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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 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out of date.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><br>
<a name="devices"></a>
<h3>Emulation of hardware devices</h3>

Each file called <tt>dev_*.c</tt> in the <tt>src/device/</tt> directory is
responsible for one hardware device. These are used from
<tt>src/machines/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>(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 = malloc(sizeof(struct foo_data));

                if (d == NULL) {
                        fprintf(stderr, "out of memory\n");
                        exit(1);
                }
                memset(d, 0, sizeof(struct foo_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, 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 {
                int     irq_nr;
                /*  ...  */
        }
</pre><br>
        (There is an exception to this rule; ugly hacks which allow
        code in <tt>src/machine.c</tt> to use some structures makes it
        necessary to place the <tt>struct foo_data</tt> in
        <tt>src/include/devices.h</tt> instead of in <tt>dev_foo.c</tt>
        itself. This is useful for example for interrupt controllers.)
  <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

        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>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;

                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>
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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	24	$Id: technical.html,v 1.74 2006/06/17 10:16:22 debug Exp $
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15	dpavlin	22	Copyright (C) 2004-2006 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:
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20			1. Redistributions of source code must retain the above copyright
21			notice, this list of conditions and the following disclaimer.
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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	10	<font color="#ff0000">NOTE/TODO: This section is very old and a bit
111			out of date.</font>
112	dpavlin	2
113	dpavlin	10	<p>Running an entire operating system under emulation is very interesting
114			in itself, but for several reasons, running a modern OS without access to
115			TCP/IP networking is a bit akward. Hence, I feel the need to implement
116			TCP/IP (networking) support in the emulator.
117
118	dpavlin	2	<p>
119			As far as I have understood it, there seems to be two different ways to go:
120
121			<ol>
122			<li>Forward ethernet packets from the emulated ethernet controller to
123			the host machine's ethernet controller, and capture incoming
124			packets on the host's controller, giving them back to the
125			emulated OS. Characteristics are:
126			<ul>
127			<li>Requires <i>direct</i> access to the host's NIC, which
128			means on most platforms that the emulator cannot be
129			run as a normal user!
130			<li>Reduced portability, as not every host operating system
131			uses the same programming interface for dealing with
132			hardware ethernet controllers directly.
133			<li>When run on a switched network, it might be problematic to
134			connect from the emulated OS to the OS running on the
135			host, as packets sent out on the host's NIC are not
136			received by itself. (?)
137	dpavlin	6	<li>All specific networking protocols will be handled by the
138			physical network.
139	dpavlin	2	</ul>
140			<p>
141			or
142			<p>
143			<li>Whenever the emulated ethernet controller wishes to send a packet,
144			the emulator looks at the packet and creates a response. Packets
145			that can have an immediate response never go outside the emulator,
146			other packet types have to be converted into suitable other
147			connection types (UDP, TCP, etc). Characteristics:
148			<ul>
149			<li>Each packet type sent out on the emulated NIC must be handled.
150			This means that I have to do a lot of coding.
151			(I like this, because it gives me an opportunity to
152			learn about networking protocols.)
153			<li>By not relying on access to the host's NIC directly,
154			portability is maintained. (It would be sad if the networking
155			portion of a portable emulator isn't as portable as the
156			rest of the emulator.)
157			<li>The emulator can be run as a normal user process, does
158			not require root privilegies.
159			<li>Connecting from the emulated OS to the host's OS should
160			not be problematic.
161			<li>The emulated OS will experience the network just as a single
162			machine behind a NAT gateway/firewall would. The emulated
163			OS is thus automatically protected from the outside world.
164			</ul>
165			</ol>
166
167	dpavlin	6	<p>
168			Some emulators/simulators use the first approach, while others use the
169			second. I think that SIMH and QEMU are examples of emulators using the
170			first and second approach, respectively.
