serial.html

FreeBSD操作系统的详细使用手册

</ul>

<p>If you have connected a terminal to the first serial port (<tt
class="DEVICENAME">COM1</tt> in <span class="TRADEMARK">MS-DOS</span>&reg;), then you
will use <tt class="FILENAME">/dev/ttyd0</tt> to refer to the terminal. If the terminal
is on the second serial port (also known as <tt class="DEVICENAME">COM2</tt>), use <tt
class="FILENAME">/dev/ttyd1</tt>, and so forth.</p>
</div>
</div>
</div>

<div class="SECT2">
<h2 class="SECT2"><a id="AEN28570" name="AEN28570">20.2.3 Kernel Configuration</a></h2>

<p>FreeBSD supports four serial ports by default. In the <span
class="TRADEMARK">MS-DOS</span> world, these are known as <tt
class="DEVICENAME">COM1</tt>, <tt class="DEVICENAME">COM2</tt>, <tt
class="DEVICENAME">COM3</tt>, and <tt class="DEVICENAME">COM4</tt>. FreeBSD currently
supports ``dumb'' multiport serial interface cards, such as the BocaBoard 1008 and 2016,
as well as more intelligent multi-port cards such as those made by Digiboard and Stallion
Technologies. However, the default kernel only looks for the standard COM ports.</p>

<p>To see if your kernel recognizes any of your serial ports, watch for messages while
the kernel is booting, or use the <tt class="COMMAND">/sbin/dmesg</tt> command to replay
the kernel's boot messages. In particular, look for messages that start with the
characters <var class="LITERAL">sio</var>.</p>

<div class="TIP">
<blockquote class="TIP">
<p><b>Tip:</b> To view just the messages that have the word <var
class="LITERAL">sio</var>, use the command:</p>

<pre class="SCREEN">
<samp class="PROMPT">#</samp> <kbd class="USERINPUT">/sbin/dmesg | grep 'sio'</kbd>
</pre>
</blockquote>
</div>

<p>For example, on a system with four serial ports, these are the serial-port specific
kernel boot messages:</p>

<pre class="SCREEN">
sio0 at 0x3f8-0x3ff irq 4 on isa
sio0: type 16550A
sio1 at 0x2f8-0x2ff irq 3 on isa
sio1: type 16550A
sio2 at 0x3e8-0x3ef irq 5 on isa
sio2: type 16550A
sio3 at 0x2e8-0x2ef irq 9 on isa
sio3: type 16550A
</pre>

<p>If your kernel does not recognize all of your serial ports, you will probably need to
configure a custom FreeBSD kernel for your system. For detailed information on
configuring your kernel, please see <a href="kernelconfig.html">Chapter 8</a>.</p>

<p>The relevant device lines for your kernel configuration file would look like this, for
FreeBSD&nbsp;4.X:</p>

<pre class="PROGRAMLISTING">
device     sio0    at isa? port IO_COM1 irq 4
device      sio1    at isa? port IO_COM2 irq 3
device      sio2    at isa? port IO_COM3 irq 5
device      sio3    at isa? port IO_COM4 irq 9
</pre>

<p>and like this, for FreeBSD&nbsp;5.X:</p>

<pre class="PROGRAMLISTING">
device     sio
</pre>

<p>You can comment-out or completely remove lines for devices you do not have in the case
of FreeBSD&nbsp;4.X; for FreeBSD&nbsp;5.X you have to edit your <tt
class="FILENAME">/boot/device.hints</tt> file to configure your serial ports. Please
refer to the <a href="http://www.FreeBSD.org/cgi/man.cgi?query=sio&sektion=4"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">sio</span>(4)</span></a> manual page for
more information on serial ports and multiport boards configuration. Be careful if you
are using a configuration file that was previously used for a different version of
FreeBSD because the device flags and the syntax have changed between versions.</p>

