctrl+[1-9]             Set byte group size
    Ctrl+Z                 Undo last safe mode edit
    Insert                 Toggle safe mode
    Enter                  Write safe-edited data
    Page Down              Advance base address down
    Page Up                Advance base address up
    Home                   Return to caret position
    Arrows                 Move caret position
    Ctrl+Arrows            Move caret position (single nibble while in the hex column)
    Shift+Arrows           Adjust selection range
    Delete                 Zero-fill selection
    Backspace              Zero-fill previous nibble/character or zero-fill selection
    Click                  Set caret position
    Mouse drag             Make selection
    Double click           Select byte group
    Right click            Show context menu

Editor color legend

Tab bar mouse commands

    Double click           Duplicate tab
    Right click            Close tab

Status bar mouse commands

    Click address range    Copy address range to clipboard
    Click "Have DMA"       Show DMA information

Safe mode

Safe mode is a setting that may be toggled via the insert key or from the option in the context menu. While safe mode is enabled, edits made by the user are not written into memory until the enter key is pressed. This can make it easier to edit pointers and touchy variables without crashing your game.

Memory Scanner

(Debugger > Memory > Search...)

The memory scanner is used to locate variables and strings in memory. Advanced search features are included to aid in searching for variables of unknown values and strings of unknown 1-byte encodings. Found variables may be added to the watch-list so that they may be labeled and monitored.

Watch-list tables are automatically saved as a CSV-like format to "Save/<GAME NAME>.wlst".

Video demonstration

Memory Dumper

(Debugger > Memory > Dump...)

The memory dumper is used to dump a chunk of virtual memory to a file. Supported dump formats include raw binary and MIPS disassembly.

Script Console

(Debugger > Scripts...)

The script console is used to execute Javascript files from the “Scripts” directory. Project64's scripting API provides hooks for various events, and access to system memory and registers. It also includes file management and networking capabilities which enable it to interact with other programs.

A script may be executed by double-clicking its name in the list. While a script is waiting for events it will be highlighted green in the list, during which time code may be typed into the console to be evaluated in the script’s context.

See “apidoc.htm” for API documentation and examples.

Video demonstration

Symbol Manager

(Debugger > Memory > Symbols...)

The symbol manager is used to apply names to addresses of functions and variables in memory and monitor their values real-time.

Locating SDK symbols

n64sym ( may be used to generate SDK symbol tables from RAM dumps. Similar functionality may be added to the debugger in the future.

Linker maps

Currently there is no built-in way to load symbols from a linker map or ELF. However, it's easy to convert a linker map to a Project64 symbol table using a script. An example is available here: mapsym.js.


Symbol tables are automatically saved as a CSV-like format to "Save/<GAME NAME>.sym".


(Debugger > Memory > DMA Log...)

The DMA log is used to monitor PI DMA transfers from cartridge ROM to RDRAM. Yellow entries indicate adjacent data chunks.

Signature detection

If the first four bytes of a data chunk are valid alphanumeric ASCII characters, they are displayed in the “Signature” column. This is occasionally useful for file-format identification.


The RAM and ROM address fields at the bottom of the window may be used to lookup corresponding source and destination addresses.


(Debugger > R4300i > Command Log...)

The CPU log is used to log the state of the CPU at every opcode execution.


This tool can be enabled or disabled via the "Enable CPU Logging" checkbox. The list is not refreshed until CPU logging is disabled or a breakpoint is hit.

Note that this tool incurs a massive performance penalty while enabled, so remember to turn it off when it's not needed.

Buffer size

The buffer size specifies the maximum number of operations that should be logged. This setting exists to ensure the log does not take up too much host RAM. The default of 1024 is good enough for most use cases.

Exception Breakpoints

(Debugger > R4300i > Exceptions...)

This window is used to set breakpoints on specific CPU exceptions and interrupts.

Crash diagnosis

To diagnose crashes, all exception codes should be checked. TLB-related codes may need to be unchecked for games that use TLB exceptions to their advantage.

When an exception breakpoint is hit, the CPU will pause at one of the exception vectors (usually at 0x80000180 or 0x80000000) and the COP0 registers (EPC, Cause, BadVAddr) will indicate the cause of the exception. COP0 registers can be viewed in the Commands window under the COP0 tab.

Stack Viewer

(Debugger > R4300i > Stack...)

This tool shows the memory region that the CPU's stack pointer (SP) register is pointing to, so that the current subroutine’s stack variables may be monitored.

Stack Trace

(Debugger > R4300i > Stack Trace...)

The Stack Trace tool shows the current call stack.