trunk/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 1.108 2007/04/12 16:57:22 debug Exp $

Copyright (C) 2003-2007  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="#hosts">Which host architectures are supported?</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>Devices and processors are not simulated with 100% accuracy. They are 
only ``faked'' well enough to allow guest operating systems to 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, Dreamcast 
emulation, or when booting from generic ISO9660 CDROM images if the 
kernel is included in the image as a plain file.)

<p>Thanks to (in no specific order) Joachim Buss, Olivier Houchard, Juli 
Mallett, Juan Romero Pardines, Alec Voropay, Göran Weinholt, Alexander 
Yurchenko, and everyone else who has provided me with feedback.


<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</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>

The architectures that are emulated well enough to let at least one 
guest operating system run (per architecture) are ARM, MIPS, PowerPC,
and SuperH.

<p>Please read the page about <a href="guestoses.html">guest operating
systems</a> for more information about the machines and operating systems 
that can be considered "working" in the emulator.


<p><br>
<a name="hosts"></a>
<h3>Which host architectures are supported?</h3>

GXemul should compile and run on any modern host architecture (64-bit or 
32-bit word-length).

<p>Note: The <a href="translation.html">dynamic translation</a> engine 
does <i>not</i> require backends for native code generation to be written 
for each individual host architecture; the intermediate representation 
that the dyntrans system uses can be executed on any host architecture.


<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 (e.g. 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>The existance of instruction and data caches is "faked" to let
operating systems think that they are there, but for all practical
purposes, these caches are non-working.

<p>The emulator is in general <i>not</i> timing-accurate, neither at the
instruction level nor on any higher level. An attempt is made to let
emulated clocks run at the same speed as the host (i.e. an emulated timer
running at 100 Hz will interrupt around 100 times per real second), but
since the host speed may vary, e.g. because of other running processes,
there is no guarantee as to how many instructions will be executed in
each of these 100 Hz cycles.

<p>If the host is very slow, the emulated clocks might even lag behind
the real-world clock.


<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>ARM</u></b>
  <ul>
    <li><b>CATS</b> (<a href="guestoses.html#netbsdcatsinstall">NetBSD/cats</a>,
        <a href="guestoses.html#openbsdcatsinstall">OpenBSD/cats</a>)
    <li><b>IQ80321</b> (<a href="guestoses.html#netbsdevbarminstall">NetBSD/evbarm</a>)
    <li><b>NetWinder</b> (<a href="guestoses.html#netbsdnetwinderinstall">NetBSD/netwinder</a>)
  </ul>
  <p>
  <li><b><u>MIPS</u></b>
  <ul>
    <li><b>DECstation 5000/200</b> (<a href="guestoses.html#netbsdpmaxinstall">NetBSD/pmax</a>,
        <a href="guestoses.html#openbsdpmaxinstall">OpenBSD/pmax</a>,
        <a href="guestoses.html#ultrixinstall">Ultrix</a>,
        <a href="guestoses.html#declinux">Linux/DECstation</a>,
        <a href="guestoses.html#sprite">Sprite</a>)
    <li><b>Acer Pica-61</b> (<a href="guestoses.html#netbsdarcinstall">NetBSD/arc</a>)
    <li><b>NEC MobilePro 770, 780, 800, 880</b> (<a href="guestoses.html#netbsdhpcmipsinstall">NetBSD/hpcmips</a>)
    <li><b>Cobalt</b> (<a href="guestoses.html#netbsdcobaltinstall">NetBSD/cobalt</a>)
    <li><b>Malta</b> (<a href="guestoses.html#netbsdevbmipsinstall">NetBSD/evbmips</a>, Linux/Malta <font color="#0000e0">(<super>*1</super>)</font>)
    <li><b>Algorithmics P5064</b> (<a href="guestoses.html#netbsdalgorinstall">NetBSD/algor</a>)
    <li><b>SGI O2 (aka IP32)</b> <font color="#0000e0">(<super>*2</super>)</font>
        (<a href="guestoses.html#netbsdsgimips">NetBSD/sgi</a>)
  </ul>
  <p>
  <li><b><u>PowerPC</u></b>
  <ul>
    <li><b>IBM 6050/6070 (PReP, PowerPC Reference Platform)</b> (<a href="guestoses.html#netbsdprepinstall">NetBSD/prep</a>)
    <li><b>MacPPC (generic "G4" Macintosh)</b> (<a href="guestoses.html#netbsdmacppcinstall">NetBSD/macppc</a>)
  </ul>
  <p>
  <li><b><u>SuperH</u></b>
  <ul>
    <li><b>Sega Dreamcast</b> (<a href="dreamcast.html#netbsd_generic_md">NetBSD/dreamcast</a>, <a href="dreamcast.html#linux_live_cd">Linux/dreamcast</a>)
  </ul>
</ul>