<div class="NOTE">
<blockquote class="NOTE">
<p><b>Note:</b> <var class="LITERAL">port IO_COM1</var> is a substitution for <var
class="LITERAL">port 0x3f8</var>, <var class="LITERAL">IO_COM2</var> is <var
class="LITERAL">0x2f8</var>, <var class="LITERAL">IO_COM3</var> is <var
class="LITERAL">0x3e8</var>, and <var class="LITERAL">IO_COM4</var> is <var
class="LITERAL">0x2e8</var>, which are fairly common port addresses for their respective
serial ports; interrupts 4, 3, 5, and 9 are fairly common interrupt request lines. Also
note that regular serial ports <span class="emphasis"><i
class="EMPHASIS">cannot</i></span> share interrupts on ISA-bus PCs (multiport boards have
on-board electronics that allow all the 16550A's on the board to share one or two
interrupt request lines).</p>
</blockquote>
</div>
</div>

<div class="SECT2">
<h2 class="SECT2"><a id="AEN28612" name="AEN28612">20.2.4 Device Special Files</a></h2>

<p>Most devices in the kernel are accessed through ``device special files'', which are
located in the <tt class="FILENAME">/dev</tt> directory. The <tt
class="DEVICENAME">sio</tt> devices are accessed through the <tt
class="FILENAME">/dev/ttyd<var class="REPLACEABLE">N</var></tt> (dial-in) and <tt
class="FILENAME">/dev/cuaa<var class="REPLACEABLE">N</var></tt> (call-out) devices.
FreeBSD also provides initialization devices (<tt class="FILENAME">/dev/ttyid<var
class="REPLACEABLE">N</var></tt> and <tt class="FILENAME">/dev/cuaia<var
class="REPLACEABLE">N</var></tt>) and locking devices (<tt
class="FILENAME">/dev/ttyld<var class="REPLACEABLE">N</var></tt> and <tt
class="FILENAME">/dev/cuala<var class="REPLACEABLE">N</var></tt>). The initialization
devices are used to initialize communications port parameters each time a port is opened,
such as <var class="LITERAL">crtscts</var> for modems which use <var
class="LITERAL">RTS/CTS</var> signaling for flow control. The locking devices are used to
lock flags on ports to prevent users or programs changing certain parameters; see the
manual pages <a href="http://www.FreeBSD.org/cgi/man.cgi?query=termios&sektion=4"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">termios</span>(4)</span></a>, <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=sio&sektion=4"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">sio</span>(4)</span></a>, and <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=stty&sektion=1"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">stty</span>(1)</span></a> for
information on the terminal settings, locking and initializing devices, and setting
terminal options, respectively.</p>

<div class="SECT3">
<h3 class="SECT3"><a id="AEN28641" name="AEN28641">20.2.4.1 Making Device Special
Files</a></h3>

<div class="NOTE">
<blockquote class="NOTE">
<p><b>Note:</b> FreeBSD&nbsp;5.0 includes the <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=devfs&sektion=5&manpath=FreeBSD+6-current">
<span class="CITEREFENTRY"><span class="REFENTRYTITLE">devfs</span>(5)</span></a>
filesystem which automatically creates device nodes as needed. If you are running a
version of FreeBSD with <var class="LITERAL">devfs</var> enabled then you can safely skip
this section.</p>
</blockquote>
</div>

<p>A shell script called <tt class="COMMAND">MAKEDEV</tt> in the <tt
class="FILENAME">/dev</tt> directory manages the device special files. To use <tt
class="COMMAND">MAKEDEV</tt> to make dial-up device special files for <tt
class="DEVICENAME">COM1</tt> (port 0), <tt class="COMMAND">cd</tt> to <tt
class="FILENAME">/dev</tt> and issue the command <tt class="COMMAND">MAKEDEV ttyd0</tt>.
Likewise, to make dial-up device special files for <tt class="DEVICENAME">COM2</tt> (port
1), use <tt class="COMMAND">MAKEDEV ttyd1</tt>.</p>

