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<head><title>GXemul documentation: Introduction</title> |
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<td align="left" valign=center bgcolor="#d0efff"><font color="#6060e0" size="6"> |
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<b>GXemul documentation:</b></font> |
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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 1.46 2005/06/04 12:02:17 debug Exp $ |
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Copyright (C) 2003-2005 Anders Gavare. All rights reserved. |
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|
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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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notice, this list of conditions and the following disclaimer. |
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2. Redistributions in binary form must reproduce the above copyright |
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notice, this list of conditions and the following disclaimer in the |
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documentation and/or other materials provided with the distribution. |
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3. The name of the author may not be used to endorse or promote products |
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derived from this software without specific prior written permission. |
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THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND |
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IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE |
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ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE |
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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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|
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<p> |
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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 CPU types does GXemul emulate?</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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<li><a href="#guestos">Which guest OSes are possible to run?</a> |
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</ul> |
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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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|
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GXemul is a machine emulator, which can be used to experiment with |
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binary code for (among others) MIPS-based machines. Several emulation |
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modes are available. For some emulation modes, processors and surrounding |
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hardware components are emulated well enough to let unmodified operating |
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systems run as if they were running on a real machine. |
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|
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<p> |
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Devices and CPUs are not simulated with 100% accuracy. They are only |
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"faked" well enough to make operating systems (eg NetBSD) 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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|
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<p> |
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The emulator is written in C, does not depend on external libraries (except |
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X11, but that is optional), and should compile and run on most Unix-like |
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systems. If it doesn't, then that is a bug. |
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(You do not need any MIPS compiler toolchain to build or use GXemul. |
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If you need to compile MIPS binaries from sources, then of course you need |
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such a toolchain, but that is completely separate from GXemul.) |
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|
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<p> |
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The emulator contains code which tries to emulate the workings of CPUs and |
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surrounding hardware found in real machines, but it does not contain any |
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ROM code. You will need some form of program (in binary form) to run in |
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the emulator. For many 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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|
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<p> |
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You can use pre-compiled kernels (for example NetBSD kernels, or Linux), |
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or other programs that are in binary format, and in some cases even actual |
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ROM images. A couple of different file formats are supported (ELF, a.out, |
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ECOFF, SREC, and raw binaries). |
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<p> |
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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, or when booting |
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from ISO9660 CDROM images.) |
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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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|
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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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|
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<p> |
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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 |
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<a href="http://www.gnu.org/philosophy/bsd.html">GNU jargon</a>). |
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Apart from the code I have written, some files are copied from other sources |
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such as NetBSD, for example header files containing symbolic names of |
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bitfields in device registers. They are also covered by similar licenses, |
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but with some additional clauses. If you plan to redistribute GXemul |
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(for example as a binary package), or reuse code from GXemul, |
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then you should check those files for their license terms. |
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|
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<p> |
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(The licenses usually require that the original Copyright and license |
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terms are included when you make a copy or modification. The "easiest way |
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out" if you plan to redistribute code from GXemul is to simply supply |
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the source code. You should however check individual files for details.) |
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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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|
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<p> |
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This should work on most Unix-like systems. If it doesn't, then |
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mail me a bug report. |
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|
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<p> |
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(Note for Windows users: there is a possibility that some releases |
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and/or snapshots will also work with Cygwin, but I can't promise that.) |
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|
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<p> |
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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 different |
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CC and CFLAGS environment variable values. For example, on a modern PC, |
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you could try the following: |
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<p> |
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<pre> |
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$ <b>CFLAGS="-mcpu=pentium4 -O3" ./configure</b> |
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$ <b>make</b> |
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</pre> |
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|
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<p> |
