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<b>Gavare's eXperimental Emulator:</b></font><br>
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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, target architecture, host clock speed, which compiler
and compiler flags were used to build the emulator, what the workload is,
what additional runtime flags are given to the emulator, and so on.

<p>Devices are generally not timing-accurate: 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, e.g.:

<ul>
  <li>"How long does it take to install NetBSD onto a disk image?"
  <li>"How long does it take to compile XYZ inside NetBSD
        in the emulator?".
</ul>

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


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

<font color="#ff0000">NOTE/TODO: This section is very old.</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><br>
<a name="devices"></a>
<h3>Emulation of hardware devices</h3>

Each file called <tt>dev_*.c</tt> in the 
<a href="../src/devices/"><tt>src/devices/</tt></a> directory is
responsible for one hardware device. These are used from
<a href="../src/machines/"><tt>src/machines</tt></a><tt>/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
<a href="configfiles.html">configuration files</a>.

<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)
        {
                struct foo_data *d;

                CHECK_ALLOCATION(d = malloc(sizeof(struct foo_data)));
                memset(d, 0, sizeof(struct foo_data));

                /*
                 *  Set up stuff here, for example fill d with useful
                 *  data. devinit contains settings like address, irq path,
                 *  and other things.
                 *
                 *  ...
                 */

                INTERRUPT_CONNECT(devinit->interrupt_path, d->irq);
        
                memory_device_register(devinit->machine->memory, devinit->name,
                    devinit->addr, DEV_FOO_LENGTH,
                    dev_foo_access, (void *)d, DM_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>

        <p><tt>DEVINIT(foo)</tt> is defined as <tt>int devinit_foo(struct devinit *devinit)</tt>,
        and the <tt>devinit</tt> argument contains everything that the device driver's
        initialization function needs.

  <p>
  <li>At the top of <tt>dev_foo.c</tt>, the <tt>foo_data</tt> struct
        should be defined.
<pre>
        struct foo_data {
                struct interrupt        irq;
                /*  ...  */
        }
</pre><br>
        (There is an exception to this rule; some legacy code and other
        ugly hacks have their device structs defined in
        <tt>src/include/devices.h</tt> instead of <tt>dev_foo.c</tt>.
        New code should not add stuff to <tt>devices.h</tt>.)
  <p>
  <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           14

        DEVICE_TICK(foo)
        {
                struct foo_data *d = extra;

                if (.....)
                        INTERRUPT_ASSERT(d->irq);
                else
                        INTERRUPT_DEASSERT(d->irq);
        }
</pre><br>

  <li>Does this device belong to a standard bus?
        <ul>
          <li>If this device should be detectable as a PCI device, then
                glue code should be added to
                <tt>src/devices/bus_pci.c</tt>.
          <li>If this is a legacy ISA device which should be usable by
                any machine which has an ISA bus, then the device should
                be added to <tt>src/devices/bus_isa.c</tt>.
        </ul>
  <p>
  <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. To
        simplify things a little, a macro <tt>DEVICE_ACCESS(x)</tt>
        is expanded into<pre>
        int dev_x_access(struct cpu *cpu, struct memory *mem,
            uint64_t relative_addr, unsigned char *data, size_t len,
            int writeflag, void *extra)
</pre>  The access function can look like this:
<pre>
        DEVICE_ACCESS(foo)
        {
                struct foo_data *d = extra;
                uint64_t idata = 0, odata = 0;

                if (writeflag == MEM_WRITE)
                        idata = memory_readmax64(cpu, data, len);

                switch (relative_addr) {

                /*  Handle accesses to individual addresses within
                    the device here.  */

