Editorial review of Serial Port Configuration.
Minor shuffling to remove redundancy. Sponsored by: iXsystems
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Dru Lavigne
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2020-12-08 03:00:23 +00:00
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1 changed files with 50 additions and 79 deletions
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@ -534,68 +534,19 @@
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signal.</para>
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</listitem>
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</itemizedlist>
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</sect2>
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<sect2>
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<title>Kernel Configuration</title>
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<para>&os; supports four serial ports by default. In the
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&ms-dos; world, these are known as <filename>COM1</filename>,
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<filename>COM2</filename>, <filename>COM3</filename>, and
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<filename>COM4</filename>. &os; currently supports
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<quote>dumb</quote> multiport serial interface cards, such as
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the BocaBoard 1008 and 2016, as well as more intelligent
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multi-port cards such as those made by Digiboard and Stallion
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Technologies. However, the default kernel only looks for the
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standard COM ports.</para>
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<para>To see if the kernel recognizes the serial ports, watch
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for messages while the kernel is booting, or use
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<command>/sbin/dmesg</command> to replay the kernel's boot
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messages. Look for messages that start with the characters
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<literal>uart</literal>:</para>
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<screen>&prompt.root; <userinput>/sbin/dmesg | grep 'uart'</userinput></screen>
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<para>If the kernel does not recognize all of the serial ports,
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configure <filename>/boot/device.hints</filename>. When
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editing this file, one can comment out or completely remove
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lines for devices that do not exist on the system.</para>
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<note>
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<para><literal>port IO_COM1</literal> is a substitution for
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<literal>port 0x3f8</literal>, <literal>IO_COM2</literal> is
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<literal>0x2f8</literal>, <literal>IO_COM3</literal> is
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<literal>0x3e8</literal>, and <literal>IO_COM4</literal> is
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<literal>0x2e8</literal>. These are fairly common port
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addresses for their respective serial ports and interrupts
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4, 3, 5, and 9 are fairly common interrupt request lines.
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Regular serial ports <emphasis>cannot</emphasis> share
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interrupts on ISA-bus PCs. Multiport boards have on-board
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electronics that allow all the 16550A's on the board to
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share one or two interrupt request lines.</para>
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</note>
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</sect2>
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<sect2>
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<title>Device Special Files</title>
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<para>Most devices in the kernel are accessed through
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<quote>device special files</quote> which are located in
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<filename class="directory">/dev</filename>. The
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<filename>sio</filename> devices are accessed through the
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<filename>/dev/ttyu<replaceable>N</replaceable></filename>
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(dial-in) and
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<filename>/dev/cuau<replaceable>N</replaceable></filename>
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(call-out) devices. &os; also provides initialization
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<para>&os; also provides initialization
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devices
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(<filename>/dev/ttyu<replaceable>N</replaceable>.init</filename>
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and
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<filename>/dev/cuau<replaceable>N</replaceable>.init</filename>)
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(<filename>/dev/ttyu<replaceable>N</replaceable>.init</filename> and
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<filename>/dev/cuau<replaceable>N</replaceable>.init</filename>
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or
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<filename>/dev/cuad<replaceable>N</replaceable>.init</filename>)
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and locking devices
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(<filename>/dev/ttyu<replaceable>N</replaceable>.lock</filename>
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and
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<filename>/dev/cuau<replaceable>N</replaceable>.lock</filename>).
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<filename>/dev/cuau<replaceable>N</replaceable>.lock</filename>
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or
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<filename>/dev/cuad<replaceable>N</replaceable>.lock</filename>).
