# General Debugger Commands

help

  displays built-in help in the console

do

  evaluates the given expression

symlist

  lists registered symbols

softreset

  executes a soft reset

hardreset

  executes a hard reset

print

  prints one or more <item>s to the console

printf

  prints one or more <item>s to the console using <format>

logerror

  outputs one or more <item>s to the error.log

tracelog

  outputs one or more <item>s to the trace file using <format>

tracesym

  outputs one or more <item>s to the trace file

history

  displays recently visited PC addresses and opcodes

trackpc

  visually track visited opcodes

trackmem

  record which PC writes to each memory address

pcatmem

  query which PC wrote to a given memory address

rewind

  go back in time by loading the most recent rewind state

statesave

  save a state file for the emulated system

stateload

  load a state file for the emulated system

snap

  save a screen snapshot

source

  read commands from file and executes them one by one

time

  prints the current machine time to the console

quit

  exit the debugger and end the emulation session

## help

help [<topic>]

Displays built-in debugger help in the debugger console. If no <topic> is specified, top-level topics are listed. Most debugger commands have correspondingly named help topics.

Examples:

`help`

  Lists top-level help topics.

`help expressions`

  Displays built-in help for debugger expression syntax.

`help wpiset`

  Displays built-in help for the wpiset command.

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## do

do <expression>

The do command simply evaluates the supplied expression. This is often used to set or modify device state variable (e.g. CPU registers), or to write to memory. See Debugger expression syntax for details about expression syntax.

Examples:

`do pc = 0`

  Sets the register pc to 0.

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## symlist

symlist [<cpu>]

Lists registered symbols and their values. If <cpu> is not specified, symbols in the global symbol table are displayed; otherwise, symbols specific to the device <cpu> are displayed. Symbols are listed alphabetically. Read-only symbols are noted. See Specifying devices and address spaces for details on how to specify a CPU.

Examples:

`symlist`

  Displays the global symbol table.

`symlist 2`

  Displays the symbols for the third CPU in the system (zero-based index).

`symlist audiocpu`

  Displays symbols for the CPU with the absolute tag `:audiocpu`.

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## softreset

softreset

Executes a soft reset. This calls the reset member functions of all the devices in the system (by default, pressing F3 during emulation has the same effect).

Examples:

`softreset`

  Executes a soft reset.

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## hardreset

hardreset

Executes a hard reset. This tears down the emulation session and starts another session with the same system and options (by default, pressing Shift+F3 during emulation has the same effect). Note that this will lose history in the debugger console and error log.

Examples:

`hardreset`

  Executes a hard reset.

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## print

print <item>[,…]

The print command prints the results of one or more expressions to the debugger console as hexadecimal numbers.

Examples:

`print pc`

  Prints the value of the pc register the console as a hex number.

`print a,b,a+b`

  Prints a, b, and the value of a+b to the console as hex numbers.

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## printf

printf <format>[,<argument>[,…]]

Prints a C-style formatted message to the debugger console. Only a very limited subset of format specifiers and escape sequences are available:

%c

  Prints the corresponding argument as an 8-bit character.

%[-][0][<n>]d

  Prints the corresponding argument as a decimal number with optional left justification, zero fill and minimum field width.

%[-][0][<n>]o

  Prints the corresponding argument as an octal number with optional left justification, zero fill and minimum field width.

%[-][0][<n>]x

  Prints the corresponding argument as a lowercase hexadecimal number with optional left justification, zero fill and minimum field width.

%[-][0][<n>]X

  Prints the corresponding argument as an uppercase hexadecimal number with optional left justification, zero fill and minimum field width.

%[-][<n>][.[<n>]]s

  Prints a null-terminated string of 8-bit characters from the address and address space given by the corresponding argument, with optional left justification, minimum and maximum field widths.

%%

  Prints a literal percent symbol.

\n

  Prints a line break.

\\

  Prints a literal backslash.

