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+.\" $NetBSD: console.4,v 1.1 2021/06/03 07:41:26 wiz Exp $
+.\"
+.Dd September 6, 2006
+.Dt CONS 4 x86
+.Os
+.Sh NAME
+.Nm console
+.Nd x86 console interface
+.Sh SYNOPSIS
+.Cd options CONSDEVNAME=string
+.Cd options CONADDR=integer
+.Cd options CONSPEED=integer
+.Cd options CONS_OVERRIDE
+.Cd options CONMODE=integer
+.Sh DESCRIPTION
+The
+.Dq console
+device is used for
+.Em kernel printf
+messages and accesses to the
+.Pa /dev/console
+character special device in user mode.
+It is attached to a hardware interface at boot time controlled by options
+in the kernel configuration file, or information passed by the boot loader.
+.Pp
+Bootblocks from
+.Nx 1.4
+or newer select their console device from a compiled-in list,
+and then pass their choice of console device and console parameters to
+the kernel.
+.Pp
+As of
+.Nx 1.5 ,
+the
+.Ic consdev
+bootblock command allows changing the console device on-the-fly.
+.Pp
+The kernel will use the same console device as the
+bootblock; no special kernel configuration is required.
+.Pp
+To override
+the bootblock's choice of console, or to use a serial kernel console
+with older bootblocks, you must specify kernel config-file options to
+override the information passed by the bootblock.
+The current option choices are:
+.Bl -tag -width aaa
+.It - the standard PC keyboard and display
+(with either the
+.Dq pc
+or the
+.Xr wscons 4
+driver)
+.It - standard PC serial ports
+(with
+.Xr com 4
+driver)
+.El
+.Pp
+The available
+.Em kernel configuration
+options are:
+.Bl -ohang
+.It Cd options CONSDEVNAME=string
+specifies the name of the console device.
+Valid values are
+.Dq pc
+for the pc keyboard / display (default)
+and
+.Dq com
+for a serial port.
+.It Cd options CONADDR=integer
+sets the base address for the serial console port (default: 0x3f8).
+.It Cd options CONSPEED=integer
+sets the baudrate for the serial console (default: 9600).
+.It Cd options CONS_OVERRIDE
+causes console information passed by the bootloader to be ignored and
+the settings specified by the three options above (or the defaults) to be
+used.
+Default behaviour is to use the settings from the bootloader if
+present, and to use option / default values only if no information was
+passed.
+.It Cd options CONMODE=integer
+allows to specify terminal control flags.
+The argument is a
+.Dq cflag
+value, see
+.Xr termios 4
+for details.
+Default is
+.Li ( CREAD | CS8 | HUPCL )
+(8N1).
+This option takes always effect, because mode settings are not passed
+by the bootloader.
+.El
+.Sh FILES
+.Bl -tag -width /dev/console
+.It Pa /dev/console
+.El
+.Sh EXAMPLES
+.Cd options CONSDEVNAME=\&"\e"com\e"\&",CONADDR=0x2f8,CONSPEED=57600
+.Sh SEE ALSO
+.Xr config 1 ,
+.Xr tty 4 ,
+.Xr boot 8
+.Sh BUGS
+The console device is chosen early in system startup regardless
+if the specified driver / device is present in the system configuration file.
+If the driver asked for by the bootloader or
+.Dq Cd options CONSDEVNAME
+is not configured into the system, a panic is caused.
+Because there is
+no console device, no explaining message will be printed.
+If the driver is present, but the specific device instance not, kernel
+printf will work, but
+.Pa /dev/console
+becomes a dummy.