0.3.8/doc/intro.html

<html><head><title>Gavare's eXperimental Emulator:&nbsp;&nbsp;&nbsp;Introduction</title>
<meta name="robots" content="noarchive,nofollow,noindex"></head>
<body bgcolor="#f8f8f8" text="#000000" link="#4040f0" vlink="#404040" alink="#ff0000">
<table border=0 width=100% bgcolor="#d0d0d0"><tr>
<td width=100% align=center valign=center><table border=0 width=100%><tr>
<td align="left" valign=center bgcolor="#d0efff"><font color="#6060e0" size="6">
<b>Gavare's eXperimental Emulator:</b></font><br>
<font color="#000000" size="6"><b>Introduction</b>
</font></td></tr></table></td></tr></table><p>

<!--

$Id: intro.html,v 1.73 2006/02/18 14:02:19 debug Exp $

Copyright (C) 2003-2006  Anders Gavare.  All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright
   notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
   notice, this list of conditions and the following disclaimer in the
   documentation and/or other materials provided with the distribution.
3. The name of the author may not be used to endorse or promote products
   derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
SUCH DAMAGE.

-->

<a href="./">Back to the index</a>

<p><br>
<h2>Introduction</h2>

<p>
<table border="0" width="99%"><tr><td valign="top" align="left">
<ul>
  <li><a href="#overview">Overview</a>
  <li><a href="#free">Is GXemul Free software?</a>
  <li><a href="#build">How to compile/build the emulator</a>
  <li><a href="#run">How to run the emulator</a>
  <li><a href="#cpus">Which processor architectures does GXemul emulate?</a>
  <li><a href="#accuracy">Emulation accuracy</a>
  <li><a href="#emulmodes">Which machines does GXemul emulate?</a>
</ul>
</td><td valign="center" align="center">
<a href="20050317-example.png"><img src="20050317-example_small.png"></a>
<p>NetBSD/pmax 1.6.2 with X11<br>running in GXemul</td></tr></table>


<p><br>
<a name="overview"></a>
<h3>Overview:</h3>

GXemul is an experimental instruction-level machine emulator. Several
emulation modes are available. In some modes, processors and surrounding
hardware components are emulated well enough to let unmodified operating
systems (e.g. NetBSD) run as if they were running on a real machine.

<p>The processor architecture best emulated by GXemul is MIPS, but other
architectures such as ARM and PowerPC are also partially emulated.

<p>Devices and CPUs are not simulated with 100% accuracy. They are only
``faked'' well enough to allow guest operating systems run without
complaining too much. Still, the emulator could be of interest for
academic research and experiments, such as when learning how to write
operating system code.

<p>The emulator is written in C, does not depend on third-party libraries,
and should compile and run on most 64-bit and 32-bit Unix-like systems.

<p>The emulator contains code which tries to emulate the workings of CPUs
and surrounding hardware found in real machines, but it does not contain
any ROM code. You will need some form of program (in binary form) to run
in the emulator. For many emulation modes, PROM calls are handled by the
emulator itself, so you do not need to use any ROM image at all.

<p>You can use pre-compiled kernels (for example NetBSD kernels, or
Linux), or other programs that are in binary format, and in some cases
even actual ROM images. A couple of different file formats are supported
(ELF, a.out, ECOFF, SREC, and raw binaries).

<p>If you do not have a kernel as a separate file, but you have a bootable
disk image, then it is sometimes possible to boot directly from that
image. (This works for example with DECstation emulation, or when booting
from ISO9660 CDROM images.)


<p><br>
<a name="free"></a>
<h3>Is GXemul Free software?</h3>

Yes. I have released GXemul under a Free license. The code in GXemul is
Copyrighted software, it is <i>not</i> public domain. (If this is
confusing to you, you might want to read up on the definitions of the
four freedoms associated with Free software, <a
href="http://www.gnu.org/philosophy/free-sw.html">http://www.gnu.org/philosophy/free-sw.html</a>.)

<p>The code I have written is released under a 3-clause BSD-style license
(or "revised BSD-style" if one wants to use <a
href="http://www.gnu.org/philosophy/bsd.html">GNU jargon</a>). Apart from
the code I have written, some files are copied from other sources such as
NetBSD, for example header files containing symbolic names of bitfields in
device registers. They are also covered by similar licenses, but with some
additional clauses. The main point, however, is that the licenses require
that the original Copyright and license terms are included when you make a
copy or modification.

