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<b>GXemul documentation:</b></font> |
<b>Gavare's eXperimental Emulator: </b></font> |
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<font color="#000000" size="6"><b>Introduction</b> |
<font color="#000000" size="6"><b>Introduction</b> |
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$Id: intro.html,v 1.40 2005/04/27 15:22:17 debug Exp $ |
$Id: intro.html,v 1.61 2005/08/16 05:15:24 debug Exp $ |
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Copyright (C) 2003-2005 Anders Gavare. All rights reserved. |
Copyright (C) 2003-2005 Anders Gavare. All rights reserved. |
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<li><a href="#overview">Overview</a> |
<li><a href="#overview">Overview</a> |
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<li><a href="#free">Is GXemul Free software?</a> |
<li><a href="#free">Is GXemul Free software?</a> |
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<li><a href="#build">How to compile/build the emulator</a> |
<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> |
<li><a href="#cpus">Which CPU types does GXemul emulate?</a> |
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<li><a href="#accuracy">Emulation accuracy</a> |
<li><a href="#accuracy">Emulation accuracy</a> |
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<li><a href="#emulmodes">Which machines does GXemul emulate?</a> |
<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> |
<li><a href="#guestos">Which guest OSes are possible to run in GXemul?</a> |
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</ul> |
</ul> |
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<a name="overview"></a> |
<a name="overview"></a> |
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<h3>Overview:</h3> |
<h3>Overview:</h3> |
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GXemul is a machine emulator, which can be used to experiment with |
GXemul is an experimental instruction-level machine emulator. It can be |
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binary code for (among others) MIPS-based machines. Several emulation |
used to run binary code for MIPS-based machines, regardless of host |
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modes are available. For some emulation modes, processors and surrounding |
platform. Several emulation modes are available. For some modes, |
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hardware components are emulated well enough to let unmodified operating |
processors and surrounding hardware components are emulated well enough to |
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systems run as if they were running on a real machine. |
let unmodified operating systems run as if they were running on a real |
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machine. |
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<p> |
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It is important to keep in mind that devices and CPUs are not simulated |
<p>(Non-MIPS emulation modes are also under development, but so far none |
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with 100% accuracy. They are only "faked" well enough to make operating |
of those modes has reached the completeness required to run unmodified |
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systems (eg NetBSD) run. Still, the emulator could be of interest for |
operating systems.) |
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academic research and experiments, such as when learning how to write |
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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 make operating systems (e.g. 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. |
operating system code. |
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<p> |
<p>The emulator is written in C, does not depend on external libraries |
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The emulator is written in C, does not depend on external libraries (except |
(except X11, but that is optional), and should compile and run on most |
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X11, but that is optional), and should compile and run on most Unix-like |
Unix-like systems. If it doesn't, then that is a bug. |
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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. |
<p>The emulator contains code which tries to emulate the workings of CPUs |
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If you need to compile MIPS binaries from sources, then of course you need |
and surrounding hardware found in real machines, but it does not contain |
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such a toolchain, but that is completely separate from GXemul. There |
any ROM code. You will need some form of program (in binary form) to run |
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is a <a href="technical.html#regtest">regression testing</a> framework, |
in the emulator. For many emulation modes, PROM calls are handled by the |
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which requires that a GNU CC for mips64-unknown-elf or similar is available. |
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For simply building and using the emulator, it is not required.) |
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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. |
emulator itself, so you do not need to use any ROM image at all. |
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<p> |
<p>You can use pre-compiled kernels (for example NetBSD kernels, or |
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You can use pre-compiled kernels (for example NetBSD kernels, or Linux), |
Linux), or other programs that are in binary format, and in some cases |
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or other programs that are in binary format, and in some cases even actual |
even actual ROM images. A couple of different file formats are supported |
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ROM images. A couple of different file formats are supported (ELF, a.out, |
(ELF, a.out, ECOFF, SREC, and raw binaries). |
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ECOFF, SREC, 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, or when booting |
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from ISO9660 CDROM images.) |
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<a name="free"></a> |
<a name="free"></a> |
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<h3>Is GXemul Free software?</h3> |
<h3>Is GXemul Free software?</h3> |
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Yes. I have released GXemul under a Free license. |
Yes. I have released GXemul under a Free license. The code in GXemul is |
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(For a definitions of the four freedoms associated with Free software, |
Copyrighted software, it is <i>not</i> public domain. (If this is |
