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-revision 6 by dpavlin,
Mon Oct  8 16:18:11 2007 UTC
+revision 24 by dpavlin,
Mon Oct  8 16:19:56 2007 UTC
 Line 1
- <html>
+ <html><head><title>Gavare's eXperimental Emulator:&nbsp;&nbsp;&nbsp;Introduction</title>
- <head><title>GXemul documentation: Introduction</title>
+ <meta name="robots" content="noarchive,nofollow,noindex"></head>
- </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>GXemul documentation:</b></font>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
+ <b>Gavare's eXperimental Emulator:</b></font><br>
  <font color="#000000" size="6"><b>Introduction</b>
  </font></td></tr></table></td></tr></table><p>
- <!-- The first 10 lines are cut away by the homepage updating script.  -->
  <!--
- $Id: intro.html,v 1.46 2005/06/04 12:02:17 debug Exp $
+ $Id: intro.html,v 1.87 2006/06/23 10:00:41 debug Exp $
- Copyright (C) 2003-2005  Anders Gavare.  All rights reserved.
+ 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:
-Line 48 
 SUCH DAMAGE.
+Line 45 
 SUCH DAMAGE.
  <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 CPU types does GXemul emulate?</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="#translation">What kind of translation does GXemul use?</a>
    <li><a href="#accuracy">Emulation accuracy</a>
    <li><a href="#emulmodes">Which machines does GXemul emulate?</a>
-   <li><a href="#guestos">Which guest OSes are possible to run?</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>
-Line 67 
 SUCH DAMAGE.
+Line 68 
 SUCH DAMAGE.
  <a name="overview"></a>
  <h3>Overview:</h3>
- GXemul is a machine emulator, which can be used to experiment with
+ GXemul is an experimental instruction-level machine emulator. Several
- binary code for (among others) MIPS-based machines. Several emulation
+ emulation modes are available. In some modes, processors and surrounding
- modes are available. For some emulation modes, processors and surrounding
  hardware components are emulated well enough to let unmodified operating
- systems run as if they were running on a real machine.
+ systems (e.g. NetBSD) run as if they were running on a real machine.
- <p>
- Devices and CPUs are not simulated with 100% accuracy. They are only
- "faked" well enough to make operating systems (eg NetBSD) 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>
+ <p>Devices and processors (ARM, MIPS, PowerPC) are not simulated with 100%
- The emulator is written in C, does not depend on external libraries (except
+ accuracy. They are only ``faked'' well enough to allow guest operating
- X11, but that is optional), and should compile and run on most Unix-like
+ systems run without complaining too much. Still, the emulator could be of
- systems. If it doesn't, then that is a bug.
+ interest for academic research and experiments, such as when learning how
- (You do not need any MIPS compiler toolchain to build or use GXemul.
+ to write operating system code.
- If you need to compile MIPS binaries from sources, then of course you need
- such a toolchain, but that is completely separate from GXemul.)
+ <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
+ <p>The emulator contains code which tries to emulate the workings of CPUs
- surrounding hardware found in real machines, but it does not contain any
+ and surrounding hardware found in real machines, but it does not contain
- ROM code. You will need some form of program (in binary form) to run in
+ any ROM code. You will need some form of program (in binary form) to run
- the emulator. For many emulation modes, PROM calls are handled by the
+ 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>
+ <p>You can use pre-compiled kernels (for example NetBSD kernels, or
- You can use pre-compiled kernels (for example NetBSD kernels, or Linux),
+ Linux), or other programs that are in binary format, and in some cases
- or other programs that are in binary format, and in some cases even actual
+ even actual ROM images. A couple of different file formats are supported
- ROM images. A couple of different file formats are supported (ELF, a.out,
+ (ELF, a.out, ECOFF, SREC, and raw binaries).
- ECOFF, SREC, and raw binaries).
- <p>
+ <p>If you do not have a kernel as a separate file, but you have a bootable
- 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.)
-Line 112 
 from ISO9660 CDROM images.)
+Line 103 
 from ISO9660 CDROM images.)