<p>If you plan to redistribute GXemul <i>without</i> supplying the source
code, then you need to comply with each individual source file some other
way, for example by writing additional documentation containing copyright
notes. I have not done this, since I do not plan on making distributions
without source code. You need to check all individual files for details.
The "easiest way out" if you plan to redistribute code from GXemul is, of
course, to let it remain open source and simply supply the source code.

<p>In case you want to reuse parts of GXemul, but you need to do that 
under a different license (e.g. the GPL), then contact me and I might 
re-license/dual-license files on a case-by-case basis.


<p><br>
<a name="build"></a>
<h3>How to compile/build the emulator:</h3>

Uncompress the .tar.gz distribution file, and run
<pre>
        $ <b>./configure</b>
        $ <b>make</b>
</pre>

<p>This should work on most Unix-like systems. GXemul does not require any 
specific libraries to build, however, if you build on a system which does 
not have X11 libraries installed, some functionality will be lost.

<p>The emulator's performance is highly dependent on both runtime settings
and on compiler settings, so you might want to experiment with different
CC and CFLAGS environment variable values. For example, on an AMD Athlon
host, you might want to try setting <tt>CFLAGS</tt> to <tt>-march=athlon 
-O3</tt> before running <tt>configure</tt>.


<p><br>
<a name="run"></a>
<h3>How to run the emulator:</h3>

Once you have built GXemul, running it should be rather straight-forward.
Running <tt><b>gxemul</b></tt> without arguments (or with the
<b><tt>-h</tt></b> or <b><tt>-H</tt></b> command line options) will
display a help message.

<p>
To get some ideas about what is possible to run in the emulator, please 
read the section about <a href="guestoses.html">installing "guest" 
operating systems</a>. If you are interested in using the emulator to 
develop code on your own, then you should also read the section about
<a href="experiments.html#hello">Hello World</a>.

<p>
To exit the emulator, type CTRL-C to enter the 
single-step debugger, and then type <tt><b>quit</b></tt>.

<p>
If you are starting an emulation by entering settings directly on the 
command line, and you are not using the <tt><b>-x</b></tt> option, then all 
terminal input and output will go to the main controlling terminal.
CTRL-C is used to break into the debugger, so in order to send CTRL-C to 
the running (emulated) program, you may use CTRL-B.
(This should be a reasonable compromise to allow the emulator to be usable
even on systems without X Windows.)

<p>
There is no way to send an actual CTRL-B to the emulated program, when
typing in the main controlling terminal window. The solution is to either
use <a href="configfiles.html">configuration files</a>, or use
<tt><b>-x</b></tt>. Both these solutions cause new xterms to be opened for 
each emulated serial port that is written to. CTRL-B and CTRL-C both have 
their original meaning in those xterm windows.


<p><br>
<a name="cpus"></a>
<h3>Which processor architectures does GXemul emulate?</h3>

<h4>MIPS:</h4>

Emulation of R4000, which is a 64-bit CPU, was my initial goal.
R2000/R3000-like CPUs (32-bit), R1x000, and generic MIPS32/MIPS64-style
CPUs are also emulated, and are hopefully almost as stable as the R4000 
emulation. Several guest operating systems for MIPS can run inside
the emulator.

<p>(For MIPS emulation, I have written an experimental dynamic binary
translation subsystem, for Alpha and i386 hosts. This gives higher total
performance than interpreting one instruction at a time and executing it.
If you wish to disable bintrans, add <b>-B</b> to the command line.)

<h4>ARM:</h4>

ARM emulation is good enough to run NetBSD/cats, OpenBSD/cats, and 
NetBSD/evbarm, but it is not as tested or fine-tuned as the MIPS emulation 
mode.

<h4>PowerPC:</h4>

PowerPC emulation is still in its beginning stages, but good enough
to run NetBSD/prep 2.1.

<p>Non-MIPS emulation modes use dynamic translation, but not recompilation 
into native code. This makes it possible to run on any host platform.


