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> |