  <p><br>
  <a name="free"></a>
  <h3>Is GXemul Free software?</h3>
-Line 122 
 confusing to you, you might want to read
+Line 115 
 confusing to you, you might want to read
  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>
+ <p>The code I have written is released under a 3-clause BSD-style license
- The code I have written is released under a 3-clause BSD-style license
+ (or "revised BSD-style" if one wants to use <a
- (or "revised BSD-style" if one wants to use
+ href="http://www.gnu.org/philosophy/bsd.html">GNU jargon</a>). Apart from
- <a href="http://www.gnu.org/philosophy/bsd.html">GNU jargon</a>).
+ the code I have written, some files are copied from other sources such as
- Apart from the code I have written, some files are copied from other sources
+ NetBSD, for example header files containing symbolic names of bitfields in
- such as NetBSD, for example header files containing symbolic names of
+ device registers. They are also covered by similar licenses, but with some
- bitfields in device registers. They are also covered by similar licenses,
+ additional clauses. The main point, however, is that the licenses require
- but with some additional clauses. If you plan to redistribute GXemul
+ that the original Copyright and license terms are included when you make a
- (for example as a binary package), or reuse code from GXemul,
+ copy or modification.
- then you should check those files for their license terms.
+ <p>If you plan to redistribute GXemul <i>without</i> supplying the source
- <p>
+ code, then you need to comply with each individual source file some other
- (The licenses usually require that the original Copyright and license
+ way, for example by writing additional documentation containing copyright
- terms are included when you make a copy or modification. The "easiest way
+ notes. I have not done this, since I do not plan on making distributions
- out" if you plan to redistribute code from GXemul is to simply supply
+ without source code. You need to check all individual files for details.
- the source code. You should however check 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.
-Line 153 
 Uncompress the .tar.gz distribution file
+Line 151 
 Uncompress the .tar.gz distribution file
          $ <b>make</b>
  </pre>
- <p>
+ <p>This should work on most Unix-like systems. GXemul does not require any
- This should work on most Unix-like systems. If it doesn't, then
+ specific libraries to build, however, if you build on a system which does
- mail me a bug report.
+ not have X11 libraries installed, some functionality will be lost.
- <p>
+ <p>The emulator's performance is highly dependent on both runtime settings
- (Note for Windows users: there is a possibility that some releases
- and/or snapshots will also work with Cygwin, but I can't promise that.)
- <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 a modern PC,
+ CC and CFLAGS environment variable values. For example, on an AMD Athlon
- you could try the following:
+ host, you might want to try setting <tt>CFLAGS</tt> to <tt>-march=athlon</tt>
- <p>
+ before running <tt>configure</tt>.
- <pre>
-         $ <b>CFLAGS="-mcpu=pentium4 -O3" ./configure</b>
-         $ <b>make</b>
- </pre>
- <p>
- Run <b><tt>./configure --help</tt></b> to get a list of configure options. (The
- possible options differ between different releases and snapshots.)
-Line 224 
 their original meaning in those xterm wi
+Line 210 
 their original meaning in those xterm wi
  <p><br>
  <a name="cpus"></a>
- <h3>Which CPU types does GXemul emulate?</h3>
+ <h3>Which processor architectures does GXemul emulate?</h3>
- <h4>MIPS:</h4>
+ The architectures that are emulated well enough to let at least one
+ guest operating system run (per architecture) are ARM, MIPS, and
+ PowerPC.
- 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.
- <p>
- I have written an experimental dynamic binary translation subsystem.
- This gives higher total performance than interpreting one instruction at a
- time and executing it. (If you wish to enable bintrans, add <b>-b</b> to
- the command line, but keep in mind that it is still experimental.)
- <h4>URISC:</h4>
- I have implemented an <a href="http://en.wikipedia.org/wiki/URISC">URISC</a>
+ <p><br>
- emulation mode, just for fun. The only instruction available in an URISC
+ <a name="hosts"></a>
- machine is "reverse subtract and skip on borrow". (It is probably not
+ <h3>Which host architectures are supported?</h3>
- worth trying to do bintrans with URISC, because any reasonable URISC
- program relies on self-modifying code, which is bad for bintrans
- performance.)
