| Author: | Mike Naberezny |
|---|---|
| Version: | |version| |
Overview
Simulate 6502-based microcomputer systems in Python.
Py65 includes a program called Py65Mon that functions as a machine language monitor. This kind of program is sometimes also called a debugger. Py65Mon provides a command line with many convenient commands for interacting with the simulated 6502-based system.
The monitor is started using the py65mon command:
$ py65mon
Py65 Monitor
PC AC XR YR SP NV-BDIZC
6502: 0000 00 00 00 ff 00110000
.
Once the monitor has started, it will display a register dump and the dot prompt. You can then enter commands for the monitor at this prompt.
Py65Mon uses commands that are very similar to those used by the
VICE emulator's monitor
for Commodore computers. You can get a list of available commands
with help or help on a specific command with help command.
When working with Py65Mon, you will frequently need to enter numbers, addresses, and ranges of addresses. Almost all Py65 command support entering numbers in binary, decimal, and hexadecimal.
Numbers can be entered with a prefix to specify the radix, e.g. $c000
instructs Py65Mon that the number c000 is hexadecimal. The following
prefixes are supported:
$c000: The dollar sign indicates hexadecimal.+828: The plus sign indicates decimal.%0101: The percent sign indicates binary.
Numbers can also be entered without a prefix. Most of the time, working in
hexadecimal will be the most convenient so this is the default radix. The
number c000 will be assumed to be hexadecimal unless the default radix
is changed using the radix command.
Some commands accept a range of memory addresses:
.disassemble ff80:ff84 $ff80 d8 CLD $ff81 a2 ff LDX #$ff $ff83 9a TXS $ff84 a0 1c LDY #$1c
The syntax for a range is start:end. Each of the two parts may have
a prefix to indicate the radix, or no prefix to use the default radix.
Sometimes it is useful to have the starting and ending address in a range
be the same, such as when you want to inspect a single byte of memory. In
this case, you can enter ff80:ff80 or simply ff80.
Large assembly language programs may have hundreds of procedures. It is difficult to remember the memory address of each procedure and the addresses may change if the program is reassembled.
You can add a label for any memory address using the add_label command.
This label can then be used anywhere the address could be used:
.add_label ff80 start .disassemble start $ff80 d8 CLD
When using labels, you can also specify an offset (plus or minus):
.disassemble start:start+4 $ff80 d8 CLD $ff81 a2 ff LDX #$ff $ff83 9a TXS $ff84 a0 1c LDY #$1c
Offsets are interpreted like any other numbers. In the example above,
start+4 implies that the offset (4) uses the default radix. This
could also be written as start+$04 for explicit hexadecimal.
It is possible to set breakpoints to stop execution when reaching a
given address or label. Breakpoints are added using the
add_breakpoint command:
.disassemble start:start+4
$ff80 d8 CLD
$ff81 a2 ff LDX #$ff
$ff83 9a TXS
$ff84 a0 1c LDY #$1c
.add_breakpoint $ff84
Breakpoint 0 added at $FF84
.goto $ff80
Breakpoint 0 reached.
PC AC XR YR SP NV-BDIZC
6502: ff84 00 ff 00 ff 10110000
Note that a number is assigned to each breakpoint, similar to how
VICE operates. Deleting a breakpoint can be done via the
delete_breakpoint command using the breakpoint identifier given
by add_breakpoint:
.add_breakpoint $ff84 Breakpoint 0 added at $FF84 .delete_breakpoint 0 Breakpoint 0 removed
Breakpoints can be listed using the show_breakpoints command:
.add_breakpoint $1234 Breakpoint 0 added at $1234 .add_breakpoint $5678 Breakpoint 1 added at $5678 .add_breakpoint $9ABC Breakpoint 2 added at $9ABC .show_breakpoints Breakpoint 0 : $1234 Breakpoint 1 : $5678 Breakpoint 2 : $9ABC
Keep in mind that breakpoint identifiers are not recycled throughout
a session, this means that if you add three breakpoints (#0, #1, #2)
and then delete breakpoint #1, the next breakpoint you add will be
breakpoint #3, not #1. Also, invoking reset clears breakpoints
too, not just labels.
