4.3BSD-UWisc/man/cat4/bk.4

BK(4)               UNIX Programmer's Manual                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 _t_t_y(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.  It
     may be suitable for uploading of data from microprocessors
     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 processing of such data when nor-
     mal terminal mechanisms are involved saturates 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 transmits another line of data.
     Typically several hundred bytes of data and a smaller amount
     of control information will be received on each handshake.

     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 prepare the output line by putting it
     into RAW mode using _i_o_c_t_l(2).  This must be done before
     changing the discipline with TIOCSETD, as most _i_o_c_t_l(2)
     calls are disabled while in network line-discipline mode.

     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, terminat-
     ing an input record.  Each input record must be read and
     acknowledged before the next input is read as the system



Printed 12/27/86          May 15, 1985                          1






BK(4)               UNIX Programmer's Manual                BK(4)



     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 incor-
     porated into the standard system, as it is much more suit-
     able for microprocessor connections.




































Printed 12/27/86          May 15, 1985                          2