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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>GXemul: Experimenting with GXemul</title>
<meta name="robots" content="noarchive,nofollow,noindex">
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<body style="font-family : sans-serif;">
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<h1>GXemul: Experimenting with GXemul</h1>
<p>
<a href="./">Back to the index.</a>
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<p><br>
<ul>
<li><a href="#hello">Hello world</a>
<li><a href="#testmachines">Test machines</a>
<li><a href="#expdevices">Experimental devices</a>
</ul>
<p><br>
<a name="hello"></a>
<h3>Hello world:</h3>
<p>You might want to use the emulator to develop programs on your own,
not just run already existing operating system kernels such as NetBSD.
To get started, I recommend that you do two things:
<p>
<ul>
<li>Build and install a cross-compiler for your chosen target,
e.g. <tt>mips64-unknown-elf</tt>.
<a href="http://gcc.gnu.org/">GCC</a> is usually a good compiler
choice, because it is portable and in wide-spread use.
(Other compilers should work too.)
<p>
<li>Compile the Hello World demo program for your chosen target, and run
it in the emulator.
</ul>
<p>The Hello World demo program is included in the GXemul source
code distribution, in the <a href="../demos/hello/"><tt>demos/hello/</tt></a>
subdirectory. The README files in the demo directories have several
examples of how the demo programs can be built.
<p>Once you have compiled the Hello World program into a binary,
<tt>hello_mips</tt>, start it like this:
<pre>
<b>gxemul -E testmips hello_mips</b>
</pre>
<p>Then you can experiment using the commands further up on this page.
<p>If you start the emulator in the paused state, or if you press CTRL-C
during normal execution, you will end up with a <tt><b>GXemul></b></tt>
prompt.
<p>Hopefully this is enough to get you inspired. :-)
<p><br>
<a name="testmachines"></a>
<h3>Test machines:</h3>
<p>The emulator has several modes where it doesn't emulate any real machine.
It can either run in "bare" mode, where no devices are included by default
(just the CPU), or in a "test" mode where some simple devices are
emulated. This can be used when developing e.g. operating systems, as a complement
to targeting real machines.
<p>The name of the test machine modes are <tt>testmips</tt>, <tt>testarm</tt>, etc.
Run <tt>gxemul -H</tt> for an up-to-date list.
<p>Here are some examples of guest OSes that use or (have used) the test machine modes:
<p>
<ul>
<li><p><a name="helenos">HelenOS:</a>
<br>Old versions of <a href="http://www.helenos.org/">HelenOS</a> can run in GXemul's
<tt>testarm</tt> and <tt>testmips</tt> machine modes.<pre>
<b>ftp <a href="http://www.helenos.org/releases/HelenOS-0.5.0-arm32-GXemul.boot">http://www.helenos.org/releases/HelenOS-0.5.0-arm32-GXemul.boot</a></b>
<b>gxemul -X -E testarm HelenOS-0.5.0-arm32-GXemul.boot</b>
<b>ftp <a href="http://www.helenos.org/releases/HelenOS-0.5.0-mips32-GXemul.boot">http://www.helenos.org/releases/HelenOS-0.5.0-mips32-GXemul.boot</a></b>
<b>gxemul -X -E testmips HelenOS-0.5.0-mips32-GXemul.boot</b></pre>
<p>
<li>FreeBSD/MIPS:
<br>For a while, testmips was <a href="http://web.archive.org/web/20180218123520/https://wiki.freebsd.org/FreeBSD/MipsEmulation">one of
the targets when developing the MIPS port of FreeBSD</a>.
See <a href="https://svnweb.freebsd.org/base?view=revision&revision=234920">revision 234920</a>
for more details. (The target was removed
<a href="https://reviews.freebsd.org/rS342256">in December
2018</a>; focus from now on is on the Malta board.)
<p>
<li><a name="glattmumk">Glatt MU/MK:</a>
<br>One of <a href="https://github.com/caladri/glatt">Glatt MU/MK</a>'s targets is <tt>testmips</tt>.
<p>
<li>MINIX 3.x:
<br><a href="http://yana.jp/20160811/computer/minix.ja.euc.html">http://yana.jp/20160811/computer/minix.ja.euc.html</a> indicates that an attempt was made
to port MINIX 3.x to testarm and testmips.