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please read <a href="http://www.gnu.org/philosophy/free-sw.html"> |
confusing to you, you might want to read up on the definitions of the |
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http://www.gnu.org/philosophy/free-sw.html</a>.) |
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>(If a stable release of GXemul is packaged into binary form, and it is |
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obvious which version of GXemul was used to build the package, then it can |
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be argued that the source code is available, just not in that specific |
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package. Common sense should be used in this case, and not pedanticism.) |
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<p> |
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The code in GXemul is Copyrighted software, it is <i>not</i> public |
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domain or anything like that. |
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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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<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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$ <b>make</b> |
$ <b>make</b> |
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</pre> |
</pre> |
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<p> |
<p>This should work on most Unix-like systems. If it doesn't, then |
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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. |
mail me a bug report. |
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<p> |
<p>The emulator's performance is highly dependent on both runtime settings |
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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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<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 |
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, |
CC and CFLAGS environment variable values. For example, on a modern PC, |
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you could try the following: |
you could try the following: |
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<p> |
<p><pre> |
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<pre> |
$ <b>CFLAGS="-mcpu=pentium4 -O3" ./configure</b> |
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$ <b>CFLAGS="-mcpu=pentium4 -O3" ./configure</b> |
$ <b>make</b> |
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$ <b>make</b> |
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</pre> |
</pre> |
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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> |
<p> |
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Run <b>./configure --help</b> to get a list of configure options. (The |
To get some ideas about what is possible to run in the emulator, please |
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possible options differ between different releases and snapshots.) |
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> |
<p> |
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Once you have built GXemul, running it should be rather straight-forward. |
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To exit the emulator, type CTRL-C to enter the |
To exit the emulator, type CTRL-C to enter the |
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single-step debugger, and then type <b>quit</b>. |
single-step debugger, and then type <tt><b>quit</b></tt>. |
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<p> |
<p> |
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If you are starting an emulation by entering settings directly on the |
If you are starting an emulation by entering settings directly on the |
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command line, and you are not using the <b>-x</b> option, then all |
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. |
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 |
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. |
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> |
<p> |
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(This is an ugly hack; there is no way to send an actual CTRL-B to the |
There is no way to send an actual CTRL-B to the emulated program, when |
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emulated program, when typing in the main controlling terminal window. |
typing in the main controlling terminal window. The solution is to either |
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The solution is to either use configuration files, or use <b>-x</b>. Both |
use <a href="configfiles.html">configuration files</a>, or use |
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these solutions cause new xterms to be opened for each emulated serial |
<tt><b>-x</b></tt>. Both these solutions cause new xterms to be opened for |
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port. CTRL-B and CTRL-C both have their original meaning in those |
each emulated serial port that is written to. CTRL-B and CTRL-C both have |
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xterm windows.) |
their original meaning in those xterm windows. |
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<h4>MIPS:</h4> |
<h4>MIPS:</h4> |
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Emulation of R4000, which is a 64-bit CPU, was my initial goal. Right |
Emulation of R4000, which is a 64-bit CPU, was my initial goal. |
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now, R2000/R3000-like CPUs are also emulated (32-bit), and emulation of |
R2000/R3000-like CPUs (32-bit), R1x000, and generic MIPS32/MIPS64-style |
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R1x000 (at least the parts that are similar to R4000) is beginning to work |
CPUs are also emulated, and are hopefully almost as stable as the R4000 |
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as expected. Code targeted for MIPS32 and MIPS64 also often work. |
emulation. |
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<p> |
<p>I have written an experimental dynamic binary translation subsystem. |
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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 |
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 |
time and executing it. (If you wish to disable bintrans, add <b>-B</b> to |
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the command line, but keep in mind that it is still experimental.) |
the command line.) |
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<h4>URISC:</h4> |
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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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<h4>Other CPU types:</h4> |
<h4>Other CPU types:</h4> |
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There is some code for 64-bit (and 32-bit) POWER/PowerPC emulation too, |
