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<b>Gavare's eXperimental Emulator:&nbsp;&nbsp;&nbsp;</b></font>
<font color="#000000" size="6"><b>Technical details</b>
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<a href="./">Back to the index</a>

<p><br>
<h2>Technical details</h2>

<p>This page describes some of the internals of GXemul.

<p>
<ul>
  <li><a href="#speed">Speed and emulation modes</a>
  <li><a href="#net">Networking</a>
  <li><a href="#devices">Emulation of hardware devices</a>
</ul>


<p><br>
<a name="speed"></a>
<h3>Speed and emulation modes</h3>

So, how fast is GXemul? There is no short answer to this. There is 
especially no answer to the question <b>What is the slowdown factor?</b>, 
because the host architecture and emulated architecture can usually not be 
compared just like that.

<p>Performance depends on several factors, including (but not limited to)  
host architecture, host clock speed, which compiler and compiler flags
were used to build the emulator, what the workload is, and so on. For
example, if an emulated operating system tries to read a block from disk,
from its point of view the read was instantaneous (no waiting). So 1 MIPS
in an emulated OS might have taken more than one million instructions on a
real machine.

<p>Also, if the emulator says it has executed 1 million instructions, and 
the CPU family in question was capable of scalar execution (i.e. one cycle 
per instruction), it might still have taken more than 1 million cycles on 
a real machine because of cache misses and similar micro-architectural 
penalties that are not simulated by GXemul.

<p>Because of these issues, it is in my opinion best to measure
performance as the actual (real-world) time it takes to perform a task
with the emulator. Typical examples would be "How long does it take to 
install NetBSD?", or "How long does it take to compile XYZ inside NetBSD 
in the emulator?".

<p>So, how fast is it? :-)&nbsp;&nbsp;&nbsp;Answer: it varies.

<p>The emulation technique used varies depending on which processor type 
is being emulated. (One of my main goals with GXemul is to experiment with 
different kinds of emulation, so these might change in the future.)

<ul>
  <li><b>MIPS:</b><br>
        There are two emulation modes. The most important one is an
        implementation of a <i>dynamic binary translator</i>.
        (Compared to real binary translators, though, GXemul's bintrans
        subsystem is very simple and does not perform very well.)
        This mode can be used on Alpha and i386 host. The other emulation
        mode is simple interpretation, where an instruction is read from
        emulated memory, and interpreted one-at-a-time. (Slow, but it
        works. It can be forcefully used by using the <tt>-B</tt> command
        line option.)
  <p>
  <li><b>All other modes:</b><br>
        These use a kind of dynamic translation system. (This system does
        not use host-specific backends, so it is not "recompilation" or
        anything like that.) Speed is slower than real binary translation,
        but faster than traditional interpretation, and with some tricks
        it will hopefully still give reasonable speed. ARM emulation uses
        this kind of translation, for example.
</ul>


<p><br>
<a name="net"></a>
<h3>Networking</h3>

<font color="#ff0000">NOTE/TODO: This section is very old and a bit
out of date.</font>

<p>Running an entire operating system under emulation is very interesting
in itself, but for several reasons, running a modern OS without access to
TCP/IP networking is a bit akward. Hence, I feel the need to implement
TCP/IP (networking) support in the emulator.

<p>
As far as I have understood it, there seems to be two different ways to go:

<ol>
  <li>Forward ethernet packets from the emulated ethernet controller to
        the host machine's ethernet controller, and capture incoming 
        packets on the host's controller, giving them back to the
        emulated OS. Characteristics are:
        <ul>
          <li>Requires <i>direct</i> access to the host's NIC, which
                means on most platforms that the emulator cannot be
                run as a normal user!
          <li>Reduced portability, as not every host operating system
                uses the same programming interface for dealing with
                hardware ethernet controllers directly.
          <li>When run on a switched network, it might be problematic to
                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
  <p>
  <li>Whenever the emulated ethernet controller wishes to send a packet,
        the emulator looks at the packet and creates a response. Packets
        that can have an immediate response never go outside the emulator,
        other packet types have to be converted into suitable other
        connection types (UDP, TCP, etc). Characteristics:
        <ul>
          <li>Each packet type sent out on the emulated NIC must be handled.
                This means that I have to do a lot of coding.
                (I like this, because it gives me an opportunity to
                learn about networking protocols.)
          <li>By not relying on access to the host's NIC directly,
                portability is maintained. (It would be sad if the networking
                portion of a portable emulator isn't as portable as the
                rest of the emulator.)
          <li>The emulator can be run as a normal user process, does
                not require root privilegies.
          <li>Connecting from the emulated OS to the host's OS should
                not be problematic.
          <li>The emulated OS will experience the network just as a single
                machine behind a NAT gateway/firewall would. The emulated
                OS is thus automatically protected from the outside world.
        </ul>
</ol>

<p>
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 
support explicitly for any kind of network protocol that should be
supported. As of 2004-07-09, the following has been implemented and seems 
to work under at least NetBSD/pmax and OpenBSD/pmax under DECstation 5000/200
emulation (-E dec -e 3max):

<p>
<ul>
  <li>ARP requests sent out from the emulated NIC are interpreted,
        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><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
        environment.
  <li>UDP packets are interpreted and passed along to the outside world.
        If the emulator receives an UDP packet from the outside world, it
        is converted into an UDP packet for the emulated OS. (This is not
        implemented very well yet, but seems to be enough for nameserver
        lookups, tftp file transfers, and NFS mounts using UDP.)
  <li>TCP packets are interpreted one at a time, similar to how UDP 
        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 
usually has a fixed IPv4 address of <tt>10.0.0.254</tt>. An OS running in 
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/pmax or OpenBSD/pmax, running the following 
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 <tt>129.16.1.3</tt> with the actual real-world IP address of 
your nearest nameserver.)

<p>
Now, host lookups should work:
<pre>
        # <b>host -a www.netbsd.org</b>
        Trying null domain
        rcode = 0 (Success), ancount=2
        The following answer is not authoritative:
        The following answer is not verified as authentic by the server:
        www.netbsd.org  86400 IN        AAAA    2001:4f8:4:7:290:27ff:feab:19a7
        www.netbsd.org  86400 IN        A       204.152.184.116
        For authoritative answers, see:
        netbsd.org      83627 IN        NS      uucp-gw-2.pa.dec.com
        netbsd.org      83627 IN        NS      ns.netbsd.org
        netbsd.org      83627 IN        NS      adns1.berkeley.edu
        netbsd.org      83627 IN        NS      adns2.berkeley.edu
        netbsd.org      83627 IN        NS      uucp-gw-1.pa.dec.com
        Additional information:
        ns.netbsd.org   83627 IN        A       204.152.184.164
        uucp-gw-1.pa.dec.com    172799 IN       A       204.123.2.18
        uucp-gw-2.pa.dec.com    172799 IN       A       204.123.2.19
</pre>

<p>
At this point, UDP and TCP should (mostly) work.

<p>
Here is an example of how to configure a server machine and an emulated 
client machine for sharing files via NFS:

<p>
(This is very useful if you want to share entire directory trees
between the emulated environment and another machine. These instruction
will work for FreeBSD, if you are running something else, use your
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>
        <b>/tftpboot -mapall=nobody -ro 123.11.22.33</b>
</pre>
        where 123.11.22.33 is the IP address of the machine running the
        emulator process, as seen from the outside world.
  <p>
  <li>Then start up the programs needed to serve NFS via UDP. Note the
        -n argument to mountd. This is needed to tell mountd to accept
        connections from unprivileged ports (because the emulator does
        not need to run as root).<pre>
        # <b>portmap</b>
        # <b>nfsd -u</b>       &lt;--- u for UDP
        # <b>mountd -n</b>
</pre>
  <li>In the guest OS in the emulator, once you have ethernet and IPv4
        configured so that you can use UDP, mounting the filesystem
        should now be possible:  (this example is for NetBSD/pmax
        or OpenBSD/pmax)<pre>
        # <b>mount -o ro,-r=1024,-w=1024,-U,-3 my.server.com:/tftpboot /mnt</b>
    or
        # <b>mount my.server.com:/tftpboot /mnt</b>
</pre>
        If you don't supply the read and write sizes, there is a risk
        that the default values are too large. The emulator currently
        does not handle fragmentation/defragmentation of <i>outgoing</i>
        packets, so going above the ethernet frame size (1518) is a very
        bad idea. Incoming packets (reading from nfs) should work, though,
        for example during an NFS install.
</ul>