<p>
<small><font color="#0000e0">(<super>*1</super>)</font> =
Linux/Malta may be run as a guest OS, however I have not yet found any stable
URL to pre-compiled Linux/Malta kernels. Thus, Linux/Malta emulation is not
tested for every release of the emulator; sometimes it works, sometimes
it doesn't.</small>

<br><small><font color="#0000e0">(<super>*2</super>)</font> =
SGI O2 emulation is 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 disk controller
  <li>a simple ethernet controller
  <li>a real-time clock device
</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 1.108 2007/04/12 16:57:22 debug Exp $
14
15	Copyright (C) 2003-2007 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="#hosts">Which host architectures are supported?</a>
56	<li><a href="#accuracy">Emulation accuracy</a>
57	<li><a href="#emulmodes">Which machines does GXemul emulate?</a>
58	</ul>
59	</td><td valign="center" align="center">
60	<a href="20050317-example.png"><img src="20050317-example_small.png"></a>
61	<p>NetBSD/pmax 1.6.2 with X11<br>running in GXemul</td></tr></table>
62
63
64
65
66	<p><br>
67	<a name="overview"></a>
68	<h3>Overview:</h3>
69
70	GXemul is an experimental instruction-level machine emulator. Several
71	emulation modes are available. In some modes, processors and surrounding
72	hardware components are emulated well enough to let unmodified operating
73	systems (e.g. NetBSD) run as if they were running on a real machine.
74
75	<p>Devices and processors are not simulated with 100% accuracy. They are
76	only ``faked'' well enough to allow guest operating systems to run without
77	complaining too much. Still, the emulator could be of interest for
78	academic research and experiments, such as when learning how to write
79	operating system code.
80
81	<p>The emulator is written in C, does not depend on third-party libraries,
82	and should compile and run on most 64-bit and 32-bit Unix-like systems.
83
84	<p>The emulator contains code which tries to emulate the workings of CPUs
85	and surrounding hardware found in real machines, but it does not contain
86	any ROM code. You will need some form of program (in binary form) to run
87	in the emulator. For many emulation modes, PROM calls are handled by the
88	emulator itself, so you do not need to use any ROM image at all.
89
90	<p>You can use pre-compiled kernels (for example NetBSD kernels, or
91	Linux), or other programs that are in binary format, and in some cases
92	even actual ROM images. A couple of different file formats are supported
93	(ELF, a.out, ECOFF, SREC, and raw binaries).
94
95	<p>If you do not have a kernel as a separate file, but you have a bootable
96	disk image, then it is sometimes possible to boot directly from that
97	image. (This works for example with DECstation emulation, Dreamcast
98	emulation, or when booting from generic ISO9660 CDROM images if the
99	kernel is included in the image as a plain file.)
100
101	<p>Thanks to (in no specific order) Joachim Buss, Olivier Houchard, Juli
102	Mallett, Juan Romero Pardines, Alec Voropay, Göran Weinholt, Alexander
103	Yurchenko, and everyone else who has provided me with feedback.
104
105
106
107
108
109
110
111	<p><br>
112	<a name="free"></a>
113	<h3>Is GXemul Free software?</h3>
114
115	Yes. I have released GXemul under a Free license. The code in GXemul is
116	Copyrighted software, it is <i>not</i> public domain. (If this is
117	confusing to you, you might want to read up on the definitions of the
118	four freedoms associated with Free software, <a
119	href="http://www.gnu.org/philosophy/free-sw.html">http://www.gnu.org/philosophy/free-sw.html</a>.)
120
121	<p>The code I have written is released under a 3-clause BSD-style license
122	(or "revised BSD-style" if one wants to use <a
123	href="http://www.gnu.org/philosophy/bsd.html">GNU jargon</a>). Apart from
124	the code I have written, some files are copied from other sources such as
125	NetBSD, for example header files containing symbolic names of bitfields in
126	device registers. They are also covered by similar licenses, but with some
127	additional clauses. The main point, however, is that the licenses require
128	that the original Copyright and license terms are included when you make a
129	copy or modification.
130
131	<p>If you plan to redistribute GXemul <i>without</i> supplying the source
132	code, then you need to comply with each individual source file some other