<p>
<li><a name="ycx5">YCX5:</a>
<br>One of <a href="http://gavare.se/ycx5/">YCX5</a>'s primary development targets is <tt>testmips</tt>.
</ul>
<p><br>
<a name="expdevices"></a>
<h3>Experimental devices:</h3>
<p>The test machines (<tt>testmips</tt>, <tt>testarm</tt>, etc) have the
following experimental devices:
<p>
<center><table border="0" width="80%">
<tr>
<td align="left" valign="top" width="200">
<a name="expdevices_ram"><b><tt>ram</tt>:</b></a>
<p>The first 256 MB of RAM.
<br>Physical address:  <font color="#0000f0">0x00000000</font>
</td>
<td align="left" valign="top" width="25"> </td>
<td align="left" valign="top">
<table border="0">
<tr>
<td align="left" valign="top"><i><u>Comment:</u></i></td>
</tr>
<tr>
<td align="left" valign="top"></td>
</tr>
</table>
</td>
</tr>
<tr height="15">
<td height="15"> </td>
</tr>
<tr>
<td align="left" valign="top" width="200">
<a name="expdevices_cons"><b><tt>cons</tt>:</b></a>
<p>A simple console device, for writing
characters to the controlling terminal
and receiving keypresses.
<p>Source code: <font color="#0000f0"><tt>src/devices/dev_cons.c</tt></font>
<p>Include file: <font color="#0000f0"><tt>dev_cons.h</tt></font>
<br>Physical address:  <font color="#0000f0">0x10000000</font>
</td>
<td align="left" valign="top" width="25"> </td>
<td align="left" valign="top">
<table border="0">
<tr>
<td align="left" valign="top"><i><u>Offset:</u></i> </td>
<td align="left" valign="top"><i><u>Effect:</u></i></td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x00</tt></td>
<td align="left" valign="top">
Read: <b><tt>getchar()</tt></b> (non-blocking; returns
<tt>0</tt> if no char was available)<br>
Write: <b><tt>putchar(ch)</tt></b></td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x10</tt></td>
<td align="left" valign="top">Read or write: <b><tt>halt()</tt></b><br>
(Useful for exiting the emulator.)</td>
</tr>
</table>
</td>
</tr>
<tr height="15">
<td height="15"> </td>
</tr>
<tr>
<td align="left" valign="top">
<a name="expdevices_mp"><b><tt>mp</tt>:</b></a>
<p>This device controls the behaviour of CPUs in an emulated
multi-processor system.
<p>Source code: <font color="#0000f0"><tt>src/devices/dev_mp.c</tt></font>
<p>Include file: <font color="#0000f0"><tt>dev_mp.h</tt></font>
<br>Physical address:  <font color="#0000f0">0x11000000</font>
</td>
<td></td>
<td align="left" valign="top">
<table border="0">
<tr>
<td align="left" valign="top"><i><u>Offset:</u></i> </td>
<td align="left" valign="top"><i><u>Effect:</u></i></td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x0000</tt></td>
<td align="left" valign="top">Read: <b><tt>whoami()</tt></b>.
Returns the id of the CPU doing the read.</td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x0010</tt></td>
<td align="left" valign="top">Read: <b><tt>ncpus()</tt></b>.
Returns the number of CPUs in the system.</td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x0020</tt></td>
<td align="left" valign="top">Write: <b><tt>startupcpu(i)</tt></b>.
Starts CPU i. It begins execution at the address
set by a write to startupaddr (see below).</td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x0030</tt></td>
<td align="left" valign="top">Write: <b><tt>startupaddr(addr)</tt></b>.
Sets the starting address for CPUs.</td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x0040</tt></td>
<td align="left" valign="top">Write: <b><tt>pause_addr(addr)</tt></b>.
Sets the pause address. (NOTE: This is not
used anymore.)</td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x0050</tt></td>
<td align="left" valign="top">Write: <b><tt>pause_cpu(i)</tt></b>.
Pauses all CPUs <i>except</i> CPU i.</td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x0060</tt></td>
<td align="left" valign="top">Write: <b><tt>unpause_cpu(i)</tt></b>.
Unpauses CPU i.</td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x0070</tt></td>
<td align="left" valign="top">Write: <b><tt>startupstack(addr)</tt></b>.
Sets the startup stack address. (CPUs started with
startupcpu() above will have their stack pointer
set to this value.)</td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x0080</tt></td>
<td align="left" valign="top">Read: <b><tt>hardware_random()</tt></b>.
