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README

plus4emu 1.2.11 beta
====================

plus4emu is an open source, portable emulator of the Commodore Plus/4
computer, written in C++, and supporting Windows and POSIX platforms
(32 bit Windows, 32 and 64 bit Linux, and MacOS X have been tested).
It implements accurate, high quality hardware emulation, however, the
system requirements are higher than that of most other emulators.

Features
========

Plus/4 emulation
----------------

  * cycle exact emulation of the 7501/8501 CPU, with full support for
    all documented and undocumented opcodes
  * cycle exact TED 7360/8360 emulation with very high level of
    compatibility, implements all documented video modes, PAL/NTSC mode
    switching, accurate sound emulation, as well as all known display
    artifacts; all registers can be read and written, and the internal
    operation and timing is reproduced with very good accuracy
  * RAM size can be 16, 32, 64, 256, or 1024 kilobytes (the latter two
    using the Hannes memory expansion)
  * up to 8 16 kilobyte banks of ROM can be loaded from external image
    files; using custom ROM files for the emulated floppy drives and
    printer is also possible
  * limited emulation of the ACIA 6551 registers
  * tape emulation with playback, recording, and setting tape position;
    markers can be created for quick positioning to specific tape
    locations (useful for tapes with multiple files); uses custom file
    format which is PCM audio data with 1 to 8 bits of sample resolution
    and variable sample rate, and header including the table of markers;
    there is also limited (read only) support for the commonly used MTAP
    file format, as well as read-write (although without markers)
    support for sound files like WAV, AIFF, etc.
  * hardware level emulation of the 1541, 1551, and 1581 floppy disk
    drives, with support for D64 and D81 files; compatibility with 1541
    and 1551 fast loaders is fairly good in recent versions of the
    emulator
  * IEC level 1551 floppy drive emulation for accessing .PRG, .P00,
    .R00, .S00, and .U00 files on the PC filesystem; this also supports
    the C, I, N, P, R, S, and V DOS commands
  * light pen emulation (compatible with the Trojan Light Pen software)
  * IEC level MPS-801 printer emulation
  * hardware level 1526/MPS-802 printer emulation
  * load and automatically start .PRG, .P00, .D64, .D81, or .TAP file on
    start-up
  * .PRG, .P00, .D64, and .D81 files can be associated with plus4emu on
    Windows
  * SID chip (MOS 6581 and 8580) emulation using version 1.0 of the
    reSID library written by Dag Lem; the Digi-Blaster expansion by
    Solder is also supported

General
-------

  * graphical user interface using the FLTK library
  * software (FLTK based) or OpenGL video, with resizable emulator
    window, fullscreen mode, brightness/contrast/gamma can be set
    globally or separately for red/green/blue channels, color
    saturation control; additional features in OpenGL mode only: single
    or double buffered (with synchronization to vertical refresh) mode,
    linear texture filtering, and some display effects
  * high quality television (PAL and NTSC) emulation; implements full
    horizontal and vertical synchronization, blanking, equalization,
    sync, and burst signals, interlace, and (if OpenGL 2.0 shaders are
    available) separate luma/chroma filtering to emulate the blurredness
    of the TV picture
  * real time audio output uses the PortAudio library (v18 or v19), with
    support for many native audio APIs (MME/DirectSound/ASIO on Windows,
    OSS/ALSA/JACK on Linux, and CoreAudio on MacOS X); high quality
    sample rate conversion with low aliasing; volume control, two first
    order highpass filters with configurable cutoff frequency, and an
    optional parametric equalizer can be applied to the audio signal
  * recording audio output to a WAV format sound file
  * recording video and sound output to an AVI format video file, with
    RLE8 or uncompressed YV12 video at 24 to 60 frames per second, and
    48000 Hz 16-bit PCM audio
  * saving screenshots as 768x576 PNG format files
  * saving and loading snapshots of the state of the emulated machine
  * demo recording (snapshot combined with stream of keyboard events
    which can be played back with accurate timing)
  * GUI debugger with support for breakpoints/watchpoints, viewing the
    current state of CPU registers and memory paging, displaying memory
    dump or loading from or saving to a file in ASCII or binary format,
    and disassembler with support for all undocumented 6502 opcodes.
    The debugger also includes a TEDMON-like monitor with support for
    all the commands, as well as some improvements and additional
    features (assemble/disassemble offset, saving disassembly to a file,
    physical (22 bit) memory addressing mode, undocumented CPU opcodes
    in the assembler and disassembler, trace, search/replace pattern in
    memory, and more).
    It is also possible to debug the 6502 compatible CPUs in floppy
    drives and printers.
    The debugger supports scripting in the Lua language, to allow for
    advanced uses like breakpoints with custom defined, complex set of
    conditions.
  * configurable keyboard map for the emulated machine; it is also
    possible to use external game controller devices like joysticks and
    gamepads
  * mouse and clipboard support for setting the cursor position,
    copying, and pasting text in the emulated machine:
      left click: sets the cursor position
      right click: sets the cursor position, and copies the selected
        word to the clipboard
      ctrl + right click: sets the cursor position, and copies text from
        the selected line to the clipboard
      shift + right click: copies text from the whole screen to the
        clipboard without changing the cursor position
      middle click: sets the cursor position, and pastes text from the
        clipboard
      shift + middle click: pastes text from the clipboard without
        changing the cursor position
  * the Plus/4 emulation can be used in other programs as a shared
    library with a C interface; see the plus4lib/plus4emu.h header file
    for details, and also plus4lib/sample.c for a simple example of
    using the interface

