XRoar is a Dragon emulator that runs on a wide variety of platforms. Due to hardware similarities, XRoar also emulates the Tandy Colour Computer (CoCo) models 1 & 2. Some features are:
To start, you will need to acquire (and maybe build) the software and install it. Pre-built binary packages are available from the XRoar home page. If one is not available for your architecture, you will have to build from source. XRoar should build and run on any POSIX-like system for which SDL is available.
You'll also need to get hold of firmware ROM images for the machine you wish to emulate. As Microsoft wrote the BASIC ROM, I don't feel comfortable offering them up myself, but they may well be obtainable elsewhere on the Web.
For instructions on installing from source or binary package, and where to put firmware images, see Installation.
Once you've installed XRoar, run it and an emulator screen should appear. It tries to be a Dragon 64 first, but if ROM images can't be found for that, it then tries Dragon 32 and CoCo in that order. If you just get a strange checkerboard pattern of orange and inverse '@' signs, it probably failed to find any ROM images - check that first.
From here you can attach tapes (.cas or .wav files) with Control+L. To load a program from tape, type CLOADM (machine code) or CLOAD (BASIC). If the program does not start automatically when it has loaded (i.e., returns you to the “OK” prompt), you will have to type EXEC (machine code) or RUN (BASIC) to start it.
XRoar will make use of attached joysticks, but can also emulate them with the cursor keys and Left Alt. Press Control+J to cycle through three emulation modes: No joystick emulation (default), Left joystick, Right joystick.
Mount the downloaded disk image and drag the XRoar application icon into your Applications directory.
Firmware ROM images can be stored either in ~/Library/XRoar/Roms/ or ~/.xroar/roms/. See Firmware ROM image names for filenames the emulator will search for.
XRoar can be started by double-clicking the application icon.
First, unpack the downloaded ZIP file. A subdirectory should be created containing the main binary, supporting DLL files and documentation.
Firmware images can be copied to this directory, or in a directory called USERPROFILE/Application Data/XRoar/roms/. USERPROFILE is usually something like C:/Documents and Settings/username or C:/Users/username. See Firmware ROM image names for filenames the emulator will search for.
XRoar can be started by running xroar.exe either from a file browser or the command line.
If there is no binary package for your system, you will have to build from source. Before doing so, you should ensure you have the dependencies required to build:
If you use a modern Linux or Unix distribution, it's likely that most of these packages will be installed by default, or easily available through its package management system.
The actual build process should be fairly straightforward and follows the same steps as many other software packages. Unpack the source code, change into the created source directory, run configure and then if everything looks good, run make. Example:
$ gzip -dc xroar-0.27.tar.gz | tar xvf -
$ cd xroar-0.27
$ ./configure
$ make
By default, configure will set things up to install to /usr/local, but this can be changed by using the --prefix=/path/to/destination option.
configure will detect any optionally supported drivers like Sun audio, OpenGL video, etc.
Once built, run make install to install the binary and info documentation on your system. Firmware ROM images should be placed either in your home directory under .xroar/roms/, or in PREFIX/share/xroar/roms/, where PREFIX is the install prefix as above.
XRoar can be built on one platform to run on another. The Windows binary package is built like this.
To specify a cross-compile, use the --target=TARGET argument to configure. For example, to build for Windows, you might use ‘./configure --target=i586-mingw32’. configure will detect Windows headers and configure the build accordingly.
XRoar has built-in definitions for the following machines, selectable with the -machine NAME option:
If no machine is specified on the command line, XRoar will try and find a good default machine to emulate based on which ROM images you have installed (see Firmware ROM image names). Alternatively, once started, pressing Control+M cycles through all the supported machine types.
Additionally extra machines can be configured, or existing ones reconfigured, with the following options:
Dragon machines all contain a complete version of Extended BASIC; CoCos are able to run with a much reduced Color BASIC, with Extended BASIC being optional.
