TERMIO(7I) Ioctl Requests TERMIO(7I)

NAME


termio - general terminal interface

SYNOPSIS


#include <termio.h>

ioctl(int fildes, int request, struct termio *arg);

ioctl(int fildes, int request, int arg);

#include <termios.h>

ioctl(int fildes, int request, struct termios *arg);

DESCRIPTION


This release supports a general interface for asynchronous communications
ports that is hardware-independent. The user interface to this
functionality is using function calls (the preferred interface) described
in termios(3C) or ioctl() commands described in this section. This section
also discusses the common features of the terminal subsystem which are
relevant with both user interfaces.

When a terminal file is opened, it normally causes the process to wait
until a connection is established. In practice, user programs seldom open
terminal files; they are opened by the system and become a user's standard
input, output, and error files. The first terminal file opened by the
session leader that is not already associated with a session becomes the
controlling terminal for that session. The controlling terminal plays a
special role in handling quit and interrupt signals, as discussed below.
The controlling terminal is inherited by a child process during a fork(2).
A process can break this association by changing its session using
setsid(2).

A terminal associated with one of these files ordinarily operates in full-
duplex mode. Characters may be typed at any time, even while output is
occurring, and are only lost when the character input buffers of the system
become completely full, which is rare. For example, the number of
characters in the line discipline buffer may exceed {MAX_CANON} and IMAXBEL
(see below) is not set, or the user may accumulate {MAX_INPUT} number of
input characters that have not yet been read by some program. When the
input limit is reached, all the characters saved in the buffer up to that
point are thrown away without notice.

Session Management (Job Control)
A control terminal will distinguish one of the process groups in the
session associated with it to be the foreground process group. All other
process groups in the session are designated as background process groups.
This foreground process group plays a special role in handling signal-
generating input characters, as discussed below. By default, when a
controlling terminal is allocated, the controlling process's process group
is assigned as foreground process group.

Background process groups in the controlling process's session are subject
to a job control line discipline when they attempt to access their
controlling terminal. Process groups can be sent signals that will cause
them to stop, unless they have made other arrangements. An exception is
made for members of orphaned process groups.

An orphaned process group is one where the process group (see getpgid(2))
has no members with a parent in a different process group but sharing the
same controlling terminal. When a member of an orphaned process group
attempts to access its controlling terminal, EIO is returned because there
would be no way to restart the process if it were stopped on one of these
signals.

If a member of a background process group attempts to read its controlling
terminal, its process group will be sent a SIGTTIN signal, which will
normally cause the members of that process group to stop. If, however, the
process is ignoring or holding SIGTTIN, or is a member of an orphaned
process group, the read will fail with errno set to EIO, and no signal is
sent.

If a member of a background process group attempts to write its controlling
terminal and the TOSTOP bit is set in the c_lflag field, its process group
is sent a SIGTTOU signal, which will normally cause the members of that
process group to stop. If, however, the process is ignoring or holding
SIGTTOU, the write will succeed. If the process is not ignoring or holding
SIGTTOU and is a member of an orphaned process group, the write will fail
with errno set to EIO, and no signal will be sent.

If TOSTOP is set and a member of a background process group attempts to
ioctl() its controlling terminal, and that ioctl() will modify terminal
parameters (for example, TCSETA, TCSETAW, TCSETAF, or TIOCSPGRP), its
process group will be sent a SIGTTOU signal, which will normally cause the
members of that process group to stop. If, however, the process is
ignoring or holding SIGTTOU, the ioctl will succeed. If the process is not
ignoring or holding SIGTTOU and is a member of an orphaned process group,
the write will fail with errno set to EIO, and no signal will be sent.

Canonical Mode Input Processing


Normally, terminal input is processed in units of lines. A line is
delimited by a newline (ASCII LF) character, an end-of-file (ASCII EOT)
character, or an end-of-line character. This means that a program
attempting to read will block until an entire line has been typed. Also,
no matter how many characters are requested in the read call, at most one
line will be returned. It is not necessary, however, to read a whole line
at once; any number of characters may be requested in a read, even one,
without losing information.

During input, erase, erase2, and kill processing is normally done. The
ERASE and ERASE2 character (by default, the character DEL for ERASE and
Control-h for ERASE2) erases the last character typed. The WERASE
character (the character Control-w) erases the last "word" typed in the
current input line (but not any preceding spaces or tabs). A "word" is
defined as a sequence of non-blank characters, with tabs counted as blanks.
None of ERASE or ERASE2 or WERASE will erase beyond the beginning of the
line. The KILL character (by default, the character NAK) kills (deletes)
the entire input line, and optionally outputs a newline character. All
these characters operate on a key stroke basis, independent of any
backspacing or tabbing that may have been done. The REPRINT character (the
character Control-r) prints a newline followed by all characters that have
not been read. Reprinting also occurs automatically if characters that
would normally be erased from the screen are fouled by program output. The
characters are reprinted as if they were being echoed; consequencely, if
ECHO is not set, they are not printed.