The emulator package also includes some utilities:

  * (p4)compress - compresses Plus/4 .PRG and .P00 files with very good
    compression ratio (CA65 assembler source code for the decompressor
    is available)
  * (p4)makecfg - reinstalls the configuration files of the emulator
  * p4fliconv - converts JPEG and other format images to various Plus/4
    video modes (hires/multicolor, FLI, interlace, etc.); it can be used
    both from the command line, and as a GUI program which uses the
    emulator for accurate previews. CA65 assembler sources for the FLI
    viewer are also available.
  * p4sconv - converts PixelShop .P4S images to any of the output
    formats supported by p4fliconv
  * (p4)tapconv - converts MTAP format tape files to the native plus4emu
    tape format

Installation
============

Linux
-----

On Linux and other POSIX platforms, the emulator is installed from the
source code, available at the GitHub download page
  https://github.com/istvan-v/plus4emu/releases/
or the most recent state of the code can be downloaded from Git with the
following command:
  git clone https://github.com/istvan-v/plus4emu.git
In addition to the standard development tools (a recent version of the
GNU C/C++ compiler, binutils, etc.), you need the following packages:

  * SCons (http://www.scons.org/)
  * Python interpreter for running SCons
  * FLTK 1.3.x (http://www.fltk.org/software.php?VERSION=1.3.4) or
    1.1.x (http://www.fltk.org/software.php?VERSION=1.1.10)
    NOTES:
      * this library should be compiled with the --enable-threads
        'configure' option - many Linux distributions include binaries
        of the FLTK library built without --enable-threads, so you may
        need to compile it from sources
      * on MacOS X, FLTK 1.1.7 needs to be patched with the included
        fltk-1.1.7-MacOSX.patch file
  * PortAudio (http://www.portaudio.com/download.html), version 18 and
    19 are supported, but v19 is recommended
  * libsndfile (http://www.mega-nerd.com/libsndfile/#Download)
  * SDL (http://www.libsdl.org/) 1.2 for joystick input (optional);
    NOTE: on Linux, versions 1.2.10 and newer do not work if they are
    statically linked and were built with video support (--enable-video)
  * Lua (http://www.lua.org/ or http://www.luajit.org/) 5.1, 5.2, or 5.3
    for scripting in the debugger (optional)

Once these are installed, you can edit the file 'SConstruct' in the top
level source directory for setting compiler flags etc., and run the
command 'scons -j 4' for building the emulator. The resulting executable
files (plus4emu and the utilities listed above) can be copied to any
directory that is in the PATH; on MacOS X, an .app package is created in
'plus4emu.app'.
When installing the first time, you also need to set up configuration
files and ROM images:

  * copy all .rom files from the roms directory to ~/.plus4emu/roms (or,
    in the case of MacOS X, ~/Library/Application Support/plus4emu/roms)
  * after installing the ROM images, run 'plus4emu', and click OK to the
    windows that pop up asking for the base directory of configuration
    and data files, and if configuration files should be installed

It is possible to reinstall configuration files later by running the
'p4makecfg' utility.

