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20060626	Continuing on SPARC emulation (beginning on the 'save'
		instruction, register windows, etc).
20060629	Planning statistics gathering (new -s command line option),
		and renaming speed_tricks to allow_instruction_combinations.
20060630	Some minor manual page updates.
		Various cleanups.
		Implementing the -s command line option.
20060701	FINALLY found the bug which prevented Linux and Ultrix from
		running without the ugly hack in the R2000/R3000 cache isol
		code; it was the phystranslation hint array which was buggy.
		Removing the phystranslation hint code completely, for now.
20060702	Minor dyntrans cleanups; invalidation of physpages now only
		invalidate those parts of a page that have actually been
		translated. (32 parts per page.)
		Some MIPS non-R3000 speed fixes.
		Experimenting with MIPS instruction combination for some
		addiu+bne+sw loops, and sw+sw+sw.
		Adding support (again) for larger-than-4KB pages in MIPS tlbw*.
		Continuing on SPARC emulation: adding load/store instructions.
20060704	Fixing a virtual vs physical page shift bug in the new tlbw*
		implementation. Problem noticed by Jakub Jermar. (Many thanks.)
		Moving rfe and eret to cpu_mips_instr.c, since that is the
		only place that uses them nowadays.
20060705	Removing the BSD license from the "testmachine" include files,
		placing them in the public domain instead; this enables the
		testmachine stuff to be used from projects which are
		incompatible with the BSD license for some reason.
20060707	Adding instruction combinations for the R2000/R3000 L1
		I-cache invalidation code used by NetBSD/pmax 3.0, lui+addiu,
		various branches followed by addiu or nop, and jr ra followed
		by addiu. The time it takes to perform a full NetBSD/pmax R3000
		install on the laptop has dropped from 573 seconds to 539. :-)
20060708	Adding a framebuffer controller device (dev_fbctrl), which so
		far can be used to change the fb resolution during runtime, but
		in the future will also be useful for accelerated block fill/
		copy, and possibly also simplified character output.
		Adding an instruction combination for NetBSD/pmax' strlen.
20060709	Minor fixes: reading raw files in src/file.c wasn't memblock
		aligned, removing buggy multi_sw MIPS instruction combination,
		etc.
20060711	Adding a machine_qemu.c, which contains a "qemu_mips" machine.
		(It mimics QEMU's MIPS machine mode, so that a test kernel
		made for QEMU_MIPS also can run in GXemul... at least to some
		extent.)  Adding a short section about how to run this mode to
		doc/guestoses.html.
20060714	Misc. minor code cleanups.
20060715	Applying a patch which adds getchar() to promemul/yamon.c
		(from Oleksandr Tymoshenko).
		Adding yamon.h from NetBSD, and rewriting yamon.c to use it
		(instead of ugly hardcoded numbers) + some cleanup.
20060716	Found and fixed the bug which broke single-stepping of 64-bit
		programs between 0.4.0 and 0.4.0.1 (caused by too quick
		refactoring and no testing). Hopefully this fix will not
		break too many other things.
20060718	Continuing on the 8253 PIT; it now works with Linux/QEMU_MIPS.
		Re-adding the sw+sw+sw instr comb (the problem was that I had
		ignored endian issues); however, it doesn't seem to give any
		big performance gain.
20060720	Adding a dummy Transputer mode (T414, T800 etc) skeleton (only
		the 'j' and 'ldc' instructions are implemented so far). :-}
20060721	Adding gtreg.h from NetBSD, updating dev_gt.c to use it, plus
		misc. other updates to get Linux 2.6 for evbmips/malta working
		(thanks to Alec Voropay for the details).
		FINALLY found and fixed the bug which made tlbw* for non-R3000
		buggy; it was a reference count problem in the dyntrans core.