171	dpavlin	2
172			<p>
173			Since I have choosen the second kind of implementation, I have to write
174			support explicitly for any kind of network protocol that should be
175			supported. As of 2004-07-09, the following has been implemented and seems
176			to work under at least NetBSD/pmax and OpenBSD/pmax under DECstation 5000/200
177			emulation (-E dec -e 3max):
178
179			<p>
180			<ul>
181			<li>ARP requests sent out from the emulated NIC are interpreted,
182			and converted to ARP responses. (This is used by the emulated OS
183			to find out the MAC address of the gateway.)
184			<li>ICMP echo requests (that is the kind of packet produced by the
185	dpavlin	6	<b><tt>ping</tt></b> program) are interpreted and converted to ICMP echo
186	dpavlin	2	replies, <i>regardless of the IP address</i>. This means that
187			running ping from within the emulated OS will <i>always</i>
188			receive a response. The ping packets never leave the emulated
189			environment.
190			<li>UDP packets are interpreted and passed along to the outside world.
191			If the emulator receives an UDP packet from the outside world, it
192			is converted into an UDP packet for the emulated OS. (This is not
193			implemented very well yet, but seems to be enough for nameserver
194			lookups, tftp file transfers, and NFS mounts using UDP.)
195			<li>TCP packets are interpreted one at a time, similar to how UDP
196			packets are handled (but more state is kept for each connection).
197			<font color="#ff0000">NOTE: Much of the TCP handling code is very
198			ugly and hardcoded.</font>
199	dpavlin	6	<!--
200	dpavlin	2	<li>RARP is not implemented yet. (I haven't needed it so far.)
201	dpavlin	6	-->
202	dpavlin	2	</ul>
203
204	dpavlin	6	<p>
205	dpavlin	2	The gateway machine, which is the only "other" machine that the emulated
206			OS sees on its emulated network, works as a NAT-style firewall/gateway. It
207	dpavlin	6	usually has a fixed IPv4 address of <tt>10.0.0.254</tt>. An OS running in
208			the emulator would usually have an address of the form <tt>10.x.x.x</tt>;
209			a typical choice would be <tt>10.0.0.1</tt>.
210	dpavlin	2
211			<p>
212	dpavlin	6	Inside emulated NetBSD/pmax or OpenBSD/pmax, running the following
213			commands should configure the emulated NIC:
214	dpavlin	2	<pre>
215			# <b>ifconfig le0 10.0.0.1</b>
216			# <b>route add default 10.0.0.254</b>
217			add net default: gateway 10.0.0.254
218			</pre>
219
220	dpavlin	6	<p>
221	dpavlin	2	If you want nameserver lookups to work, you need a valid /etc/resolv.conf
222			as well:
223			<pre>
224			# <b>echo nameserver 129.16.1.3 > /etc/resolv.conf</b>
225			</pre>
226	dpavlin	6	(But replace <tt>129.16.1.3</tt> with the actual real-world IP address of
227			your nearest nameserver.)