<p><br>
<a name="accuracy"></a>
<h3>Emulation accuracy:</h3>

GXemul is an instruction-level emulator; things that would happen in
several steps within a real CPU are not taken into account (eg. pipe-line
stalls or out-of-order execution). Still, instruction-level accuracy seems
to be enough to be able to run complete guest operating systems inside the
emulator.

<p>Caches are by default not emulated. In some cases, the existance of
caches is "faked" to let operating systems think that they are there.
(There is some old code for R2000/R3000 caches, but it has probably
suffered from bitrot by now.)

<p>The emulator is <i>not</i> timing-accurate. It can be run in a
"deterministic" mode, <tt><b>-D</b></tt>. The meaning of deterministic is
simply that running two emulations with the same settings will result in
identical runs. Obviously, this requires that no user interaction is
taking place, and that clock speeds are fixed with the <tt><b>-I</b></tt>
option. (Deterministic in this case does <i>not</i> mean that the
emulation will be identical to some actual real-world machine.)

<p><font color="#ff0000">(Oops/TODO: User interaction means <i>both</i>
input to the emulated program/OS, and interacting with the emulator
itself. Breaking into the debugger and then continuing execution may
affect when/how interrupts occur.)</font>


<p><br>
<a name="emulmodes"></a>
<h3>Which machines does GXemul emulate?</h3>

A few different machine types are emulated. The following machine types 
are emulated well enough to run at least one "guest OS":

<p>
<ul>
  <li><b><u>MIPS</u></b>
  <ul>
    <li><b>DECstation 5000/200</b>&nbsp;&nbsp;("3max")
    <li><b>Acer Pica-61</b>&nbsp;&nbsp;(an ARC machine)
    <li><b>NEC MobilePro 770, 780, 800, and 880</b>&nbsp;&nbsp;(HPCmips machines)
    <li><b>Cobalt</b>
    <li><b>Malta</b> (evbmips)
    <li><b>SGI O2 ("IP32")</b> <font color="#0000e0">(<super>*</super>)</font>
  </ul>
  <p>
  <li><b><u>ARM</u></b>
  <ul>
    <li><b>CATS</b>
    <li><b>IQ80321</b> (evbarm)
  </ul>
  <p>
  <li><b><u>PowerPC</u></b>
  <ul>
    <li><b>PReP (PowerPC Reference Platform)</b>
  </ul>
</ul>

<p><small><font color="#0000e0">(<super>*</super>)</font> =
Enough for root-on-nfs, but not for disk boot.)</small>

<p>There is code in GXemul for emulation of many other machine types; the
degree to which these work range from almost being able to run a complete
OS, to almost completely unsupported (perhaps just enough support to
output a few boot messages via serial console).

<p>In addition to emulating real machines, there is also a "test-machine".
A test-machine consists of one or more CPUs and a few experimental devices
such as:

<p>
<ul>
  <li>a console I/O device (putchar() and getchar()...)
  <li>an inter-processor communication device, for SMP experiments
  <li>a very simple linear framebuffer device (for graphics output)
  <li>a simple SCSI disk controller
  <li>a simple ethernet controller
</ul>

<p>This mode is useful if you wish to run experimental code, but do not
wish to target any specific real-world machine type, for example for
educational purposes.

<p>You can read more about these experimental devices <a
href="experiments.html#expdevices">here</a>.