The example above uses read-only mounts. That is enough for things like
letting NetBSD/pmax or OpenBSD/pmax install via NFS, without the need for
a CDROM ISO image. You can use a read-write mount if you wish to share
files in both directions, but then you should be aware of the 
fragmentation issue mentioned above.

<p>TODO: Write a section on how to connect multiple emulator instances.
(Using the <tt>local_port</tt> and <tt>add_remote</tt> configuration file
commands.)


<p><br>
<a name="devices"></a>
<h3>Emulation of hardware devices</h3>

Each file in the <tt>src/device/</tt> directory is responsible for one
hardware device. These are used from <tt>src/machine.c</tt>, when
initializing which hardware a particular machine model will be using, or
when adding devices to a machine using the <tt>device()</tt> command in
configuration files.

<p><font color="#ff0000">NOTE: The device registry subsystem is currently
in a state of flux, as it is being redesigned.</font>

<p>(I'll be using the name "<tt>foo</tt>" as the name of the device in all
these examples.  This is pseudo code, it might need some modification to
actually compile and run.)

<p>Each device should have the following:

<p>
<ul>
  <li>A <tt>devinit</tt> function in <tt>src/devices/dev_foo.c</tt>. It
        would typically look something like this:
<pre>
        /*
         *  devinit_foo():
         */
        int devinit_foo(struct devinit *devinit)
        {
                struct foo_data *d = malloc(sizeof(struct foo_data));

                if (d == NULL) {
                        fprintf(stderr, "out of memory\n");
                        exit(1);
                }
                memset(d, 0, sizeof(struct foon_data));

                /*
                 *  Set up stuff here, for example fill d with useful
                 *  data. devinit contains settings like address, irq_nr,
                 *  and other things.
                 *
                 *  ...
                 */
        
                memory_device_register(devinit->machine->memory, devinit->name,
                    devinit->addr, DEV_FOO_LENGTH,
                    dev_foo_access, (void *)d, MEM_DEFAULT, NULL);
        
                /*  This should only be here if the device
                    has a tick function:  */
                machine_add_tickfunction(machine, dev_foo_tick, d,
                    FOO_TICKSHIFT);

                /*  Return 1 if the device was successfully added.  */
                return 1;       
        }       
</pre><br>

  <li>At the top of <tt>dev_foo.c</tt>, the <tt>foo_data</tt> struct
        should be defined.
<pre>
        struct foo_data {
                int     irq_nr;
                /*  ...  */
        }
</pre><br>

  <li>If <tt>foo</tt> has a tick function (that is, something that needs to be
        run at regular intervals) then <tt>FOO_TICKSHIFT</tt> and a tick 
        function need to be defined as well:
<pre>
        #define FOO_TICKSHIFT           10

        void dev_foo_tick(struct cpu *cpu, void *extra)
        {
                struct foo_data *d = (struct foo_data *) extra;

                if (.....)
                        cpu_interrupt(cpu, d->irq_nr);
                else
                        cpu_interrupt_ack(cpu, d->irq_nr);
        }
</pre><br>

  <li>And last but not least, the device should have an access function.
        The access function is called whenever there is a load or store
        to an address which is in the device' memory mapped region.
<pre>
        int dev_foo_access(struct cpu *cpu, struct memory *mem,
            uint64_t relative_addr, unsigned char *data, size_t len,
            int writeflag, void *extra)
        {
                struct foo_data *d = extra;
                uint64_t idata = 0, odata = 0;

                idata = memory_readmax64(cpu, data, len);
                switch (relative_addr) {
                /* .... */
                }

                if (writeflag == MEM_READ)
                        memory_writemax64(cpu, data, len, odata);

                /*  Perhaps interrupts need to be asserted or
                    deasserted:  */
                dev_foo_tick(cpu, extra);

                /*  Return successfully.  */
                return 1;
        }
</pre><br>
</ul>

<p>
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.

