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33 .\" Author: Archie Cobbs <archie@FreeBSD.org>
36 .\" $Whistle: ng_tty.8,v 1.5 1999/01/25 23:46:28 archie Exp $
43 .Nd netgraph node type that is also a line discipline
51 node type is both a netgraph node type and a line discipline.
52 A new node is created when the corresponding line discipline,
54 is registered on a tty device (see
57 The node has a single hook called
59 Incoming bytes received on the tty device are sent out on this hook,
60 and frames received on
62 are transmitted out on the tty device.
63 No modification to the data is performed in either direction.
64 While the line discipline is installed on a tty, the normal
65 read and write operations are unavailable, returning
68 The node supports an optional
70 If set to non-zero, incoming
71 data from the tty device is queued until this character is seen.
72 This avoids sending lots of mbufs containing a small number of bytes,
73 but introduces potentially infinite latency.
74 The default hot character is 0x7e, consistent with
79 The hot character has no effect on the transmission of data.
81 The node will attempt to give itself the same netgraph name as the name
83 In any case, information about the node is available via the netgraph
87 This command returns a
91 netgraph control message.
93 This node type supports the following hooks:
95 .Bl -tag -width foobar
98 serial data contained in
100 structures, with arbitrary inter-frame boundaries.
103 This node type supports the generic control messages, plus the following:
105 .It Dv NGM_TTY_SET_HOTCHAR
106 This command takes an integer argument and sets the hot character
107 from the lower 8 bits.
108 A hot character of zero disables queueing,
109 so that all received data is forwarded immediately.
110 .It Dv NGM_TTY_GET_HOTCHAR
111 Returns an integer containing the current hot character in the lower
115 This node shuts down when the corresponding device is closed
116 (or the line discipline is uninstalled on the device).
119 control message is not valid, and always returns the error
130 node type was implemented in
133 .An Archie Cobbs Aq archie@FreeBSD.org
135 The serial driver code also has a notion of a
137 Unfortunately, this value is statically defined in terms of the
138 line discipline and cannot be changed.
139 Therefore, if a hot character other than 0x7e (the default) is set for the
141 node, the node has no way to convey this information to the
142 serial driver, and sub-optimal performance may result.