Alternatively, the emulator and all required files can be installed
under ~/bin and ~/.local/share with the command 'scons install', which
also runs p4makecfg.

Windows
-------

A binary package with an installer is available at the GitHub download
page:
  https://github.com/istvan-v/plus4emu/releases/
Older (pre-1.2.10) versions can be downloaded from SourceForge:
  https://sourceforge.net/projects/plus4emu/files/
To install, just run the executable, and follow the instructions.
When asked if configuration files should be reinstalled, click 'OK'
when installing the first time, but this step can be skipped in later
installations to preserve the configuration.

Usage
=====

Command line options
--------------------

  -h
  -help
  --help
    print the list of available command line options
  -cfg <FILENAME>
    load an ASCII format configuration file on startup, and apply
    settings
  -prg <FILENAME>
    load and run program file on startup
  -disk <FILENAME>
    load and automatically start disk image on startup
  -tape <FILENAME>
    load and automatically start tape image on startup
  -snapshot <FILENAME>
    load snapshot or demo file on startup
  -keybuf <TEXT>
    type TEXT on startup (can be any length, or @FILENAME to read from a
    file)
  -opengl
    use OpenGL video driver (this is the default, and is recommended
    when hardware accelerated OpenGL is available)
  -no-opengl
    use software video driver; this is slower than OpenGL when used at
    high resolutions, and also disables many display effects, but should
    work on all machines; however, it will use a color depth of 24 bits,
    while in OpenGL mode the textures are 16 bit (R5G6B5) only, to
    improve performance
  -colorscheme <N>
    select GUI color scheme N (0, 1, 2, or 3)
  OPTION=VALUE
    set configuration variable 'OPTION' to 'VALUE'; the available
    variable names are the same as those used in ASCII format
    configuration files
  OPTION
    set boolean configuration variable 'OPTION' to true
  FILENAME
    load and automatically start a file with .prg, .p00, .d64, .d81, or
    .tap extension

'File' menu
-----------

Configuration / Load from ASCII file

  Select and load an ASCII format configuration file and apply the new
  settings. If the configuration file does not include all the supported
  options, those that are omitted are left unchanged.

Configuration / Load from binary file

  Load a plus4emu format binary file, which may be a previously saved
  snapshot or demo, a binary format configuration file, or a program
  file with plus4emu header.

Configuration / Save as ASCII file

  Save the current emulator configuration to an ASCII text file, which
  can be edited with any text editor, and can be loaded at a later time.

Configuration / Save

  Save the current emulator configuration in binary format to the
  default file (~/.plus4emu/plus4cfg.dat). This is also automatically
  done when exiting the emulator.

Configuration / Revert

  Reload emulator configuration from ~/.plus4emu/plus4cfg.dat, and apply
  the original settings.

Save snapshot

  Save a snapshot of the current state of the emulated machine to the
  selected file. The snapshot will also include the current memory
  configuration and ROM images, but clock frequency and timing settings
  are not restored when loading a snapshot. The file format may be
  subject to changes between different releases of the emulator. Note
  that the state of any floppy drives is currently not saved, and the
  drives are reset on loading a snapshot.

Load snapshot (F7)

  Load a plus4emu format binary file, which may be a previously saved
  snapshot or demo, a binary format configuration file, or a program
  file with plus4emu header.

Quick snapshot / Set file name

  Select file name for quick snapshots. The default is
  ~/.plus4emu/qs_plus4.dat. This setting is not saved on exit.

Quick snapshot / Save (Ctrl + F9)

  Save snapshot to the quick snapshot file (see notes above).

Quick snapshot / Load (Ctrl + F10)

  Load the quick snapshot file if it exists.

