4.3BSD - /usr/man/cat4/bk.0

BK(4)                                                                    BK(4)


NAME
       bk - line discipline for machine-machine communication (obsolete)

SYNOPSIS
       pseudo-device bk

DESCRIPTION
       This  line  discipline  provides  a replacement for the old and new tty
       drivers described in 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 Berke‐
       ley  network.   It may be suitable for uploading of data from micropro‐
       cessors into the system.  If you are going  to  send  data  over  asyn‐
       chronous  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 pro‐
       cessing of such data when normal terminal mechanisms are involved satu‐
       rates the system.

       The line discipline is enabled by a sequence:

            #include <sgtty.h>
            int ldisc = NETLDISC, fildes; ...
            ioctl(fildes, TIOCSETD, &ldisc);

       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 trans‐
       mits another line of data.  Typically several hundred bytes of data and
       a  smaller amount of control information will be received on each hand‐
       shake.

       The old standard teletype discipline can be restored by doing:

            ldisc = OTTYDISC;
            ioctl(fildes, TIOCSETD, &ldisc);

       While in networked mode, normal teletype output functions  take  place.
       Thus,  if an 8 bit output data path is desired, it is necessary to pre‐
       pare the output line by putting it into RAW mode using ioctl(2).   This
       must  be  done  before  changing  the discipline with TIOCSETD, as most
       ioctl(2) calls are disabled while in network line-discipline mode.

       When in network mode, input processing is very limited to reduce  over‐
       head.   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.

       User  level  programs  should  provide  sequencing and checksums on the
       information to guarantee accurate data transfer.

SEE ALSO
       tty(4)

DIAGNOSTICS
       None.

BUGS
       The Purdue uploading line discipline, which provides 8  bits  and  uses
       timeout’s  to  terminate  uploading  should  be  incorporated  into the
       standard system, as it is much more suitable for microprocessor connec‐
       tions.


4th Berkeley Distribution        May 15, 1985                            BK(4)