                /*  ...  */

                }

                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>
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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>Technical details</b>
9			</font></td></tr></table></td></tr></table><p>
10	dpavlin	2
11			<!--
12
13	dpavlin	42	$Id: technical.html,v 1.76 2007/06/15 18:07:08 debug Exp $
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15	dpavlin	34	Copyright (C) 2004-2007 Anders Gavare. All rights reserved.
16	dpavlin	2
17			Redistribution and use in source and binary forms, with or without
18			modification, are permitted provided that the following conditions are met:
19
20			1. Redistributions of source code must retain the above copyright
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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
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33			DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
34			OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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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	dpavlin	24	host architecture, target architecture, host clock speed, which compiler
74			and compiler flags were used to build the emulator, what the workload is,
75			what additional runtime flags are given to the emulator, and so on.
76	dpavlin	2
77	dpavlin	24	<p>Devices are generally not timing-accurate: for example, if an emulated
78			operating system tries to read a block from disk, from its point of view
79			the read was instantaneous (no waiting). So 1 MIPS in an emulated OS might
80			have taken more than one million instructions on a real machine.
81
82	dpavlin	10	<p>Also, if the emulator says it has executed 1 million instructions, and
83			the CPU family in question was capable of scalar execution (i.e. one cycle
84			per instruction), it might still have taken more than 1 million cycles on
85			a real machine because of cache misses and similar micro-architectural
86			penalties that are not simulated by GXemul.
87	dpavlin	2
88	dpavlin	10	<p>Because of these issues, it is in my opinion best to measure
89			performance as the actual (real-world) time it takes to perform a task
90	dpavlin	24	with the emulator, e.g.:
91	dpavlin	2
92	dpavlin	24	<ul>
93			<li>"How long does it take to install NetBSD onto a disk image?"
94			<li>"How long does it take to compile XYZ inside NetBSD
95			in the emulator?".
96			</ul>
97
98	dpavlin	14	<p>So, how fast is it? :-)   Answer: it varies.
99
100	dpavlin	2
101
102
103
104
105
106			<p><br>
107			<a name="net"></a>
108			<h3>Networking</h3>
109
110	dpavlin	42	<font color="#ff0000">NOTE/TODO: This section is very old.</font>
111	dpavlin	2
112	dpavlin	10	<p>Running an entire operating system under emulation is very interesting
113			in itself, but for several reasons, running a modern OS without access to
114			TCP/IP networking is a bit akward. Hence, I feel the need to implement
115			TCP/IP (networking) support in the emulator.
116
117	dpavlin	2	<p>
118			As far as I have understood it, there seems to be two different ways to go:
119
120			<ol>
121			<li>Forward ethernet packets from the emulated ethernet controller to
122			the host machine's ethernet controller, and capture incoming
123			packets on the host's controller, giving them back to the
124			emulated OS. Characteristics are:
125			<ul>
126			<li>Requires <i>direct</i> access to the host's NIC, which
127			means on most platforms that the emulator cannot be
128			run as a normal user!
129			<li>Reduced portability, as not every host operating system
130			uses the same programming interface for dealing with
131			hardware ethernet controllers directly.
132			<li>When run on a switched network, it might be problematic to
133			connect from the emulated OS to the OS running on the
134			host, as packets sent out on the host's NIC are not
135			received by itself. (?)
136	dpavlin	6	<li>All specific networking protocols will be handled by the
137			physical network.
138	dpavlin	2	</ul>
139			<p>
140			or
141			<p>
142			<li>Whenever the emulated ethernet controller wishes to send a packet,
143			the emulator looks at the packet and creates a response. Packets
144			that can have an immediate response never go outside the emulator,
145			other packet types have to be converted into suitable other