20060722	Testing stuff; things seem stable enough for a new release.

==============  RELEASE 0.4.1  ==============


1 dpavlin 12 <html><head><title>Gavare's eXperimental Emulator:&nbsp;&nbsp;&nbsp;Introduction</title>
2     <meta name="robots" content="noarchive,nofollow,noindex"></head>
3 dpavlin 4 <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 dpavlin 22 <b>Gavare's eXperimental Emulator:</b></font><br>
8 dpavlin 4 <font color="#000000" size="6"><b>Introduction</b>
9     </font></td></tr></table></td></tr></table><p>
10 dpavlin 2
11     <!--
12    
13 dpavlin 28 $Id: intro.html,v 1.88 2006/06/27 05:25:46 debug Exp $
14 dpavlin 2
15 dpavlin 22 Copyright (C) 2003-2006 Anders Gavare. All rights reserved.
16 dpavlin 2
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18     modification, are permitted provided that the following conditions are met:
19    
20     1. Redistributions of source code must retain the above copyright
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41    
42     <a href="./">Back to the index</a>
43    
44     <p><br>
45     <h2>Introduction</h2>
46    
47     <p>
48 dpavlin 22 <table border="0" width="99%"><tr><td valign="top" align="left">
49 dpavlin 2 <ul>
50     <li><a href="#overview">Overview</a>
51 dpavlin 4 <li><a href="#free">Is GXemul Free software?</a>
52 dpavlin 2 <li><a href="#build">How to compile/build the emulator</a>
53 dpavlin 6 <li><a href="#run">How to run the emulator</a>
54 dpavlin 22 <li><a href="#cpus">Which processor architectures does GXemul emulate?</a>
55 dpavlin 24 <li><a href="#hosts">Which host architectures are supported?</a>
56     <li><a href="#translation">What kind of translation does GXemul use?</a>
57 dpavlin 2 <li><a href="#accuracy">Emulation accuracy</a>
58     <li><a href="#emulmodes">Which machines does GXemul emulate?</a>
59     </ul>
60 dpavlin 22 </td><td valign="center" align="center">
61     <a href="20050317-example.png"><img src="20050317-example_small.png"></a>
62     <p>NetBSD/pmax 1.6.2 with X11<br>running in GXemul</td></tr></table>
63 dpavlin 2
64    
65    
66    
67     <p><br>
68     <a name="overview"></a>
69     <h3>Overview:</h3>
70    
71 dpavlin 14 GXemul is an experimental instruction-level machine emulator. Several
72     emulation modes are available. In some modes, processors and surrounding
73     hardware components are emulated well enough to let unmodified operating
74     systems (e.g. NetBSD) run as if they were running on a real machine.
75 dpavlin 2
76 dpavlin 24 <p>Devices and processors (ARM, MIPS, PowerPC) are not simulated with 100%
77     accuracy. They are only ``faked'' well enough to allow guest operating
78     systems run without complaining too much. Still, the emulator could be of
79     interest for academic research and experiments, such as when learning how
80     to write operating system code.
81 dpavlin 12
82 dpavlin 22 <p>The emulator is written in C, does not depend on third-party libraries,
83     and should compile and run on most 64-bit and 32-bit Unix-like systems.
84 dpavlin 2
85 dpavlin 10 <p>The emulator contains code which tries to emulate the workings of CPUs
86     and surrounding hardware found in real machines, but it does not contain
87     any ROM code. You will need some form of program (in binary form) to run
88     in the emulator. For many emulation modes, PROM calls are handled by the
89 dpavlin 2 emulator itself, so you do not need to use any ROM image at all.
90    
91 dpavlin 10 <p>You can use pre-compiled kernels (for example NetBSD kernels, or
92     Linux), or other programs that are in binary format, and in some cases
93     even actual ROM images. A couple of different file formats are supported
94     (ELF, a.out, ECOFF, SREC, and raw binaries).
95 dpavlin 2
96 dpavlin 10 <p>If you do not have a kernel as a separate file, but you have a bootable
97 dpavlin 6 disk image, then it is sometimes possible to boot directly from that
98     image. (This works for example with DECstation emulation, or when booting
99     from ISO9660 CDROM images.)