Defining extra machines is most usefully done in the configuration file. For example:
machine pippin
machine-desc Dragon Pippin (prototype)
machine-arch dragon32
ram 16
This will define a machine named “pippin” that is basically a Dragon 32 with only 16K or RAM.
The Dragon is a UK machine, and as such generates a 50Hz PAL output. The video chip targets 60Hz NTSC displays, so extra work is required to pad this out to a 50Hz signal. This is done by stopping the video chip at two points each field and generating extra scanlines.
However a US version, the Tano Dragon, exists for use with 60Hz NTSC televisions and US CoCo machines all use NTSC. When you select which machine to emulate (see Emulated machines), XRoar picks the appropriate mode. This can be overridden with the -pal or -ntsc command line options.
On NTSC televisions, high frequency changes in luminance create cross-colour artifacts (harmonics that interfere with the embedded chroma signal). Some games use this to their advantage, creating colours in the otherwise black and white high resolution video modes. XRoar can approximate the colours generated in these modes to varying levels of detail. The default approach is to use a 5 bit lookup table, but a faster four colour mode can be selected by running with -ccr simple.
NTSC machines have another peculiarity in that from reset, the video chip could settle into one of two states (180° out of phase with each other) that affected how the cross-colour interference was interpreted by the television. Games often prompt the user to “Press Enter if the screen is red” (for example) to identify which phase the machine started in. You can adjust which state it's in by pressing Control+A, which cycles through three artifacted colour modes: Off, Blue-red and Red-blue.
The Dragon can route analogue audio from three different sources: attached cartridges, the cassette port and an internal 6-bit DAC. Additionally, a PIA line is connected to the audio output stage, so manipulating that gives a single-bit sound source. XRoar supports the DAC and the single bit audio.
Rarely, a game generates audio by toggling the analogue sound select source rapidly. XRoar will cope with this, but needs to work harder. Disable support for this with the -fast-sound command line option.
As it is connected to the output of the analogue mux, if the single bit sound output is instead configured as an input, the analogue level will be reflected fed back. While I can't claim that XRoar exactly simulates the electrical characteristics, it will emulate this as a trigger level from the DAC output derived from experimentation.
The layout of the Dragon's keyboard is a little different to that of modern PCs, so XRoar tries to approximate the Dragon's layout on your PC keyboard as closely as possible, so that game controls will remain in usable positions. That said, they are different, so some compromises need to be made: Escape is mapped to the Dragon's BREAK key and ` (grave / back-tick) maps to the Dragon's CLEAR key. There are no good nearby PC keys that directly correspond to the Dragon's cursor keys, so the PC's cursors are used for these.
If you don't use a UK keyboard, but want a close Dragon keyboard layout, you can run with the -keymap CODE command-line option, where CODE is a country code: “uk” (British), “us” (American), “fr” (French AZERTY) or “de” (German QWERTZ).
XRoar can also be put into “translated” keyboard mode, where characters typed on a PC keyboard are translated into the equivalent keystrokes on the Dragon. Run with the -kbd-translate option to start with this enabled. Press Control+Z to toggle this mode.
The keyboards of the Dragon and Tandy CoCo are connected in the same way, but the matrix is layed out slightly differently. When you select a machine (see Emulated machines), the appropriate matrix layout is selected for you, but you can toggle between the two layouts by pressing Control+K.
Additionally, most emulator functions are currently accessed through key combinations. See Keyboard commands for a list.
XRoar supports attached joysticks, or can emulate them from the keyboard.
Joystick emulation starts off disabled, but you can cycle through three states by pressing Control+J: Off, Left Joystick and Right Joystick. When emulating a joystick, the cursor keys control the axes and Left Alt maps to the fire button.
By default, the first real joystick found is mapped to the Dragon's left joystick port, and the second real joystick to the right port. Left and right joystick mapping can be easily swapped by pressing Control+Shift+J.
