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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