The ERASE, ERASE2, and KILL characters may be entered literally by
preceding them with the escape character. In this case, the escape
character is not read. The erase, erase2, and kill characters may be
changed.

Non-canonical Mode Input Processing
In non-canonical mode input processing, input characters are not assembled
into lines, and erase and kill processing does not occur. The MIN and TIME
values are used to determine how to process the characters received.

MIN represents the minimum number of characters that should be received
when the read is satisfied (that is, when the characters are returned to
the user). TIME is a timer of 0.10-second granularity that is used to
timeout bursty and short-term data transmissions. The four possible values
for MIN and TIME and their interactions are described below.

Case A: MIN > 0, TIME > 0 In this case, TIME serves as an intercharacter
timer and is activated after the first character
is received. Since it is an intercharacter
timer, it is reset after a character is
received. The interaction between MIN and TIME
is as follows: as soon as one character is
received, the intercharacter timer is started.
If MIN characters are received before the
intercharacter timer expires (note that the
timer is reset upon receipt of each character),
the read is satisfied. If the timer expires
before MIN characters are received, the
characters received to that point are returned
to the user. Note that if TIME expires, at
least one character will be returned because the
timer would not have been enabled unless a
character was received. In this case (MIN > 0,
TIME > 0), the read sleeps until the MIN and
TIME mechanisms are activated by the receipt of
the first character. If the number of
characters read is less than the number of
characters available, the timer is not
reactivated and the subsequent read is satisfied
immediately.

Case B: MIN > 0, TIME = 0 In this case, since the value of TIME is zero,
the timer plays no role and only MIN is
significant. A pending read is not satisfied
until MIN characters are received (the pending
read sleeps until MIN characters are received).
A program that uses this case to read record
based terminal I/O may block indefinitely in the
read operation.

Case C: MIN = 0, TIME > 0 In this case, since MIN 0, TIME no longer
represents an intercharacter timer: it now
serves as a read timer that is activated as soon
as a read(2) is done. A read is satisfied as
soon as a single character is received or the
read timer expires. Note that, in this case, if
the timer expires, no character is returned. If
the timer does not expire, the only way the read
can be satisfied is if a character is received.
In this case, the read will not block
indefinitely waiting for a character; if no
character is received within TIME *.10 seconds
after the read is initiated, the read returns
with zero characters.

Case D: MIN = 0, TIME = 0 In this case, return is immediate. The minimum
of either the number of characters requested or
the number of characters currently available is
returned without waiting for more characters to
be input.

Comparing Different Cases of MIN, TIME Interaction
Some points to note about MIN and TIME:

+o In the following explanations, note that the interactions of MIN and
TIME are not symmetric. For example, when MIN > 0 and TIME = 0, TIME
has no effect. However, in the opposite case, where MIN = 0 and TIME
> 0, both MIN and TIME play a role in that MIN is satisfied with the
receipt of a single character.

+o Also note that in case A (MIN > 0, TIME > 0), TIME represents an
intercharacter timer, whereas in case C (MIN = 0, TIME > 0), TIME
represents a read timer.

These two points highlight the dual purpose of the MIN/TIME feature. Cases
A and B, where MIN > 0, exist to handle burst mode activity (for example,
file transfer programs), where a program would like to process at least MIN
characters at a time. In case A, the inteercharacter timer is activated by
a user as a safety measure; in case B, the timer is turned off.

Cases C and D exist to handle single character, timed transfers. These
cases are readily adaptable to screen-based applications that need to know
if a character is present in the input queue before refreshing the screen.
In case C, the read is timed, whereas in case D, it is not.

Another important note is that MIN is always just a minimum. It does not
denote a record length. For example, if a program does a read of 20 bytes,
MIN is 10, and 25 characters are present, then 20 characters will be
returned to the user.

Writing Characters


When one or more characters are written, they are transmitted to the
terminal as soon as previously written characters have finished typing.
nputt characters are echoed as they are typed if echoing has been enabled.
If a process produces characters more rapidly than they can be typed, it
will be suspended when its output queue exceeds some limit. When the queue
is drained down to some threshold, the program is resumed.

Special Characters


Certain characters have special functions on input. These functions and
their default character values are summarized as follows:

INTR (Control-c or ASCII ETX) generates a SIGINT signal. SIGINT is
sent to all foreground processes associated with the controlling
terminal. Normally, each such process is forced to terminate, but
arrangements may be made either to ignore the signal or to receive
a trap to an agreed upon location. (See signal.h(3HEAD)).