.. describe:: add_breakpoint <address|label>
Sets a breakpoint on execution at the given address or at the
address represented by the given label::
.add_breakpoint $1234
.add_label f000 start
.add_breakpoint start
Breakpoints get a numeric identifier to be used with
``delete_breakpoint``, the list of identifiers can be retrieved
with ``show_breakpoints``.
.. describe:: add_label <address> <label>
Assign a label to an address::
.add_label f000 start
Once defined, the label may be used in place of the address in other
commands. If a label already exists at the address, it will be silently
overwritten.
.. describe:: assemble <address> [<statement>]
Assemble a single statement at an address::
.assemble c000 lda $a0,x
$c000 b5 a0 LDA $a0,X
If no statement is given, interactive assembly mode will start::
.assemble c000
$c000
Enter a statement and it will be assembled at the current address. The
address will then be incremented and another statement may be entered.
Press Enter or Return without entering a statement to exit interactive
assembly mode.
If you have defined labels with add_label, you may use those labels in
the address and the operand.
.. describe:: cd <path>
Change the current working directory to the path specified::
.cd /path/to/my/files
/path/to/my/files
After changing the directory, the new working directory will be displayed.
The default working directory is the directory from which the monitor was
started.
.. describe:: cycles
Display the number of cycles that the microprocessor has run
since it was last reset::
.cycles
12
.. describe:: delete_breakpoint <breakpoint_id>
Removes the breakpoint associated with the given identifier::
.add_breakpoint $1234
Breakpoint 0 added at $1234
.add_label f000 start
.add_breakpoint start
Breakpoint 1 added at $F000
.delete_breakpoint 0
Breakpoint 0 removed
The list of identifiers added with ``add_breakpoint`` can be
retrieved with ``show_breakpoints``.
.. describe:: delete_label <label>
Delete a label that was previously defined with ``add_label``::
.delete_label foo
If the label does not exist, the command will fail silently.
.. describe:: disassemble <address_range>
Disassemble a range of memory::
.disassemble ff80:ff84
$ff80 d8 CLD
$ff81 a2 ff LDX #$ff
$ff83 9a TXS
$ff84 a0 1c LDY #$1c
The disassembly will use the instruction set of the selected MPU. For
example, the extra instructions of the 65C02 will only be displayed if
a 65C02 MPU is selected. On an NMOS 6502, those instructions would be
disassembled as ``???``.
If labels have been defined, they will be substituted for
addresses in the operands.
.. describe:: fill <address_range> <byte> [<byte> <byte> ...]
Fill a range of memory using one or more bytes from the list::
.fill c000:c003 aa bb
Wrote +4 bytes from $c000 to $c003
.mem c000:c003
c000: aa bb aa bb
If the range is larger than the number of bytes in the list, the list
will repeat as shown above.
.. describe:: goto <address>
Set the program counter to an address and resume execution::
.goto c000
.. describe:: help [<command>]
Display help for all commands or a single command. If no command is
given, a list of commands will be displayed::
.help
If a command is given, help for that comand is displayed::
.help disassemble
disassemble <address_range>
Disassemble instructions in the address range.
.. describe:: show_breakpoints
Lists all the breakpoints that have been set so far::
.add_breakpoint $1234
Breakpoint 0 added at $1234
.add_breakpoint $5678
Breakpoint 1 added at $5678
.add_breakpoint $9ABC
Breakpoint 2 added at $9ABC
.show_breakpoints
Breakpoint 0 : $1234
Breakpoint 1 : $5678
Breakpoint 2 : $9ABC
.. describe:: load <filename> <address>
Load a binary file into memory starting at the address specified::
.load hello.bin c000
Wrote +29 bytes from $c000 to $c01c
The file will be loaded relative to the current working directory. You
may also specify an absolute path. If the filename contains spaces, use
quotes around it::
.load "say hello.bin" c000
Wrote +29 bytes from $c000 to $c01c
.. note::
Unlike the VICE monitor, Py65Mon's ``load`` command does not expect
the first two bytes to be a Commodore-style load address. It will start
reading the data at byte 0, not byte 2.