</body>
</html>
1	<html><head><title>Gavare's eXperimental Emulator:   Introduction</title>
2	<meta name="robots" content="noarchive,nofollow,noindex"></head>
3	<body bgcolor="#f8f8f8" text="#000000" link="#4040f0" vlink="#404040" alink="#ff0000">
4	<table border=0 width=100% bgcolor="#d0d0d0"><tr>
5	<td width=100% align=center valign=center><table border=0 width=100%><tr>
6	<td align="left" valign=center bgcolor="#d0efff"><font color="#6060e0" size="6">
7	<b>Gavare's eXperimental Emulator:</b></font><br>
8	<font color="#000000" size="6"><b>Introduction</b>
9	</font></td></tr></table></td></tr></table><p>
10
11	<!--
12
13	$Id: intro.html,v 1.73 2006/02/18 14:02:19 debug Exp $
14
15	Copyright (C) 2003-2006 Anders Gavare. All rights reserved.
16
17	Redistribution and use in source and binary forms, with or without
18	modification, are permitted provided that the following conditions are met:
19
20	1. Redistributions of source code must retain the above copyright
21	notice, this list of conditions and the following disclaimer.
22	2. Redistributions in binary form must reproduce the above copyright
23	notice, this list of conditions and the following disclaimer in the
24	documentation and/or other materials provided with the distribution.
25	3. The name of the author may not be used to endorse or promote products
26	derived from this software without specific prior written permission.
27
28	THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
29	ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
30	IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
31	ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
32	FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
33	DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
34	OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
35	HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
36	LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
37	OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
38	SUCH DAMAGE.
39
40	-->
41
42	<a href="./">Back to the index</a>
43
44	<p><br>
45	<h2>Introduction</h2>
46
47	<p>
48	<table border="0" width="99%"><tr><td valign="top" align="left">
49	<ul>
50	<li><a href="#overview">Overview</a>
51	<li><a href="#free">Is GXemul Free software?</a>
52	<li><a href="#build">How to compile/build the emulator</a>
53	<li><a href="#run">How to run the emulator</a>
54	<li><a href="#cpus">Which processor architectures does GXemul emulate?</a>
55	<li><a href="#accuracy">Emulation accuracy</a>
56	<li><a href="#emulmodes">Which machines does GXemul emulate?</a>
57	</ul>
58	</td><td valign="center" align="center">
59	<a href="20050317-example.png"><img src="20050317-example_small.png"></a>
60	<p>NetBSD/pmax 1.6.2 with X11<br>running in GXemul</td></tr></table>
61
62
63
64
65	<p><br>
66	<a name="overview"></a>
67	<h3>Overview:</h3>
68
69	GXemul is an experimental instruction-level machine emulator. Several
70	emulation modes are available. In some modes, processors and surrounding
71	hardware components are emulated well enough to let unmodified operating
72	systems (e.g. NetBSD) run as if they were running on a real machine.
73
74	<p>The processor architecture best emulated by GXemul is MIPS, but other
75	architectures such as ARM and PowerPC are also partially emulated.
76
77	<p>Devices and CPUs are not simulated with 100% accuracy. They are only
78	``faked'' well enough to allow guest operating systems run without
79	complaining too much. Still, the emulator could be of interest for
80	academic research and experiments, such as when learning how to write
81	operating system code.
82
83	<p>The emulator is written in C, does not depend on third-party libraries,
84	and should compile and run on most 64-bit and 32-bit Unix-like systems.
85
86	<p>The emulator contains code which tries to emulate the workings of CPUs
87	and surrounding hardware found in real machines, but it does not contain
88	any ROM code. You will need some form of program (in binary form) to run
89	in the emulator. For many emulation modes, PROM calls are handled by the
90	emulator itself, so you do not need to use any ROM image at all.
91
92	<p>You can use pre-compiled kernels (for example NetBSD kernels, or
93	Linux), or other programs that are in binary format, and in some cases
94	even actual ROM images. A couple of different file formats are supported
95	(ELF, a.out, ECOFF, SREC, and raw binaries).
96
97	<p>If you do not have a kernel as a separate file, but you have a bootable
98	disk image, then it is sometimes possible to boot directly from that
99	image. (This works for example with DECstation emulation, or when booting