More fine-grained mappings can be specified with the -joy-left and -joy-right command line options. The argument to these command consists of three pairs of numbers in the format JOYSTICK-NUMBER,INDEX. The pairs map the X axis, Y axis and fire button respectively, and the joystick number is optional if previously specified. For example, -joy-left 0,1:0:0 maps axes 1 and 0 on joystick 0 to the X and Y axis on the left emulated joystick respectively. Button 2 of joystick 0 is mapped to the left fire button.
Previous versions defaulted to a mapping suitable for using a PS2 adaptor. To get this old behaviour, use the command line options -joy-left 0,3:2:0 -joy-right 0,0:1:1.
XRoar supports three types of cassette image: .cas files, audio files such as .wav and ASCII text files containing BASIC programs (.bas or .asc). .cas files contain a binary representation of what would be loaded from tape, audio files are a recording of the tape itself, and ASCII files contain plain text that is automatically wrapped up as an ASCII BASIC file for loading.
To attach a cassette image, press Control+L and select it from the file requester. If instead you press Control+Shift+L and select a .cas file, XRoar can attempt to look into the file and determine whether the program is BASIC or machine code and then autorun it by typing the appropriate BASIC command(s) for you (either CLOAD then RUN or CLOADM:EXEC).
To create a cassette image for writing to (with CSAVE or CSAVEM for example), press Control+W and enter a filename. Created files will be truncated to zero length, so be careful not to overwrite any existing files with this command.
The currently open tape files used for reading and writing are distinct.
Three command line options affect how tapes are read:
The -tape-fast option accelerates tape loading by intercepting ROM calls and performing the action outside the emulation. Disable with -no-tape-fast. On by default.
The -tape-pad option monitors ROM calls in order to insert extra leader bytes where appropriate (long leaders when the motor is switched on, short leaders between blocks). Disable with -no-tape-pad.
The -tape-pad-auto option will, for .cas files, automatically switch on leader padding when insufficient initial leader bytes are found. Disable with -no-tape-pad-auto. On by default.
The -tape-rewrite option enables rewriting of anything read from the input tape to the output tape. This is useful for creating “well formed” cassette images.
Where available, these options can be changed on the fly in the GUI. See Tape control.
XRoar has built-in definitions for three types of cartridge, selectable with the -cart NAME option:
Additionally extra cartridges can be configured, or existing ones reconfigured, with the following options:
If no ROM is configured for a cartridge, there is a built-in list to search for each of the disk controller types. A ROM image will be required if you want to use virtual disks.
Defining extra cartridges is most usefully done in the configuration file, for example:
cart sdose6
cart-desc SuperDOS E6
cart-type dragondos
cart-rom sdose6
cart-rom2 dosdream
This will define a cartridge called “sdose6” that is basically a DragonDOS cartridge with its ROM replaced with sdose6, and an additional ROM called dosdream.
XRoar will automatically attempt to find a disk controller cartridge relevant to the current machine unless the -nodos option is specified.
Loading a ROM image file with Control+L or Control+Shift_L will attach a ROM cartridge.
Within the emulator, cartridges can be enabled or disabled by pressing Control+E. You will almost certainly want to follow this with a hard reset (Control+Shift+R).
If a disk controller cartridge is selected, XRoar supports virtual disks.
Three virtual disk formats are supported (see Supported file types). Of these, DMK retains the most information about the actual layout of the floppy disk, and is the only one that XRoar will recognise as containing single-density data (as used by the Delta system).
When you attach a disk, it is read into memory, and subsequent disk operations are performed on this in-memory copy. Write enable defaults to on (so write operations on the copy will work), but write back defaults to off, so updates will not be written to the disk image file. To toggle write enable, press Control+[5-8], where the number to press is the drive number plus 4. To toggle write back, press Control+Shift+[5-8]. Even with write back enabled, image files will not be updated until the disk in a virtual drive is changed, or you quit the emulator.
Where available, these options can also be changed on the fly in the GUI. See Drive control.
Write back can be set to default to on with the -disk-write-back command line option.
You can create a new blank disk in a virtual drive by pressing Control+Shift+[1-4]. You will be a prompted for a filename, and the extension determines which type of file will be written.