<p>
Some devices are converted to support arbitrary memory latency
values. The return value is the number of cycles that the read or 
write access took. A value of 1 means one cycle, a value of 10 means 10 
cycles. Negative values are used for device access failures, and the 
absolute value of the value is then the number of cycles; a value of -5 
means that the access failed, and took 5 cycles.

<p>
To be compatible with pre-20040702 devices, a return value of 0 is treated 
by the caller (in <tt>src/memory_rw.c</tt>) as a value of -1.


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1	dpavlin	12	<html><head><title>Gavare's eXperimental Emulator:   Technical details</title>
2	dpavlin	8	<meta name="robots" content="noarchive,nofollow,noindex"></head>
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6			<td align="left" valign=center bgcolor="#d0efff"><font color="#6060e0" size="6">
7	dpavlin	12	<b>Gavare's eXperimental Emulator:   </b></font>
8	dpavlin	4	<font color="#000000" size="6"><b>Technical details</b>
9			</font></td></tr></table></td></tr></table><p>
10	dpavlin	2
11			<!--
12
13	dpavlin	14	$Id: technical.html,v 1.63 2005/10/07 15:10:00 debug Exp $
14	dpavlin	2
15			Copyright (C) 2004-2005 Anders Gavare. All rights reserved.
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17			Redistribution and use in source and binary forms, with or without
18			modification, are permitted provided that the following conditions are met:
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26			derived from this software without specific prior written permission.
27
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30			IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
31			ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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33			DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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41
42
43	dpavlin	12
44	dpavlin	2	<a href="./">Back to the index</a>
45
46			<p><br>
47			<h2>Technical details</h2>
48
49	dpavlin	10	<p>This page describes some of the internals of GXemul.
50	dpavlin	2
51			<p>
52			<ul>
53	dpavlin	10	<li><a href="#speed">Speed and emulation modes</a>
54	dpavlin	2	<li><a href="#net">Networking</a>
55			<li><a href="#devices">Emulation of hardware devices</a>
56			</ul>
57
58
59
60
61
62
63			<p><br>
64			<a name="speed"></a>
65	dpavlin	10	<h3>Speed and emulation modes</h3>
66	dpavlin	2
67	dpavlin	14	So, how fast is GXemul? There is no short answer to this. There is
68	dpavlin	10	especially no answer to the question <b>What is the slowdown factor?</b>,
69			because the host architecture and emulated architecture can usually not be
70			compared just like that.
71	dpavlin	2
72	dpavlin	10	<p>Performance depends on several factors, including (but not limited to)
73			host architecture, host clock speed, which compiler and compiler flags
74			were used to build the emulator, what the workload is, and so on. For
75			example, if an emulated operating system tries to read a block from disk,
76			from its point of view the read was instantaneous (no waiting). So 1 MIPS
77			in an emulated OS might have taken more than one million instructions on a
78			real machine.
79	dpavlin	2
80	dpavlin	10	<p>Also, if the emulator says it has executed 1 million instructions, and
81			the CPU family in question was capable of scalar execution (i.e. one cycle
82			per instruction), it might still have taken more than 1 million cycles on
83			a real machine because of cache misses and similar micro-architectural
84			penalties that are not simulated by GXemul.
85	dpavlin	2
86	dpavlin	10	<p>Because of these issues, it is in my opinion best to measure
87			performance as the actual (real-world) time it takes to perform a task
88			with the emulator. Typical examples would be "How long does it take to