100 dpavlin 2
101    
102    
103    
104 dpavlin 6
105    
106 dpavlin 10
107    
108 dpavlin 2 <p><br>
109     <a name="free"></a>
110 dpavlin 4 <h3>Is GXemul Free software?</h3>
111 dpavlin 2
112 dpavlin 6 Yes. I have released GXemul under a Free license. The code in GXemul is
113     Copyrighted software, it is <i>not</i> public domain. (If this is
114     confusing to you, you might want to read up on the definitions of the
115     four freedoms associated with Free software, <a
116     href="http://www.gnu.org/philosophy/free-sw.html">http://www.gnu.org/philosophy/free-sw.html</a>.)
117 dpavlin 2
118 dpavlin 12 <p>The code I have written is released under a 3-clause BSD-style license
119     (or "revised BSD-style" if one wants to use <a
120     href="http://www.gnu.org/philosophy/bsd.html">GNU jargon</a>). Apart from
121     the code I have written, some files are copied from other sources such as
122     NetBSD, for example header files containing symbolic names of bitfields in
123     device registers. They are also covered by similar licenses, but with some
124     additional clauses. The main point, however, is that the licenses require
125     that the original Copyright and license terms are included when you make a
126     copy or modification.
127 dpavlin 2
128 dpavlin 12 <p>If you plan to redistribute GXemul <i>without</i> supplying the source
129     code, then you need to comply with each individual source file some other
130     way, for example by writing additional documentation containing copyright
131     notes. I have not done this, since I do not plan on making distributions
132     without source code. You need to check all individual files for details.
133     The "easiest way out" if you plan to redistribute code from GXemul is, of
134     course, to let it remain open source and simply supply the source code.
135 dpavlin 2
136 dpavlin 22 <p>In case you want to reuse parts of GXemul, but you need to do that
137     under a different license (e.g. the GPL), then contact me and I might
138     re-license/dual-license files on a case-by-case basis.
139 dpavlin 2
140    
141    
142    
143 dpavlin 12
144 dpavlin 2 <p><br>
145     <a name="build"></a>
146     <h3>How to compile/build the emulator:</h3>
147    
148     Uncompress the .tar.gz distribution file, and run
149     <pre>
150     $ <b>./configure</b>
151     $ <b>make</b>
152     </pre>
153    
154 dpavlin 22 <p>This should work on most Unix-like systems. GXemul does not require any
155     specific libraries to build, however, if you build on a system which does
156     not have X11 libraries installed, some functionality will be lost.
157 dpavlin 2
158 dpavlin 12 <p>The emulator's performance is highly dependent on both runtime settings
159 dpavlin 2 and on compiler settings, so you might want to experiment with different
160 dpavlin 20 CC and CFLAGS environment variable values. For example, on an AMD Athlon
161 dpavlin 24 host, you might want to try setting <tt>CFLAGS</tt> to <tt>-march=athlon</tt>
162     before running <tt>configure</tt>.
163 dpavlin 2
164    
165 dpavlin 6
166    
167    
168    
169    
170     <p><br>
171     <a name="run"></a>
172     <h3>How to run the emulator:</h3>
173    
174     Once you have built GXemul, running it should be rather straight-forward.
175     Running <tt><b>gxemul</b></tt> without arguments (or with the
176     <b><tt>-h</tt></b> or <b><tt>-H</tt></b> command line options) will
177     display a help message.
178    
179 dpavlin 2 <p>
180 dpavlin 6 To get some ideas about what is possible to run in the emulator, please
181     read the section about <a href="guestoses.html">installing "guest"
182     operating systems</a>. If you are interested in using the emulator to
183     develop code on your own, then you should also read the section about
184     <a href="experiments.html#hello">Hello World</a>.