228
229	dpavlin	2	<p>
230			Now, host lookups should work:
231			<pre>
232			# <b>host -a www.netbsd.org</b>
233			Trying null domain
234			rcode = 0 (Success), ancount=2
235			The following answer is not authoritative:
236			The following answer is not verified as authentic by the server:
237			www.netbsd.org 86400 IN AAAA 2001:4f8:4:7:290:27ff:feab:19a7
238			www.netbsd.org 86400 IN A 204.152.184.116
239			For authoritative answers, see:
240			netbsd.org 83627 IN NS uucp-gw-2.pa.dec.com
241			netbsd.org 83627 IN NS ns.netbsd.org
242			netbsd.org 83627 IN NS adns1.berkeley.edu
243			netbsd.org 83627 IN NS adns2.berkeley.edu
244			netbsd.org 83627 IN NS uucp-gw-1.pa.dec.com
245			Additional information:
246			ns.netbsd.org 83627 IN A 204.152.184.164
247			uucp-gw-1.pa.dec.com 172799 IN A 204.123.2.18
248			uucp-gw-2.pa.dec.com 172799 IN A 204.123.2.19
249			</pre>
250
251	dpavlin	6	<p>
252			At this point, UDP and TCP should (mostly) work.
253	dpavlin	2
254	dpavlin	6	<p>
255			Here is an example of how to configure a server machine and an emulated
256			client machine for sharing files via NFS:
257	dpavlin	2
258	dpavlin	6	<p>
259			(This is very useful if you want to share entire directory trees
260			between the emulated environment and another machine. These instruction
261			will work for FreeBSD, if you are running something else, use your
262			imagination to modify them.)
263	dpavlin	2
264			<p>
265			<ul>
266			<li>On the server, add a line to your /etc/exports file, exporting
267			the files you wish to use in the emulator:<pre>
268			<b>/tftpboot -mapall=nobody -ro 123.11.22.33</b>
269			</pre>
270			where 123.11.22.33 is the IP address of the machine running the
271			emulator process, as seen from the outside world.
272			<p>
273			<li>Then start up the programs needed to serve NFS via UDP. Note the
274			-n argument to mountd. This is needed to tell mountd to accept
275			connections from unprivileged ports (because the emulator does
276			not need to run as root).<pre>
277			# <b>portmap</b>
278			# <b>nfsd -u</b> <--- u for UDP
279			# <b>mountd -n</b>
280			</pre>
281			<li>In the guest OS in the emulator, once you have ethernet and IPv4
282			configured so that you can use UDP, mounting the filesystem
283			should now be possible: (this example is for NetBSD/pmax
284			or OpenBSD/pmax)<pre>
285			# <b>mount -o ro,-r=1024,-w=1024,-U,-3 my.server.com:/tftpboot /mnt</b>
286			or
287			# <b>mount my.server.com:/tftpboot /mnt</b>
288			</pre>
289			If you don't supply the read and write sizes, there is a risk
290			that the default values are too large. The emulator currently
291			does not handle fragmentation/defragmentation of <i>outgoing</i>
292			packets, so going above the ethernet frame size (1518) is a very
293			bad idea. Incoming packets (reading from nfs) should work, though,
294			for example during an NFS install.
295			</ul>
296
297			The example above uses read-only mounts. That is enough for things like
298			letting NetBSD/pmax or OpenBSD/pmax install via NFS, without the need for
299			a CDROM ISO image. You can use a read-write mount if you wish to share
300			files in both directions, but then you should be aware of the
301			fragmentation issue mentioned above.
302
303
304
305
306
307	dpavlin	10
308
309	dpavlin	2	<p><br>
310			<a name="devices"></a>
311			<h3>Emulation of hardware devices</h3>
312
313	dpavlin	20	Each file called <tt>dev_*.c</tt> in the <tt>src/device/</tt> directory is
314			responsible for one hardware device. These are used from
315	dpavlin	22	<tt>src/machines/machine_*.c</tt>, when initializing which hardware a particular
316	dpavlin	20	machine model will be using, or when adding devices to a machine using the
317			<tt>device()</tt> command in configuration files.
318	dpavlin	2
319	dpavlin	10	<p>(I'll be using the name "<tt>foo</tt>" as the name of the device in all
320			these examples. This is pseudo code, it might need some modification to
321	dpavlin	2	actually compile and run.)
322
323	dpavlin	10	<p>Each device should have the following:
324	dpavlin	2
325			<p>
326			<ul>
327	dpavlin	10	<li>A <tt>devinit</tt> function in <tt>src/devices/dev_foo.c</tt>. It
328			would typically look something like this:
329	dpavlin	2	<pre>
330	dpavlin	22	DEVINIT(foo)
331	dpavlin	2	{
332			struct foo_data *d = malloc(sizeof(struct foo_data));
333
334			if (d == NULL) {
335			fprintf(stderr, "out of memory\n");
336			exit(1);
337			}
338	dpavlin	22	memset(d, 0, sizeof(struct foo_data));
339	dpavlin	2
340			/*
341			* Set up stuff here, for example fill d with useful
342			* data. devinit contains settings like address, irq_nr,
343			* and other things.