89			install NetBSD?", or "How long does it take to compile XYZ inside NetBSD
90			in the emulator?".
91	dpavlin	2
92	dpavlin	14	<p>So, how fast is it? :-)   Answer: it varies.
93
94	dpavlin	10	<p>The emulation technique used varies depending on which processor type
95			is being emulated. (One of my main goals with GXemul is to experiment with
96			different kinds of emulation, so these might change in the future.)
97	dpavlin	2
98	dpavlin	10	<ul>
99	dpavlin	12	<li><b>MIPS:</b><br>
100	dpavlin	10	There are two emulation modes. The most important one is an
101			implementation of a <i>dynamic binary translator</i>.
102			(Compared to real binary translators, though, GXemul's bintrans
103			subsystem is very simple and does not perform very well.)
104			This mode can be used on Alpha and i386 host. The other emulation
105			mode is simple interpretation, where an instruction is read from
106			emulated memory, and interpreted one-at-a-time. (Slow, but it
107			works. It can be forcefully used by using the <tt>-B</tt> command
108			line option.)
109			<p>
110	dpavlin	12	<li><b>All other modes:</b><br>
111	dpavlin	14	These use a kind of dynamic translation system. (This system does
112			not use host-specific backends, so it is not "recompilation" or
113			anything like that.) Speed is slower than real binary translation,
114			but faster than traditional interpretation, and with some tricks
115			it will hopefully still give reasonable speed. ARM emulation uses
116			this kind of translation, for example.
117	dpavlin	10	</ul>
118	dpavlin	2
119
120
121
122
123
124			<p><br>
125			<a name="net"></a>
126			<h3>Networking</h3>
127
128	dpavlin	10	<font color="#ff0000">NOTE/TODO: This section is very old and a bit
129			out of date.</font>
130	dpavlin	2
131	dpavlin	10	<p>Running an entire operating system under emulation is very interesting
132			in itself, but for several reasons, running a modern OS without access to
133			TCP/IP networking is a bit akward. Hence, I feel the need to implement
134			TCP/IP (networking) support in the emulator.
135
136	dpavlin	2	<p>
137			As far as I have understood it, there seems to be two different ways to go:
138
139			<ol>
140			<li>Forward ethernet packets from the emulated ethernet controller to
141			the host machine's ethernet controller, and capture incoming
142			packets on the host's controller, giving them back to the
143			emulated OS. Characteristics are:
144			<ul>
145			<li>Requires <i>direct</i> access to the host's NIC, which
146			means on most platforms that the emulator cannot be
147			run as a normal user!
148			<li>Reduced portability, as not every host operating system
149			uses the same programming interface for dealing with
150			hardware ethernet controllers directly.
151			<li>When run on a switched network, it might be problematic to
152			connect from the emulated OS to the OS running on the
153			host, as packets sent out on the host's NIC are not
154			received by itself. (?)
155	dpavlin	6	<li>All specific networking protocols will be handled by the
156			physical network.
157	dpavlin	2	</ul>
158			<p>
159			or
160			<p>
161			<li>Whenever the emulated ethernet controller wishes to send a packet,
162			the emulator looks at the packet and creates a response. Packets
163			that can have an immediate response never go outside the emulator,
164			other packet types have to be converted into suitable other
165			connection types (UDP, TCP, etc). Characteristics:
166			<ul>
167			<li>Each packet type sent out on the emulated NIC must be handled.
168			This means that I have to do a lot of coding.
169			(I like this, because it gives me an opportunity to
170			learn about networking protocols.)
171			<li>By not relying on access to the host's NIC directly,
