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<b>Gavare's eXperimental Emulator:</b></font><br> |
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<font color="#000000" size="6"><b>Introduction</b> |
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</font></td></tr></table></td></tr></table><p> |
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$Id: intro.html,v 1.118 2007/06/15 21:43:09 debug Exp $ |
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Copyright (C) 2003-2007 Anders Gavare. All rights reserved. |
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Redistribution and use in source and binary forms, with or without |
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modification, are permitted provided that the following conditions are met: |
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1. Redistributions of source code must retain the above copyright |
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3. The name of the author may not be used to endorse or promote products |
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<a href="./">Back to the index</a> |
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<p><br> |
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<h2>Introduction</h2> |
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<p> |
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<table border="0" width="99%"><tr><td valign="top" align="left"> |
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<ul> |
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<li><a href="#overview">Overview</a> |
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<li><a href="#free">Is GXemul Free software?</a> |
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<li><a href="#build">How to compile/build the emulator</a> |
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<li><a href="#run">How to run the emulator</a> |
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<li><a href="#cpus">Which processor architectures does GXemul emulate?</a> |
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<li><a href="#hosts">Which host architectures/platforms are supported?</a> |
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<li><a href="#accuracy">Emulation accuracy</a> |
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<li><a href="#emulmodes">Which machines does GXemul emulate?</a> |
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</ul> |
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</td><td valign="center" align="center"> |
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<a href="20050317-example.png"><img src="20050317-example_small.png"></a> |
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<p>NetBSD/pmax 1.6.2 with X11<br>running in GXemul</td></tr></table> |
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<p><br> |
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<a name="overview"></a> |
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<h3>Overview:</h3> |
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GXemul is an experimental <a href="#accuracy">instruction-level</a> |
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machine emulator. Several emulation modes are available. In some modes, |
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processors and surrounding hardware components are emulated well enough to |
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let <a href="#emulmodes">unmodified operating systems (e.g. NetBSD) |
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run</a> as if they were running on a real machine. |
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<p>The emulator is written in C, does not depend on third-party libraries, |
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and should compile and run on most 64-bit and 32-bit Unix-like systems, |
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with few or no modifications. |
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<p>Devices and processors are not simulated with 100% accuracy. They are |
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only ``faked'' well enough to allow guest operating systems to run without |
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complaining too much. Still, the emulator could be of interest for |
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academic research and experiments, such as when learning how to write |
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operating system code. |
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<p>The emulator contains code which tries to emulate the workings of CPUs |
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and surrounding hardware found in real machines, but it does not contain |
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any ROM code. You will need some form of program (in binary form) to run |
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in the emulator. For some emulation modes, PROM calls are handled by the |
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emulator itself, so you do not need to use any ROM image at all. |
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<p>You can use pre-compiled kernels (for example <a href="http://www.netbsd.org/">NetBSD</a> |
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kernels, or Linux), or other programs that are in binary format, and in some cases |
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even actual ROM images. A couple of different file formats are supported: |
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<a href="http://en.wikipedia.org/wiki/Executable_and_Linkable_Format">ELF</a>, |
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<a href="http://en.wikipedia.org/wiki/A.out">a.out</a>, |
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<a href="http://en.wikipedia.org/wiki/COFF">COFF</a>/<a href="http://en.wikipedia.org/wiki/ECOFF">ECOFF</a>, |
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<a href="http://en.wikipedia.org/wiki/SREC_%28file_format%29">SREC</a>, and raw binaries. |
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<p>If you do not have a kernel as a separate file, but you have a bootable |
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disk image, then it is sometimes possible to boot directly from that |
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image. This works for example with DECstation emulation, <a href="dreamcast.html">Dreamcast |
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emulation</a>, or when booting from generic <a href="http://en.wikipedia.org/wiki/ISO9660">ISO9660</a> |
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CDROM images if the kernel is included in the image as a plain file. |
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<p>Thanks to (in no specific order) Joachim Buss, Olivier Houchard, Juli |
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Mallett, Juan Romero Pardines, Carl van Schaik, Miod Vallat, Alec Voropay, |
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Göran Weinholt, Alexander Yurchenko, and everyone else who has provided me |
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with feedback. |
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<p><br> |
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<a name="free"></a> |
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<h3>Is GXemul Free software?</h3> |