344			*
345			* ...
346			*/
347
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			int irq_nr;
372			/* ... */
373			}
374			</pre><br>
375	dpavlin	20	(There is an exception to this rule; ugly hacks which allow
376			code in <tt>src/machine.c</tt> to use some structures makes it
377			necessary to place the <tt>struct foo_data</tt> in
378			<tt>src/include/devices.h</tt> instead of in <tt>dev_foo.c</tt>
379			itself. This is useful for example for interrupt controllers.)
380			<p>
381	dpavlin	10	<li>If <tt>foo</tt> has a tick function (that is, something that needs to be
382			run at regular intervals) then <tt>FOO_TICKSHIFT</tt> and a tick
383			function need to be defined as well:
384	dpavlin	2	<pre>
385	dpavlin	20	#define FOO_TICKSHIFT 14
386	dpavlin	2
387			void dev_foo_tick(struct cpu cpu, void extra)
388			{
389			struct foo_data d = (struct foo_data ) extra;
390
391			if (.....)
392			cpu_interrupt(cpu, d->irq_nr);
393			else
394			cpu_interrupt_ack(cpu, d->irq_nr);
395			}
396			</pre><br>
397
398	dpavlin	20	<li>Does this device belong to a standard bus?
399			<ul>
400			<li>If this device should be detectable as a PCI device, then
401			glue code should be added to
402			<tt>src/devices/bus_pci.c</tt>.
403			<li>If this is a legacy ISA device which should be usable by
404			any machine which has an ISA bus, then the device should
405			be added to <tt>src/devices/bus_isa.c</tt>.
406			</ul>
407			<p>
408	dpavlin	2	<li>And last but not least, the device should have an access function.
409			The access function is called whenever there is a load or store
410	dpavlin	22	to an address which is in the device' memory mapped region. To
411			simplify things a little, a macro <tt>DEVICE_ACCESS(x)</tt>
412			is expanded into<pre>
413			int dev_x_access(struct cpu cpu, struct memory mem,
414	dpavlin	2	uint64_t relative_addr, unsigned char *data, size_t len,
415			int writeflag, void *extra)
416	dpavlin	22	</pre> The access function can look like this:
417			<pre>
418			DEVICE_ACCESS(foo)
419	dpavlin	2	{
420			struct foo_data *d = extra;
421			uint64_t idata = 0, odata = 0;
422
423			idata = memory_readmax64(cpu, data, len);
424			switch (relative_addr) {
425			/* .... */
426			}
427
428			if (writeflag == MEM_READ)
429			memory_writemax64(cpu, data, len, odata);
430
431			/* Perhaps interrupts need to be asserted or
432			deasserted: */
433			dev_foo_tick(cpu, extra);
434
435			/* Return successfully. */
436			return 1;
437			}
438			</pre><br>
439			</ul>
440
441			<p>
442	dpavlin	6	The return value of the access function has until 2004-07-02 been a
443	dpavlin	2	true/false value; 1 for success, or 0 for device access failure. A device
444			access failure (on MIPS) will result in a DBE exception.
445
446			<p>
447			Some devices are converted to support arbitrary memory latency
448			values. The return value is the number of cycles that the read or
449			write access took. A value of 1 means one cycle, a value of 10 means 10
450			cycles. Negative values are used for device access failures, and the
451			absolute value of the value is then the number of cycles; a value of -5
452			means that the access failed, and took 5 cycles.
453
454			<p>
455			To be compatible with pre-20040702 devices, a return value of 0 is treated
456	dpavlin	6	by the caller (in <tt>src/memory_rw.c</tt>) as a value of -1.
457	dpavlin	2
458
459
460
461
462
463			</body>
464			</html>