172			portability is maintained. (It would be sad if the networking
173			portion of a portable emulator isn't as portable as the
174			rest of the emulator.)
175			<li>The emulator can be run as a normal user process, does
176			not require root privilegies.
177			<li>Connecting from the emulated OS to the host's OS should
178			not be problematic.
179			<li>The emulated OS will experience the network just as a single
180			machine behind a NAT gateway/firewall would. The emulated
181			OS is thus automatically protected from the outside world.
182			</ul>
183			</ol>
184
185	dpavlin	6	<p>
186			Some emulators/simulators use the first approach, while others use the
187			second. I think that SIMH and QEMU are examples of emulators using the
188			first and second approach, respectively.
189	dpavlin	2
190			<p>
191			Since I have choosen the second kind of implementation, I have to write
192			support explicitly for any kind of network protocol that should be
193			supported. As of 2004-07-09, the following has been implemented and seems
194			to work under at least NetBSD/pmax and OpenBSD/pmax under DECstation 5000/200
195			emulation (-E dec -e 3max):
196
197			<p>
198			<ul>
199			<li>ARP requests sent out from the emulated NIC are interpreted,
200			and converted to ARP responses. (This is used by the emulated OS
201			to find out the MAC address of the gateway.)
202			<li>ICMP echo requests (that is the kind of packet produced by the
203	dpavlin	6	<b><tt>ping</tt></b> program) are interpreted and converted to ICMP echo
204	dpavlin	2	replies, <i>regardless of the IP address</i>. This means that
205			running ping from within the emulated OS will <i>always</i>
206			receive a response. The ping packets never leave the emulated
207			environment.
208			<li>UDP packets are interpreted and passed along to the outside world.
209			If the emulator receives an UDP packet from the outside world, it
210			is converted into an UDP packet for the emulated OS. (This is not
211			implemented very well yet, but seems to be enough for nameserver
212			lookups, tftp file transfers, and NFS mounts using UDP.)
213			<li>TCP packets are interpreted one at a time, similar to how UDP
214			packets are handled (but more state is kept for each connection).
215			<font color="#ff0000">NOTE: Much of the TCP handling code is very
216			ugly and hardcoded.</font>
217	dpavlin	6	<!--
218	dpavlin	2	<li>RARP is not implemented yet. (I haven't needed it so far.)
219	dpavlin	6	-->
220	dpavlin	2	</ul>
221
222	dpavlin	6	<p>
223	dpavlin	2	The gateway machine, which is the only "other" machine that the emulated
224			OS sees on its emulated network, works as a NAT-style firewall/gateway. It
225	dpavlin	6	usually has a fixed IPv4 address of <tt>10.0.0.254</tt>. An OS running in
226			the emulator would usually have an address of the form <tt>10.x.x.x</tt>;
227			a typical choice would be <tt>10.0.0.1</tt>.
228	dpavlin	2
229			<p>
230	dpavlin	6	Inside emulated NetBSD/pmax or OpenBSD/pmax, running the following
231			commands should configure the emulated NIC:
232	dpavlin	2	<pre>
233			# <b>ifconfig le0 10.0.0.1</b>
234			# <b>route add default 10.0.0.254</b>
235			add net default: gateway 10.0.0.254
236			</pre>
237
238	dpavlin	6	<p>
239	dpavlin	2	If you want nameserver lookups to work, you need a valid /etc/resolv.conf
240			as well:
241			<pre>
242			# <b>echo nameserver 129.16.1.3 > /etc/resolv.conf</b>
243			</pre>
244	dpavlin	6	(But replace <tt>129.16.1.3</tt> with the actual real-world IP address of
245			your nearest nameserver.)
246
247	dpavlin	2	<p>
248			Now, host lookups should work:
249			<pre>
250			# <b>host -a www.netbsd.org</b>
251			Trying null domain
252			rcode = 0 (Success), ancount=2
253			The following answer is not authoritative:
254			The following answer is not verified as authentic by the server:
255			www.netbsd.org 86400 IN AAAA 2001:4f8:4:7:290:27ff:feab:19a7
256			www.netbsd.org 86400 IN A 204.152.184.116
257			For authoritative answers, see:
258			netbsd.org 83627 IN NS uucp-gw-2.pa.dec.com
259			netbsd.org 83627 IN NS ns.netbsd.org
260			netbsd.org 83627 IN NS adns1.berkeley.edu
261			netbsd.org 83627 IN NS adns2.berkeley.edu
262			netbsd.org 83627 IN NS uucp-gw-1.pa.dec.com
263			Additional information:
264			ns.netbsd.org 83627 IN A 204.152.184.164
265			uucp-gw-1.pa.dec.com 172799 IN A 204.123.2.18
266			uucp-gw-2.pa.dec.com 172799 IN A 204.123.2.19
267			</pre>
268
269	dpavlin	6	<p>
270			At this point, UDP and TCP should (mostly) work.
271	dpavlin	2
272	dpavlin	6	<p>
273			Here is an example of how to configure a server machine and an emulated
274			client machine for sharing files via NFS:
275	dpavlin	2
276	dpavlin	6	<p>
277			(This is very useful if you want to share entire directory trees
278			between the emulated environment and another machine. These instruction
279			will work for FreeBSD, if you are running something else, use your
280			imagination to modify them.)
281	dpavlin	2
282			<p>
283			<ul>
284			<li>On the server, add a line to your /etc/exports file, exporting
285			the files you wish to use in the emulator:<pre>
286			<b>/tftpboot -mapall=nobody -ro 123.11.22.33</b>
287			</pre>
288			where 123.11.22.33 is the IP address of the machine running the
289			emulator process, as seen from the outside world.
290			<p>
291			<li>Then start up the programs needed to serve NFS via UDP. Note the
292			-n argument to mountd. This is needed to tell mountd to accept
293			connections from unprivileged ports (because the emulator does
294			not need to run as root).<pre>
295			# <b>portmap</b>
296			# <b>nfsd -u</b> <--- u for UDP
297			# <b>mountd -n</b>
298			</pre>
299			<li>In the guest OS in the emulator, once you have ethernet and IPv4
300			configured so that you can use UDP, mounting the filesystem
301			should now be possible: (this example is for NetBSD/pmax
302			or OpenBSD/pmax)<pre>
303			# <b>mount -o ro,-r=1024,-w=1024,-U,-3 my.server.com:/tftpboot /mnt</b>
304			or
305			# <b>mount my.server.com:/tftpboot /mnt</b>
306			</pre>
307			If you don't supply the read and write sizes, there is a risk
308			that the default values are too large. The emulator currently
309			does not handle fragmentation/defragmentation of <i>outgoing</i>
310			packets, so going above the ethernet frame size (1518) is a very
311			bad idea. Incoming packets (reading from nfs) should work, though,
312			for example during an NFS install.
313			</ul>
314
315			The example above uses read-only mounts. That is enough for things like
316			letting NetBSD/pmax or OpenBSD/pmax install via NFS, without the need for
317			a CDROM ISO image. You can use a read-write mount if you wish to share
318			files in both directions, but then you should be aware of the
319			fragmentation issue mentioned above.
320
321	dpavlin	10	<p>TODO: Write a section on how to connect multiple emulator instances.
322			(Using the <tt>local_port</tt> and <tt>add_remote</tt> configuration file
323			commands.)
324	dpavlin	2
325
326
327
328	dpavlin	10
329
330	dpavlin	2	<p><br>
331			<a name="devices"></a>
332			<h3>Emulation of hardware devices</h3>
333
334	dpavlin	12	Each file in the <tt>src/device/</tt> directory is responsible for one
335	dpavlin	10	hardware device. These are used from <tt>src/machine.c</tt>, when
336			initializing which hardware a particular machine model will be using, or
337			when adding devices to a machine using the <tt>device()</tt> command in
338			configuration files.
339	dpavlin	2
340	dpavlin	10	<p><font color="#ff0000">NOTE: The device registry subsystem is currently
341			in a state of flux, as it is being redesigned.</font>
342	dpavlin	2