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Yes. I have released GXemul under a Free license. The code in GXemul is |
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Copyrighted software, it is <i>not</i> public domain. (If this is |
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confusing to you, you might want to read up on the definitions of the |
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four freedoms associated with Free software, <a |
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href="http://www.gnu.org/philosophy/free-sw.html">http://www.gnu.org/philosophy/free-sw.html</a>.) |
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<p>The code I have written is released under a 3-clause BSD-style license |
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(or "revised BSD-style" if one wants to use <a |
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href="http://www.gnu.org/philosophy/bsd.html">GNU jargon</a>). Apart from |
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the code I have written, some files are copied from other sources such as |
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NetBSD, for example header files containing symbolic names of bitfields in |
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device registers. They are also covered by similar licenses, but with some |
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additional clauses. The main point, however, is that the licenses require |
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that the original Copyright and license terms are included when you make a |
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copy or modification. |
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<p>If you plan to redistribute GXemul <i>without</i> supplying the source |
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code, then you need to comply with each individual source file some other |
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way, for example by writing additional documentation containing copyright |
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notes. I have not done this, since I do not plan on making distributions |
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without source code. You need to check all individual files for details. |
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The "easiest way out" if you plan to redistribute code from GXemul is, of |
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course, to let it remain open source and simply supply the source code. |
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<p>In case you want to reuse parts of GXemul, but you need to do that |
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under a different license (e.g. the GPL), then contact me and I might |
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re-license/dual-license files on a case-by-case basis. |
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<p><br> |
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<a name="build"></a> |
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<h3>How to compile/build the emulator:</h3> |
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|
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Uncompress the .tar.gz distribution file, and run |
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<pre> |
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$ <b>./configure</b> |
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$ <b>make</b> |
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</pre> |
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<p>This should work on most Unix-like systems. GXemul does not require any |
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specific libraries to build, however, if you build on a system which does |
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not have X11 libraries installed, some functionality will be lost. |
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<p>The emulator's performance is highly dependent on both runtime settings |
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and on compiler settings, so you might want to experiment with |
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using different CC and CFLAGS environment variable values when running the |
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<tt>configure</tt> script. |
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<p>Note that there is no <tt>make install</tt> functionality; package |
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maintainers for individual operating systems solve this for their |
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corresponding OSes. |
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<p><br> |
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<a name="run"></a> |
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<h3>How to run the emulator:</h3> |
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Once you have built GXemul, running it should be rather straight-forward. |
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Running <tt><b>gxemul</b></tt> without arguments (or with the |
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<b><tt>-h</tt></b> or <b><tt>-H</tt></b> command line options) will |
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display a help message. |
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<p>To get some ideas about what is possible to run in the emulator, please |
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read the section about <a href="guestoses.html">installing "guest" |
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operating systems</a>. The most straight forward guest operating to |
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install is NetBSD/pmax; the instructions provided <a |
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href="guestoses.html#netbsdpmaxinstall">here</a> should let you install |
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NetBSD/pmax in a way very similar to how it is done on a real DECstation. |
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<p>If you are interested in using the emulator to develop code on your |
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own, then you should also read the section about <a |
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href="experiments.html#hello">Hello World</a>. |
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<p>To exit the emulator, type CTRL-C to enter the |
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single-step debugger, and then type <tt><b>quit</b></tt>. |
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<p>If you are starting an emulation by entering settings directly on the |
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command line, and you are not using the <tt><b>-x</b></tt> option, then |
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all terminal input and output will go to the main controlling terminal. |
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CTRL-C is used to break into the debugger, so in order to send CTRL-C to |
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the running (emulated) program, you may use CTRL-B. (This should be a |
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reasonable compromise to allow the emulator to be usable even on systems |
