term% cat index.txt TTYLD(4) Kernel Interfaces Manual TTYLD(4)
NAME
ttyld - terminal processing
SYNOPSIS
#include <sgtty.h>
DESCRIPTION
This processing module is usually inserted into a stream(4) connected
to a terminal device. It gathers input into lines, performs erase and
kill processing, and translates control sequences.
Certain special characters have particular meaning on input. These
characters are not passed to a program except in raw mode, where they
lose their special character. It is possible to change these charac‐
ters from the default.
# erases the last-typed character. It will not erase beyond the
beginning of a line or an EOT.
@ erases the entire preceding part of the line, but not beyond an
EOT.
EOT (Control-D) may be used to generate an end of file from a termi‐
nal. When an EOT is received, all the characters waiting to be
read are immediately passed to the program, without waiting for
a new-line, and the EOT is discarded. Thus if there are no
characters waiting, which is to say the EOT occurred at the be‐
ginning of a line, zero characters will be passed back, and this
is the standard end-of-file indication.
\ escapes a following erase, kill, or EOT character and allows it
to be treated as ordinary data.
DEL is not passed to a program but generates the interrupt signal
(2). The signal is sent to any processes in the process group
of the stream; see stream(4).
FS generates the quit signal (3).
DC3 delays all printing on the terminal until something is typed in.
DC1 restarts printing after DC3 without generating any input to a
program.
Several ioctl(2) calls apply to terminals. Most of them use the fol‐
lowing structure, defined in <sgtty.h>:
struct sgttyb {
char sg_ispeed;
char sg_ospeed;
char sg_erase;
char sg_kill;
int sg_flags;
};
The sg_ispeed and sg_ospeed fields describe the input and output speeds
of the device according to the following table. They are not inter‐
preted by the tty line discipline, but merely passed on to the device.
Devices ignore impossible speed changes. Symbolic values in the table
are as defined in <sgtty.h>.
B0 0 (hang up device)
B50 1 50 baud
B75 2 75 baud
B110 3 110 baud
B134 4 134.5 baud
B150 5 150 baud
B200 6 200 baud
B300 7 300 baud
B600 8 600 baud
B1200 9 1200 baud
B1800 10 1800 baud
B2400 11 2400 baud
B4800 12 4800 baud
B9600 13 9600 baud
EXTA 14 External A
EXTB 15 External B
The sg_erase and sg_kill fields of the argument structure specify the
erase and kill characters respectively. (Defaults are # and @.)
The sg_flags field of the argument structure contains several bits that
determine the system's treatment of the terminal:
ALLDELAY 0177400 Delay algorithm selection
VTDELAY 0040000 Select form-feed and vertical-tab delays:
FF0 0
FF1 0100000
CRDELAY 0030000 Select carriage-return delays:
CR0 0
CR1 0010000
CR2 0020000
CR3 0030000
TBDELAY 0006000 Select tab delays:
TAB0 0
TAB1 0001000
TAB2 0004000
XTABS 0006000
NLDELAY 0001400 Select new-line delays:
NL0 0
NL1 0000400
NL2 0001000
NL3 0001400
EVENP 0000200 Even parity allowed on input (most terminals)
ODDP 0000100 Odd parity allowed on input
RAW 0000040 Raw mode: wake up on all characters, 8-bit interface
CRMOD 0000020 Map CR into LF; echo LF or CR as CR-LF
ECHO 0000010 Echo (full duplex)
LCASE 0000004 Map upper case to lower on input
CBREAK 0000002 Return each character as soon as typed
TANDEM 0000001 Automatic flow control
The delay bits specify how long transmission stops to allow for mechan‐
ical or other movement when certain characters are sent to the termi‐
nal. In all cases a value of 0 indicates no delay.
If a form-feed/vertical tab delay is specified, it lasts for about 2
seconds.
Carriage-return delay type 1 lasts about .08 seconds. Delay type 2
lasts about .16 seconds. Delay type 3 is supposed to be for the Con‐
cept 100.
New-line delay type 1 is supposed to be for the Teletype model 37.
Type 2 is about .10 seconds. Type 3 is unimplemented and is 0.
Tab delay type 1 is supposed to be for the Teletype model 37. Type 3,
called XTABS, is not a delay at all but causes tabs to be replaced by
the appropriate number of spaces on output.
In raw mode, every character is passed immediately to the program with‐
out waiting until a full line has been typed. No erase or kill pro‐
cessing is done; the end-of-file indicator (EOT), the interrupt charac‐
ter (DEL) and the quit character (FS) are not treated specially. There
are no delays and no echoing, and no replacement of one character for
another; characters are a full 8 bits for both input and output.
Mode 020 causes input carriage returns to be turned into new-lines; in‐
put of either CR or LF causes LF-CR both to be echoed (for terminals
without a new-line function).
CBREAK is a sort of half-cooked mode. Programs read each character as
soon as typed, instead of waiting for a full line, but quit and inter‐
rupt work, and output delays CRMOD, XTABS, ECHO, and parity work nor‐
mally. On the other hand there is no erase or kill, and no special
treatment of \ or EOT.
TANDEM mode causes the system to produce a stop character (default DC3)
whenever the input queue is in danger of overflowing, and a start char‐
acter (default DC1) when the input queue has drained sufficiently. It
is useful for flow control when the ‘terminal' is actually another ma‐
chine that obeys the conventions.
Several ioctl calls have the form:
#include <sgtty.h>
ioctl(fildes, code, arg)
struct sgttyb *arg;
The applicable codes are:
TIOCGETP
Fetch the parameters associated with the terminal, and store in
the pointed-to structure.
TIOCSETP, TIOCSETN
Set the parameters according to the pointed-to structure. These
(equivalent) codes are synchronous with output data.
The following codes affect characters that are special to the terminal
interface. The argument is a pointer to the following structure, de‐
fined in <sgtty.h>:
struct tchars {
char t_intrc /* interrupt */
char t_quitc; /* quit */
char t_startc; /* start output */
char t_stopc; /* stop output */
char t_eofc; /* end-of-file */
char t_brkc; /* input delimiter (like nl) */
};
The default values for these characters are DEL, FS, DC1, DC3, EOT, and
-1. A character value of -1 eliminates the effect of that character.
The t_brkc character, by default -1, acts like a new-line in that it
terminates a ‘line,' is echoed, and is passed to the program. The
‘stop' and ‘start' characters may be the same, to produce a toggle ef‐
fect. It is counterproductive to make other special characters (in‐
cluding erase and kill) identical.
TIOCSETC
Change the various special characters to those given in the
structure.
TIOCGETC
Fill in the structure with the current special characters.
SEE ALSO
getty(8), stty(1), signal(2), ioctl(2), stream(4)
TTYLD(4)