343	dpavlin	10	<p>(I'll be using the name "<tt>foo</tt>" as the name of the device in all
344			these examples. This is pseudo code, it might need some modification to
345	dpavlin	2	actually compile and run.)
346
347	dpavlin	10	<p>Each device should have the following:
348	dpavlin	2
349			<p>
350			<ul>
351	dpavlin	10	<li>A <tt>devinit</tt> function in <tt>src/devices/dev_foo.c</tt>. It
352			would typically look something like this:
353	dpavlin	2	<pre>
354			/*
355			* devinit_foo():
356			*/
357			int devinit_foo(struct devinit *devinit)
358			{
359			struct foo_data *d = malloc(sizeof(struct foo_data));
360
361			if (d == NULL) {
362			fprintf(stderr, "out of memory\n");
363			exit(1);
364			}
365			memset(d, 0, sizeof(struct foon_data));
366
367			/*
368			* Set up stuff here, for example fill d with useful
369			* data. devinit contains settings like address, irq_nr,
370			* and other things.
371			*
372			* ...
373			*/
374
375			memory_device_register(devinit->machine->memory, devinit->name,
376			devinit->addr, DEV_FOO_LENGTH,
377			dev_foo_access, (void *)d, MEM_DEFAULT, NULL);
378
379			/* This should only be here if the device
380			has a tick function: */
381			machine_add_tickfunction(machine, dev_foo_tick, d,
382			FOO_TICKSHIFT);
383
384			/* Return 1 if the device was successfully added. */
385			return 1;
386			}
387			</pre><br>
388
389	dpavlin	10	<li>At the top of <tt>dev_foo.c</tt>, the <tt>foo_data</tt> struct
390			should be defined.
391	dpavlin	2	<pre>
392			struct foo_data {
393			int irq_nr;
394			/* ... */
395			}
396			</pre><br>
397
398	dpavlin	10	<li>If <tt>foo</tt> has a tick function (that is, something that needs to be
399			run at regular intervals) then <tt>FOO_TICKSHIFT</tt> and a tick
400			function need to be defined as well:
401	dpavlin	2	<pre>
402			#define FOO_TICKSHIFT 10
403
404			void dev_foo_tick(struct cpu cpu, void extra)
405			{
406			struct foo_data d = (struct foo_data ) extra;
407
408			if (.....)
409			cpu_interrupt(cpu, d->irq_nr);
410			else
411			cpu_interrupt_ack(cpu, d->irq_nr);
412			}
413			</pre><br>
414
415			<li>And last but not least, the device should have an access function.
416			The access function is called whenever there is a load or store
417			to an address which is in the device' memory mapped region.
418			<pre>
419			int dev_foo_access(struct cpu cpu, struct memory mem,
420			uint64_t relative_addr, unsigned char *data, size_t len,
421			int writeflag, void *extra)
422			{
423			struct foo_data *d = extra;
424			uint64_t idata = 0, odata = 0;
425
426			idata = memory_readmax64(cpu, data, len);
427			switch (relative_addr) {
428			/* .... */
429			}
430
431			if (writeflag == MEM_READ)
432			memory_writemax64(cpu, data, len, odata);
433
434			/* Perhaps interrupts need to be asserted or
435			deasserted: */
436			dev_foo_tick(cpu, extra);
437
438			/* Return successfully. */
439			return 1;
440			}
441			</pre><br>
442			</ul>
443
444			<p>
445	dpavlin	6	The return value of the access function has until 2004-07-02 been a
446	dpavlin	2	true/false value; 1 for success, or 0 for device access failure. A device
447			access failure (on MIPS) will result in a DBE exception.
448
449			<p>
450			Some devices are converted to support arbitrary memory latency
451			values. The return value is the number of cycles that the read or
452			write access took. A value of 1 means one cycle, a value of 10 means 10
453			cycles. Negative values are used for device access failures, and the
454			absolute value of the value is then the number of cycles; a value of -5
455			means that the access failed, and took 5 cycles.
456
457			<p>
458			To be compatible with pre-20040702 devices, a return value of 0 is treated
459	dpavlin	6	by the caller (in <tt>src/memory_rw.c</tt>) as a value of -1.
460	dpavlin	2
461
462
463
464
465
466			</body>
467			</html>