+ As of release 0.4.0 of GXemul, the old binary translation subsystem, which
+ was used for emulation of MIPS processors on Alpha and i386 hosts, has
+ been removed. The current dynamic translation subsystem should work on any
+ host.
- <h4>POWER/PowerPC</h4>
- There is some code for 64-bit (and 32-bit) POWER/PowerPC emulation, enough
- to run "Hello World", but not enough to run complete operating systems.
- This mode isn't really working yet.
- <h4>Other CPU types:</h4>
- Some other CPU architectures (such as x86) can also be partially emulated.
+ <p><br>
- These are not enabled by default though, because of their unstable-ness.
+ <a name="translation"></a>
+ <h3>What kind of translation does GXemul use?</h3>
+ <b>Static vs. dynamic:</b>
+ <p>In order to support guest operating systems, which can overwrite old
+ code pages in memory with new code, it is necessary to translate code
+ dynamically. It is not possible to do a "one-pass" (static) translation.
+ Self-modifying code and Just-in-Time compilers running inside
+ the emulator are other things that would not work with a static
+ translator. GXemul is a dynamic translator. However, it does not
+ necessarily translate into native code, like many other emulators.
+ <p><b>"Runnable" Intermediate Representation:</b>
+ <p>Dynamic translators usually translate from the emulated architecture
+ (e.g. MIPS) into a kind of <i>intermediate representation</i> (IR), and then
+ to native code (e.g. AMD64 or x86 code). Since one of my main goals for
+ GXemul is to keep everything as portable as possible, I have tried to make
+ sure that the IR is something which can be executed regardless of whether
+ the final step (translation from IR to native code) has been implemented
+ or not.
+ <p>The IR in GXemul consists of arrays of pointers to functions, and a few
+ arguments which are passed along to those functions. The functions are
+ implemented in either manually hand-coded C, or automatically generated C.
+ In any case, this is all statically linked into the GXemul binary at link
+ time.
+ <p>Here is a simplified diagram of how these arrays work.
+ <p><center><img src="simplified_dyntrans.png"></center>
+ <p>There is one instruction call slot for every possible program counter
+ location. In the MIPS case, instruction words are 32 bits in length,
+ and pages are (usually) 4 KB large, resulting in 1024 instruction call
+ slots. After the last of these instruction calls, there is an additional
+ call to a special "end of page" function (which doesn't count as an executed
+ instruction). This function switches to the first instruction
+ on the next virtual page (which might cause exceptions, etc).
+ <p>The complexity of individual instructions vary. A simple example of
+ what an instruction can look like is the MIPS <tt>addiu</tt> instruction:
+ <pre>
+         X(addiu)
+         {
+                 reg(ic->arg[1]) = (int32_t)
+                     ((int32_t)reg(ic->arg[0]) + (int32_t)ic->arg[2]);
+         }
+ </pre>
+ <p>It stores the result of a 32-bit addition of the register at arg[0]
+ with the immediate value arg[2] (treating both as signed 32-bit
+ integers) into register arg[1]. If the emulated CPU is a 64-bit CPU,
+ then this will store a correctly sign-extended value into arg[1].
+ If it is a 32-bit CPU, then only the lowest 32 bits will be stored,
+ and the high part ignored. <tt>X(addiu)</tt> is expanded to
+ <tt>mips_instr_addiu</tt> in the 64-bit case, and <tt>mips32_instr_addiu</tt>
+ in the 32-bit case. Both are compiled into the GXemul executable; no code
+ is created during run-time.
