bk man page on Ultrix

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bk(4)				  Unsupported				 bk(4)

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

Syntax
       pseudo-device bk

Description
       This  line  discipline  provides	 a replacement for the old and new tty
       drivers described in when high speed output  to	and  especially	 input
       from  another machine is to be transmitted over a asynchronous communi‐
       cations line.  The discipline was designed for use by the Berkeley net‐
       work.   It  may	be suitable for uploading of data from microprocessors
       into the system.	 If you are going to send data over asynchronous  com‐
       munications lines at high speed into the system, you must use this dis‐
       cipline, 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.

       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	This  must  be
       done  before  changing  the discipline with TIOCSETD, as most 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)

				      VAX				 bk(4)
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