133	way, for example by writing additional documentation containing copyright
134	notes. I have not done this, since I do not plan on making distributions
135	without source code. You need to check all individual files for details.
136	The "easiest way out" if you plan to redistribute code from GXemul is, of
137	course, to let it remain open source and simply supply the source code.
138
139	<p>In case you want to reuse parts of GXemul, but you need to do that
140	under a different license (e.g. the GPL), then contact me and I might
141	re-license/dual-license files on a case-by-case basis.
142
143
144
145
146
147	<p><br>
148	<a name="build"></a>
149	<h3>How to compile/build the emulator:</h3>
150
151	Uncompress the .tar.gz distribution file, and run
152	<pre>
153	$ <b>./configure</b>
154	$ <b>make</b>
155	</pre>
156
157	<p>This should work on most Unix-like systems. GXemul does not require any
158	specific libraries to build, however, if you build on a system which does
159	not have X11 libraries installed, some functionality will be lost.
160
161	<p>The emulator's performance is highly dependent on both runtime settings
162	and on compiler settings, so you might want to experiment with different
163	CC and CFLAGS environment variable values. For example, on an AMD Athlon
164	host, you might want to try setting <tt>CFLAGS</tt> to <tt>-march=athlon</tt>
165	before running <tt>configure</tt>.
166
167
168
169
170
171
172
173	<p><br>
174	<a name="run"></a>
175	<h3>How to run the emulator:</h3>
176
177	Once you have built GXemul, running it should be rather straight-forward.
178	Running <tt><b>gxemul</b></tt> without arguments (or with the
179	<b><tt>-h</tt></b> or <b><tt>-H</tt></b> command line options) will
180	display a help message.
181
182	<p>
183	To get some ideas about what is possible to run in the emulator, please
184	read the section about <a href="guestoses.html">installing "guest"
185	operating systems</a>. If you are interested in using the emulator to
186	develop code on your own, then you should also read the section about
187	<a href="experiments.html#hello">Hello World</a>.
188
189	<p>
190	To exit the emulator, type CTRL-C to enter the
191	single-step debugger, and then type <tt><b>quit</b></tt>.
192
193	<p>
194	If you are starting an emulation by entering settings directly on the
195	command line, and you are not using the <tt><b>-x</b></tt> option, then all
196	terminal input and output will go to the main controlling terminal.
197	CTRL-C is used to break into the debugger, so in order to send CTRL-C to
198	the running (emulated) program, you may use CTRL-B.
199	(This should be a reasonable compromise to allow the emulator to be usable
200	even on systems without X Windows.)
201
202	<p>
203	There is no way to send an actual CTRL-B to the emulated program, when
204	typing in the main controlling terminal window. The solution is to either
205	use <a href="configfiles.html">configuration files</a>, or use
206	<tt><b>-x</b></tt>. Both these solutions cause new xterms to be opened for
207	each emulated serial port that is written to. CTRL-B and CTRL-C both have
208	their original meaning in those xterm windows.
209
210
211
212
213
214	<p><br>
215	<a name="cpus"></a>
216	<h3>Which processor architectures does GXemul emulate?</h3>
217
218	The architectures that are emulated well enough to let at least one
219	guest operating system run (per architecture) are ARM, MIPS, PowerPC,
220	and SuperH.
221
222	<p>Please read the page about <a href="guestoses.html">guest operating
223	systems</a> for more information about the machines and operating systems
224	that can be considered "working" in the emulator.
225
226
227
228
229
230
231	<p><br>
232	<a name="hosts"></a>
233	<h3>Which host architectures are supported?</h3>
234
235	GXemul should compile and run on any modern host architecture (64-bit or
236	32-bit word-length).
237
238	<p>Note: The <a href="translation.html">dynamic translation</a> engine
239	does <i>not</i> require backends for native code generation to be written
240	for each individual host architecture; the intermediate representation
241	that the dyntrans system uses can be executed on any host architecture.
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 (e.g. 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>The existance of instruction and data caches is "faked" to let
258	operating systems think that they are there, but for all practical
259	purposes, these caches are non-working.