Under the SDL user interface, three video output modules are available, selectable with the -vo MODULE command line option:
When using OpenGL output, the -gl-filter option selects a filtering method when scaling the image. -gl-filter linear averages nearby pixels (blur), -gl-filter nearest selects nearest neighbour pixels (hard edges) and -gl-filter auto (the default) selects nearest when the image size is an exact integer multiple of the base size, otherise selects linear.
OpenGL output might not be available if you built from source without the appropriate support. Use -vo help for a list of available modules.
On slower machines, you can specify a value for frameskip with -fskip FRAMES. For every frame drawn to screen this amount of frames are then skipped before the next one is drawn, reducing the amount of work needed. The default is -fskip 0, meaning no frames are skipped.
XRoar can be started full-screen by specifying -fs.
Specific audio modules exist for OSS, ALSA, Sun audio, Mac OS X coreaudio and PulseAudio. If none of these are available, generic SDL audio will be used.
Use of a specific module can be forced using -ao MODULE. Use -ao null to disable audio, or -ao help for a list of available modules.
For most audio modules, the -ao-rate HZ option can be used to specify a sample rate in Hz. The default will usually be 44100. The -ao-buffer-ms MS or -ao-buffer-samples N options may be used (where supported) to set an audio buffer size, either in milliseconds or number of samples.
Currently only available in the GTK+ interface. Pressing Control+D, or selecting “Drive Control” from the “Tool” menu will open the drive control window.
This window allows you to insert and eject disk images, and toggle their write-enable and write-back states. See Disks.
Currently only available in the GTK+ interface. Pressing Control+T, or selecting “Tape Control” from the “Tool” menu will open the tape control window.
This window shows the current tape image filename and position. The input tape image is scanned, and any recognised file header blocks listed, along with their position within the image. Double clicking a filename will seek to that point in the tape image.
Certain tape options can be configured here. See Cassettes.
XRoar supports redirecting Dragon printer output to a file or pipe with the -lp-file or -lp-pipe option. Printed data will be sent to the appropriate stream. Pressing Control+Shift+P will flush the current stream by closing it (so if the stream is a pipe, the filter will complete). The stream will be re-opened when any new data is sent.
The pipe feature allows you to use useful print filters such as enscript, e.g., -lp-pipe ``enscript -B -N r -d printer-name''. This will send a job to your printer, using carriage returns as line feeds (the Dragon default), each time you press Control+Shift+P (or exit the emulator).
XRoar's user interface is currently based around SDL. The emulator video output window is shown, and all operations are performed with keyboard combinations, usually accessed as Control+KEY:
When using Control+L or Control+Shift+L to load a file, the action to be taken is determined by its extension. See Supported file types for details.
XRoar still supports the use of some old keyboard commands that were used to attach specific types of file. Control+B and Control+H are synonymous with Control+L.
XRoar can save out a snapshot of the emulated machine state and read such snapshots back in later. To save a snapshot, press Control+S. When using Control+L to load a file, anything ending in .sna will be recognised as a snapshot.
What is included in snapshots: Selected machine architecture, complete hardware state, current keyboard map, filenames of attached disk image files.
What is not (yet) included: Actual disk image data (only where to find it), attached cassettes or cartridges.
XRoar contains a “trace mode”, where it will dump a disassembly of every instruction it executes to the console. Trace mode defaults to off unless you run with -trace. Toggle trace mode on or off with Control+V.
Many emulator functions can be changed using keyboard shortcuts (see Keyboard commands), but some behaviour can also be changed from the command line.
If you run the Windows pre-built binary, you might find that emulator output gets written to a file called stderr.txt instead of to the console.
See Emulated machines for more information.
See Cartridges for more information.