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without X Windows.) |
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<p>There is no way to send an actual CTRL-B to the emulated program, when |
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typing in the main controlling terminal window. The solution is to either |
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use <a href="configfiles.html">configuration files</a>, or use |
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<tt><b>-x</b></tt>. Both these solutions cause new xterms to be opened for |
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each emulated serial port that is written to. CTRL-B and CTRL-C both have |
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their original meaning in those xterm windows. |
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<p><br> |
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<a name="cpus"></a> |
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<h3>Which processor architectures does GXemul emulate?</h3> |
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|
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The architectures that are emulated well enough to let at least one |
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guest operating system run (per architecture) are ARM, MIPS, PowerPC, |
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and SuperH. |
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<p>Please read the page about <a href="guestoses.html">guest operating |
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systems</a> for more information about the machines and operating systems |
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that can be considered "working" in the emulator. (There is some code in |
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GXemul for emulation of other architectures, but they are not stable or |
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complete enough to be listed among the "working" architectures.) |
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<p><br> |
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<a name="hosts"></a> |
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<h3>Which host architectures/platforms are supported?</h3> |
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|
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GXemul should compile and run on any modern host architecture (64-bit or |
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32-bit word-length). I generally test it on FreeBSD/amd64 6.x, |
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FreeBSD/alpha 4.x, sometimes also on Linux (various platforms), and every |
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now and then also on NetBSD inside the emulator itself (various platforms). |
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|
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<p>Note 1: The <a href="translation.html">dynamic translation</a> engine |
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does <i>not</i> require backends for native code generation to be written |
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for each individual host architecture; the intermediate representation |
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that the dyntrans system uses can be executed on any host architecture. |
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<p>Note 2: Although GXemul may build and run on non-Unix-like platforms, |
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such as Cygwin, Unix-like systems are the primary platform. Some |
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functionality may be lost when running on Cygwin. |
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<p><br> |
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<a name="accuracy"></a> |
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<h3>Emulation accuracy:</h3> |
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|
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GXemul is an instruction-level emulator; things that would happen in |
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several steps within a real CPU are not taken into account (e.g. pipe-line |
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stalls or out-of-order execution). Still, instruction-level accuracy seems |
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to be enough to be able to run complete guest operating systems inside the |
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emulator. |
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|
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<p>The existance of instruction and data caches is "faked" to let |
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operating systems think that they are there, but for all practical |
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purposes, these caches are non-working. |
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<p>The emulator is in general <i>not</i> timing-accurate, neither at the |
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instruction level nor on any higher level. An attempt is made to let |
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emulated clocks run at the same speed as the host (i.e. an emulated timer |
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running at 100 Hz will interrupt around 100 times per real second), but |
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since the host speed may vary, e.g. because of other running processes, |
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there is no guarantee as to how many instructions will be executed in |
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each of these 100 Hz cycles. |
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<p>If the host is very slow, the emulated clocks might even lag behind |
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the real-world clock. |
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<p><br> |
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<a name="emulmodes"></a> |
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<h3>Which machines does GXemul emulate?</h3> |
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|
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A few different machine types are emulated. The following machine types |
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are emulated well enough to run at least one "guest OS": |
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<p> |
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<ul> |
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<li><b><u>ARM</u></b> |
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<ul> |
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<li><b>CATS</b> (<a href="guestoses.html#netbsdcatsinstall">NetBSD/cats</a>, |
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<a href="guestoses.html#openbsdcatsinstall">OpenBSD/cats</a>) |
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<li><b>IQ80321</b> (<a href="guestoses.html#netbsdevbarminstall">NetBSD/evbarm</a>) |
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<li><b>NetWinder</b> (<a href="guestoses.html#netbsdnetwinderinstall">NetBSD/netwinder</a>) |
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</ul> |