All other format specifiers are ignored.

Examples:

`printf "PC=%04X",pc`

  Prints `PC=<pcval>` where <pcval> is the hexadecimal value of the pc register with a minimum of four digits and zero fill.

`printf "A=%d, B=%d\\nC=%d",a,b,a+b`

  Prints `A=<aval>, B=<bval>` on one line, and `C=<a+bval>` on a second line.

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## logerror

logerror <format>[,<argument>[,…]]

Prints a C-style formatted message to the error log. See printf for details about the limited set of supported format specifiers and escape sequences.

Examples:

`logerror "PC=%04X",pc`

  Logs `PC=<pcval>` where <pcval> is the hexadecimal value of the pc register with a minimum of four digits and zero fill.

`logerror "A=%d, B=%d\\nC=%d",a,b,a+b`

  Logs `A=<aval>, B=<bval>` on one line, and `C=<a+bval>` on a second line.

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## tracelog

tracelog <format>[,<argument>[,…]]

Prints a C-style formatted message to the currently open trace file (see trace for more information). If no trace file is open, this command has no effect. See printf for details about the limited set of supported format specifiers and escape sequences.

Examples:

`tracelog "PC=%04X",pc`

  Outputs `PC=<pcval>` where <pcval> is the hexadecimal value of the pc register with a minimum of four digits and zero fill if a trace log file is open.

`tracelog "A=%d, B=%d\\nC=%d",a,b,a+b`

  Outputs `A=<aval>, B=<bval>` on one line, and `C=<a+bval>` on a second line if a trace log file is open.

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## tracesym

tracesym <item>[,…]

Prints the specified symbols to the currently open trace file (see trace for more information). If no trace file is open, this command has no effect.

Examples:

`tracesym pc`

  Outputs `PC=<pcval>` where <pcval> is the value of the pc register in its default format if a trace log file is open.

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## history

history [<CPU>[,<length>]]

Displays recently visited PC addresses, and disassembly of the instructions at those addresses. If present, the first argument selects the CPU (see Specifying devices and address spaces for details); if no CPU is specified, the visible CPU is assumed. The second argument, if present, limits the maximum number of addresses shown. Addresses are shown in order from least to most recently visited.

Examples:

`history ,5`

  Displays up to five most recently visited PC addresses and instructions for the visible CPU.

`history 3`

  Displays recently visited PC addresses and instructions for the fourth CPU in the system (zero-based index).

`history audiocpu,1`

  Displays the most recently visited PC address and instruction for the CPU with the absolute tag `:audiocpu`.

## trackpc

trackpc [<enable>[,<CPU>[,<clear>]]]

Turns visited PC address tracking for disassembly views on or off. Instructions at addresses visited while tracking is on are highlighted in debugger disassembly views. The first argument is a Boolean specifying whether tracking should be turned on or off (defaults to on). The second argument specifies the CPU to enable or disable tracking for (see Specifying devices and address spaces for details); if no CPU is specified, the visible CPU is assumed. The third argument is a Boolean specifying whether existing data should be cleared (defaults to false).

Examples:

`trackpc 1`

  Begin or tracking the current CPU’s PC.

`trackpc 1,0,1`

  Begin or continue tracking PC on the first CPU in the system (zero-based index), but clear the history tracked so far.

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## trackmem

trackmem [<enable>,[<CPU>,[<clear>]]]

Enables or disables logging the PC address each time a memory address is written to. The first argument is a Boolean specifying whether tracking should be enabled or disabled (defaults to enabled). The second argument specifies the CPU to enable or disable tracking for (see Specifying devices and address spaces for details); if no CPU is specified, the visible CPU is assumed. The third argument is a Boolean specifying whether existing data should be cleared (defaults to false).

Use pcatmem to retrieve this data. Right-clicking a debugger memory view will also display the logged PC value for the given address in some configurations.

Examples:

`trackmem`

  Begin or continue tracking memory writes for the visible CPU.