XRoar can do useful things with a variety of file types. The type of a file is determined by its extension. Supported file extensions are:
| Extension | Description | Read/write?
|
|---|---|---|
| .dmk | Disk image file in a format defined by David Keil. They store a lot of information about the structure of a disk and support both single and double density data. All disk images are manipulated internally in (near enough) this format. See Disks. | Read & write
|
| .jvc .dsk | Disk image file in a basic sector-by-sector format with optional header information. See Disks. | Read-only
|
| .vdk | Another disk image file format. See Disks. | Read-only
|
| .bin | Binary file (DragonDOS or CoCo). XRoar can load these directly into memory and optionally autorun them. | Read-only
|
| .sna | XRoar snapshot. Contains a complete dump of RAM from a running emulator session along with information like which machine was being emulated, what DOS was attached, etc. See Snapshots. | Read & write
|
| .hex | Intel hex record. An ASCII format that encodes binary data and where in memory to load it. | Read-only
|
| .cas | Cassette file. Simple binary representation of data contained on a tape. Cannot represent silence, or some custom encodings. See Cassettes. | Read & write
|
| .wav | Cassette audio file. XRoar can read sampled audio from original cassettes. Actually, as audio input uses libsndfile, any file with an unknown extension is passed to libsndfile to see if it recognises it as an audio file. See Cassettes. | Read-only
|
| .rom | This represents two things: when starting, XRoar looks for firmware ROM images with this extension. When subsequently told to load one, however, they are assumed to be dumps of cartridge ROMs. See Cartridges. | Read-only
|
In general, to load or attach a file, press Control+L and choose a file from the requester that appears. What XRoar does with it will depend on its file extension. You can also automatically attach (and optionally start) files from the command line by using the -load FILE or -run FILE options. If you -load or -run a cassette image, XRoar will automatically disable any DOS cartridge emulation for you, as this can interfere with some cassette-based games. In addition, the first non-option argument to XRoar is taken as a filename and treated as though it were the argument to the -run option.
XRoar searches for ROM images in a variety of locations. See Installation for where your particular platform will search. The search path can be overridden by including a colon-separated list of paths in the XROAR_ROM_PATH environment variable.
Images are expected to have certain names. Here's a table showing the names it searches for each ROM in each system. ROM images can have either a .rom or a .dgn extension. .dgn files contain a 16 byte header, which is ignored.
| Machine | ROM search order | Description
|
|---|---|---|
| dragon32 | d32 dragon32 d32rom dragon | Dragon BASIC.
|
| dragon64 tano | d64_1 d64rom1 dragrom dragon | 32K-mode Dragon BASIC.
|
| d64_2 d64rom2 | 64K-mode Dragon BASIC.
| |
| coco cocous | bas13 bas12 bas11 bas10 | Color BASIC 1.3, 1.2, 1.1 or 1.0.
|
| extbas11 extbas10 | Extended Color BASIC 1.1 or 1.0.
|
Further, emulating a floppy drive controller cartridge requires that you have an image of the DOS ROM that would have been part of it.
| Controller type | ROM search order | Description
|
|---|---|---|
| dragondos | dplus49b dplus48 sdose6 sdose5 sdose4 ddos40 ddos15 ddos10 | DragonDOS (using DOSplus, SuperDOS or original DragonDOS ROM).
|
| delta | delta deltados | Delta System.
|
| rsdos | disk11 disk10 | Disk Extended Color BASIC 1.1 or 1.0.
|
All command-line options can also be used as directives in a configuration file called xroar.conf. This file is searched for in a variety of locations:
| System | Search order
|
|---|---|
| Unix Mac OS X | Current working directory ~/.xroar/ ~/Library/XRoar/ PREFIX/share/xroar/ |
| Windows | Current working directory ~/Local Settings/Application Data/XRoar/ ~/Application Data/XRoar/ |
‘~’ indicates the user's home directory. On Unix systems this is held in the HOME environment variable (often /home/username), on Windows systems it is in the USERPROFILE environment variable (often c:/Documents and Settings/username or c:/Users/username). PREFIX is the installation prefix, usually /usr/local.
Directives are listed one per line without the leading dashes of the command line option.
I made reference to the MAME 6809 core for clues on how the overflow bit in the condition code register was handled.
Thanks to all the people on the Dragon Archive Forums for helpful feedback and insight.