This produces a "random" number.</td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x0090</tt></td>
<td align="left" valign="top">Read: <b><tt>memory()</tt></b>.
Returns the number of bytes of RAM in the system.</td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x00a0</tt></td>
<td align="left" valign="top">Write: <b><tt>ipi_one((nr << 16) + cpuid)</tt></b>.
Sends IPI <tt>nr</tt> to a specific CPU.</td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x00b0</tt></td>
<td align="left" valign="top">Write: <b><tt>ipi_many((nr << 16) + cpuid)</tt></b>.
Sends IPI <tt>nr</tt> to all CPUs <i>except</i>
the specified one.</td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x00c0</tt></td>
<td align="left" valign="top">Read: <b><tt>ipi_read()</tt></b>.
Returns the next pending IPI. 0 is returned if there is no
pending IPI (so 0 shouldn't be used for valid IPIs).
Hardware int 6 is deasserted when the IPI queue is empty.
<br>Write: <b><tt>ipi_flush()</tt></b>.
Clears the IPI queue, discarding any pending IPIs.</td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x00d0</tt></td>
<td align="left" valign="top">Read: <b><tt>ncycles()</tt></b>.
Returns approximately the number of cycles executed on
this CPU. Note: this value is not updated for every instruction,
so it cannot be used for small measurements.</td>
</tr>
</table>
</td>
</tr>
<tr height="15">
<td height="15"> </td>
</tr>
<tr>
<td align="left" valign="top">
<a name="expdevices_fb"><b><tt>fb</tt>:</b></a>
<p>A simple linear framebuffer, for graphics output.
Initial resolution is 640 x 480 pixels, with 3 bytes per pixel
(red, green, blue, 8 bits each).
<p>Source code: <font color="#0000f0"><tt>src/devices/dev_fb.c</tt></font>
<p>Include file: <font color="#0000f0"><tt>dev_fb.h</tt></font>
<br>Physical address:  <font color="#0000f0">0x12000000</font>
</td>
<td></td>
<td align="left" valign="top">
<table border="0">
<tr>
<td align="left" valign="top"><i><u>Offset:</u></i> </td>
<td align="left" valign="top"><i><u>Effect:</u></i></td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x00000000</tt> </td>
<td align="left" valign="top">Read: read pixel values.
Write: write pixel values.</td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x00f00000</tt> </td>
<td align="left" valign="top">Read/Write: Control ports for changing the
resolution at runtime, etc. See <tt>dev_fb.h</tt> and
<tt>dev_fbctrl.cc</tt> for more details.
<p>If the resolution is read back as X=0 Y=0, then that
means that graphics is not used, only serial console.</td>
</tr>
</table>
</td>
</tr>
<tr height="15">
<td height="15"> </td>
</tr>
<tr>
<td align="left" valign="top">
<a name="expdevices_disk"><b><tt>disk</tt>:</b></a>
<p>Disk controller, which can read from and write
to emulated IDE disks. It does not use interrupts; read and
write operations finish instantaneously.
<p>Source code: <font color="#0000f0"><tt>src/devices/dev_disk.c</tt></font>
<p>Include file: <font color="#0000f0"><tt>dev_disk.h</tt></font>
<br>Physical address:  <font color="#0000f0">0x13000000</font>
</td>
<td></td>
<td align="left" valign="top">
<table border="0">
<tr>
<td align="left" valign="top"><i><u>Offset:</u></i> </td>
<td align="left" valign="top"><i><u>Effect:</u></i></td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x0000</tt></td>
<td align="left" valign="top">Write: Set the offset (in bytes) from the beginning
of the disk image. This offset will be used for the next read/write operation.</td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x0008</tt></td>
<td align="left" valign="top">Write: Set the high 32
bits of the offset (in bytes). (*)</td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x0010</tt></td>
<td align="left" valign="top">Write: Select the IDE ID to be used in the next
read/write operation.</td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x0020</tt></td>
<td align="left" valign="top">Write: Start a read or write operation.
(Writing <tt>0</tt> means a Read operation, a <tt>1</tt> means a
Write operation.)</td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x0030</tt></td>
<td align="left" valign="top">Read: Get status of the last operation.
