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.\" $FreeBSD: head/share/man/man4/nmdm.4 140899 2005-01-27 10:30:53Z ru $
.\"
.Dd January 27, 2005
.Dt NMDM 4
.Os
.Sh NAME
.Nm nmdm
.Nd nullmodem terminal driver
.Sh SYNOPSIS
.Cd "device nmdm"
.Sh DESCRIPTION
The
.Nm
driver provides two
.Xr tty 4
devices connected
by a virtual
.Dq "null modem"
cable.
.Pp
If either of the two tty devices have the
.Dv CDSR_OFLOW
bit
.Pq Dq Li "stty dsrflow"
set in their line discipline, the
.Nm
device will emulate the speed configured in the
.Xr termios 4
settings.
The speed emulation works independently in the two directions,
controlled by the slower end's termios settings
.Va ( c_ispeed , c_ospeed ,
.Dv CS5 ... CS8 , CSTOPB
and
.Dv PARENB ) .
.Sh FILES
.Bl -tag -width ".Pa /dev/nmdm Ns Ar N Ns Op Pa AB" -compact
.It Pa /dev/nmdm Ns Ar N Ns Op Pa AB
nullmodem device nodes.
Where the
.Pa A
node has a matching
.Pa B
node.
.El
.Pp
The
.Nm
driver implements
.Dq "on-demand device creation"
so simply accessing a given instance in
.Pa /dev
will create it.
.Sh DIAGNOSTICS
None.
.Sh SEE ALSO
.Xr stty 1 ,
.Xr termios 4 ,
.Xr tty 4
.Sh HISTORY
The
.Nm
driver first appeared in
.Fx 4.4 .