+ <p>Here are examples of what the <tt>addiu</tt> instruction actually
+ looks like when it is compiled, on various host architectures:
+ <p><center><table border="0">
+     <tr><td><b>GCC 4.0.1 on Alpha:</b></td>
+         <td width="35"></td><td></td>
+     <tr>
+         <td valign="top">
+ <pre>mips_instr_addiu:
+      ldq     t1,8(a1)
+      ldq     t2,24(a1)
+      ldq     t3,16(a1)
+      ldq     t0,0(t1)
+      addl    t0,t2,t0
+      stq     t0,0(t3)
+      ret</pre>
+         </td>
+         <td></td>
+         <td valign="top">
+ <pre>mips32_instr_addiu:
+      ldq     t2,8(a1)
+      ldq     t0,24(a1)
+      ldq     t3,16(a1)
+      ldl     t1,0(t2)
+      addq    t0,t1,t0
+      stl     t0,0(t3)
+      ret</pre>
+         </td>
+     </tr>
+     <tr><td><b><br>GCC 3.4.4 on AMD64:</b></td>
+     <tr>
+         <td valign="top">
+ <pre>mips_instr_addiu:
+      mov    0x8(%rsi),%rdx
+      mov    0x18(%rsi),%rax
+      mov    0x10(%rsi),%rcx
+      add    (%rdx),%eax
+      cltq
+      mov    %rax,(%rcx)
+      retq</pre>
+         </td>
+         <td></td>
+         <td valign="top">
+ <pre>mips32_instr_addiu:
+      mov    0x8(%rsi),%rcx
+      mov    0x10(%rsi),%rdx
+      mov    (%rcx),%eax
+      add    0x18(%rsi),%eax
+      mov    %eax,(%rdx)
+      retq</pre>
+         </td>
+     </tr>
+     <tr><td><b><br>GCC 4.0.1 on i386:</b></td>
+     <tr>
+         <td valign="top">
+ <pre>mips_instr_addiu:
+      mov    0x8(%esp),%eax
+      mov    0x8(%eax),%ecx
+      mov    0x4(%eax),%edx
+      mov    0xc(%eax),%eax
+      add    (%edx),%eax
+      mov    %eax,(%ecx)
+      cltd
+      mov    %edx,0x4(%ecx)
+      ret</pre>
+         </td>
+         <td></td>
+         <td valign="top">
+ <pre>mips32_instr_addiu:
+      mov    0x8(%esp),%eax
+      mov    0x8(%eax),%ecx
+      mov    0x4(%eax),%edx
+      mov    0xc(%eax),%eax
+      add    (%edx),%eax
+      mov    %eax,(%ecx)
+      ret</pre>
+         </td>
+     </tr>
+ </table></center>
+ <p>On 64-bit hosts, there is not much difference, but on 32-bit hosts (and
+ to some extent on AMD64), the difference is enough to make it worthwhile.
+ <p><b>Performance:</b>
+ <p>The performance of using this kind of runnable IR is obviously lower
+ than what can be achieved by emulators using native code generation, but
+ can be significantly higher than using a naive fetch-decode-execute
+ interpretation loop. In my opinion, using a runnable IR is an interesting
+ compromise.
+ <p>The overhead per emulated instruction is usually around or below
+ approximately 10 host instructions. This is very much dependent on your
+ host architecture and what compiler and compiler switches you are using.
+ Added to this instruction count is (of course) also the C code used to
+ implement each specific instruction.
+ <p><b>Instruction Combinations:</b>
+ <p>Short, common instruction sequences can sometimes be replaced by a
+ "compound" instruction. An example could be a compare instruction followed
+ by a conditional branch instruction. The advantages of instruction
+ combinations are that
+ <ul>
+   <li>the amortized overhead per instruction is slightly reduced, and
+   <p>
+   <li>the host's compiler can make a good job at optimizing the common
+         instruction sequence.
+ </ul>
+ <p>The special cases where instruction combinations give the most gain
+ are in the cores of string/memory manipulation functions such as
+ <tt>memset()</tt> or <tt>strlen()</tt>. The core loop can then (at least
+ to some extent) be replaced by a native call to the equivalent function.
+ <p>The implementations of compound instructions still keep track of the
+ number of executed instructions, etc. When single-stepping, these
+ translations are invalidated, and replaced by normal instruction calls
+ (one per emulated instruction).
+ <p><b>Native Code Back-ends: (not in this release)</b>
+ <p>In theory, it will be possible to implement native code generation
+ (similar to what is used in high-performance emulators such as QEMU),
+ as long as that generated code abides to the C ABI on the host, but
+ for now I wanted to make sure that GXemul works without such native
+ code back-ends. For this reason, as of release 0.4.0, GXemul is
+ completely free of native code back-ends.