Record demo

  Save snapshot (including clock frequency and timing settings) and
  record keyboard events to the selected file until the recording is
  stopped. The events can be replayed with accurate timing when the
  file is loaded later. Note that the file format may change between
  different releases of the emulator, and the timing may also be
  incorrect when using a different version to play a demo file.

Stop demo (Ctrl + F12)

  Stop any currently running demo playback or recording.

Load demo (F7)

  Load a plus4emu format binary file, which may be a previously saved
  snapshot or demo, a binary format configuration file, or a program
  file with plus4emu header.

Record audio / Start...

  Write 16 bit signed PCM sound output to a WAV format sound file.

Record audio / Stop

  Close sound output file if it is currently being written.

Record video / Start...

  Open new AVI file for video recording. This increases the CPU usage
  significantly, and since the data is written without compression, it
  will take up a lot of disk space. If the size of the output file
  reaches 2 GB, it is automatically closed, and the emulator asks for
  a new file to continue the recording.
  NOTE: the video and audio streams in the AVI file are not affected by
  any of the display or sound configuration settings.

Record video / Stop

  Stop video capture, and close any AVI file that is currently being
  written.

Save screenshot (F6)

  Save a screenshot in PNG format. The video output is captured
  immediately after activating this menu item, and is saved at a
  resolution of 768x576 without any processing (color correction,
  effects, etc.).

Quit (Shift + F12)

  Exit the emulator.

'Machine' menu
--------------

Reset / Reset (F11)

  This has the same effect as using the reset button on the real
  machine.

Reset / Force reset (Ctrl + F11)

  In addition to a normal reset, make sure that the emulated machine is
  really restarted using the standard ROM reset routines, and do not
  allow programs to disable reset by setting custom (RAM) handlers;
  however, most of the RAM data is still preserved.
  This option will also turn off automatically enabled extensions that
  increase CPU usage, such as SID emulation and 1541/1551/1581 drives
  with no disk opened.

Reset / Reset clock frequencies

  Reset clock frequency and timing settings to those specified in the
  machine configuration; this is normally only useful after demo
  playback, which may override the settings. The SID and ACIA
  configuration, which may be changed by snapshot or demo loading, are
  also reset.

Reset / Reset machine configuration (Shift + F11)

  Reset memory configuration (RAM size, ROM images), clock frequency,
  and timing settings according to the machine configuration, and clear
  all RAM data. Implies 'Force reset' and 'Reset clock frequencies'.
  Reverting the configuration can be useful after snapshot loading or
  demo playback, as these may change the settings.

Quick configuration / Load config 1 (PageDown)

  Load the configuration file ~/.plus4emu/p4vmcfg1.cfg, and apply the
  new settings.

Quick configuration / Load config 2 (PageUp)

  Load the configuration file ~/.plus4emu/p4vmcfg2.cfg, and apply the
  new settings.

Quick configuration / Save config 1

  Save the current clock frequency and timing settings to
  ~/.plus4emu/p4vmcfg1.cfg.

Quick configuration / Save config 2

  Save the current clock frequency and timing settings to
  ~/.plus4emu/p4vmcfg2.cfg.

Printer / Disable printer
Printer / MPS-801 (IEC level)
Printer / MPS-802 (hardware level)
Printer / MPS-802 (1525 mode)

  If enabled, an MPS-801 or 1526/MPS-802 printer is emulated as device 4
  on the serial bus. The MPS-802 printer emulation is implemented at the
  hardware level for full compatibility with a real printer. On the
  other hand, the IEC level MPS-801 emulation uses less CPU time, prints
  faster, and supports printing graphics.

Printer / View printer output

  Shows the printer output in real time in a window. It is also possible
  to save the page as a 520x736 (MPS-801) or 700x990 (MPS-802) 8-bit PNG
  format image file. When the printing reaches the bottom of the page,
  it stops, and the LED will flash; you can then save the page to a
  file, click the 'Clear' button, and turn on and then off 'Form feed'
  to continue printing.
  In the case of MPS-801 emulation, the form feed button is ignored, so
  it is enough to click the 'Clear' button to continue with printing the
  next page; in this mode, there is also an input buffer of 128
  kilobytes - until the buffer is full, the printing (and writing the
  output to a text file if enabled) is not blocked on the Plus/4.
  NOTE: it is recommended to close this window while using the debugger,
  since it cannot display printer output then, and may slow down the
  GUI.