100	from ISO9660 CDROM images.)
101
102
103
104
105
106
107
108
109	<p><br>
110	<a name="free"></a>
111	<h3>Is GXemul Free software?</h3>
112
113	Yes. I have released GXemul under a Free license. The code in GXemul is
114	Copyrighted software, it is <i>not</i> public domain. (If this is
115	confusing to you, you might want to read up on the definitions of the
116	four freedoms associated with Free software, <a
117	href="http://www.gnu.org/philosophy/free-sw.html">http://www.gnu.org/philosophy/free-sw.html</a>.)
118
119	<p>The code I have written is released under a 3-clause BSD-style license
120	(or "revised BSD-style" if one wants to use <a
121	href="http://www.gnu.org/philosophy/bsd.html">GNU jargon</a>). Apart from
122	the code I have written, some files are copied from other sources such as
123	NetBSD, for example header files containing symbolic names of bitfields in
124	device registers. They are also covered by similar licenses, but with some
125	additional clauses. The main point, however, is that the licenses require
126	that the original Copyright and license terms are included when you make a
127	copy or modification.
128
129	<p>If you plan to redistribute GXemul <i>without</i> supplying the source
130	code, then you need to comply with each individual source file some other
131	way, for example by writing additional documentation containing copyright
132	notes. I have not done this, since I do not plan on making distributions
133	without source code. You need to check all individual files for details.
134	The "easiest way out" if you plan to redistribute code from GXemul is, of
135	course, to let it remain open source and simply supply the source code.
136
137	<p>In case you want to reuse parts of GXemul, but you need to do that
138	under a different license (e.g. the GPL), then contact me and I might
139	re-license/dual-license files on a case-by-case basis.
140
141
142
143
144
145	<p><br>
146	<a name="build"></a>
147	<h3>How to compile/build the emulator:</h3>
148
149	Uncompress the .tar.gz distribution file, and run
150	<pre>
151	$ <b>./configure</b>
152	$ <b>make</b>
153	</pre>
154
155	<p>This should work on most Unix-like systems. GXemul does not require any
156	specific libraries to build, however, if you build on a system which does
157	not have X11 libraries installed, some functionality will be lost.
158
159	<p>The emulator's performance is highly dependent on both runtime settings
160	and on compiler settings, so you might want to experiment with different
161	CC and CFLAGS environment variable values. For example, on an AMD Athlon
162	host, you might want to try setting <tt>CFLAGS</tt> to <tt>-march=athlon
163	-O3</tt> before running <tt>configure</tt>.
164
165
166
167
168
169
170
171	<p><br>
172	<a name="run"></a>
173	<h3>How to run the emulator:</h3>
174
175	Once you have built GXemul, running it should be rather straight-forward.
176	Running <tt><b>gxemul</b></tt> without arguments (or with the
177	<b><tt>-h</tt></b> or <b><tt>-H</tt></b> command line options) will
178	display a help message.
179
180	<p>
181	To get some ideas about what is possible to run in the emulator, please
182	read the section about <a href="guestoses.html">installing "guest"
183	operating systems</a>. If you are interested in using the emulator to
184	develop code on your own, then you should also read the section about
185	<a href="experiments.html#hello">Hello World</a>.
186
187	<p>
188	To exit the emulator, type CTRL-C to enter the
189	single-step debugger, and then type <tt><b>quit</b></tt>.
190
191	<p>
192	If you are starting an emulation by entering settings directly on the
193	command line, and you are not using the <tt><b>-x</b></tt> option, then all
194	terminal input and output will go to the main controlling terminal.
195	CTRL-C is used to break into the debugger, so in order to send CTRL-C to
196	the running (emulated) program, you may use CTRL-B.
197	(This should be a reasonable compromise to allow the emulator to be usable
198	even on systems without X Windows.)
199
200	<p>
201	There is no way to send an actual CTRL-B to the emulated program, when
202	typing in the main controlling terminal window. The solution is to either
203	use <a href="configfiles.html">configuration files</a>, or use
204	<tt><b>-x</b></tt>. Both these solutions cause new xterms to be opened for
205	each emulated serial port that is written to. CTRL-B and CTRL-C both have
206	their original meaning in those xterm windows.
207
208
209
210
211
212	<p><br>
213	<a name="cpus"></a>
214	<h3>Which processor architectures does GXemul emulate?</h3>
215
216	<h4>MIPS:</h4>