-Line 271 
 These are not enabled by default though,
+Line 437 
 These are not enabled by default though,
  <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
+ 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>
+ <p>The existance of instruction and data caches is "faked" to let
- Caches are by default not emulated. In some cases, the existance of caches
+ operating systems think that they are there, but for all practical
- is "faked" to let operating systems think that they are there. (There is
+ purposes, these caches are non-working.
- 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>(Note that user interaction means <i>both</i> input to the emulated
+ program/OS, and interaction with the emulator's debugger. Breaking into the
+ debugger and then continuing execution may affect when/how interrupts
+ occur.)
- <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.)
-Line 304 
 are emulated well enough to run at least
+Line 473 
 are emulated well enough to run at least
  <p>
  <ul>
-   <li><b>DECstation 5000/200</b>&nbsp;&nbsp;("3max")
+   <li><b><u>ARM</u></b>
-         <br>Serial controller (including keyboard and mouse), ethernet,
+   <ul>
-         SCSI, and graphical framebuffers.
+     <li><b>CATS</b> (NetBSD/cats, OpenBSD/cats)
+     <li><b>IQ80321</b> (NetBSD/evbarm)
+   </ul>
    <p>
-   <li><b>Acer Pica-61</b>&nbsp;&nbsp;(an ARC machine)
+   <li><b><u>MIPS</u></b>
-         <br>Serial controller, "VGA" text console, and SCSI.
+   <ul>
+     <li><b>DECstation 5000/200</b> (NetBSD/pmax, OpenBSD/pmax, Ultrix,
+         Linux/DECstation, Sprite)
+     <li><b>Acer Pica-61</b> (NetBSD/arc)
+     <li><b>NEC MobilePro 770, 780, 800, and 880</b> (NetBSD/hpcmips)
+     <li><b>Cobalt</b> (NetBSD/cobalt)
+     <li><b>Malta</b> (NetBSD/evbmips)
+     <li><b>SGI O2 (aka IP32)</b> <font color="#0000e0">(<super>*</super>)</font>
+         (NetBSD/sgi)
+   </ul>
    <p>
-   <li><b>NEC MobilePro 770, 780, 800, and 880</b>&nbsp;&nbsp;(HPCmips machines)
+   <li><b><u>PowerPC</u></b>
-         <br>Framebuffer, keyboard, and a PCMCIA IDE controller.
+   <ul>
-   <p>
+     <li><b>IBM 6050/6070 (PReP, PowerPC Reference Platform)</b> (NetBSD/prep)
-   <li><b>Cobalt</b>
+   </ul>
-         <br>Serial controller and PCI IDE.
  </ul>
- <p>
+ <p><small><font color="#0000e0">(<super>*</super>)</font> =
- There is code in GXemul for emulation of many other machine types;
+ Enough for root-on-nfs, but not for disk boot.)</small>
- 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>
+ <p>There is code in GXemul for emulation of many other machine types; the
- In addition to emulating real machines, there is also a "test-machine".
+ degree to which these work range from almost being able to run a complete
- A test-machine consists of one or more CPUs and a few experimental
+ OS, to almost completely unsupported (perhaps just enough support to
- devices such as:
+ 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>
+ <p>This mode is useful if you wish to run experimental code, but do not
- 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>
+ <p>You can read more about these experimental devices <a
- You can read more about these experimental devices
+ href="experiments.html#expdevices">here</a>.
- <a href="experiments.html#expdevices">here</a>.
- <p><br>
- <a name="guestos"></a>
- <h3>Which guest OSes are possible to run?</h3>
- This table lists the guest OSes that run well enough to be considered
- working in the emulator. They can boot from a harddisk image and be
- interacted with similar to a real machine.