<p><tt class="COMMAND">MAKEDEV</tt> not only creates the <tt
class="FILENAME">/dev/ttyd<var class="REPLACEABLE">N</var></tt> device special files, but
also the <tt class="FILENAME">/dev/cuaa<var class="REPLACEABLE">N</var></tt>, <tt
class="FILENAME">/dev/cuaia<var class="REPLACEABLE">N</var></tt>, <tt
class="FILENAME">/dev/cuala<var class="REPLACEABLE">N</var></tt>, <tt
class="FILENAME">/dev/ttyld<var class="REPLACEABLE">N</var></tt>, and <tt
class="FILENAME">/dev/ttyid<var class="REPLACEABLE">N</var></tt> nodes.</p>

<p>After making new device special files, be sure to check the permissions on the files
(especially the <tt class="FILENAME">/dev/cua*</tt> files) to make sure that only users
who should have access to those device special files can read and write on them -- you
probably do not want to allow your average user to use your modems to dial-out. The
default permissions on the <tt class="FILENAME">/dev/cua*</tt> files should be
sufficient:</p>

<pre class="SCREEN">
crw-rw----    1 uucp     dialer    28, 129 Feb 15 14:38 /dev/cuaa1
crw-rw----    1 uucp     dialer    28, 161 Feb 15 14:38 /dev/cuaia1
crw-rw----    1 uucp     dialer    28, 193 Feb 15 14:38 /dev/cuala1
</pre>

<p>These permissions allow the user <tt class="USERNAME">uucp</tt> and users in the group
<tt class="USERNAME">dialer</tt> to use the call-out devices.</p>
</div>
</div>

<div class="SECT2">
<h2 class="SECT2"><a id="SERIAL-HW-CONFIG" name="SERIAL-HW-CONFIG">20.2.5 Serial Port
Configuration</a></h2>

<p>The <tt class="DEVICENAME">ttyd<var class="REPLACEABLE">N</var></tt> (or <tt
class="DEVICENAME">cuaa<var class="REPLACEABLE">N</var></tt>) device is the regular
device you will want to open for your applications. When a process opens the device, it
will have a default set of terminal I/O settings. You can see these settings with the
command</p>

<pre class="SCREEN">
<samp class="PROMPT">#</samp> <kbd class="USERINPUT">stty -a -f /dev/ttyd1</kbd>
</pre>

<p>When you change the settings to this device, the settings are in effect until the
device is closed. When it is reopened, it goes back to the default set. To make changes
to the default set, you can open and adjust the settings of the ``initial state'' device.
For example, to turn on <var class="OPTION">CLOCAL</var> mode, 8 bit communication, and
<var class="OPTION">XON/XOFF</var> flow control by default for <tt
class="DEVICENAME">ttyd5</tt>, type:</p>

<pre class="SCREEN">
<samp class="PROMPT">#</samp> <kbd
class="USERINPUT">stty -f /dev/ttyid5 clocal cs8 ixon ixoff</kbd>
</pre>

<p>System-wide initialization of the serial devices is controlled in <tt
class="FILENAME">/etc/rc.serial</tt>. This file affects the default settings of serial
devices.</p>

<p>To prevent certain settings from being changed by an application, make adjustments to
the ``lock state'' device. For example, to lock the speed of <tt
class="DEVICENAME">ttyd5</tt> to 57600&nbsp;bps, type:</p>

<pre class="SCREEN">
<samp class="PROMPT">#</samp> <kbd class="USERINPUT">stty -f /dev/ttyld5 57600</kbd>
</pre>

<p>Now, an application that opens <tt class="DEVICENAME">ttyd5</tt> and tries to change
the speed of the port will be stuck with 57600&nbsp;bps.</p>

<p>Naturally, you should make the initial state and lock state devices writable only by
the <tt class="USERNAME">root</tt> account.</p>
</div>
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