Some other CPU architectures can also be partially emulated. These are not |
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but it only works for "Hello World" and similarly trivial programs. (There |
working well enough yet to run guest operating systems. |
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are some other CPU modes too, but they are working even less.) |
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<a name="accuracy"></a> |
<a name="accuracy"></a> |
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<h3>Emulation accuracy:</h3> |
<h3>Emulation accuracy:</h3> |
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GXemul is an instruction-level simulator; things that would happen in |
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 |
several steps within a real CPU are not taken into account (eg. pipe-line |
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stages or out-of-order execution). Still, instruction-level accuracy seems |
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 |
to be enough to be able to run complete guest operating systems inside the |
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emulator. |
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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<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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<p> |
<p> |
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<li><b>Cobalt</b> |
<li><b>Cobalt</b> |
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<br>Serial controller and PCI IDE. |
<br>Serial controller and PCI IDE. |
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<p> |
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<li><b>Malta (evbmips)</b> |
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<br>Serial controller and PCI IDE. |
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<p> |
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<li><b>SGI O2 ("IP32")</b> |
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<br>Serial controller and ethernet. <small>(Enough for |
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root-on-nfs, but not for disk boot.)</small> |
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</ul> |
</ul> |
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<p> |
<p>There is code in GXemul for emulation of many other machine types; the |
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There is code in GXemul for emulation of many other machine types; |
degree to which these work range from almost being able to run a complete |
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the degree to which these work range from "almost" being able to run |
OS, to almost completely unsupported (perhaps just enough support to |
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a complete OS, to almost completely unsupported (perhaps just enough |
output a few boot messages via serial console). |
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support to output a few boot messages via serial console). |
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<p>In addition to emulating real machines, there is also a "test-machine". |
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<p> |
A test-machine consists of one or more CPUs and a few experimental devices |
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In addition to emulating real machines, there is also a "test-machine". |
such as: |
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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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<p> |
<p> |
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<ul> |
<ul> |
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<li>a console I/O device (putchar() and getchar()...) |
<li>a console I/O device (putchar() and getchar()...) |
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<li>an inter-processor communication device, for SMP experiments |
<li>an inter-processor communication device, for SMP experiments |
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<li>a very simple linear framebuffer device (for graphics output) |
<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> |
</ul> |
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<p> |
<p>This mode is useful if you wish to run experimental code, but do not |
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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 |
wish to target any specific real-world machine type, for example for |
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educational purposes. |
educational purposes. |
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<p> |
<p>You can read more about these experimental devices <a |
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You can read more about these experimental devices |
href="experiments.html#expdevices">here</a>. |
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<a href="experiments.html#expdevices">here</a>. |
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<p><br> |
<p><br> |
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<a name="guestos"></a> |
<a name="guestos"></a> |
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<h3>Which guest OSes are possible to run?</h3> |
<h3>Which guest OSes are possible to run in GXemul?</h3> |
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This table lists the guest OSes that run well enough to be considered |
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 |
working in the emulator. They can boot from a harddisk image and be |
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<center><table border="0"> |
<center><table border="0"> |
344 |
<tr> |
<tr> |
345 |
<td width="10"></td> |
<td width="10"></td> |
346 |
<td align="center"><a href="netbsd-pmax-20040630.png"><img src="netbsd-pmax-20040630_small.png"></a></td> |
<td align="center"><a href="20050317-example.png"><img src="20050317-example_small.png"></a></td> |
347 |
<td width="15"></td> |
<td width="15"></td> |
348 |
<td><a href="http://www.netbsd.org/Ports/pmax/">NetBSD/pmax</a> |
<td><a href="http://www.netbsd.org/Ports/pmax/">NetBSD/pmax</a> |
349 |
<br>DECstation 5000/200</td> |
<br>DECstation 5000/200</td> |
414 |
<br>Cobalt</td> |
<br>Cobalt</td> |
415 |
</tr> |
</tr> |
416 |
|
|
417 |
|
<tr><td height="10"></td></tr> |
418 |
|
|
419 |
|
<tr> |
420 |
|
<td></td> |
421 |
|
<td align="center"><a href="20050626-netbsd-sgimips-netboot.png"><img src="20050626-netbsd-sgimips-netboot_small.png"></a></td> |
422 |
|
<td></td> |
423 |
|
<td><a href="http://www.netbsd.org/Ports/sgimips/">NetBSD/sgimips</a> |
424 |
|
<br>SGI O2 ("IP32")</td> |
425 |
|
<td></td> |
426 |
|
<td align="center"><a href="20050622-netbsd-evbmips-malta.png"><img src="20050622-netbsd-evbmips-malta_small.png"></a></td> |
427 |
|
<td></td> |
428 |
|
<td><a href="http://www.netbsd.org/Ports/evbmips/">NetBSD/evbmips</a> |
429 |
|
<br>5Kc (and 4Kc) Malta<br>evaluation boards</td> |
430 |
|
<td></td> |
431 |
|
</tr> |
432 |
|
|
433 |
</table></center> |
</table></center> |
434 |
|
|
435 |
|
|