(Status 0 means failure, non-zero means success.)</td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x4000-</tt><br><tt>0x41ff</tt> </td>
<td align="left" valign="top">Read/Write: 512 bytes data buffer.</td>
</tr>
</table>
</td>
</tr>
<tr height="15">
<td height="15"> </td>
</tr>
<tr>
<td align="left" valign="top">
<a name="expdevices_ether"><b><tt>ether</tt>:</b></a>
<p>A simple ethernet controller, enough to send
and receive packets on a simulated network.
<p>Source code: <font color="#0000f0"><tt>src/devices/dev_ether.c</tt></font>
<p>Include file: <font color="#0000f0"><tt>dev_ether.h</tt></font>
<br>Physical address:  <font color="#0000f0">0x14000000</font>
</td>
<td></td>
<td align="left" valign="top">
<table border="0">
<tr>
<td align="left" valign="top"><i><u>Offset:</u></i> </td>
<td align="left" valign="top"><i><u>Effect:</u></i></td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x0000-</tt><br><tt>0x3fff</tt></td>
<td align="left" valign="top">Read/write buffer for the packet to be sent/received.</td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x4000</tt></td>
<td align="left" valign="top">Read: status word, one or more of these:
<br><tt>0x01</tt> = something was received (because of
the last command)
<br><tt>0x02</tt> = more packets are available
<br><i>NOTE:</i> Whenever the status word is non-zero,
an interrupt is asserted. Reading the status word
clears it, and deasserts the interrupt.</td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x4010</tt></td>
<td align="left" valign="top">Read: get the Length of the received packet
<br>Write: set the Length of the next packet to transmit</td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x4020</tt></td>
<td align="left" valign="top">Write: command:
<br><tt>0x00:</tt> receive a packet
<br><tt>0x01:</tt> send a packet</td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x4040</tt></td>
<td align="left" valign="top">Write: an address, where the emulated
MAC address will be copied to.
</tr>
</table>
</td>
</tr>
<tr height="15">
<td height="15"> </td>
</tr>
<tr>
<td align="left" valign="top">
<a name="expdevices_rtc"><b><tt>rtc</tt>:</b></a>
<p>A Real-Time Clock, used to retrieve the current time
and to cause periodic interrupts.
<p>Source code: <font color="#0000f0"><tt>src/devices/dev_rtc.c</tt></font>
<p>Include file: <font color="#0000f0"><tt>dev_rtc.h</tt></font>
<br>Physical address:  <font color="#0000f0">0x15000000</font>
</td>
<td></td>
<td align="left" valign="top">
<table border="0">
<tr>
<td align="left" valign="top"><i><u>Offset:</u></i> </td>
<td align="left" valign="top"><i><u>Effect:</u></i></td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x0000</tt></td>
<td align="left" valign="top">Read or Write: Trigger a clock update (a gettimeofday() on the host).</td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x0010</tt></td>
<td align="left" valign="top">Read: Seconds since 1st January 1970</td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x0020</tt></td>
<td align="left" valign="top">Read: Microseconds</td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x0100</tt></td>
<td align="left" valign="top">Read: Get the current
timer interrupt frequency.<br>Write: Set the timer
interrupt frequency. (Writing 0 disables the timer.)</td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x0110</tt></td>
<td align="left" valign="top">Read or Write: Acknowledge
one timer interrupt. (Note that if multiple interrupts
are pending, only one is acknowledged.)</td>
</tr>
</table>
</td>
</tr>
<tr height="15">
<td height="15"> </td>
</tr>
<tr>
<td align="left" valign="top">
<a name="expdevices_irqc"><b><tt>irqc</tt>:</b></a>
<p>An Interrupt Controller. (Note: Not used for the MIPS test machine.)
<p>Source code: <font color="#0000f0"><tt>src/devices/dev_irqc.c</tt></font>
<p>Include file: <font color="#0000f0"><tt>dev_irqc.h</tt></font>
<br>Physical address:  <font color="#0000f0">0x16000000</font>
</td>
<td></td>
<td align="left" valign="top">
<table border="0">
<tr>
<td align="left" valign="top"><i><u>Offset:</u></i> </td>
<td align="left" valign="top"><i><u>Effect:</u></i></td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x0</tt></td>
<td align="left" valign="top">Read: IRQ status as a 32-bit word, one bit per interrupt source.</td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x4</tt></td>
<td align="left" valign="top">Write: Mask one interrupt source. Value should be an integer 0..31.</td>
</tr>
<tr>
<td align="left" valign="top"><tt>0x8</tt></td>
<td align="left" valign="top">Write: Unmask one interrupt source. Value should be an integer 0..31.</td>
</tr>
</table>
</td>
</tr>
</table></center>
<p>(*) Note: If the emulated architecture has the capability to write 64-bit
words atomically, then writing to offset 0x0000 of the
<tt>disk</tt> device should be enough to set the offset. For 32-bit
architectures, the lowest 32 bits of the disk offset should first be
written to the register at offset 0x0000, and the top 32 bits should
then be written to the register at offset 0x0008.