Enable light pen

  Emulate a Trojan Light Pen connected to the first joystick port. Light
  pen input is only generated when a mouse button is held down while the
  mouse cursor is in the emulation display area.

SID emulation / Enable

  Turn on SID emulation, making the SID registers appear at FD40-FD5F
  and FE80-FE9F; this increases the CPU usage of the emulator.
  SID emulation is also automatically enabled when a byte is written to
  the above mentioned address ranges, but some programs detect if a SID
  card is present by only reading the registers, and in those cases
  using this option is needed. SID emulation remains active until the
  next use of 'Force reset' or 'Reset machine configuration', and
  snapshot data includes SID state and whether it was enabled or not at
  the time of saving the snapshot.

SID emulation / Disable

  Turn off SID emulation if it is currently enabled.

'Options' menu
--------------

Display / Set size to 384x288
Display / Set size to 768x576
Display / Set size to 1152x864

  Resize the emulator window to predefined width/height values; this has
  no effect in fullscreen mode. While the window can also be resized
  using the window manager, sizes that are integer multiples of the
  actual screen resolution of the emulated machine may look better,
  particularly when texture filtering is not used, and are also slightly
  faster when using the software video driver.

Display / Cycle display mode (F9)

  Cycle between these four display modes:
    window with no menu bar
    window with menu bar (this is the default)
    fullscreen with menu bar
    fullscreen with no menu bar

Sound / Increase volume

  Increase sound output volume by about 2 dB.

Sound / Decrease volume

  Decrease sound output volume by about 2 dB.

Floppy / Configure... (Alt + D)

  Opens a dialog for setting up floppy drive emulation.
  For each drive, an image file can be selected. If the file name is
  left empty, that means having no disk in that particular drive.
  It may also be possible to directly access a real 1581 800k disk by
  using the /dev/fd* devices (on Linux) or \\.\A: (on Windows) as the
  image file.
  The file format must be either D64 or D81; the type is determined from
  the file size. Opening a D64 file will enable 1541 or 1551 emulation
  for that particular drive, while the 1581 will be emulated for D81
  files.
  Since these drives are emulated at the hardware level (with a 6502
  CPU, etc.), enabling them increases the CPU usage. A drive will remain
  active until a different type of image file is opened, or a snapshot
  is loaded or 'Force reset' (or anything that implies it) is used while
  there is no disk opened.
  Setting the drive type of unit 8 or unit 9 to 1551, and leaving the
  image file name empty enables IEC level 1551 drive emulation instead
  of true (hardware level) drive emulation. This can be used to access
  .PRG, .P00, .R00, .S00, and .U00 files in the currently selected
  working directory, and also has the advantage of not increasing the
  CPU usage.

  New in version 1.2.11: if the specified image file does not exist, it
  is automatically created as a formatted empty disk, with the format
  (D64 or D81), disk name and ID determined from the file name and
  extension. It is also possible to open disk and tape images archived
  in .zip format, the first packed file with matching extension is
  temporarily extracted and used in read-only mode.

Floppy / Remove disk / Unit 8
Floppy / Remove disk / Unit 9
Floppy / Remove disk / Unit 10
Floppy / Remove disk / Unit 11
Floppy / Remove disk / All drives

  These are just shortcuts for setting the image file name for a
  specific floppy drive to an empty string.

Floppy / Replace disk / Unit 8
Floppy / Replace disk / Unit 9
Floppy / Replace disk / Unit 10
Floppy / Replace disk / Unit 11
Floppy / Replace disk / All drives

  Set the image file name for a specific (or all) floppy drive to an
  empty string, and then set the original file name again. This is
  mostly useful when accessing real floppy disks, after the disk is
  changed.

