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<html><head><title>Gavare's eXperimental Emulator: Introduction</title> |
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<meta name="robots" content="noarchive,nofollow,noindex"></head> |
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<body bgcolor="#f8f8f8" text="#000000" link="#4040f0" vlink="#404040" alink="#ff0000"> |
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<table border=0 width=100% bgcolor="#d0d0d0"><tr> |
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<td width=100% align=center valign=center><table border=0 width=100%><tr> |
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<td align="left" valign=center bgcolor="#d0efff"><font color="#6060e0" size="6"> |
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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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<!-- |
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$Id: intro.html,v 1.73 2006/02/18 14:02:19 debug Exp $ |
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Copyright (C) 2003-2006 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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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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ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE |
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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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FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL |
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DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS |
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OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) |
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HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT |
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LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY |
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OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF |
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SUCH DAMAGE. |
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--> |
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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="#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 instruction-level machine emulator. Several |
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emulation modes are available. In some modes, processors and surrounding |
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hardware components are emulated well enough to let unmodified operating |
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systems (e.g. NetBSD) run as if they were running on a real machine. |
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|
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<p>The processor architecture best emulated by GXemul is MIPS, but other |
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architectures such as ARM and PowerPC are also partially emulated. |
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|
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<p>Devices and CPUs are not simulated with 100% accuracy. They are only |
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``faked'' well enough to allow guest operating systems 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>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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|
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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 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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<p>You can use pre-compiled kernels (for example NetBSD kernels, or |
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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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(ELF, a.out, ECOFF, SREC, and raw binaries). |
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|
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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, 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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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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|
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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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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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|
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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 different |
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CC and CFLAGS environment variable values. For example, on an AMD Athlon |
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host, you might want to try setting <tt>CFLAGS</tt> to <tt>-march=athlon |
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-O3</tt> before running <tt>configure</tt>. |
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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> |
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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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<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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<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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<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 processor architectures does GXemul emulate?</h3> |
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<h4>MIPS:</h4> |
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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. Several guest operating systems for MIPS can run inside |
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the emulator. |
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<p>(For MIPS emulation, I have written an experimental dynamic binary |
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translation subsystem, for Alpha and i386 hosts. This gives higher total |
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performance than interpreting one instruction at a time and executing it. |
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If you wish to disable bintrans, add <b>-B</b> to the command line.) |
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<h4>ARM:</h4> |
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ARM emulation is good enough to run NetBSD/cats, OpenBSD/cats, and |
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NetBSD/evbarm, but it is not as tested or fine-tuned as the MIPS emulation |
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mode. |
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<h4>PowerPC:</h4> |
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PowerPC emulation is still in its beginning stages, but good enough |
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to run NetBSD/prep 2.1. |
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|
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<p>Non-MIPS emulation modes use dynamic translation, but not recompilation |
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into native code. This makes it possible to run on any host platform. |
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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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<p>Caches are by default not emulated. In some cases, the existance of |
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caches is "faked" to let operating systems think that they are there. |
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(There is some old code for R2000/R3000 caches, but it has probably |
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suffered from bitrot by now.) |
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|
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<p>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 |
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emulation will be identical to some actual real-world machine.) |
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|
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<p><font color="#ff0000">(Oops/TODO: User interaction means <i>both</i> |
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input to the emulated program/OS, and interacting with the emulator |
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itself. Breaking into the debugger and then continuing execution may |
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affect when/how interrupts occur.)</font> |
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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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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>MIPS</u></b> |
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<ul> |
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<li><b>DECstation 5000/200</b> ("3max") |
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<li><b>Acer Pica-61</b> (an ARC machine) |
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<li><b>NEC MobilePro 770, 780, 800, and 880</b> (HPCmips machines) |
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<li><b>Cobalt</b> |
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<li><b>Malta</b> (evbmips) |
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<li><b>SGI O2 ("IP32")</b> <font color="#0000e0">(<super>*</super>)</font> |
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</ul> |
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<p> |
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<li><b><u>ARM</u></b> |
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<ul> |
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<li><b>CATS</b> |
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<li><b>IQ80321</b> (evbarm) |
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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>PReP (PowerPC Reference Platform)</b> |
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</ul> |
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</ul> |
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<p><small><font color="#0000e0">(<super>*</super>)</font> = |
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Enough for root-on-nfs, but not for disk boot.)</small> |
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|
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<p>There is code in GXemul for emulation of many 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). |
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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 SCSI disk controller |
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<li>a simple ethernet controller |
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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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</body> |
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</html> |