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-revision 4 by dpavlin,
Mon Oct  8 16:18:00 2007 UTC
+revision 8 by dpavlin,
Mon Oct  8 16:18:19 2007 UTC
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- <html>
+ <html><head><title>GXemul documentation: Technical details</title>
- <head><title>GXemul documentation: Technical details</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>
-Line 8
+Line 7
  <b>GXemul documentation:</b></font>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
  <font color="#000000" size="6"><b>Technical details</b>
  </font></td></tr></table></td></tr></table><p>
- <!-- The first 10 lines are cut away by the homepage updating script.  -->
  <!--
- $Id: technical.html,v 1.49 2005/04/16 00:29:45 debug Exp $
+ $Id: technical.html,v 1.51 2005/06/04 22:47:49 debug Exp $
  Copyright (C) 2004-2005  Anders Gavare.  All rights reserved.
-Line 52 
 SUCH DAMAGE.
+Line 49 
 SUCH DAMAGE.
  This page describes some of the internals of GXemul.
  <p>
+ <font color="#e00000"><b>NOTE: This page is probably not
+ very up-to-date by now.</b></font>
+ <p>
  <ul>
    <li><a href="#overview">Overview</a>
    <li><a href="#speed">Speed</a>
-Line 128 
 code into machine code that can be execu
+Line 129 
 code into machine code that can be execu
  on-the-fly. The translation itself obviously takes some time, but this is
  usually made up for by the fact that the translated code chunks are
  executed multiple times.
- To run the emulator with binary translation enabled, just add <b>-b</b>
+ To run the emulator with binary translation enabled, just add
- to the command line.
+ <tt><b>-b</b></tt> to the command line.
  <p>
  Only small pieces of MIPS machine code are translated, usually the size of
-Line 138 
 all translations are done directly from
+Line 139 
 all translations are done directly from
  <p>
  The default bintrans cache size is 16 MB, but you can change this by adding
- -DDEFAULT_BINTRANS_SIZE_IN_MB=<i>xx</i> to your CFLAGS environment variable
+ <tt>-DDEFAULT_BINTRANS_SIZE_IN_MB=<i>xx</i></tt> to your CFLAGS environment
- before running the configure script, or by using the bintrans_size()
+ variable before running the configure script, or by using the
- configuration file option when running the emulator.
+ <tt>bintrans_size()</tt> configuration file option when running the emulator.
  <p>
  By default, an emulated OS running under DECstation emulation which listens to
-Line 149 
 host's clock. That is, if the emulated O
+Line 150 
 host's clock. That is, if the emulated O
  second, it will get approximately 100 interrupts per real second.
  <p>
- There is however a -I option, which sets the number of emulated cycles per
+ There is however a <tt><b>-I</b></tt> option, which sets the number of
- seconds to a fixed value. Let's say you wish to make the emulated OS think it
+ emulated cycles per seconds to a fixed value. Let's say you wish to make the
- is running on a 40 MHz DECstation, and not a 7 MHz one, then you can add
+ emulated OS think it is running on a 40 MHz DECstation, and not a 7 MHz one,
- -I 40000000 to the command line. This will not make the emulation faster, of
+ then you can add <tt><b>-I 40000000</b></tt> to the command line. This will not
- course. It might even make it seem slower; for example, if NetBSD/pmax waits
+ make the emulation faster, of course. It might even make it seem slower; for
-seconds for SCSI devices to settle during bootup, those 2 seconds will take
+ example, if NetBSD/pmax waits 2 seconds for SCSI devices to settle during
-*40000000 cycles (which will take more time than 2*7000000).
+ bootup, those 2 seconds will take 2*40000000 cycles (which will take more
+ time than 2*7000000).
  <p>
- The -I option is also necessary if you want to run deterministic experiments,
+ The <b><tt>-I</tt></b> option is also necessary if you want to run
- if a mc146818 device is present.
+ deterministic experiments, if a mc146818 (or similar) device is present.
  <p>
  Some emulators make claims such as "x times slowdown," but in the case of
-Line 205 
 As far as I have understood it, there se
+Line 207 
 As far as I have understood it, there se
                  connect from the emulated OS to the OS running on the
                  host, as packets sent out on the host's NIC are not
                  received by itself. (?)
+           <li>All specific networking protocols will be handled by the
+                 physical network.
          </ul>
    <p>
    or
-Line 233 
 As far as I have understood it, there se
+Line 237 
 As far as I have understood it, there se
          </ul>
  </ol>
- Other emulators that I have heard of seem to use the first one, if they
+ <p>
- support networking.
+ Some emulators/simulators use the first approach, while others use the
+ second. I think that SIMH and QEMU are examples of emulators using the
+ first and second approach, respectively.
  <p>
  Since I have choosen the second kind of implementation, I have to write
-Line 249 
 emulation (-E dec -e 3max):
+Line 255 
 emulation (-E dec -e 3max):
          and converted to ARP responses. (This is used by the emulated OS
          to find out the MAC address of the gateway.)
    <li>ICMP echo requests (that is the kind of packet produced by the
-         <b>ping</b> program) are interpreted and converted to ICMP echo
+         <b><tt>ping</tt></b> program) are interpreted and converted to ICMP echo
          replies, <i>regardless of the IP address</i>. This means that
          running ping from within the emulated OS will <i>always</i>
          receive a response. The ping packets never leave the emulated
-Line 263 
 emulation (-E dec -e 3max):
+Line 269 
 emulation (-E dec -e 3max):
          packets are handled (but more state is kept for each connection).
          <font color="#ff0000">NOTE: Much of the TCP handling code is very
          ugly and hardcoded.</font>
+ <!--
    <li>RARP is not implemented yet. (I haven't needed it so far.)