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The initialization devices are used to initialize
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communications port parameters each time a port is opened,
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such as <literal>crtscts</literal> for modems which use
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@ -607,28 +558,56 @@
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devices, and setting terminal options, respectively.</para>
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</sect2>
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<sect2 xml:id="serial-hw-config">
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<title>Serial Port Configuration</title>
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<para>By default, &os; supports four serial ports which are
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commonly known as <filename>COM1</filename>,
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<filename>COM2</filename>, <filename>COM3</filename>, and
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<filename>COM4</filename>. &os; also supports
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dumb multi-port serial interface cards, such as
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the BocaBoard 1008 and 2016, as well as more intelligent
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multi-port cards such as those made by Digiboard. However,
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the default kernel only looks for the
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standard <filename>COM</filename> ports.</para>
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<para>To see if the system recognizes the serial ports, look for
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system boot messages that start with
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<literal>uart</literal>:</para>
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<screen>&prompt.root; <userinput>grep uart /var/run/dmesg.boot</userinput></screen>
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<para>If the system does not recognize all of the needed serial ports,
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additional entries can be added to
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<filename>/boot/device.hints</filename>. This file already
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contains <literal>hint.uart.0.*</literal> entries for
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<filename>COM1</filename> and <literal>hint.uart.1.*</literal> entries
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for <filename>COM2</filename>. When adding a port entry for
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<filename>COM3</filename> use
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<literal>0x3E8</literal>, and for <filename>COM4</filename> use
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<literal>0x2E8</literal>. Common <acronym>IRQ</acronym> addresses
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are <literal>5</literal> for <filename>COM3</filename> and
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<literal>9</literal> for <filename>COM4</filename>.</para>
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<indexterm><primary><filename>ttyu</filename></primary></indexterm>
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<indexterm><primary><filename>cuau</filename></primary></indexterm>
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<para>The
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<filename>ttyu<replaceable>N</replaceable></filename> (or
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<filename>cuau<replaceable>N</replaceable></filename>)
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is the regular device to open for applications. When a
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process opens the device, it will have a default set of
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terminal I/O settings. These settings can be viewed with the
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command:</para>
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<para>To determine the default set of terminal
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<acronym>I/O</acronym> settings used by the port, specify its
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device name. This example determines the settings for the
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call-in port on <filename>COM2</filename>:</para>
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<screen>&prompt.root; <userinput>stty -a -f /dev/ttyu1</userinput></screen>
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<screen>&prompt.root; <userinput>stty -a -f /dev/<replaceable>ttyu1</replaceable></userinput></screen>
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<para>When the settings are changed for a device, the settings
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are in effect until the device is closed. When the device is
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<para>System-wide initialization of serial devices is
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controlled by <filename>/etc/rc.d/serial</filename>. This
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file affects the default settings of serial devices. To
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change the settings for a device, use <command>stty</command>.
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By default, the changed settings
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are in effect until the device is closed and when the device is
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reopened, it goes back to the default set. To permanently
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change the default set, open and adjust the settings of the
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<quote>initial state</quote> device. For example, to turn on
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initialization device. For example, to turn on
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<option>CLOCAL</option> mode, 8 bit communication, and
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<option>XON/XOFF</option> flow control for
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<filename>ttyu5</filename>, type:</para>
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@ -640,24 +619,16 @@
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<secondary><filename>rc.serial</filename></secondary>
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</indexterm>
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<para>System-wide initialization of serial devices is
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controlled by <filename>/etc/rc.d/serial</filename>. This
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file affects the default settings of serial devices.</para>
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<para>To prevent certain settings from being changed by an
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application, make adjustments to the <quote>lock state</quote>
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application, make adjustments to the locking
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device. For example, to lock the speed of
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<filename>ttyu5</filename> to 57600 bps, type:</para>
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<screen>&prompt.root; <userinput>stty -f /dev/ttyu5.lock 57600</userinput></screen>
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<para>Now, an application that opens
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<para>Now, any application that opens
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<filename>ttyu5</filename> and tries to change the speed
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of the port will be stuck with 57600 bps.</para>
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<para>The initial state and lock state devices should only be
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writable by <systemitem
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class="username">root</systemitem>.</para>
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</sect2>
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</sect1>
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