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NG_TTY(4)	       FreeBSD Kernel Interfaces Manual		     NG_TTY(4)

NAME
     ng_tty -- netgraph	node type that is also a line discipline

SYNOPSIS
     #include <sys/types.h>
     #include <sys/ttycom.h>
     #include <netgraph/ng_tty.h>

DESCRIPTION
     The tty node type is both a netgraph node type and	a line discipline.  A
     new node is created when the corresponding	line discipline, NETGRAPHDISC,
     is	registered on a	tty device (see	tty(4)).

     The node has a single hook	called hook.  Incoming bytes received on the
     tty device	are sent out on	this hook, and frames received on hook are
     transmitted out on	the tty	device.	 No modification to the	data is	per-
     formed in either direction.  While	the line discipline is installed on a
     tty, the normal read and write operations are unavailable,	returning EIO.

     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 hook	being connected	to a ng_async(4) type node.
     The hot character has no effect on	the transmission of data.

     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 ioctl(2) command NGIOCGINFO.  This command returns a
     struct nodeinfo similar to	the NGM_NODEINFO netgraph control message.

HOOKS
     This node type supports the following hooks:

     hook    tty(4) serial data	contained in mbuf structures, with arbitrary
	     inter-frame boundaries.

CONTROL	MESSAGES
     This node type supports the generic control messages, plus	the following:

     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.

     NGM_TTY_GET_HOTCHAR
	  Returns an integer containing	the current hot	character in the lower
	  eight	bits.

SHUTDOWN
     This node shuts down when the corresponding device	is closed (or the line
     discipline	is uninstalled on the device).	The NGM_SHUTDOWN control mes-
     sage is not valid,	and always returns the error EOPNOTSUPP.

SEE ALSO
     ioctl(2), netgraph(4), ng_async(4), tty(4), ngctl(8)

HISTORY
     The ng_tty	node type was implemented in FreeBSD 4.0.

AUTHORS
     Archie Cobbs <archie@FreeBSD.org>

BUGS
     The serial	driver code also has a notion of a ``hot character''.  Unfor-
     tunately, this value is statically	defined	in terms of the	line disci-
     pline and cannot be changed.  Therefore, if a hot character other than
     0x7e (the default)	is set for the ng_tty node, the	node has no way	to
     convey this information to	the serial driver, and sub-optimal performance
     may result.

FreeBSD	9.2		       January 19, 1999			   FreeBSD 9.2

NAME | SYNOPSIS | DESCRIPTION | HOOKS | CONTROL MESSAGES | SHUTDOWN | SEE ALSO | HISTORY | AUTHORS | BUGS

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