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Annotation of 43BSDTahoe/man/man4/bk.4, revision 1.1.1.1

1.1       root        1: .\" Copyright (c) 1980 Regents of the University of California.
                      2: .\" All rights reserved.  The Berkeley software License Agreement
                      3: .\" specifies the terms and conditions for redistribution.
                      4: .\"
                      5: .\"    @(#)bk.4        6.1 (Berkeley) 5/15/85
                      6: .\"
                      7: .TH BK 4 "May 15, 1985"
                      8: .UC 4
                      9: .SH NAME
                     10: bk \- line discipline for machine-machine communication (obsolete)
                     11: .SH SYNOPSIS
                     12: .B pseudo-device bk
                     13: .SH DESCRIPTION
                     14: This line discipline provides a replacement for the old and new
                     15: tty drivers described in
                     16: .IR tty (4)
                     17: when high speed output to
                     18: and especially input from another machine is to be transmitted
                     19: over a asynchronous communications line.  The discipline
                     20: was designed for use by the Berkeley network.
                     21: It may be suitable for uploading of data from microprocessors into
                     22: the system.  If you are going to send data over asynchronous
                     23: communications lines at high speed into the system, you must
                     24: use this discipline, as the system otherwise may detect high
                     25: input data rates on terminal lines and disables the lines;
                     26: in any case the processing of such data when normal terminal
                     27: mechanisms are involved saturates the system.
                     28: .PP
                     29: The line discipline is enabled by a sequence:
                     30: .PP
                     31: .nf
                     32: .ft B
                     33:        #include <sgtty.h>
                     34:        int ldisc = NETLDISC, fildes; ...
                     35:        ioctl(fildes, TIOCSETD, &ldisc);
                     36: .fi
                     37: .ft R
                     38: .PP
                     39: A typical application program then reads a sequence of lines from
                     40: the terminal port, checking header and sequencing information on each
                     41: line and acknowledging receipt of each line to the sender, who then
                     42: transmits another line of data.  Typically several hundred bytes of
                     43: data and a smaller amount of control information will be received on
                     44: each handshake.
                     45: .PP
                     46: The old standard teletype discipline can be restored by doing:
                     47: .PP
                     48: .nf
                     49: .ft B
                     50:        ldisc = OTTYDISC;
                     51:        ioctl(fildes, TIOCSETD, &ldisc);
                     52: .fi
                     53: .ft R
                     54: .PP
                     55: While in networked mode, normal teletype output functions take place.
                     56: Thus, if an 8 bit output data path is desired, it is necessary
                     57: to prepare the output line by putting it into RAW mode using
                     58: .IR ioctl (2).
                     59: This must be done
                     60: .B before
                     61: changing the discipline with TIOCSETD, as most
                     62: .IR ioctl (2)
                     63: calls are disabled while in network line-discipline mode.
                     64: .PP
                     65: When in network mode, input processing is very limited to reduce overhead.
                     66: Currently the input path is only 7 bits wide, with newline the only
                     67: recognized character, terminating an input record.
                     68: Each input record must be read and acknowledged before the next input
                     69: is read as the system refuses to accept any new data when there
                     70: is a record in the buffer.  The buffer is limited in length, but the
                     71: system guarantees to always be willing to accept input resulting in
                     72: 512 data characters and then the terminating newline.
                     73: .PP
                     74: User level programs should provide sequencing and checksums on the
                     75: information to guarantee accurate data transfer.
                     76: .SH "SEE ALSO"
                     77: tty(4)
                     78: .SH DIAGNOSTICS
                     79: None.
                     80: .SH BUGS
                     81: The Purdue uploading line discipline, which provides 8 bits and uses
                     82: timeout's to terminate uploading should be incorporated into the standard
                     83: system, as it is much more suitable for microprocessor connections.

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