Floppy / Reset / Unit 8
Floppy / Reset / Unit 9
Floppy / Reset / Unit 10
Floppy / Reset / Unit 11
Floppy / Reset / All drives

  Reset a specific (or all) floppy drive.

Floppy / Disable unused drives

  Turn off the emulation of all floppy drives that are currently active,
  but have no disk image attached. This can be useful to reduce CPU
  usage when a drive is no longer needed, without having to reset the
  emulated machine. Using this option may also be needed to enable IEC
  level drive emulation, which cannot be used while hardware level
  emulation on the same unit is still active.

Set working directory (Alt + Q)

  Set the directory to be accessed by the IEC level drive emulation.
  The filesystem access is read-only by default, but writing can be
  enabled in the machine configuration.
  This directory is also used by monitor commands that take a file name
  argument.

'Debug' menu
------------

Start debugger (Alt + M)

  Shows the debugger window. Many functions in the debugger can be used
  either in CPU addressing mode where the 16 bit address space of the
  currently selected CPU can be accessed, or physical address mode that
  allows access to all memory in the emulated system, regardless of any
  memory banking or the debug context selected. The following table
  shows the memory map in physical address mode; the 8-bit codes on the
  left are used in the 'Memory paging' window:

    00      000000-003FFF   Basic ROM
    01      004000-007FFF   Kernal ROM
    02, 03  008000-00FFFF   Function (3-plus-1) ROM
    04, 05  010000-017FFF   Cartridge 1
    06, 07  018000-01FFFF   Cartridge 2 (used by p4fileio.rom)
    0A      028000-02BFFF   MPS-801 printer ROM (4K, repeated 4x)
    0C      030000-033FFF   1526/MPS-802 printer ROM (8K, repeated 2x)
    10      040000-043FFF   1541 floppy drive ROM
    20      080000-083FFF   1551 floppy drive ROM
    30, 31  0C0000-0C7FFF   1581 floppy drive ROM
    40-43   100000-10FFFF   Main CPU address space
    50-53   140000-14FFFF   Printer CPU address space (MPS-802 only)
    60-63   180000-18FFFF   Floppy unit 8 CPU address space
    64-67   190000-19FFFF   Floppy unit 9 CPU address space
    68-6B   1A0000-1AFFFF   Floppy unit 10 CPU address space
    6C-6F   1B0000-1BFFFF   Floppy unit 11 CPU address space
    FF      3FC000-3FFFFF   RAM (16K)
    FE-FF   3F8000-3FFFFF   RAM (32K)
    FC-FF   3F0000-3FFFFF   RAM (64K; also the default bank for >64K)
    F0-FF   3C0000-3FFFFF   RAM (256K)
    C0-FF   300000-3FFFFF   RAM (1024K)

    TED and I/O registers are not mapped into the RAM or ROM areas in
    physical address mode.

  The monitor commands are mostly similar to those in TEDMON, although
  most commands - with the exception of G and TR - support CPU/physical
  address mode switching, and the following have some improvements:

    A       supports undocumented opcodes (using opcode names from
            64doc.txt), $ characters and leading zeros are optional,
            assemble offset can be used to write the code to a different
            area than where it will actually run
    D       can disassemble to a file, supports undocumented opcodes and
            disassemble offset
    F       it is possible to fill memory with a pattern of any length,
            not just a single byte
    H       more advanced pattern matching (specific bits or bytes can
            be ignored); note that strings should be enclosed within
            double quote characters
    T       allows the source and destination areas to overlap

  There are also these new commands:

    ?       prints the list of available commands
    ? CMD   prints help for command 'CMD'
    AM      set/toggle CPU/physical address mode
    AO      set/clear assemble and disassemble offset
    I       prints the current monitor settings (address mode, etc.)
    SR      search for and replace pattern in memory; uses the same
            rules as the H command, and can also ignore (not change)
            bits or bytes when writing the replacement pattern
    TR      logs CPU instructions to a file until the debugger is opened
            again, or the number of instructions exceeds a specified
            limit
    W       set debug context
    X       same as the 'Continue' button
    Y       same as the 'Step over' button
    Z       same as the 'Step' button

  Lua scripting
  -------------

  Starting from version 1.2.5, it is possible to run scripts written in
  Lua from the debugger. This document only describes the use of scripts
  in the emulator, and the new API functions added; for general
  information about programming in Lua, see http://www.lua.org/docs.html

  Clicking the 'Run' button will run the script, and also enable the
  breakpoint callback function (see below) if it is defined. If there
  are any syntax or runtime errors, the script is terminated, and the
  breakpoint callback is disabled. After making any changes to the
  script, you need to click 'Run' and restart the script for the changes
  to take effect.

