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><H1
><A
NAME="BIOS"
></A
>Chapter 3. Optionally configure the <SPAN
CLASS="ACRONYM"
>BIOS</SPAN
></H1
><P
>Some <SPAN
CLASS="ACRONYM"
>BIOS</SPAN
>s provide support for serial
consoles. If your computer's <SPAN
CLASS="ACRONYM"
>BIOS</SPAN
> is one of
these you should investigate the extent of the support provided.
Depending upon the extent of serial console support you may not need
to explicitly configure the boot loader to use the serial
port.</P
><P
>The contributors to this <I
CLASS="CITETITLE"
>HOWTO</I
> have
encountered the following styles of <SPAN
CLASS="ACRONYM"
>BIOS</SPAN
> support
for serial consoles.</P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
>Redirection of textual VGA output to the serial port</DT
><DD
><P
>The <SPAN
CLASS="ACRONYM"
>BIOS</SPAN
> takes the interrupt 0x10
<SPAN
CLASS="QUOTE"
>"video"</SPAN
> requests used to write to the screen and
sends the characters that would have appeared on the screen to
the serial port. Characters recieved from the serial port are
used to supply characters to <SPAN
CLASS="ACRONYM"
>BIOS</SPAN
> interrupt
0x16 <SPAN
CLASS="QUOTE"
>"read key"</SPAN
> requests.</P
><P
>Any 16-bit application which uses the
<SPAN
CLASS="ACRONYM"
>BIOS</SPAN
> functions for outputing text to the
screen and reading from the keyboard is redirected to the serial
port. This includes the <SPAN
CLASS="ACRONYM"
>BIOS</SPAN
> itself, the boot
loader, and 16-bit operating systems (such as
<SPAN
CLASS="PRODUCTNAME"
><SPAN
CLASS="ACRONYM"
>MS-DOS</SPAN
></SPAN
>).</P
><P
>When a 32-bit operating system (such as <SPAN
CLASS="SYSTEMITEM"
>Linux</SPAN
>, <SPAN
CLASS="SYSTEMITEM"
>BSD</SPAN
> or <SPAN
CLASS="SYSTEMITEM"
>Windows NT/2000/XP</SPAN
>) loads the 16-bit
<SPAN
CLASS="ACRONYM"
>BIOS</SPAN
> is no longer accessible and the
<SPAN
CLASS="ACRONYM"
>BIOS</SPAN
> can no longer be used for input and
output. The 32-bit operating system loads its own device drivers
for this purpose. These device drivers then need to provide the
redirection of console <SPAN
CLASS="ACRONYM"
>I/O</SPAN
> to the serial
port.</P
><P
>If your <SPAN
CLASS="ACRONYM"
>BIOS</SPAN
> uses this technique then
you should:</P
><DIV
CLASS="PROCEDURE"
><OL
TYPE="1"
><LI
><P
>Configure the <SPAN
CLASS="ACRONYM"
>BIOS</SPAN
> to redirect
keyboard input and video output to the serial port.</P
></LI
><LI
><P
>Do not configure the boot loader, as the
<SPAN
CLASS="ACRONYM"
>BIOS</SPAN
> will redirect this 16-bit application's
input and output to the serial port.</P
></LI
><LI
><P
>Configure <SPAN
CLASS="SYSTEMITEM"
>Linux</SPAN
>
to use the serial port as a console, as <SPAN
CLASS="SYSTEMITEM"
>Linux</SPAN
> is a 32-bit operating
system.</P
></LI
></OL
></DIV
></DD
><DT
><SPAN
CLASS="ACRONYM"
>BIOS</SPAN
> configuration and power on self-test
uses the serial port</DT
><DD
><P
>These <SPAN
CLASS="ACRONYM"
>BIOS</SPAN
>s use the serial port for
configuration and the power-on self-test, but do not redirect the
interrupt 0x10 <SPAN
CLASS="QUOTE"
>"video"</SPAN
> requests interrupt 0x16
<SPAN
CLASS="QUOTE"
>"read key"</SPAN
> requests to the serial port.</P
><P
>Some <SPAN
CLASS="ACRONYM"
>BIOS</SPAN
>s which usually redirect all
keyboard and video output to the serial port can be configured in
only to redirect <SPAN
CLASS="ACRONYM"
>BIOS</SPAN
> input and output. Look
for a <SPAN
CLASS="ACRONYM"
>BIOS</SPAN
> configuration option similar to
<SPAN
CLASS="GUIMENUITEM"
>Cease redirection after boot</SPAN
>.</P
><P
>If your <SPAN
CLASS="ACRONYM"
>BIOS</SPAN
> uses this technique or you
choose to set <SPAN
CLASS="GUIMENUITEM"
>Cease redirection after
boot</SPAN
> then you should:</P
><DIV
CLASS="PROCEDURE"
><OL
TYPE="1"
><LI
><P
>Configure the <SPAN
CLASS="ACRONYM"
>BIOS</SPAN
> to send its output
to the serial port.</P
></LI
><LI
><P
>Configure the boot loader to use the serial port.</P
></LI
><LI
><P
>Configure <SPAN
CLASS="SYSTEMITEM"
>Linux</SPAN
>
to use the serila port as the console, as <SPAN
CLASS="SYSTEMITEM"
>Linux</SPAN
> is a 32-bit operating
system.</P
></LI
></OL
></DIV
></DD
><DT
>Redirection of graphical <SPAN
CLASS="ACRONYM"
>VGA</SPAN
> output to
the serial port</DT
><DD
><P
>Some graphical 32-bit operating systems do not provide
their own facilities to send console output to the serial port.
Some BIOSs attempt to overcome this shortcoming, using a
propietary serial protocol to send graphical output to a remote
serial client.</P
><P
>As these machines cannot be connected to from a standard
terminal emulator this facility is best left unconfigured when
using the <SPAN
CLASS="SYSTEMITEM"
>Linux</SPAN
> operating
system.</P
><DIV
CLASS="PROCEDURE"
><OL
TYPE="1"
><LI
><P
>Configure the <SPAN
CLASS="ACRONYM"
>BIOS</SPAN
> not to send output
to the serial port.</P
></LI
><LI
><P
>Configure the boot loader to use the serial port.</P
></LI
><LI
><P
>Configure <SPAN
CLASS="SYSTEMITEM"
>Linux</SPAN
>
to use the serial port as the console.</P
></LI
></OL
></DIV
></DD
><DT
>No serial port facilities</DT
><DD
><P
>The <SPAN
CLASS="ACRONYM"
>BIOS</SPAN
> cannot be accessed from the
serial port, so power-on self-test messages cannot be
seen.</P
><P
>Note that <SPAN
CLASS="ACRONYM"
>BIOS</SPAN
> may still be able to be
configured remotely using the <TT
CLASS="FILENAME"
>/dev/nvram</TT
> device. This takes some
care.</P
><DIV
CLASS="PROCEDURE"
><OL
TYPE="1"
><LI
><P
>Configure the boot loader to use the serial port.</P
></LI
><LI
><P
>Configure <SPAN
CLASS="SYSTEMITEM"
>Linux</SPAN
>
to use the serial port as the console.</P
></LI
></OL
></DIV
></DD
></DL
></DIV
><P
>If you need to configure the boot loader to use the serial
port then continue to <A
HREF="configure-boot-loader.html"
>Chapter 4</A
>.
Otherwise go directly to <A
HREF="configure-kernel.html"
>Chapter 5</A
> to
configure the kernel; this is done by configuring the boot loader to
pass boot parameters to the <SPAN
CLASS="SYSTEMITEM"
>Linux</SPAN
> kernel.</P
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