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Run <b><tt>./configure --help</tt></b> to get a list of configure options. (The |
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possible options differ between different releases and snapshots.) |
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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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|
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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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|
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<p> |
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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>. If you are interested in using the emulator to |
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develop code on your own, then you should also read the section about |
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<a href="experiments.html#hello">Hello World</a>. |
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|
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<p> |
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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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|
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<p> |
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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 all |
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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. |
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(This should be a reasonable compromise to allow the emulator to be usable |
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even on systems without X Windows.) |
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|
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<p> |
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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 CPU types does GXemul emulate?</h3> |
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|
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<h4>MIPS:</h4> |
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|
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Emulation of R4000, which is a 64-bit CPU, was my initial goal. |
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R2000/R3000-like CPUs (32-bit), R1x000, and generic MIPS32/MIPS64-style |
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CPUs are also emulated, and are hopefully almost as stable as the R4000 |
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emulation. |
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|
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<p> |
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I have written an experimental dynamic binary translation subsystem. |
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This gives higher total performance than interpreting one instruction at a |
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time and executing it. (If you wish to enable bintrans, add <b>-b</b> to |
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the command line, but keep in mind that it is still experimental.) |
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|
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|
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<h4>URISC:</h4> |
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|
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I have implemented an <a href="http://en.wikipedia.org/wiki/URISC">URISC</a> |
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emulation mode, just for fun. The only instruction available in an URISC |
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machine is "reverse subtract and skip on borrow". (It is probably not |
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worth trying to do bintrans with URISC, because any reasonable URISC |
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program relies on self-modifying code, which is bad for bintrans |
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performance.) |
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|
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|
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<h4>POWER/PowerPC</h4> |
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|
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There is some code for 64-bit (and 32-bit) POWER/PowerPC emulation, enough |
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to run "Hello World", but not enough to run complete operating systems. |
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This mode isn't really working yet. |
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|
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|
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<h4>Other CPU types:</h4> |
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|
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Some other CPU architectures (such as x86) can also be partially emulated. |
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These are not enabled by default though, because of their unstable-ness. |
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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 (eg. 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> |
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Caches are by default not emulated. In some cases, the existance of caches |
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is "faked" to let operating systems think that they are there. (There is |
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some old code for R2000/R3000 caches, but it has probably suffered from |
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bitrot by now.) |
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|
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<p> |
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The emulator is <i>not</i> timing-accurate. It can be run in a |
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"deterministic" mode, <tt><b>-D</b></tt>. The meaning of deterministic is |
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simply that running two emulations with the same settings will result in |
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identical runs. Obviously, this requires that no user interaction is |
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taking place, and that clock speeds are fixed with the <tt><b>-I</b></tt> |
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option. (Deterministic in this case does <i>not</i> mean that the emulation |
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will be identical to some actual real-world machine.) |
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|
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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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|
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<p> |
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<ul> |
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<li><b>DECstation 5000/200</b> ("3max") |
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<br>Serial controller (including keyboard and mouse), ethernet, |
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SCSI, and graphical framebuffers. |
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<p> |
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<li><b>Acer Pica-61</b> (an ARC machine) |
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<br>Serial controller, "VGA" text console, and SCSI. |
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<p> |
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<li><b>NEC MobilePro 770, 780, 800, and 880</b> (HPCmips machines) |
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<br>Framebuffer, keyboard, and a PCMCIA IDE controller. |
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<p> |
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<li><b>Cobalt</b> |
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<br>Serial controller and PCI IDE. |
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</ul> |
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|
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<p> |
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There is code in GXemul for emulation of many other machine types; |
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the degree to which these work range from "almost" being able to run |
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a complete OS, to almost completely unsupported (perhaps just enough |
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support to output a few boot messages via serial console). |
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|
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<p> |
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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 |
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devices such as: |
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|
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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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</ul> |
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|