185    
186     <p>
187 dpavlin 2 To exit the emulator, type CTRL-C to enter the
188 dpavlin 6 single-step debugger, and then type <tt><b>quit</b></tt>.
189 dpavlin 2
190 dpavlin 4 <p>
191     If you are starting an emulation by entering settings directly on the
192 dpavlin 6 command line, and you are not using the <tt><b>-x</b></tt> option, then all
193 dpavlin 4 terminal input and output will go to the main controlling terminal.
194     CTRL-C is used to break into the debugger, so in order to send CTRL-C to
195     the running (emulated) program, you may use CTRL-B.
196 dpavlin 6 (This should be a reasonable compromise to allow the emulator to be usable
197     even on systems without X Windows.)
198 dpavlin 2
199 dpavlin 4 <p>
200 dpavlin 6 There is no way to send an actual CTRL-B to the emulated program, when
201     typing in the main controlling terminal window. The solution is to either
202     use <a href="configfiles.html">configuration files</a>, or use
203     <tt><b>-x</b></tt>. Both these solutions cause new xterms to be opened for
204     each emulated serial port that is written to. CTRL-B and CTRL-C both have
205     their original meaning in those xterm windows.
206 dpavlin 2
207    
208    
209    
210 dpavlin 4
211 dpavlin 2 <p><br>
212     <a name="cpus"></a>
213 dpavlin 22 <h3>Which processor architectures does GXemul emulate?</h3>
214 dpavlin 2
215 dpavlin 24 The architectures that are emulated well enough to let at least one
216     guest operating system run (per architecture) are ARM, MIPS, and
217     PowerPC.
218 dpavlin 2
219    
220    
221    
222 dpavlin 14
223 dpavlin 24 <p><br>
224     <a name="hosts"></a>
225     <h3>Which host architectures are supported?</h3>
226 dpavlin 2
227 dpavlin 24 As of release 0.4.0 of GXemul, the old binary translation subsystem, which
228     was used for emulation of MIPS processors on Alpha and i386 hosts, has
229     been removed. The current dynamic translation subsystem should work on any
230     host.
231 dpavlin 2
232 dpavlin 6
233 dpavlin 2
234    
235    
236 dpavlin 24 <p><br>
237     <a name="translation"></a>
238     <h3>What kind of translation does GXemul use?</h3>
239 dpavlin 2
240 dpavlin 24 <b>Static vs. dynamic:</b>
241    
242     <p>In order to support guest operating systems, which can overwrite old
243     code pages in memory with new code, it is necessary to translate code
244     dynamically. It is not possible to do a "one-pass" (static) translation.
245     Self-modifying code and Just-in-Time compilers running inside
246     the emulator are other things that would not work with a static
247     translator. GXemul is a dynamic translator. However, it does not
248     necessarily translate into native code, like many other emulators.
249    
250     <p><b>"Runnable" Intermediate Representation:</b>
251    
252     <p>Dynamic translators usually translate from the emulated architecture
253     (e.g. MIPS) into a kind of <i>intermediate representation</i> (IR), and then
254     to native code (e.g. AMD64 or x86 code). Since one of my main goals for
255     GXemul is to keep everything as portable as possible, I have tried to make
256     sure that the IR is something which can be executed regardless of whether
257     the final step (translation from IR to native code) has been implemented
258     or not.
259    
260     <p>The IR in GXemul consists of arrays of pointers to functions, and a few
261     arguments which are passed along to those functions. The functions are
262     implemented in either manually hand-coded C, or automatically generated C.
263     In any case, this is all statically linked into the GXemul binary at link
264     time.
265    
266     <p>Here is a simplified diagram of how these arrays work.
267    
268     <p><center><img src="simplified_dyntrans.png"></center>
269    
270     <p>There is one instruction call slot for every possible program counter
271     location. In the MIPS case, instruction words are 32 bits in length,
272     and pages are (usually) 4 KB large, resulting in 1024 instruction call
273     slots. After the last of these instruction calls, there is an additional
274     call to a special "end of page" function (which doesn't count as an executed
275     instruction). This function switches to the first instruction
276     on the next virtual page (which might cause exceptions, etc).