217
218	Emulation of R4000, which is a 64-bit CPU, was my initial goal.
219	R2000/R3000-like CPUs (32-bit), R1x000, and generic MIPS32/MIPS64-style
220	CPUs are also emulated, and are hopefully almost as stable as the R4000
221	emulation. Several guest operating systems for MIPS can run inside
222	the emulator.
223
224	<p>(For MIPS emulation, I have written an experimental dynamic binary
225	translation subsystem, for Alpha and i386 hosts. This gives higher total
226	performance than interpreting one instruction at a time and executing it.
227	If you wish to disable bintrans, add <b>-B</b> to the command line.)
228
229	<h4>ARM:</h4>
230
231	ARM emulation is good enough to run NetBSD/cats, OpenBSD/cats, and
232	NetBSD/evbarm, but it is not as tested or fine-tuned as the MIPS emulation
233	mode.
234
235	<h4>PowerPC:</h4>
236
237	PowerPC emulation is still in its beginning stages, but good enough
238	to run NetBSD/prep 2.1.
239
240	<p>Non-MIPS emulation modes use dynamic translation, but not recompilation
241	into native code. This makes it possible to run on any host platform.
242
243
244
245
246
247	<p><br>
248	<a name="accuracy"></a>
249	<h3>Emulation accuracy:</h3>
250
251	GXemul is an instruction-level emulator; things that would happen in
252	several steps within a real CPU are not taken into account (eg. pipe-line
253	stalls or out-of-order execution). Still, instruction-level accuracy seems
254	to be enough to be able to run complete guest operating systems inside the
255	emulator.
256
257	<p>Caches are by default not emulated. In some cases, the existance of
258	caches is "faked" to let operating systems think that they are there.
259	(There is some old code for R2000/R3000 caches, but it has probably
260	suffered from bitrot by now.)
261
262	<p>The emulator is <i>not</i> timing-accurate. It can be run in a
263	"deterministic" mode, <tt><b>-D</b></tt>. The meaning of deterministic is
264	simply that running two emulations with the same settings will result in
265	identical runs. Obviously, this requires that no user interaction is
266	taking place, and that clock speeds are fixed with the <tt><b>-I</b></tt>
267	option. (Deterministic in this case does <i>not</i> mean that the
268	emulation will be identical to some actual real-world machine.)
269
270	<p><font color="#ff0000">(Oops/TODO: User interaction means <i>both</i>
271	input to the emulated program/OS, and interacting with the emulator
272	itself. Breaking into the debugger and then continuing execution may
273	affect when/how interrupts occur.)</font>
274
275
276
277
278
279
280	<p><br>
281	<a name="emulmodes"></a>
282	<h3>Which machines does GXemul emulate?</h3>
283
284	A few different machine types are emulated. The following machine types
285	are emulated well enough to run at least one "guest OS":
286
287	<p>
288	<ul>
289	<li><b><u>MIPS</u></b>
290	<ul>
291	<li><b>DECstation 5000/200</b>  ("3max")
292	<li><b>Acer Pica-61</b>  (an ARC machine)
293	<li><b>NEC MobilePro 770, 780, 800, and 880</b>  (HPCmips machines)
294	<li><b>Cobalt</b>
295	<li><b>Malta</b> (evbmips)
296	<li><b>SGI O2 ("IP32")</b> <font color="#0000e0">(<super>*</super>)</font>
297	</ul>
298	<p>
299	<li><b><u>ARM</u></b>
300	<ul>
301	<li><b>CATS</b>
302	<li><b>IQ80321</b> (evbarm)
303	</ul>
304	<p>
305	<li><b><u>PowerPC</u></b>
306	<ul>
307	<li><b>PReP (PowerPC Reference Platform)</b>
308	</ul>
309	</ul>
310
311	<p><small><font color="#0000e0">(<super>*</super>)</font> =
312	Enough for root-on-nfs, but not for disk boot.)</small>
313
314	<p>There is code in GXemul for emulation of many other machine types; the
315	degree to which these work range from almost being able to run a complete
316	OS, to almost completely unsupported (perhaps just enough support to
317	output a few boot messages via serial console).
318
319	<p>In addition to emulating real machines, there is also a "test-machine".
320	A test-machine consists of one or more CPUs and a few experimental devices
321	such as:
322
323	<p>
324	<ul>
325	<li>a console I/O device (putchar() and getchar()...)
326	<li>an inter-processor communication device, for SMP experiments
327	<li>a very simple linear framebuffer device (for graphics output)
328	<li>a simple SCSI disk controller
329	<li>a simple ethernet controller
330	</ul>
331
332	<p>This mode is useful if you wish to run experimental code, but do not
333	wish to target any specific real-world machine type, for example for
334	educational purposes.
335
336	<p>You can read more about these experimental devices <a
337	href="experiments.html#expdevices">here</a>.
338
339
340
341
342
343
344	</body>
345	</html>