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<p> |
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<li><b><u>MIPS</u></b> |
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<ul> |
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<li><b>DECstation 5000/200</b> (<a href="guestoses.html#netbsdpmaxinstall">NetBSD/pmax</a>, |
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<a href="guestoses.html#openbsdpmaxinstall">OpenBSD/pmax</a>, |
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<a href="guestoses.html#ultrixinstall">Ultrix</a>, |
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<a href="guestoses.html#declinux">Linux/DECstation</a>, |
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<a href="guestoses.html#sprite">Sprite</a>) |
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<li><b>Acer Pica-61</b> (<a href="guestoses.html#netbsdarcinstall">NetBSD/arc</a>) |
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<li><b>NEC MobilePro 770, 780, 800, 880</b> (<a href="guestoses.html#netbsdhpcmipsinstall">NetBSD/hpcmips</a>) |
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<li><b>Cobalt</b> (<a href="guestoses.html#netbsdcobaltinstall">NetBSD/cobalt</a>) |
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<li><b>Malta</b> (<a href="guestoses.html#netbsdevbmipsinstall">NetBSD/evbmips</a>, Linux/Malta <font color="#0000e0">(<super>*1</super>)</font>) |
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<li><b>Algorithmics P5064</b> (<a href="guestoses.html#netbsdalgorinstall">NetBSD/algor</a>) |
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<li><b>SGI O2 (aka IP32)</b> <font color="#0000e0">(<super>*2</super>)</font> |
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(<a href="guestoses.html#netbsdsgimips">NetBSD/sgi</a>) |
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</ul> |
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<p> |
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<li><b><u>PowerPC</u></b> |
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<ul> |
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<li><b>IBM 6050/6070 (PReP, PowerPC Reference Platform)</b> (<a href="guestoses.html#netbsdprepinstall">NetBSD/prep</a>) |
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<li><b>MacPPC (generic "G4" Macintosh)</b> (<a href="guestoses.html#netbsdmacppcinstall">NetBSD/macppc</a>) |
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<li><b>Artesyn PM/PPC</b> (<a href="guestoses.html#netbsdpmppc">NetBSD/pmppc</a>) |
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</ul> |
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<p> |
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<li><b><u>SuperH</u></b> |
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<ul> |
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<li><b>Sega Dreamcast</b> (<a href="dreamcast.html#netbsd_generic_md">NetBSD/dreamcast</a>, <a href="dreamcast.html#linux_live_cd">Linux/dreamcast</a>) |
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<li><b>Landisk I-O DATA USL-5P</b> (<a href="guestoses.html#openbsdlandiskinstall">OpenBSD/landisk</a>) |
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</ul> |
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</ul> |
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|
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<p> |
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<small><font color="#0000e0">(<super>*1</super>)</font> = |
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Linux/Malta may be run as a guest OS, however I have not yet found any stable |
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URL to pre-compiled Linux/Malta kernels. Thus, Linux/Malta emulation is not |
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tested for every release of the emulator; sometimes it works, sometimes |
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it doesn't.</small> |
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|
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<br><small><font color="#0000e0">(<super>*2</super>)</font> = |
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SGI O2 emulation is enough for root-on-nfs, but not for disk boot.</small> |
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|
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<p>Note that of all of the machines above, none of them is emulated to |
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100%. The most complete emulation mode is probably the DECstation |
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5000/200. Things that will most likely <b>not</b> work include running |
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raw PROM images for most machines, SGI IRIX, MacOS X or Darwin, Windows |
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NT, or Dreamcast games. |
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|
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<p>There is code in GXemul for emulation of several other machine types; the |
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degree to which these work range from almost being able to run a complete |
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OS, to almost completely unsupported, perhaps just enough support to |
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output a few boot messages via serial console. (See the end of |
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<a href="guestoses.html#generalnotes">this section</a> on the Guest OSes |
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page for some examples, but remember that these do not necessarily work.) |
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|
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<p>In addition to emulating real machines, there is also a "test-machine". |
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A test-machine consists of one or more CPUs and a few experimental devices |
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such as: |
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<p> |
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<ul> |
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<li>a console I/O device (putchar() and getchar()...) |
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<li>an inter-processor communication device, for SMP experiments |
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<li>a very simple linear framebuffer device (for graphics output) |
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<li>a simple disk controller |
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<li>a simple ethernet controller |
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<li>a real-time clock device |
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</ul> |
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<p>This mode is useful if you wish to run experimental code, but do not |
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wish to target any specific real-world machine type, for example for |
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educational purposes. |
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<p>You can read more about these experimental devices <a |
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href="experiments.html#expdevices">here</a>. |
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