277    
278     <p>The complexity of individual instructions vary. A simple example of
279     what an instruction can look like is the MIPS <tt>addiu</tt> instruction:
280     <pre>
281     X(addiu)
282     {
283     reg(ic->arg[1]) = (int32_t)
284     ((int32_t)reg(ic->arg[0]) + (int32_t)ic->arg[2]);
285     }
286     </pre>
287    
288     <p>It stores the result of a 32-bit addition of the register at arg[0]
289     with the immediate value arg[2] (treating both as signed 32-bit
290     integers) into register arg[1]. If the emulated CPU is a 64-bit CPU,
291     then this will store a correctly sign-extended value into arg[1].
292     If it is a 32-bit CPU, then only the lowest 32 bits will be stored,
293     and the high part ignored. <tt>X(addiu)</tt> is expanded to
294     <tt>mips_instr_addiu</tt> in the 64-bit case, and <tt>mips32_instr_addiu</tt>
295     in the 32-bit case. Both are compiled into the GXemul executable; no code
296     is created during run-time.
297    
298     <p>Here are examples of what the <tt>addiu</tt> instruction actually
299     looks like when it is compiled, on various host architectures:
300    
301     <p><center><table border="0">
302     <tr><td><b>GCC 4.0.1 on Alpha:</b></td>
303     <td width="35"></td><td></td>
304     <tr>
305     <td valign="top">
306     <pre>mips_instr_addiu:
307     ldq t1,8(a1)
308     ldq t2,24(a1)
309     ldq t3,16(a1)
310     ldq t0,0(t1)
311     addl t0,t2,t0
312     stq t0,0(t3)
313     ret</pre>
314     </td>
315     <td></td>
316     <td valign="top">
317     <pre>mips32_instr_addiu:
318     ldq t2,8(a1)
319     ldq t0,24(a1)
320     ldq t3,16(a1)
321     ldl t1,0(t2)
322     addq t0,t1,t0
323     stl t0,0(t3)
324     ret</pre>
325     </td>
326     </tr>
327    
328     <tr><td><b><br>GCC 3.4.4 on AMD64:</b></td>
329     <tr>
330     <td valign="top">
331     <pre>mips_instr_addiu:
332     mov 0x8(%rsi),%rdx
333     mov 0x18(%rsi),%rax
334     mov 0x10(%rsi),%rcx
335     add (%rdx),%eax
336     cltq
337     mov %rax,(%rcx)
338     retq</pre>
339     </td>
340     <td></td>
341     <td valign="top">
342     <pre>mips32_instr_addiu:
343     mov 0x8(%rsi),%rcx
344     mov 0x10(%rsi),%rdx
345     mov (%rcx),%eax
346     add 0x18(%rsi),%eax
347     mov %eax,(%rdx)
348     retq</pre>
349     </td>
350     </tr>
351    
352     <tr><td><b><br>GCC 4.0.1 on i386:</b></td>
353     <tr>
354     <td valign="top">
355     <pre>mips_instr_addiu:
356     mov 0x8(%esp),%eax
357     mov 0x8(%eax),%ecx
358     mov 0x4(%eax),%edx
359     mov 0xc(%eax),%eax
360     add (%edx),%eax
361     mov %eax,(%ecx)
362     cltd
363     mov %edx,0x4(%ecx)
364     ret</pre>
365     </td>
366     <td></td>
367     <td valign="top">
368     <pre>mips32_instr_addiu:
369     mov 0x8(%esp),%eax
370     mov 0x8(%eax),%ecx
371     mov 0x4(%eax),%edx
372     mov 0xc(%eax),%eax
373     add (%edx),%eax
374     mov %eax,(%ecx)
375     ret</pre>
376     </td>
377     </tr>
378     </table></center>
379    
380     <p>On 64-bit hosts, there is not much difference, but on 32-bit hosts (and
381     to some extent on AMD64), the difference is enough to make it worthwhile.