  It is possible to define a breakpoint callback function in the script,
  which will be automatically called whenever a breakpoint is triggered,
  and the debugger window would be shown. This function has the
  following syntax:

    function breakPointCallback(debugContext, bpType, addr, value)
      ...
      return showWindow
    end

  where 'showWindow' is a boolean value, which, if true, will allow the
  debugger window to be shown like normal, or have the emulated program
  continue without any break if it is false. The four parameters passed
  to the function are as follows:

    debugContext

      The debugging context from which the break was triggered. The
      possible values are:
        0: the main CPU
        1: floppy drive / unit 8
        2: floppy drive / unit 9
        3: floppy drive / unit 10
        4: floppy drive / unit 11
        5: printer

    bpType

      The type of break, one of the following:
        0: breakpoint at opcode read by the CPU
        1: data read from memory
        2: data written to memory
        3: opcode read in single step mode; this happens when 'Step' or
           'Step over' are being used, and if the breakpoint callback
           function returns false, breaks will continue to occur until
           true is returned
        4: video breakpoint; the address is encoded in a special way in
           this case (see below at setBreakPoint()), and the value is
           not used

    addr

      This is the 16 bit address where the break occured.

    value

      The value or CPU opcode read from or written to memory. Not used
      (always zero) by video breakpoints.

  The breakpoint callback function will remain active until either a new
  script is run which does not define one, or the 'Stop' button is
  clicked.

  NOTE: an infinite loop in the script will hang the emulator, and a
  very frequently called and/or complex breakpoint callback may slow
  down the emulation.

  The following new functions are defined by the emulator for use in the
  scripts:

    AND(...)    OR(...)    XOR(...)    SHL(a, b)    SHR(a, b)

      These simple helper functions implement bitwise operations that
      are not available in the Lua language by default. AND, OR, and XOR
      can take any number of integer arguments, and return the bitwise
      AND, OR, and XOR of the values, respectively. In the case of zero
      arguments, OR and XOR return zero, while AND returns -1.
      SHL returns 'a' shifted to the left by 'b' bits, and SHR returns
      'a' shifted to the right by 'b' bits. If 'b' is zero, the value is
      not changed, while a negative 'b' will reverse the direction of
      shifting. The result of shifting negative values to the right is
      unspecified.

    getDebugContext()

      Returns the current debugging context, which can be one of the
      following:

        0: the main CPU
        1: floppy drive / unit 8
        2: floppy drive / unit 9
        3: floppy drive / unit 10
        4: floppy drive / unit 11
        5: printer

    setDebugContext(n)

      Set the debugging context to 'n' (0 to 5, see above). It is
      recommended to restore the original debugging context before the
      script returns.

    setBreakPoint(bptype, addr, priority)

      Set a breakpoint or watchpoint at address 'addr' (0-0xFFFF) for
      the current debugging context, with priority 'priority' (0 to 3).
      'bptype' can be one of the following values:

        0: any memory access (read, write or CPU opcode read)
        1: memory read
        2: memory write
        3: any memory access, same as bptype == 0
        4: video breakpoint, breaks at the TED video position defined by
           'addr'; this is only allowed for the main CPU, and cannot be
           set for floppy drives or printers. Bits 7 to 15 of the
           address are the vertical position (which is compared against
           the latched value of the vertical counter in the TED), and
           bits 0 to 6 are the most significant bits of the horizontal
           position (compared against the value that would be read from
           $FF1E)
        5: ignore other breakpoints if the program counter is at this
           address (note: the priority parameter is ignored)
        6: CPU opcode read

      A 'priority' value of -1 will delete an existing breakpoint at the
      specified address.
      The read, write, execute, and ignore flags are combined if
      multiple breakpoints are set at the same address, while the
      priority will be the highest value specified.

