bk(4) Unsupported bk(4)Namebk - line discipline for machine-machine communication (obsolete)
Syntax
pseudo-device bkDescription
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 Alsotty(4)
VAX bk(4)
