1BK(4) Kernel Interfaces Manual BK(4)
2
6 bk - line discipline for machine-machine communication (obsolete)
7
9 Not currently supported under 2.11BSD
10
12 This line discipline provides a replacement for the old and new tty
13 drivers described in tty(4) when high speed output to and especially
14 input from another machine is to be transmitted over a asynchronous
15 communications line. The discipline was designed for use by the Berke‐
16 ley network. It may be suitable for uploading of data from micropro‐
17 cessors into the system. If you are going to send data over asynchro‐
18 nous communications lines at high speed into the system, you must use
19 this discipline, as the system otherwise may detect high input data
20 rates on terminal lines and disables the lines; in any case the pro‐
21 cessing of such data when normal terminal mechanisms are involved satu‐
22 rates the system.
23 The line discipline is enabled by a sequence:
25 #include <sgtty.h>
27 int ldisc = NETLDISC, fildes; ...
28 ioctl(fildes, TIOCSETD, &ldisc);
29 A typical application program then reads a sequence of lines from the
31 terminal port, checking header and sequencing information on each line
32 and acknowledging receipt of each line to the sender, who then trans‐
33 mits another line of data. Typically several hundred bytes of data and
34 a smaller amount of control information will be received on each hand‐
35 shake.
36 The old standard teletype discipline can be restored by doing:
38 ldisc = OTTYDISC;
40 ioctl(fildes, TIOCSETD, &ldisc);
41 While in networked mode, normal teletype output functions take place.
43 Thus, if an 8 bit output data path is desired, it is necessary to pre‐
44 pare the output line by putting it into RAW mode using ioctl(2). This
45 must be done before changing the discipline with TIOCSETD, as most
46 ioctl(2) calls are disabled while in network line-discipline mode.
47 When in network mode, input processing is very limited to reduce over‐
49 head. Currently the input path is only 7 bits wide, with newline the
50 only recognized character, terminating an input record. Each input
51 record must be read and acknowledged before the next input is read as
52 the system refuses to accept any new data when there is a record in the
53 buffer. The buffer is limited in length, but the system guarantees to
54 always be willing to accept input resulting in 512 data characters and
55 then the terminating newline.
56 User level programs should provide sequencing and checksums on the
58 information to guarantee accurate data transfer.
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61 tty(4)
62
64 None.
65
67 The Purdue uploading line discipline, which provides 8 bits and uses
68 timeout's to terminate uploading should be incorporated into the stan‐
69 dard system, as it is much more suitable for microprocessor connec‐
70 tions.
714th Berkeley Distribution January 27, 1996 BK(4)