382    
383    
384     <p><b>Performance:</b>
385    
386     <p>The performance of using this kind of runnable IR is obviously lower
387     than what can be achieved by emulators using native code generation, but
388     can be significantly higher than using a naive fetch-decode-execute
389     interpretation loop. In my opinion, using a runnable IR is an interesting
390     compromise.
391    
392     <p>The overhead per emulated instruction is usually around or below
393     approximately 10 host instructions. This is very much dependent on your
394     host architecture and what compiler and compiler switches you are using.
395     Added to this instruction count is (of course) also the C code used to
396     implement each specific instruction.
397    
398     <p><b>Instruction Combinations:</b>
399    
400     <p>Short, common instruction sequences can sometimes be replaced by a
401     "compound" instruction. An example could be a compare instruction followed
402     by a conditional branch instruction. The advantages of instruction
403     combinations are that
404     <ul>
405     <li>the amortized overhead per instruction is slightly reduced, and
406     <p>
407     <li>the host's compiler can make a good job at optimizing the common
408     instruction sequence.
409     </ul>
410    
411     <p>The special cases where instruction combinations give the most gain
412     are in the cores of string/memory manipulation functions such as
413     <tt>memset()</tt> or <tt>strlen()</tt>. The core loop can then (at least
414     to some extent) be replaced by a native call to the equivalent function.
415    
416     <p>The implementations of compound instructions still keep track of the
417     number of executed instructions, etc. When single-stepping, these
418     translations are invalidated, and replaced by normal instruction calls
419     (one per emulated instruction).
420    
421     <p><b>Native Code Back-ends: (not in this release)</b>
422    
423     <p>In theory, it will be possible to implement native code generation
424     (similar to what is used in high-performance emulators such as QEMU),
425     as long as that generated code abides to the C ABI on the host, but
426     for now I wanted to make sure that GXemul works without such native
427     code back-ends. For this reason, as of release 0.4.0, GXemul is
428     completely free of native code back-ends.
429    
430    
431    
432    
433    
434    
435 dpavlin 2 <p><br>
436     <a name="accuracy"></a>
437     <h3>Emulation accuracy:</h3>
438    
439 dpavlin 6 GXemul is an instruction-level emulator; things that would happen in
440 dpavlin 24 several steps within a real CPU are not taken into account (e.g. pipe-line
441 dpavlin 6 stalls or out-of-order execution). Still, instruction-level accuracy seems
442     to be enough to be able to run complete guest operating systems inside the
443 dpavlin 2 emulator.
444    
445 dpavlin 24 <p>The existance of instruction and data caches is "faked" to let
446     operating systems think that they are there, but for all practical
447     purposes, these caches are non-working.
448 dpavlin 2
449 dpavlin 12 <p>The emulator is <i>not</i> timing-accurate. It can be run in a
450     "deterministic" mode, <tt><b>-D</b></tt>. The meaning of deterministic is
451     simply that running two emulations with the same settings will result in
452     identical runs. Obviously, this requires that no user interaction is
453     taking place, and that clock speeds are fixed with the <tt><b>-I</b></tt>
454     option. (Deterministic in this case does <i>not</i> mean that the
455     emulation will be identical to some actual real-world machine.)
456 dpavlin 2
457 dpavlin 24 <p>(Note that user interaction means <i>both</i> input to the emulated
458     program/OS, and interaction with the emulator's debugger. Breaking into the
459     debugger and then continuing execution may affect when/how interrupts
460     occur.)
