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+.\" Copyright (c) 1996-1999 Whistle Communications, Inc.
+.\" All rights reserved.
+.\" 
+.\" Subject to the following obligations and disclaimer of warranty, use and
+.\" redistribution of this software, in source or object code forms, with or
+.\" without modifications are expressly permitted by Whistle Communications;
+.\" provided, however, that:
+.\" 1. Any and all reproductions of the source or object code must include the
+.\"    copyright notice above and the following disclaimer of warranties; and
+.\" 2. No rights are granted, in any manner or form, to use Whistle
+.\"    Communications, Inc. trademarks, including the mark "WHISTLE
+.\"    COMMUNICATIONS" on advertising, endorsements, or otherwise except as
+.\"    such appears in the above copyright notice or in the software.
+.\" 
+.\" THIS SOFTWARE IS BEING PROVIDED BY WHISTLE COMMUNICATIONS "AS IS", AND
+.\" TO THE MAXIMUM EXTENT PERMITTED BY LAW, WHISTLE COMMUNICATIONS MAKES NO
+.\" REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED, REGARDING THIS SOFTWARE,
+.\" INCLUDING WITHOUT LIMITATION, ANY AND ALL IMPLIED WARRANTIES OF
+.\" MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR NON-INFRINGEMENT.
+.\" WHISTLE COMMUNICATIONS DOES NOT WARRANT, GUARANTEE, OR MAKE ANY
+.\" REPRESENTATIONS REGARDING THE USE OF, OR THE RESULTS OF THE USE OF THIS
+.\" SOFTWARE IN TERMS OF ITS CORRECTNESS, ACCURACY, RELIABILITY OR OTHERWISE.
+.\" IN NO EVENT SHALL WHISTLE COMMUNICATIONS BE LIABLE FOR ANY DAMAGES
+.\" RESULTING FROM OR ARISING OUT OF ANY USE OF THIS SOFTWARE, INCLUDING
+.\" WITHOUT LIMITATION, ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
+.\" PUNITIVE, OR CONSEQUENTIAL DAMAGES, PROCUREMENT OF SUBSTITUTE GOODS OR
+.\" SERVICES, LOSS OF USE, DATA OR PROFITS, HOWEVER CAUSED AND UNDER ANY
+.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+.\" THIS SOFTWARE, EVEN IF WHISTLE COMMUNICATIONS IS ADVISED OF THE POSSIBILITY
+.\" OF SUCH DAMAGE.
+.\" 
+.\" Author: Archie Cobbs <archie@whistle.com>
+.\"
+.\" $FreeBSD$
+.\" $Whistle: ng_tty.8,v 1.5 1999/01/25 23:46:28 archie Exp $
+.\"
+.Dd January 19, 1999
+.Dt NG_TTY 8
+.Os FreeBSD 3
+.Sh NAME
+.Nm ng_tty
+.Nd netgraph node type that is also a line discipline
+.Sh SYNOPSIS
+.Fd #include <netgraph/ng_message.h>
+.Fd #include <netgraph/ng_tty.h>
+.Sh DESCRIPTION
+The
+.Nm tty
+node type is both a netgraph node type and a line discipline.
+A new node is created when the corresponding line discipline is
+registered on a tty device (see
+.Xr tty 4 ")."
+.Pp
+The node has a single hook called
+.Dv hook .
+Incoming bytes received on the tty device are sent out on this hook,
+and frames received on
+.Dv hook
+are transmitted out on the tty device.
+No modification to the data is performed in either direction.
+While the line discipline is installed on a tty, the normal
+read and write operations are unavailable, returning
+.Er EIO .
+.Pp
+The node supports an optional ``hot character.'' If set to non-zero, incoming
+data from the tty device is queued until this character is seen.
+This avoids sending lots of mbufs containing a small number of bytes,
+but introduces potentially infinite latency.
+The default hot character is 0x7e, consistent with
+.Dv hook
+being connected to a
+.Xr ng_async 8
+type node. The hot character has no effect on the transmission of data.
+.Pp
+The node will attempt to give itself the same netgraph name as the name
+of the tty device.
+In any case, information about the node is available via the netgraph
+.Xr ioctl 2
+command
+.Dv NGIOCGINFO .
+This command returns a
+.Dv "struct nodeinfo"
+similar to the
+.Dv NGM_NODEINFO
+netgraph control message.
+.Sh HOOKS
+This node type supports the following hooks:
+.Pp
+.Bl -tag -width foobar
+.It Dv hook
+.Xr tty 4
+serial data contained in
+.Dv mbuf
+structures, with arbitrary inter-frame boundaries.
+.El
+.Sh CONTROL MESSAGES
+This node type supports the generic control messages, plus the following:
+.Bl -tag -width foo
+.It Dv NGM_TTY_SET_HOTCHAR
+This command takes an integer argument and sets the hot character
+from the lower 8 bits. A hot character of zero disables queueing,
+so that all received data is forwarded immediately.
+.It Dv NGM_TTY_GET_HOTCHAR
+Returns an integer containing the current hot character in the lower
+eight bits.
+.Sh SHUTDOWN
+This node shuts down when the corresponding device is closed
+(or the line discipline is uninstalled on the device).
+The
+.Dv NGM_SHUTDOWN
+control message is not valid, and always returns the error
+.Er EOPNOTSUPP .
+.Sh BUGS
+The
+.Nm tty
+type registers its line discipline when the type is installed,
+where it is dynamically assigned an integer index.
+Unfortunately, there's no way to know what this integer is
+except by reading the output of
+.Xr dmesg 8 .
+The fix for this is to have line disciplines identified by
+unique ASCII strings instead of fixed integer constants,
+or else to assign one of those constants to
+.Nm ng_tty .
+.Pp
+The serial driver code also has a notion of a ``hot character.''
+Unfortunately, this value is statically defined in terms of the
+line discipline and cannot be changed.
+Therefore, if a hot character other than 0x7e (the default) is set for the
+.Nm tty
+node, the node has no way to convey this information to the
+serial driver, and sub-optimal performance may result.
+.Sh SEE ALSO
+.Xr ioctl 2 ,
+.Xr netgraph 4 ,
+.Xr tty 4 ,
+.Xr ng_async 8 ,
+.Xr ngctl 8 .
+.Sh AUTHOR
+Archie Cobbs <archie@whistle.com>