AT&T UNIX™PC Unix System V Users Manual - tenox

XT(7)
NAME
xt - multiplexed tty driver for AT&T windowing terminals
XT( 7)
DESCRIPTION
The xt driver provides virtual tty(7) circuits multiplexed onto real tty (7)
lines. It interposes its own channel multiplexing protocol as a line dis- �
cipline between the real device driver and the standard tty (7) line discip- )
lines.
Virtual tty (1) circuits are named by character-special files of the form
!devlxt? ?? . Filenames end in three digits, where the first two represent
the channel group and the last represents the virtual tty (7) number (0-7)
of the channel group. Allocation of a new channel group is done dynamically
by attempting to open a name ending in 0 with the O_EXCL flag
set. After a successful open, the tty (1) file onto which the channels are to
be multiplexed should be passed to xt via the XTIOCLINK ioctl (2)
request. Afterwards, all the channels in the group will behave as normal
tty (7) files, with data passed in packets via the real tty (1) line.
The xt driver implements the protocol described in xtproto (S) and in
layers(S). Packets are formatted as described in xtproto (S), while the
contents of packets conform to the description in layers(S).
There are three groups of ioctl (2) requests recognized by xt . The first
group contains all the normal tty ioctl (2) requests described in termio (7),
with the addition of the following:
TIOCEXCL Set exclusive use mode; no further opens are permitted
until the file has been closed.
TIOCNXCL Reset exclusive use mode; further opens are once
again permitted.
The second group of ioctl(2) requests concerns control of the windowing
terminal, and is described in the header file . The requests
are as follows:
JTYPE, JMPX Both return the value JMPX • These are used to
identify a terminal device as an xt channel.
JBOOT,JTERM Both generate an appropriate command packet to
the windowing terminal affecting the layer associated
with the file descriptor argument to ioctl (2).
They may return the error code EIO if the system
clist is empty.
JTIMO, JTIMOM JTIMO specifies the timeouts in seconds, and
JTIMOM in milliseconds. Invalid except on channel
0. They may return the error code EIO if the
system clist is empty.
JWINSIZE
JZOMBOOT
Requires the address of a jwinsize structure as an
argument The window sizes of the layer associated
with the file descriptor argument to ioctl(2) are
copied to the structure.
Generate a command packet to the windowing terminal
to enter download mode on the channel associated
with the file descriptor argument to ioctl (2),
like JBOOT; but when the download is finished,
make the layer a zombie (ready for debugging). It
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