461 dpavlin 2
462    
463 dpavlin 6
464    
465 dpavlin 20
466    
467 dpavlin 2 <p><br>
468     <a name="emulmodes"></a>
469     <h3>Which machines does GXemul emulate?</h3>
470    
471 dpavlin 4 A few different machine types are emulated. The following machine types
472     are emulated well enough to run at least one "guest OS":
473 dpavlin 2
474     <p>
475     <ul>
476 dpavlin 24 <li><b><u>ARM</u></b>
477 dpavlin 14 <ul>
478 dpavlin 28 <li><b>CATS</b> (<a href="guestoses.html#netbsdcatsinstall">NetBSD/cats</a>,
479     <a href="guestoses.html#openbsdcatsinstall">OpenBSD/cats</a>)
480     <li><b>IQ80321</b> (<a href="guestoses.html#netbsdevbarminstall">NetBSD/evbarm</a>)
481 dpavlin 14 </ul>
482     <p>
483 dpavlin 24 <li><b><u>MIPS</u></b>
484 dpavlin 14 <ul>
485 dpavlin 28 <li><b>DECstation 5000/200</b> (<a href="guestoses.html#netbsdpmaxinstall">NetBSD/pmax</a>,
486     <a href="guestoses.html#openbsdpmaxinstall">OpenBSD/pmax</a>,
487     <a href="guestoses.html#ultrixinstall">Ultrix</a>,
488     <a href="guestoses.html#declinux">Linux/DECstation</a>,
489     <a href="guestoses.html#sprite">Sprite</a>)
490     <li><b>Acer Pica-61</b> (<a href="guestoses.html#netbsdarcinstall">NetBSD/arc</a>)
491     <li><b>NEC MobilePro 770, 780, 800, and 880</b> (<a href="guestoses.html#netbsdhpcmipsinstall">NetBSD/hpcmips</a>)
492     <li><b>Cobalt</b> (<a href="guestoses.html#netbsdcobaltinstall">NetBSD/cobalt</a>)
493     <li><b>Malta</b> (<a href="guestoses.html#netbsdevbmipsinstall">NetBSD/evbmips</a>)
494 dpavlin 24 <li><b>SGI O2 (aka IP32)</b> <font color="#0000e0">(<super>*</super>)</font>
495 dpavlin 28 (<a href="guestoses.html#netbsdsgimips">NetBSD/sgi</a>)
496 dpavlin 14 </ul>
497 dpavlin 20 <p>
498     <li><b><u>PowerPC</u></b>
499     <ul>
500 dpavlin 28 <li><b>IBM 6050/6070 (PReP, PowerPC Reference Platform)</b> (<a href="guestoses.html#netbsdprepinstall">NetBSD/prep</a>)
501 dpavlin 20 </ul>
502 dpavlin 2 </ul>
503    
504 dpavlin 22 <p><small><font color="#0000e0">(<super>*</super>)</font> =
505     Enough for root-on-nfs, but not for disk boot.)</small>
506    
507 dpavlin 10 <p>There is code in GXemul for emulation of many other machine types; the
508     degree to which these work range from almost being able to run a complete
509     OS, to almost completely unsupported (perhaps just enough support to
510     output a few boot messages via serial console).
511 dpavlin 2
512 dpavlin 10 <p>In addition to emulating real machines, there is also a "test-machine".
513     A test-machine consists of one or more CPUs and a few experimental devices
514     such as:
515 dpavlin 2
516     <p>
517     <ul>
518     <li>a console I/O device (putchar() and getchar()...)
519     <li>an inter-processor communication device, for SMP experiments
520     <li>a very simple linear framebuffer device (for graphics output)
521 dpavlin 12 <li>a simple SCSI disk controller
522     <li>a simple ethernet controller
523 dpavlin 2 </ul>
524    
525 dpavlin 10 <p>This mode is useful if you wish to run experimental code, but do not
526 dpavlin 2 wish to target any specific real-world machine type, for example for
527     educational purposes.
528    
529 dpavlin 10 <p>You can read more about these experimental devices <a
530     href="experiments.html#expdevices">here</a>.
531 dpavlin 2
532    
533    
534    
535    
536    
537     </body>
538     </html>

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