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<p> |
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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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|
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<p> |
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You can read more about these experimental devices |
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<a href="experiments.html#expdevices">here</a>. |
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<p><br> |
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<a name="guestos"></a> |
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<h3>Which guest OSes are possible to run?</h3> |
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|
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This table lists the guest OSes that run well enough to be considered |
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working in the emulator. They can boot from a harddisk image and be |
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interacted with similar to a real machine. |
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|
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<p> |
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<center><table border="0"> |
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<tr> |
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<td width="10"></td> |
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<td align="center"><a href="20050317-example.png"><img src="20050317-example_small.png"></a></td> |
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<td width="15"></td> |
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<td><a href="http://www.netbsd.org/Ports/pmax/">NetBSD/pmax</a> |
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<br>DECstation 5000/200</td> |
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<td width="30"></td> |
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<td align="center"><a href="20041024-netbsd-arc-installed.gif"><img src="20041024-netbsd-arc-installed_small.gif"></a></td> |
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<td width="15"></td> |
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<td><a href="http://www.netbsd.org/Ports/arc/">NetBSD/arc</a> |
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<br>Acer Pica-61</td> |
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|
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</tr> |
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|
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<tr><td height="10"></td></tr> |
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|
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<tr> |
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<td></td> |
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<td align="center"><a href="openbsd-pmax-20040710.png"><img src="openbsd-pmax-20040710_small.png"></a></td> |
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<td></td> |
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<td><a href="http://www.openbsd.org/pmax.html">OpenBSD/pmax</a> |
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<br>DECstation 5000/200</td> |
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<td></td> |
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<td align="center"><a href="20041024-openbsd-arc-installed.gif"><img src="20041024-openbsd-arc-installed_small.gif"></a></td> |
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<td></td> |
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<td><a href="http://www.openbsd.org/arc.html">OpenBSD/arc</a> |
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<br>Acer Pica-61</td> |
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</tr> |
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|
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<tr><td height="10"></td></tr> |
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|
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<tr> |
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<td></td> |
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<td align="center"><a href="ultrix4.5-20040706.png"><img src="ultrix4.5-20040706_small.gif"></a></td> |
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<td></td> |
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<td>Ultrix/RISC<br>DECstation 5000/200</td> |
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<td></td> |
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<td align="center"><a href="20041213-debian_4.png"><img src="20041213-debian_4_small.gif"></a></td> |
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<td></td> |
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<td><a href="http://www.debian.org/">Debian GNU/Linux</a> <super>*</super> |
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<br>DECstation 5000/200</td> |
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</tr> |
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|
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<tr><td height="10"></td></tr> |
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|
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<tr> |
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<td></td> |
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<td align="center"><a href="sprite-20040711.png"><img src="sprite-20040711_small.png"></a></td> |
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<td></td> |
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<td><a href="http://www.cs.berkeley.edu/projects/sprite/retrospective.html">Sprite</a> |
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<br>DECstation 5000/200</td> |
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<td></td> |
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<td align="center"><a href="20041129-redhat_mips.png"><img src="20041129-redhat_mips_small.png"></a></td> |
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<td></td> |
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<td>Redhat Linux <super>*</super> |
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<br>DECstation 5000/200</td> |
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</tr> |
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|
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<tr><td height="10"></td></tr> |
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|
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<tr> |
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<td></td> |
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<td align="center"><a href="20050427-netbsd-hpcmips-2.png"><img src="20050427-netbsd-hpcmips-2_small.png"></a></td> |
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<td></td> |
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<td><a href="http://www.netbsd.org/Ports/hpcmips/">NetBSD/hpcmips</a> |
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<br>NEC MobilePro 770, 780, 800, 880</td> |
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<td></td> |
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<td align="center"><a href="20050413-netbsd-cobalt.png"><img src="20050413-netbsd-cobalt_small.png"></a></td> |
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<td></td> |
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<td><a href="http://www.netbsd.org/Ports/cobalt/">NetBSD/cobalt</a> |
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<br>Cobalt</td> |
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</tr> |
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|
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</table></center> |
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|
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|
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<p><br> |
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|
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<super>*</super> Although Linux runs under DECstation emulation, the |
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default 2.4.27 kernel in Debian GNU/Linux does not support keyboards on |
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the 5000/200 (the specific DECstation model being emulated), so when the |
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login prompt is reached you cannot interact with the system. Kaj-Michael |
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Lang has compiled and made available a newer kernel from the current |
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mips-linux development tree. You can find it here: <a |
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href="http://home.tal.org/~milang/o2/kernels/">http://home.tal.org/~milang/o2/kernels</a>/<a |
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href="http://home.tal.org/~milang/o2/kernels/vmlinux-2.4.29-rc2-r3k-mipsel-decstation">vmlinux-2.4.29-rc2-r3k-mipsel-decstation</a> |
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This newer kernel supports keyboard input, but it does not have Debian's |
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ethernet patches, so you will not be able to use keyboard/framebuffer |
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<i>and</i> networking at the same time. |
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</body> |
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</html> |
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