- <p>
- <center><table border="0">
-         <tr>
-           <td width="10"></td>
-           <td align="center"><a href="20050317-example.png"><img src="20050317-example_small.png"></a></td>
-           <td width="15"></td>
-           <td><a href="http://www.netbsd.org/Ports/pmax/">NetBSD/pmax</a>
-                 <br>DECstation 5000/200</td>
-           <td width="30"></td>
-           <td align="center"><a href="20041024-netbsd-arc-installed.gif"><img src="20041024-netbsd-arc-installed_small.gif"></a></td>
-           <td width="15"></td>
-           <td><a href="http://www.netbsd.org/Ports/arc/">NetBSD/arc</a>
-                 <br>Acer Pica-61</td>
-         </tr>
-         <tr><td height="10"></td></tr>
-         <tr>
-           <td></td>
-           <td align="center"><a href="openbsd-pmax-20040710.png"><img src="openbsd-pmax-20040710_small.png"></a></td>
-           <td></td>
-           <td><a href="http://www.openbsd.org/pmax.html">OpenBSD/pmax</a>
-                 <br>DECstation 5000/200</td>
-           <td></td>
-           <td align="center"><a href="20041024-openbsd-arc-installed.gif"><img src="20041024-openbsd-arc-installed_small.gif"></a></td>
-           <td></td>
-           <td><a href="http://www.openbsd.org/arc.html">OpenBSD/arc</a>
-                 <br>Acer Pica-61</td>
-         </tr>
-         <tr><td height="10"></td></tr>
-         <tr>
-           <td></td>
-           <td align="center"><a href="ultrix4.5-20040706.png"><img src="ultrix4.5-20040706_small.gif"></a></td>
-           <td></td>
-           <td>Ultrix/RISC<br>DECstation 5000/200</td>
-           <td></td>
-           <td align="center"><a href="20041213-debian_4.png"><img src="20041213-debian_4_small.gif"></a></td>
-           <td></td>
-           <td><a href="http://www.debian.org/">Debian&nbsp;GNU/Linux</a>&nbsp;<super>*</super>
-                 <br>DECstation 5000/200</td>
-         </tr>
-         <tr><td height="10"></td></tr>
-         <tr>
-           <td></td>
-           <td align="center"><a href="sprite-20040711.png"><img src="sprite-20040711_small.png"></a></td>
-           <td></td>
-           <td><a href="http://www.cs.berkeley.edu/projects/sprite/retrospective.html">Sprite</a>
-                 <br>DECstation 5000/200</td>
-           <td></td>
-           <td align="center"><a href="20041129-redhat_mips.png"><img src="20041129-redhat_mips_small.png"></a></td>
-           <td></td>
-           <td>Redhat&nbsp;Linux&nbsp;<super>*</super>
-                 <br>DECstation 5000/200</td>
-         </tr>
-         <tr><td height="10"></td></tr>
-         <tr>
-           <td></td>
-           <td align="center"><a href="20050427-netbsd-hpcmips-2.png"><img src="20050427-netbsd-hpcmips-2_small.png"></a></td>
-           <td></td>
-           <td><a href="http://www.netbsd.org/Ports/hpcmips/">NetBSD/hpcmips</a>
-                 <br>NEC MobilePro 770, 780, 800, 880</td>
-           <td></td>
-           <td align="center"><a href="20050413-netbsd-cobalt.png"><img src="20050413-netbsd-cobalt_small.png"></a></td>
-           <td></td>
-           <td><a href="http://www.netbsd.org/Ports/cobalt/">NetBSD/cobalt</a>
-                 <br>Cobalt</td>
-         </tr>
- </table></center>
- <p><br>
- <super>*</super> Although Linux runs under DECstation emulation, the
- default 2.4.27 kernel in Debian GNU/Linux does not support keyboards on
- the 5000/200 (the specific DECstation model being emulated), so when the
- login prompt is reached you cannot interact with the system. Kaj-Michael
- Lang has compiled and made available a newer kernel from the current
- mips-linux development tree. You can find it here: <a
- href="http://home.tal.org/~milang/o2/kernels/">http://home.tal.org/~milang/o2/kernels</a>/<a
- href="http://home.tal.org/~milang/o2/kernels/vmlinux-2.4.29-rc2-r3k-mipsel-decstation">vmlinux-2.4.29-rc2-r3k-mipsel-decstation</a>
- This newer kernel supports keyboard input, but it does not have Debian's
- ethernet patches, so you will not be able to use keyboard/framebuffer
- <i>and</i> networking at the same time.
  </body>
  </html>

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