146			connection types (UDP, TCP, etc). Characteristics:
147			<ul>
148			<li>Each packet type sent out on the emulated NIC must be handled.
149			This means that I have to do a lot of coding.
150			(I like this, because it gives me an opportunity to
151			learn about networking protocols.)
152			<li>By not relying on access to the host's NIC directly,
153			portability is maintained. (It would be sad if the networking
154			portion of a portable emulator isn't as portable as the
155			rest of the emulator.)
156			<li>The emulator can be run as a normal user process, does
157			not require root privilegies.
158			<li>Connecting from the emulated OS to the host's OS should
159			not be problematic.
160			<li>The emulated OS will experience the network just as a single
161			machine behind a NAT gateway/firewall would. The emulated
162			OS is thus automatically protected from the outside world.
163			</ul>
164			</ol>
165
166	dpavlin	6	<p>
167			Some emulators/simulators use the first approach, while others use the
168			second. I think that SIMH and QEMU are examples of emulators using the
169			first and second approach, respectively.
170	dpavlin	2
171			<p>
172			Since I have choosen the second kind of implementation, I have to write
173			support explicitly for any kind of network protocol that should be
174			supported. As of 2004-07-09, the following has been implemented and seems
175			to work under at least NetBSD/pmax and OpenBSD/pmax under DECstation 5000/200
176			emulation (-E dec -e 3max):
177
178			<p>
179			<ul>
180			<li>ARP requests sent out from the emulated NIC are interpreted,
181			and converted to ARP responses. (This is used by the emulated OS
182			to find out the MAC address of the gateway.)
183			<li>ICMP echo requests (that is the kind of packet produced by the
184	dpavlin	6	<b><tt>ping</tt></b> program) are interpreted and converted to ICMP echo
185	dpavlin	2	replies, <i>regardless of the IP address</i>. This means that
186			running ping from within the emulated OS will <i>always</i>
187			receive a response. The ping packets never leave the emulated
188			environment.
189			<li>UDP packets are interpreted and passed along to the outside world.
190			If the emulator receives an UDP packet from the outside world, it
191			is converted into an UDP packet for the emulated OS. (This is not
192			implemented very well yet, but seems to be enough for nameserver
193			lookups, tftp file transfers, and NFS mounts using UDP.)
194			<li>TCP packets are interpreted one at a time, similar to how UDP
195			packets are handled (but more state is kept for each connection).
196			<font color="#ff0000">NOTE: Much of the TCP handling code is very
197			ugly and hardcoded.</font>
198	dpavlin	6	<!--
199	dpavlin	2	<li>RARP is not implemented yet. (I haven't needed it so far.)
200	dpavlin	6	-->
201	dpavlin	2	</ul>
202
203	dpavlin	6	<p>
204	dpavlin	2	The gateway machine, which is the only "other" machine that the emulated
205			OS sees on its emulated network, works as a NAT-style firewall/gateway. It
206	dpavlin	6	usually has a fixed IPv4 address of <tt>10.0.0.254</tt>. An OS running in
207			the emulator would usually have an address of the form <tt>10.x.x.x</tt>;
208			a typical choice would be <tt>10.0.0.1</tt>.
209	dpavlin	2
210			<p>
211	dpavlin	6	Inside emulated NetBSD/pmax or OpenBSD/pmax, running the following
212			commands should configure the emulated NIC:
213	dpavlin	2	<pre>
214			# <b>ifconfig le0 10.0.0.1</b>
215			# <b>route add default 10.0.0.254</b>
216			add net default: gateway 10.0.0.254
217			</pre>
218
219	dpavlin	6	<p>
220	dpavlin	2	If you want nameserver lookups to work, you need a valid /etc/resolv.conf
221			as well:
222			<pre>
223			# <b>echo nameserver 129.16.1.3 > /etc/resolv.conf</b>
224			</pre>
225	dpavlin	6	(But replace <tt>129.16.1.3</tt> with the actual real-world IP address of
226			your nearest nameserver.)
227
228	dpavlin	2	<p>
229			Now, host lookups should work:
230			<pre>
231			# <b>host -a www.netbsd.org</b>
232			Trying null domain
233			rcode = 0 (Success), ancount=2
234			The following answer is not authoritative:
235			The following answer is not verified as authentic by the server:
236			www.netbsd.org 86400 IN AAAA 2001:4f8:4:7:290:27ff:feab:19a7
237			www.netbsd.org 86400 IN A 204.152.184.116
238			For authoritative answers, see:
239			netbsd.org 83627 IN NS uucp-gw-2.pa.dec.com
240			netbsd.org 83627 IN NS ns.netbsd.org
241			netbsd.org 83627 IN NS adns1.berkeley.edu
242			netbsd.org 83627 IN NS adns2.berkeley.edu
243			netbsd.org 83627 IN NS uucp-gw-1.pa.dec.com
244			Additional information:
245			ns.netbsd.org 83627 IN A 204.152.184.164
246			uucp-gw-1.pa.dec.com 172799 IN A 204.123.2.18
247			uucp-gw-2.pa.dec.com 172799 IN A 204.123.2.19
248			</pre>
249
250	dpavlin	6	<p>
251			At this point, UDP and TCP should (mostly) work.
252	dpavlin	2
253	dpavlin	6	<p>
254			Here is an example of how to configure a server machine and an emulated
255			client machine for sharing files via NFS:
256	dpavlin	2
257	dpavlin	6	<p>
258			(This is very useful if you want to share entire directory trees
259			between the emulated environment and another machine. These instruction
260			will work for FreeBSD, if you are running something else, use your
261			imagination to modify them.)
262	dpavlin	2
263			<p>
264			<ul>
265			<li>On the server, add a line to your /etc/exports file, exporting
266			the files you wish to use in the emulator:<pre>
267			<b>/tftpboot -mapall=nobody -ro 123.11.22.33</b>
268			</pre>
269			where 123.11.22.33 is the IP address of the machine running the
270			emulator process, as seen from the outside world.
271			<p>
272			<li>Then start up the programs needed to serve NFS via UDP. Note the
273			-n argument to mountd. This is needed to tell mountd to accept
274			connections from unprivileged ports (because the emulator does
275			not need to run as root).<pre>
276			# <b>portmap</b>
277			# <b>nfsd -u</b> <--- u for UDP
278			# <b>mountd -n</b>
279			</pre>
280			<li>In the guest OS in the emulator, once you have ethernet and IPv4
281			configured so that you can use UDP, mounting the filesystem
282			should now be possible: (this example is for NetBSD/pmax
283			or OpenBSD/pmax)<pre>
284			# <b>mount -o ro,-r=1024,-w=1024,-U,-3 my.server.com:/tftpboot /mnt</b>
285			or
286			# <b>mount my.server.com:/tftpboot /mnt</b>
287			</pre>
288			If you don't supply the read and write sizes, there is a risk
289			that the default values are too large. The emulator currently
290			does not handle fragmentation/defragmentation of <i>outgoing</i>
291			packets, so going above the ethernet frame size (1518) is a very
292			bad idea. Incoming packets (reading from nfs) should work, though,
293			for example during an NFS install.
294			</ul>
295
296			The example above uses read-only mounts. That is enough for things like
297			letting NetBSD/pmax or OpenBSD/pmax install via NFS, without the need for
298			a CDROM ISO image. You can use a read-write mount if you wish to share
299			files in both directions, but then you should be aware of the
300			fragmentation issue mentioned above.
301
302
303
304
305
306	dpavlin	10
307
308	dpavlin	2	<p><br>
309			<a name="devices"></a>
310			<h3>Emulation of hardware devices</h3>
311
312	dpavlin	42	Each file called <tt>dev_*.c</tt> in the
313			<a href="../src/devices/"><tt>src/devices/</tt></a> directory is
314	dpavlin	20	responsible for one hardware device. These are used from
315	dpavlin	42	<a href="../src/machines/"><tt>src/machines</tt></a><tt>/machine_*.c</tt>,
316			when initializing which hardware a particular machine model will be using,
317			or when adding devices to a machine using the <tt>device()</tt> command in
318			<a href="configfiles.html">configuration files</a>.
319	dpavlin	2
320	dpavlin	10	<p>(I'll be using the name "<tt>foo</tt>" as the name of the device in all
321			these examples. This is pseudo code, it might need some modification to
322	dpavlin	2	actually compile and run.)
323
324	dpavlin	10	<p>Each device should have the following:
325	dpavlin	2
326			<p>
327			<ul>
328	dpavlin	10	<li>A <tt>devinit</tt> function in <tt>src/devices/dev_foo.c</tt>. It
329			would typically look something like this:
330	dpavlin	2	<pre>
331	dpavlin	22	DEVINIT(foo)
332	dpavlin	2	{
333	dpavlin	42	struct foo_data *d;
334	dpavlin	2
335	dpavlin	42	CHECK_ALLOCATION(d = malloc(sizeof(struct foo_data)));
336	dpavlin	22	memset(d, 0, sizeof(struct foo_data));
337	dpavlin	2
338			/*
339			* Set up stuff here, for example fill d with useful
340	dpavlin	42	* data. devinit contains settings like address, irq path,
341	dpavlin	2	* and other things.
342			*
343			* ...
344			*/
345	dpavlin	42