      NOTE: the changes made to the breakpoint list by the script are
      not reflected in the breakpoint editor. To restore the previously
      defined breakpoints, click the 'Apply' button.

    clearBreakPoints()

      Deletes all breakpoints that were previously defined for the
      current debugging context.

    getMemoryPage(n)

      Returns the memory bank selected for $0000-$3FFF if 'n' is 0,
      $4000-$7FFF if 'n' is 1, $8000-$BFFF if 'n' is 2, or $C000-$FFFF
      if 'n' is 3. The returned value is a 8 bit integer, as described
      above at the beginning of the debugger documentation.

    readMemory(addr)

      Read a byte from 'addr' (0 to 0xFFFF) in the address space of the
      current debugging context.

    writeMemory(addr, value)

      Write 'value' to 'addr' (0 to 0xFFFF) in the address space of the
      current debugging context.

    readMemoryRaw(addr)

      Read a byte from 'addr' (0 to 0x3FFFFF) in the "physical" address
      space described above at the beginning of the debugger
      documentation.

    writeMemoryRaw(addr, value)

      Write 'value' to 'addr' (0 to 0x3FFFFF) in the "physical" address
      space described above at the beginning of the debugger
      documentation.

    getPC()    getSR()    getAC()    getXR()    getYR()    getSP()

      These functions return the registers of the currently selected
      CPU. PC is a 16 bit value, while the others are 8 bit.

    setPC(n)   setSR(n)   setAC(n)   setXR(n)   setYR(n)   setSP(n)

      Set registers of the currently selected CPU. 'n' should be a 16
      bit value when setting PC, and 8 bit for the other registers. Note
      that changing the program counter only takes effect after the
      execution of the current instruction is completed.

    loadProgram(fname)

      Load PRG or P00 file 'fname', which must be a full path file name.
      The current debugging context is ignored, and zeropage variables
      at $2D-$32 and $9D-$9E are updated according to the file loaded.

    saveProgram(fname)

      Save the memory area defined by zeropage variables $2B-$2E to a
      PRG file 'fname', which must be a full path file name. The current
      debugging context is ignored, and the data is always read from
      RAM, regardless of memory paging by $FF3E/$FF3F.

    mprint(...)

      Prints any number of strings or numbers to the monitor.
      No separator characters are inserted between the arguments being
      printed, and a newline character is automatically added at the end
      of the message.

  Example:

    mprint("Running Lua script example...")
    setDebugContext(0)
    clearBreakPoints()
    setBreakPoint(2, 0x0C00, 2)
    setBreakPoint(2, 0x0C01, 2)
    function breakPointCallback(d, t, a, v)
      if (a == 0x0C00 and v == 0x00) or
         (a == 0x0C01 and v == 0x01) then
        return true
      end
      return false
    end
    mprint("done.")

  This will break only when $00 is written to $0C00, or $01 is written
  to $0C01.

------------------------------------------------------------------------

Copyright
=========

plus4emu is copyright © 2003-2017 by Istvan Varga
<istvanv@users.sourceforge.net>.
reSID 1.0 copyright © 2010 by Dag Lem.
Fl_Native_File_Chooser 0.84 copyright © 2004 by Greg Ercolano.
dotconf 1.3 copyright © by Lukas Schröder and William Hubbs.

This program is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 2 of the License, or (at your
option) any later version.

This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

You should have received a copy of the GNU General Public License along
with this program; if not, write to the Free Software Foundation, Inc.,
59 Temple Place, Suite 330, Boston, MA  02111-1307 USA

Credits
-------

Thanks to:

Hársfalvi Levente - testing the emulator and providing some hardware
                    information
MagerValp         - testing on MacOS X and contributing binaries
Andrea Musuruane  - bug reports and fixes related to building the
                    emulator on Fedora Linux
Chronos / ACW     - TED and SID sound testing on the real machine
SVS / FIRE        - Windows icons