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Devices and CPUs are not simulated with 100% accuracy. They are only ``faked'' well enough to make operating systems (e.g. NetBSD) run without complaining too much. Still, the emulator could be of interest for academic research and experiments, such as when learning how to write operating system code.
The emulator is written in C, does not depend on external libraries (except X11, but that is optional), and should compile and run on most Unix-like systems. If it doesn't, then that is a bug. (You do not need any MIPS compiler toolchain to build or use GXemul. If you need to compile MIPS binaries from sources, then of course you need such a toolchain, but that is completely separate from GXemul.)
The emulator contains code which tries to emulate the workings of CPUs and surrounding hardware found in real machines, but it does not contain any ROM code. You will need some form of program (in binary form) to run in the emulator. For many emulation modes, PROM calls are handled by the emulator itself, so you do not need to use any ROM image at all.
You can use pre-compiled kernels (for example NetBSD kernels, or Linux), or other programs that are in binary format, and in some cases even actual ROM images. A couple of different file formats are supported (ELF, a.out, ECOFF, SREC, and raw binaries).
If you do not have a kernel as a separate file, but you have a bootable disk image, then it is sometimes possible to boot directly from that image. (This works for example with DECstation emulation, or when booting from ISO9660 CDROM images.)
The code I have written is released under a 3-clause BSD-style license (or "revised BSD-style" if one wants to use GNU jargon). Apart from the code I have written, some files are copied from other sources such as NetBSD, for example header files containing symbolic names of bitfields in device registers. They are also covered by similar licenses, but with some additional clauses. If you plan to redistribute GXemul (for example as a binary package), or reuse code from GXemul, then you should check those files for their license terms.
(The licenses usually require that the original Copyright and license terms are included when you make a copy or modification. The "easiest way out" if you plan to redistribute code from GXemul is to simply supply the source code. You should however check individual files for details.)
$ ./configure $ make
This should work on most Unix-like systems. If it doesn't, then mail me a bug report.
(Note for Windows users: there is a possibility that some releases and/or snapshots will also work with Cygwin, but I can't promise that.)
The emulator's performance is highly dependent on both runtime settings and on compiler settings, so you might want to experiment with different CC and CFLAGS environment variable values. For example, on a modern PC, you could try the following:
$ CFLAGS="-mcpu=pentium4 -O3" ./configure $ make
Run ./configure --help to get a list of configure options. (The possible options differ between different releases and snapshots.)
To get some ideas about what is possible to run in the emulator, please read the section about installing "guest" operating systems. If you are interested in using the emulator to develop code on your own, then you should also read the section about Hello World.
To exit the emulator, type CTRL-C to enter the single-step debugger, and then type quit.
If you are starting an emulation by entering settings directly on the command line, and you are not using the -x option, then all terminal input and output will go to the main controlling terminal. CTRL-C is used to break into the debugger, so in order to send CTRL-C to the running (emulated) program, you may use CTRL-B. (This should be a reasonable compromise to allow the emulator to be usable even on systems without X Windows.)
There is no way to send an actual CTRL-B to the emulated program, when typing in the main controlling terminal window. The solution is to either use configuration files, or use -x. Both these solutions cause new xterms to be opened for each emulated serial port that is written to. CTRL-B and CTRL-C both have their original meaning in those xterm windows.
I have written an experimental dynamic binary translation subsystem. This gives higher total performance than interpreting one instruction at a time and executing it. (If you wish to enable bintrans, add -b to the command line, but keep in mind that it is still experimental.)
Caches are by default not emulated. In some cases, the existance of caches is "faked" to let operating systems think that they are there. (There is some old code for R2000/R3000 caches, but it has probably suffered from bitrot by now.)
The emulator is not timing-accurate. It can be run in a "deterministic" mode, -D. The meaning of deterministic is simply that running two emulations with the same settings will result in identical runs. Obviously, this requires that no user interaction is taking place, and that clock speeds are fixed with the -I option. (Deterministic in this case does not mean that the emulation will be identical to some actual real-world machine.)
There is code in GXemul for emulation of many other machine types; the degree to which these work range from almost being able to run a complete OS, to almost completely unsupported (perhaps just enough support to output a few boot messages via serial console).
In addition to emulating real machines, there is also a "test-machine". A test-machine consists of one or more CPUs and a few experimental devices such as:
This mode is useful if you wish to run experimental code, but do not wish to target any specific real-world machine type, for example for educational purposes.
You can read more about these experimental devices here.
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NetBSD/pmax
DECstation 5000/200 |
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NetBSD/arc
Acer Pica-61 |
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OpenBSD/pmax
DECstation 5000/200 |
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OpenBSD/arc
Acer Pica-61 |
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Ultrix/RISC DECstation 5000/200 |
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Debian GNU/Linux DECstation 5000/200 |
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Sprite
DECstation 5000/200 |
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Redhat Linux DECstation 5000/200 |
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NetBSD/hpcmips
NEC MobilePro 770, 780, 800, 880 |
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NetBSD/cobalt
Cobalt |
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NetBSD/sgimips
SGI O2 ("IP32") |
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NetBSD/evbmips
5Kc (and 4Kc) Malta evaluation boards |