<p>The include files for the test machine devices are found in
<a href="../src/include/testmachine/"><tt>src/include/testmachine/</tt></a>.
<p>While these devices may resemble real-world hardware, they are
intentionally made simpler to use. (An exception is the framebuffer;
some machines actually have simple linear framebuffers like this.)
<p>If the physical address is <tt>0x10000000</tt>, then for MIPS that
means that it can be accessed at virtual address
<tt>0xffffffffb0000000</tt>. (Using virtual address
<tt>0xffffffff90000000</tt> may work in the emulator, but should be
avoided, since devices should in general be accessed in a non-cached manner.)
<p>When using the ARM or PPC test machines, the addresses are
<tt>0x10000000</tt>, <tt>0x11000000</tt> etc., so no need to add any
virtual displacement.
<p>The <tt>mp</tt>, <tt>disk</tt>, and <tt>ether</tt> devices are agnostic
when it comes to word-length. For example, when reading offset
<tt>0x0000</tt> of the <tt>mp</tt> device, you may use any kind of read
(an 8-bit read will work just as well as a 64-bit read, although the value
will be truncated to 8 bits in the first case). You can <i>not</i>,
however, read one byte from <tt>0x0000</tt> and one from <tt>0x0001</tt>,
and combine the result. The read from <tt>0x0001</tt> will be invalid.
<p>The <tt>cons</tt> device should be accessed using 8-bit reads
and writes. Doing a getchar() (ie reading from offset <tt>0x00</tt>)
returns <tt>0</tt> if no character was available. Whenever a character is
available, the <tt>cons</tt> device' interrupt is asserted. When there are
no more available characters, the interrupt is deasserted. (Remember that
the interrupt has to be unmasked to be able to actually cause an
interrupt.)
<p>IPIs (inter-processor interrupts) are controlled by the <tt>mp</tt>
device. Whenever an IPI is "sent" from a source to one or more target
CPUs, the interrupt is asserted on the target CPUs, and the IPI number is
added last in the IPI queue for each of the target CPUs. It is then up to
those CPUs to individually read from offset <tt>0x00c0</tt>, to figure out
what kind of IPI it was.
<p>Interrupt mappings are as follows:
<p><center>
<table border="1">
<tr><td align="center">
<b><tt>testmips</tt></b> (as native MIPS interrupts)
</td></tr>
<tr><td>
<table border="0">
<tr><td align="center">IRQ:</td><td> </td>
<td>Used for:</td></tr>
<tr><td align="center">7</td><td></td>
<td>MIPS count/compare interrupt</td></tr>
<tr><td align="center">6</td><td></td>
<td><tt>mp</tt> (inter-processor interrupts)</td></tr>
<tr><td align="center">4</td><td></td>
<td><tt>rtc</tt></td></tr>
<tr><td align="center">3</td><td></td>
<td><tt>ether</tt></td></tr>
<tr><td align="center">2</td><td></td>
<td><tt>cons</tt></td></tr>
</table>
</td></tr>
</table>
<p><table border="1">
<tr><td align="center">
<b><tt>testarm</tt> and others</b> (via the <tt>irqc</tt> device)
</td></tr>
<tr><td>
<table border="0">
<tr><td align="center">IRQ:</td><td> </td>
<td>Used for:</td></tr>
<tr><td align="center">6</td><td></td>
<td><tt>mp</tt> (inter-processor interrupts)</td></tr>
<tr><td align="center">4</td><td></td>
<td><tt>rtc</tt></td></tr>
<tr><td align="center">3</td><td></td>
<td><tt>ether</tt></td></tr>
<tr><td align="center">2</td><td></td>
<td><tt>cons</tt></td></tr>
</table>
</td></tr>
</table>
</center>
<p><br>
</p>
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