QUIT (Control-| or ASCII FS) generates a SIGQUIT signal. Its treatment
is identical to the interrupt signal except that, unless a
receiving process has made other arrangements, it will not only be
terminated but a core image file (called core) will be created in
the current working directory.

ERASE (DEL) erases the preceding character. It does not erase beyond
the start of a line, as delimited by a NL, EOF, EOL, or EOL2
character.

ERASE2 (Control-h or ASCII BS) erases the preceding character, with
behaviour identical to that of ERASE.

WERASE (Control-w or ASCII ETX) erases the preceding "word". It does not
erase beyond the start of a line, as delimited by a NL, EOF, EOL,
or EOL2 character.

KILL (Control-u or ASCII NAK) deletes the entire line, as delimited by
a NL, EOF, EOL, or EOL2 character.

REPRINT (Control-r or ASCII DC2) reprints all characters, preceded by a
newline, that have not been read.

EOF (Control-d or ASCII EOT) may be used to generate an end-of-file
from a terminal. When received, all the characters waiting to be
read are immediately passed to the program, without waiting for a
newline, and the EOF is discarded. Thus, if no characters are
waiting (that is, the EOF occurred at the beginning of a line)
zero characters are passed back, which is the standard end-of-file
indication. Unless escaped, the EOF character is not echoed.
Because EOT is the default EOF character, this prevents terminals
that respond to EOT from hanging up.

NL (ASCII LF) is the normal line delimiter. It cannot be changed or
escaped.

EOL (ASCII NULL) is an additional line delimiter, like NL. It is not
normally used.

EOL2 is another additional line delimiter.

SWTCH (Control-z or ASCII EM) Header file symbols related to this
special character are present for compatibility purposes only and
the kernel takes no special action on matching SWTCH (except to
discard the character).

SUSP (Control-z or ASCII SUB) generates a SIGTSTP signal. SIGTSTP
stops all processes in the foreground process group for that
terminal.

DSUSP (Control-y or ASCII EM). It generates a SIGTSTP signal as SUSP
does, but the signal is sent when a process in the foreground
process group attempts to read the DSUSP character, rather than
when it is typed.

STOP (Control-s or ASCII DC3) can be used to suspend output
temporarily. It is useful with CRT terminals to prevent output
from disappearing before it can be read. While output is
suspended, STOP characters are ignored and not read.

START (Control-q or ASCII DC1) is used to resume output. Output has
been suspended by a STOP character. While output is not
suspended, START characters are ignored and not read.

DISCARD (Control-o or ASCII SI) causes subsequent output to be discarded.
Output is discarded until another DISCARD character is typed, more
input arrives, or the condition is cleared by a program.

STATUS (Control-t or ASCII DC4) generates a SIGINFO signal. Processes
with a handler will output status information when they receive
SIGINFO, for example, dd(1M). If a process does not have a
SIGINFO handler, the signal will be ignored.

LNEXT (Control-v or ASCII SYN) causes the special meaning of the next
character to be ignored. This works for all the special
characters mentioned above. It allows characters to be input that
would otherwise be interpreted by the system (for example KILL,
QUIT). The character values for INTR, QUIT, ERASE, ERASE2,
WERASE, KILL, REPRINT, EOF, EOL, EOL2, SWTCH, SUSP, DSUSP, STOP,
START, DISCARD, STATUS, and LNEXT may be changed to suit
individual tastes. If the value of a special control character is
_POSIX_VDISABLE (0), the function of that special control
character is disabled. The ERASE, ERASE2, KILL, and EOF
characters may be escaped by a preceding backslash (\) character,
in which case no special function is done. Any of the special
characters may be preceded by the LNEXT character, in which case
no special function is done.

Modem Disconnect


When a modem disconnect is detected, a SIGHUP signal is sent to the
terminal's controlling process. Unless other arrangements have been made,
these signals cause the process to terminate. If SIGHUP is ignored or
caught, any subsequent read returns with an end-of-file indication until
the terminal is closed.

If the controlling process is not in the foreground process group of the
terminal, a SIGTSTP is sent to the terminal's foreground process group.
Unless other arrangements have been made, these signals cause the processes
to stop.

Processes in background process groups that attempt to access the
controlling terminal after modem disconnect while the terminal is still
allocated to the session will receive appropriate SIGTTOU and SIGTTIN
signals. Unless other arrangements have been made, this signal causes the
processes to stop.

The controlling terminal will remain in this state until it is
reinitialized ithh a successful open by the controlling process, or
deallocated by the controlling process.

