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+.TH BK 4
+.UC 4
+.SH NAME
+bk \- line discipline for machine-machine communication
+.SH SYNOPSIS
+.B #include <sgtty.h>
+.PP
+.B int ldisc = NETLDISC, fildes;
+\&...
+.PP
+.B ioctl(fildes, TIOCSETD, &ldisc);
+.SH DESCRIPTION
+This line discipline provides a replacement for the old and new
+tty drivers described in
+.IR tty (4)
+when high speed output to
+and especially input from another machine is to be transmitted
+over a asynchronous communications line.  The discipline
+was designed for use by the Berkeley network
+.IR net (1)
+but is
+well suited to uploading of data from microprocessors into
+the system.  If you are going to send data over asynchronous
+communications lines at high speed into the system, you must
+use this discipline, as the system otherwise may detect high
+input data rates on terminal lines and disables the lines;
+in any case the processing of such data when normal terminal
+mechanisms are involved saturates the system.
+.PP
+A typical application program then reads a sequence of lines from
+the terminal port, checking header and sequencing information on each
+line and acknowledging receipt of each line to the sender, who then
+transmits another line of data.  Typically several hundred bytes of
+data and a smaller amount of control information will be received on
+each handshake.
+.PP
+The old standard teletype discipline can be restored by doing:
+.sp
+.ft B
+ldisc = OTTYDISC;
+
+ioctl(fildes, TIOCSETD, &ldisc);
+.ft R
+.sp
+While in networked mode, normal teletype output functions take place.
+Thus, if an 8 bit output data path is desired, it is necessary
+to prepare the output line by putting it into RAW mode using
+.IR ioctl (2).
+This must be done
+.B before
+changing the discipline with TIOCSETD, as most
+.IR ioctl (2)
+calls are disabled while in network line-discipline mode.
+.PP
+When in network mode, input processing is very limited to reduce overhead.
+Currently the input path is only 7 bits wide, with newline the only
+recognized character, terminating an input record.
+Each input record must be read and acknowledged before the next input
+is read as the system refuses to accept any new data when there
+is a record in the buffer.  The buffer is limited in length, but the
+system guarantees to always be willing to accept input resulting in
+512 data characters and then the terminating newline.
+.PP
+User level programs should provide sequencing and checksums on the
+information to guarantee accurate data transfer.
+.SH "SEE ALSO"
+tty(4)
+.SH BUGS
+A standard program and protocol should be defined for
+uploading data from microprocessors, so that havoc doesn't
+result.
+.PP
+A full 8-bit input path should be provided with a mechanism
+for escaping newlines into an input packet.