`trackmem 1,0,1`

  Begin or continue tracking memory writes for the first CPU in the system (zero-based index), but clear existing tracking data.

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## pcatmem

pcatmem[{d|i|o}] <address>[:<space>]

Returns the PC value at the time the specified address was most recently written to. The argument is the requested address, optionally followed by a colon and a CPU and/or address space (see Specifying devices and address spaces for details). The optional d, i or o suffix controls the default address space for the command.

Tracking must be enabled for the data this command uses to be recorded (see trackmem). Right-clicking a debugger memory view will also display the logged PC value for the given address in some configurations.

Examples:

`pcatmem 400000`

  Print the PC value when location 400000 in the visible CPU’s program space was most recently written.

`pcatmem 3bc:io`

  Print the PC value when location 3bc in the visible CPU’s `io` space was most recently written.

`pcatmem 1400:audiocpu`

  Print the PC value when location 1400 in the CPU `:audiocpu`’s program space was most recently written.

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## rewind

rewind

Loads the most recent RAM-based saved state. When enabled, rewind states are saved when step, over and out commands are used, storing the machine state as of the moment before stepping. May be abbreviated to `rw`.

Consecutively loading rewind states can work like reverse execution. Depending on which steps forward were taken previously, the behavior can be similar to GDB's reverse-stepi and reverse-next commands. All output for this command is currently echoed into the running machine window.

Previous memory and PC tracking statistics are cleared. Actual reverse execution does not occur.

Examples:

`rewind`

  Load the previous RAM-based save state.

`rw`

  Abbreviated form of the command.

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## statesave

statesave <filename>

Creates a save state at the current moment in emulated time. The state file is written to the configured save state directory (see the state_directory option), and the .sta extension is automatically appended to the specified file name. May be abbreviates to `ss`.

All output from this command is currently echoed into the running machine window.

Examples:

`statesave foo`

  Saves the emulated machine state to the file foo.sta in the configured save state directory.

`ss bar`

  Abbreviated form of the command – saves the emulated machine state to bar.sta.

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## stateload

stateload <filename>

Restores a saved state file from disk. The specified state file is read from the configured save state directory (see the state_directory option), and the .sta extension is automatically appended to the specified file name. May be abbreviated to `sl`.

All output for this command is currently echoed into the running machine window. Previous memory and PC tracking statistics are cleared.

Examples:

`stateload foo`

  Loads state from file foo.sta to the configured save state directory.

`sl bar`

  Abbreviated form of the command – loads the file bar.sta.

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## snap

snap [<filename>[,<scrnum>]]

Takes a snapshot of the emulated video display and saves it to the configured snapshot directory (see the snapshot_directory option). If a file name is specified, a single screenshot for the specified screen is saved using the specified filename (or the first emulated screen in the system if a screen is not specified). If a file name is not specified, the configured snapshot view and file name pattern are used (see the snapview and snapname options).

If a file name is specified, the .png extension is automatically appended. The screen number is specified as a zero-based index, as seen in the names of automatically-generated single-screen views in MAME’s video options menus.

Examples:

`snap`

  Takes a snapshot using the configured snapshot view and file name options.

`snap shinobi`

  Takes a snapshot of the first emulated video screen and saves it as shinobi.png in the configured snapshot directory.

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## source

source <filename>

Reads the specified file in text mode and executes each line as a debugger command. This is similar to running a shell script or batch file.

Examples:

`source break_and_trace.cmd`

  Reads and executes debugger commands from break_and_trace.cmd.

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## time

Prints the total elapsed emulated time to the debugger console.

Examples:

`time`

  Prints the elapsed emulated time.

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## quit

quit

Closes the debugger and ends the emulation session immediately. Either exits MAME or returns to the system selection menu, depending on whether the system was specified on the command line when starting MAME.

Examples:

`quit`

  Exits the emulation session immediately.

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