+ -->
  </ul>
+ <p>
  The gateway machine, which is the only "other" machine that the emulated
  OS sees on its emulated network, works as a NAT-style firewall/gateway. It
- has a fixed IPv4 address of 10.0.0.254. An OS running in the emulator
+ usually has a fixed IPv4 address of <tt>10.0.0.254</tt>. An OS running in
- can thus have any 10.x.x.x address; a typical choice would be 10.0.0.1.
+ the emulator would usually have an address of the form <tt>10.x.x.x</tt>;
+ a typical choice would be <tt>10.0.0.1</tt>.
  <p>
- Inside emulated NetBSD or OpenBSD, running the following commands should
+ Inside emulated NetBSD/pmax or OpenBSD/pmax, running the following
- configure the emulated NIC:
+ commands should configure the emulated NIC:
  <pre>
          # <b>ifconfig le0 10.0.0.1</b>
          # <b>route add default 10.0.0.254</b>
          add net default: gateway 10.0.0.254
  </pre>
+ <p>
  If you want nameserver lookups to work, you need a valid /etc/resolv.conf
  as well:
  <pre>
          # <b>echo nameserver 129.16.1.3 > /etc/resolv.conf</b>
  </pre>
- (But replace 129.16.1.3 with the actual real-world IP address of your
+ (But replace <tt>129.16.1.3</tt> with the actual real-world IP address of
- nearest nameserver.)
+ your nearest nameserver.)
  <p>
  Now, host lookups should work:
  <pre>
-Line 309 
 Now, host lookups should work:
+Line 321 
 Now, host lookups should work:
          uucp-gw-2.pa.dec.com    172799 IN       A       204.123.2.19
  </pre>
- To transfer files via UDP, you can use the tftp program.
+ <p>
+ At this point, UDP and TCP should (mostly) work.
- <pre>
-         # <b>tftp 12.34.56.78</b>
-         tftp> <b>get filename</b>
-         Received XXXXXX bytes in X.X seconds
-         tftp> <b>quit</b>
-         #
- </pre>
- or, to do it non-interactively (with ugly output):
- <pre>
-         # <b>echo get filename | tftp 12.34.56.78</b>
-         tftp> Received XXXXXX bytes in X.X seconds
-         tftp> #
- </pre>
- This, of course, requires that you have put the file <i>filename</i> in
+ <p>
- the root directory of the tftp server (12.34.56.78).
+ Here is an example of how to configure a server machine and an emulated
+ client machine for sharing files via NFS:
  <p>
- It is also possible to run NFS via UDP. This is very useful if you want to
+ (This is very useful if you want to share entire directory trees
- share entire directory trees between the emulated environment and another
+ between the emulated environment and another machine. These instruction
- machine. These instruction will work for FreeBSD, if you are running
+ will work for FreeBSD, if you are running something else, use your
- something else, use your imagination to modify them:
+ imagination to modify them.)
+ <p>
  <ul>
    <li>On the server, add a line to your /etc/exports file, exporting
          the files you wish to use in the emulator:<pre>
-Line 374 
 a CDROM ISO image. You can use a read-wr
+Line 373 
 a CDROM ISO image. You can use a read-wr
  files in both directions, but then you should be aware of the
  fragmentation issue mentioned above.
- <p>
- TCP is implemented to some extent, but should not be considered to be
- stable yet. It is enough to let NetBSD/pmax and OpenBSD/pmax install via
- ftp, though.
-Line 498 
 Each device should have the following:
+Line 493 
 Each device should have the following:
  </ul>
  <p>
- The return value of the access function has until 20040702 been a
+ The return value of the access function has until 2004-07-02 been a
  true/false value; 1 for success, or 0 for device access failure. A device
  access failure (on MIPS) will result in a DBE exception.
-Line 512 
 means that the access failed, and took 5
+Line 507 
 means that the access failed, and took 5
  <p>
  To be compatible with pre-20040702 devices, a return value of 0 is treated
- by the caller (in src/memory.c) as a value of -1.
+ by the caller (in <tt>src/memory_rw.c</tt>) as a value of -1.
-Line 524 
 by the caller (in src/memory.c) as a val
+Line 519 
 by the caller (in src/memory.c) as a val
  In order to make sure that the emulator actually works like it is supposed
  to, it must be tested. For this purpose, there is a simple regression
- testing framework in the <b>tests/</b> directory.
+ testing framework in the <tt>tests/</tt> directory.
  <p>
  <i>NOTE:  The regression testing framework is basically just a skeleton so far.
-Line 534 
 probably not too incorrect. This makes i
+Line 529 
 probably not too incorrect. This makes i
  regression tests.</i>
  <p>
- To run all the regression tests, type <b>make regtest</b>. Each assembly
+ To run all the regression tests, type <tt>make regtest</tt>. Each assembly
- language file matching the pattern <b>test_*.S</b> will be compiled and
+ language file matching the pattern <tt>test_*.S</tt> will be compiled and
  linked into a 64-bit MIPS ELF (using a gcc cross compiler), and run in the
  emulator. If everything goes well, you should see something like this:
-Line 578 
 emulator. If everything goes well, you s
+Line 573 
 emulator. If everything goes well, you s
  </pre>
  <p>
- Each test writes output to stdout, and there is a <b>test_*.good</b> for
+ Each test writes output to stdout, and there is a <tt>test_*.good</tt> for
- each <b>.S</b> file which contains the wanted output. If the actual output
+ each <tt>.S</tt> file which contains the wanted output. If the actual
- matches the <b>.good</b> file, then the test passes, otherwise it fails.
+ output matches the <tt>.good</tt> file, then the test passes, otherwise it
+ fails.
  <p>
- Read <b>tests/README</b> for more information.
+ Read <tt>tests/README</tt> for more information.

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