260
261	<p>The emulator is in general <i>not</i> timing-accurate, neither at the
262	instruction level nor on any higher level. An attempt is made to let
263	emulated clocks run at the same speed as the host (i.e. an emulated timer
264	running at 100 Hz will interrupt around 100 times per real second), but
265	since the host speed may vary, e.g. because of other running processes,
266	there is no guarantee as to how many instructions will be executed in
267	each of these 100 Hz cycles.
268
269	<p>If the host is very slow, the emulated clocks might even lag behind
270	the real-world clock.
271
272
273
274
275
276
277	<p><br>
278	<a name="emulmodes"></a>
279	<h3>Which machines does GXemul emulate?</h3>
280
281	A few different machine types are emulated. The following machine types
282	are emulated well enough to run at least one "guest OS":
283
284	<p>
285	<ul>
286	<li><b><u>ARM</u></b>
287	<ul>
288	<li><b>CATS</b> (<a href="guestoses.html#netbsdcatsinstall">NetBSD/cats</a>,
289	<a href="guestoses.html#openbsdcatsinstall">OpenBSD/cats</a>)
290	<li><b>IQ80321</b> (<a href="guestoses.html#netbsdevbarminstall">NetBSD/evbarm</a>)
291	<li><b>NetWinder</b> (<a href="guestoses.html#netbsdnetwinderinstall">NetBSD/netwinder</a>)
292	</ul>
293	<p>
294	<li><b><u>MIPS</u></b>
295	<ul>
296	<li><b>DECstation 5000/200</b> (<a href="guestoses.html#netbsdpmaxinstall">NetBSD/pmax</a>,
297	<a href="guestoses.html#openbsdpmaxinstall">OpenBSD/pmax</a>,
298	<a href="guestoses.html#ultrixinstall">Ultrix</a>,
299	<a href="guestoses.html#declinux">Linux/DECstation</a>,
300	<a href="guestoses.html#sprite">Sprite</a>)
301	<li><b>Acer Pica-61</b> (<a href="guestoses.html#netbsdarcinstall">NetBSD/arc</a>)
302	<li><b>NEC MobilePro 770, 780, 800, 880</b> (<a href="guestoses.html#netbsdhpcmipsinstall">NetBSD/hpcmips</a>)
303	<li><b>Cobalt</b> (<a href="guestoses.html#netbsdcobaltinstall">NetBSD/cobalt</a>)
304	<li><b>Malta</b> (<a href="guestoses.html#netbsdevbmipsinstall">NetBSD/evbmips</a>, Linux/Malta <font color="#0000e0">(<super>*1</super>)</font>)
305	<li><b>Algorithmics P5064</b> (<a href="guestoses.html#netbsdalgorinstall">NetBSD/algor</a>)
306	<li><b>SGI O2 (aka IP32)</b> <font color="#0000e0">(<super>*2</super>)</font>
307	(<a href="guestoses.html#netbsdsgimips">NetBSD/sgi</a>)
308	</ul>
309	<p>
310	<li><b><u>PowerPC</u></b>
311	<ul>
312	<li><b>IBM 6050/6070 (PReP, PowerPC Reference Platform)</b> (<a href="guestoses.html#netbsdprepinstall">NetBSD/prep</a>)
313	<li><b>MacPPC (generic "G4" Macintosh)</b> (<a href="guestoses.html#netbsdmacppcinstall">NetBSD/macppc</a>)
314	</ul>
315	<p>
316	<li><b><u>SuperH</u></b>
317	<ul>
318	<li><b>Sega Dreamcast</b> (<a href="dreamcast.html#netbsd_generic_md">NetBSD/dreamcast</a>, <a href="dreamcast.html#linux_live_cd">Linux/dreamcast</a>)
319	</ul>
320	</ul>
321
322	<p>
323	<small><font color="#0000e0">(<super>*1</super>)</font> =
324	Linux/Malta may be run as a guest OS, however I have not yet found any stable
325	URL to pre-compiled Linux/Malta kernels. Thus, Linux/Malta emulation is not
326	tested for every release of the emulator; sometimes it works, sometimes
327	it doesn't.</small>
328
329	<br><small><font color="#0000e0">(<super>*2</super>)</font> =
330	SGI O2 emulation is enough for root-on-nfs, but not for disk boot.</small>
331
332
333	<p>There is code in GXemul for emulation of many other machine types; the
334	degree to which these work range from almost being able to run a complete
335	OS, to almost completely unsupported (perhaps just enough support to
336	output a few boot messages via serial console).
337
338	<p>In addition to emulating real machines, there is also a "test-machine".
339	A test-machine consists of one or more CPUs and a few experimental devices
340	such as:
341
342	<p>
343	<ul>
344	<li>a console I/O device (putchar() and getchar()...)
345	<li>an inter-processor communication device, for SMP experiments
346	<li>a very simple linear framebuffer device (for graphics output)
347	<li>a simple disk controller
348	<li>a simple ethernet controller
349	<li>a real-time clock device
350	</ul>
351
352	<p>This mode is useful if you wish to run experimental code, but do not
353	wish to target any specific real-world machine type, for example for
354	educational purposes.
355
356	<p>You can read more about these experimental devices <a
357	href="experiments.html#expdevices">here</a>.
358
359
360
361
362
363
364	</body>
365	</html>