If the filename is a URL, it will be retrieved::
.load https://github.com/mnaberez/py65/raw/0.11/examples/ehbasic.bin 0000
Wrote +65536 bytes from $0000 to $ffff
.. describe:: mem <address_range>
Display the contents of memory an address range::
.mem ff80:ffa0
ff80: d8 a2 ff 9a a0 1c b9 bb ff 99 04 02 88 d0 f7 b9 d8 ff
ff92: f0 06 20 a6 e0 c8 d0 f5 20 a3 e0 90 fb 29 df
The contents will be wrapped to the terminal width specified by the
``width`` command.
.. describe:: mpu [<mpu_name>]
Display or set the current microprocessor. If no argument is given, the
current microprocessor will be displayed::
.mpu
Current MPU is 6502
Available MPUs: 6502, 65C02, 65Org16
If an argument is given, the microprocessor will be changed::
.mpu 65C02
Reset with new MPU 65C02
The default microprocessor is ``6502``, the original NMOS 6502 from
MOS Technology.
.. describe:: pwd
Display the current working directory::
.pwd
/home/mnaberez
.. describe:: quit
Quit the monitor::
.quit
.. describe:: radix [<H|D|O|B>]
Display or set the default radix that is assumed for numbers that have no prefix.
If no argument is given, the default radix is displayed::
.radix
Default radix is Hexadecimal
If an argument is given, the default radix will be changed::
.radix d
Default radix is Decimal
The default radix may be changed to Hexadecimal, Decimal, Octal, or Binary.
.. describe:: registers [<name=value>, <name=value>, ...>]
Display or change the registers of the microprocessor. If no arguments are
given, the registers are displayed::
.registers
PC AC XR YR SP NV-BDIZC
6502: 0000 00 00 00 ff 00110000
Registers can changed giving ``name=value``, separated by commas if
multiple registers are to be changed::
.registers a=02, x=04
PC AC XR YR SP NV-BDIZC
6502: 0000 02 04 00 ff 00110000
.. describe:: reset
Reset the microprocessor to its default state. All memory will
also be cleared::
.reset
.. describe:: return
Continue execution and return to the monitor just before the next
RTS or RTI is executed::
.return
.. describe:: save <filename> <start_address> <end_address>
Save the specified memory range to disk as a binary file::
.save hello.bin c000 c01c
Wrote +29 bytes from $c000 to $c01c
The file will be saved relative to the current working directory. You
may also specify an absolute path. If the filename contains spaces, use
quotes around it::
.save "say hello.bin" c000 c01c
Wrote +29 bytes from $c000 to $c01c
.. note::
Unlike the VICE monitor, Py65Mon's ``save`` command does not write
the first two bytes as a Commodore-style load address. It will start
writing the data at byte 0, not byte 2.
.. describe:: show_labels
Display labels that have been defined with ``add_label``::
.show_labels
ffd2: charout
.. describe:: step
Execute a single instruction at the program counter. After the instruction
executes, the next instruction is disassembled and printed::
PC AC XR YR SP NV-BDIZC
6502: 0000 00 00 00 ff 00110000
.registers pc=c000
PC AC XR YR SP NV-BDIZC
6502: c000 00 00 00 ff 00110000
.step
$c002 a9 42 LDA #$42
PC AC XR YR SP NV-BDIZC
6502: c002 00 00 00 ff 00110000
.
In the example above, the instruction at ``$C000`` executes and the monitor
prompt returns.
.. note::
After the instruction executes, the disassembly of the **next** instruction
is printed. This allows you to see what will be executed on the next step.
.. describe:: tilde
Display a number in the supported number systems::
.~ c000
+49152
$c000
140000
1100000000000000
The number will be displayed in this order: decimal, hexadecimal, octal,
and then binary.
.. describe:: version
Display version information::
.version
Py65 Monitor
.. describe:: width [<columns>]
Display or set the terminal width. The width is used to wrap the output
of some commands like ``mem``. With no argument, the current width is
displayed::
.width
Terminal width is 78
If a column count is given, the width will be changed::
.width 130
Terminal width is 130
The number of columns is always specified as a decimal number.