346			INTERRUPT_CONNECT(devinit->interrupt_path, d->irq);
347	dpavlin	2
348			memory_device_register(devinit->machine->memory, devinit->name,
349			devinit->addr, DEV_FOO_LENGTH,
350	dpavlin	20	dev_foo_access, (void *)d, DM_DEFAULT, NULL);
351	dpavlin	2
352			/* This should only be here if the device
353			has a tick function: */
354			machine_add_tickfunction(machine, dev_foo_tick, d,
355			FOO_TICKSHIFT);
356
357			/* Return 1 if the device was successfully added. */
358			return 1;
359			}
360			</pre><br>
361
362	dpavlin	22	<p><tt>DEVINIT(foo)</tt> is defined as <tt>int devinit_foo(struct devinit *devinit)</tt>,
363			and the <tt>devinit</tt> argument contains everything that the device driver's
364			initialization function needs.
365
366			<p>
367	dpavlin	10	<li>At the top of <tt>dev_foo.c</tt>, the <tt>foo_data</tt> struct
368			should be defined.
369	dpavlin	2	<pre>
370			struct foo_data {
371	dpavlin	42	struct interrupt irq;
372	dpavlin	2	/* ... */
373			}
374			</pre><br>
375	dpavlin	42	(There is an exception to this rule; some legacy code and other
376			ugly hacks have their device structs defined in
377			<tt>src/include/devices.h</tt> instead of <tt>dev_foo.c</tt>.
378			New code should not add stuff to <tt>devices.h</tt>.)
379	dpavlin	20	<p>
380	dpavlin	10	<li>If <tt>foo</tt> has a tick function (that is, something that needs to be
381			run at regular intervals) then <tt>FOO_TICKSHIFT</tt> and a tick
382			function need to be defined as well:
383	dpavlin	2	<pre>
384	dpavlin	20	#define FOO_TICKSHIFT 14
385	dpavlin	2
386	dpavlin	42	DEVICE_TICK(foo)
387	dpavlin	2	{
388	dpavlin	42	struct foo_data *d = extra;
389	dpavlin	2
390			if (.....)
391	dpavlin	42	INTERRUPT_ASSERT(d->irq);
392	dpavlin	2	else
393	dpavlin	42	INTERRUPT_DEASSERT(d->irq);
394	dpavlin	2	}
395			</pre><br>
396
397	dpavlin	20	<li>Does this device belong to a standard bus?
398			<ul>
399			<li>If this device should be detectable as a PCI device, then
400			glue code should be added to
401			<tt>src/devices/bus_pci.c</tt>.
402			<li>If this is a legacy ISA device which should be usable by
403			any machine which has an ISA bus, then the device should
404			be added to <tt>src/devices/bus_isa.c</tt>.
405			</ul>
406			<p>
407	dpavlin	2	<li>And last but not least, the device should have an access function.
408			The access function is called whenever there is a load or store
409	dpavlin	22	to an address which is in the device' memory mapped region. To
410			simplify things a little, a macro <tt>DEVICE_ACCESS(x)</tt>
411			is expanded into<pre>
412			int dev_x_access(struct cpu cpu, struct memory mem,
413	dpavlin	2	uint64_t relative_addr, unsigned char *data, size_t len,
414			int writeflag, void *extra)
415	dpavlin	22	</pre> The access function can look like this:
416			<pre>
417			DEVICE_ACCESS(foo)
418	dpavlin	2	{
419			struct foo_data *d = extra;
420			uint64_t idata = 0, odata = 0;
421
422	dpavlin	42	if (writeflag == MEM_WRITE)
423			idata = memory_readmax64(cpu, data, len);
424
425	dpavlin	2	switch (relative_addr) {
426	dpavlin	42
427			/* Handle accesses to individual addresses within
428			the device here. */
429
430			/* ... */
431
432	dpavlin	2	}
433
434			if (writeflag == MEM_READ)
435			memory_writemax64(cpu, data, len, odata);
436
437			/* Perhaps interrupts need to be asserted or
438			deasserted: */
439			dev_foo_tick(cpu, extra);
440
441			/* Return successfully. */
442			return 1;
443			}
444			</pre><br>
445			</ul>
446
447			<p>
448	dpavlin	6	The return value of the access function has until 2004-07-02 been a
449	dpavlin	2	true/false value; 1 for success, or 0 for device access failure. A device
450			access failure (on MIPS) will result in a DBE exception.
451
452			<p>
453			Some devices are converted to support arbitrary memory latency
454			values. The return value is the number of cycles that the read or
455			write access took. A value of 1 means one cycle, a value of 10 means 10
456			cycles. Negative values are used for device access failures, and the
457			absolute value of the value is then the number of cycles; a value of -5
458			means that the access failed, and took 5 cycles.
459
460			<p>
461			To be compatible with pre-20040702 devices, a return value of 0 is treated
462	dpavlin	6	by the caller (in <tt>src/memory_rw.c</tt>) as a value of -1.
463	dpavlin	2
464
465
466
467
468
469			</body>
470			</html>