Terminal Parameters


The parameters that control the behavior of devices and modules providing
the termios interface are specified by the termios structure defined by
<termios.h>. Several ioctl(2) system calls that fetch or change these
parameters use this structure that contains the following members:

tcflag_t c_iflag; /* input modes */
tcflag_t c_oflag; /* output modes */
tcflag_t c_cflag; /* control modes */
tcflag_t c_lflag; /* local modes */
cc_t c_cc[NCCS]; /* control chars */

The special control characters are defined by the array c_cc. The symbolic
name NCCS is the size of the Control-character array and is also defined by
<termios.h>. The relative positions, subscript names, and typical default
values for each function are as follows:

Relative Position Subscript Name Typical Default Value
0 VINTR ETX
1 VQUIT FS
2 VERASE DEL
3 VKILL NAK
4 VEOF EOT
5 VEOL NUL
6 VEOL2 NUL
7 VWSTCH NUL
8 VSTART NUL
9 VSTOP DC3
10 VSUSP SUB
11 VDSUSP EM
12 VREPRINT DC2
13 VDISCARD SI
14 VWERASE ETB
15 VLNEXT SYN
16 VSTATUS DC4
17 VERASE2 BS
18-19 Reserved

Input Modes


The c_iflag field describes the basic terminal input control:

IGNBRK Ignore break condition.
BRKINT Signal interrupt on break.
IGNPAR Ignore characters with parity errors.
PARMRK Mark parity errors.
INPCK Enable input parity check.
ISTRIP Strip character.
INLCR Map NL to CR on input.
IGNCR Ignore CR.
ICRNL Map CR to NL on input.
IUCLC Map upper-case to lower-case on input.
IXON Enable start/stop output control.
IXANY Enable any character to restart output.
IXOFF Enable start/stop input control.
IMAXBEL Echo BEL on input line too long.

If IGNBRK is set, a break condition (a character framing error with data
all zeros) detected on input is ignored, that is, not put on the input
queue and therefore not read by any process. If IGNBRK is not set and
BRKINT is set, the break condition shall flush the input and output queues
and if the terminal is the controlling terminal of a foreground process
group, the break condition generates a single SIGINT signal to that
foreground process group. If neither IGNBRK nor BRKINT is set, a break
condition is read as a single `\0' (ASCII NULL) character, or if PARMRK is
set, as `\377', `\0', c, where `\377' is a single character with value 377
octal (0xff hex, 255 decimal), `\0' is a single character with value 0, and
c is the errored character received.

If IGNPAR is set, a byte with framing or parity errors (other than break)
is ignored.

If PARMRK is set, and IGNPAR is not set, a byte with a framing or parity
error (other than break) is given to the application as the three-character
sequence: `\377', `\0', c, where `\377' is a single character with value
377 octal (0xff hex, 255 decimal), `\0' is a single character with value 0,
and c is the errored character received. To avoid ambiguity in this case,
if ISTRIP is not set, a valid character of `\377' is given to the
application as `\377'. If neither IGNPAR nor PARMRK is set, a framing or
parity error (other than break) is given to the application as a single
`\0' (ASCII NULL) character.

If INPCK is set, input parity checking is enabled. If INPCK is not set,
input parity checking is disabled. This allows output parity generation
without input parity errors. Note that whether input parity checking is
enabled or disabled is independent of whether parity detection is enabled
or disabled. If parity detection is enabled but input parity checking is
disabled, the hardware to which the terminal is connected will recognize
the parity bit, but the terminal special file will not check whether this
is set correctly or not.

If ISTRIP is set, valid input characters are first stripped to seven bits,
otherwise all eight bits are processed.

If INLCR is set, a received NL character is translated into a CR character.
If IGNCR is set, a received CR character is ignored (not read). Otherwise,
if ICRNL is set, a received CR character is translated into a NL character.

If IUCLC is set, a received upper case, alphabetic character is translated
into the corresponding lower case character.

If IXON is set, start/stop output control is enabled. A received STOP
character suspends output and a received START character restarts output.
The STOP and START characters will not be read, but will merely perform
flow control functions. If IXANY is set, any input character restarts
output that has been suspended.

If IXOFF is set, the system transmits a STOP character when the input queue
is nearly full, and a START character when enough input has been read so
that the input queue is nearly empty again.

If IMAXBEL is set, the ASCII BEL character is echoed if the input stream
overflows. Further input is not stored, but any input already present in
the input stream is not disturbed. If IMAXBEL is not set, no BEL character
is echoed, and all input present in the input queue is discarded if the
input stream overflows.

Output Modes


The c_oflag field specifies the system treatment of output:

OPOST Post-process output.
OLCUC Map lower case to upper on output.
ONLCR Map NL to CR-NL on output.
OCRNL Map CR to NL on output.
ONOCR No CR output at column 0.
ONLRET NL performs CR function.
OFILL Use fill characters for delay.
OFDEL Fill is DEL, else INULL.
NLDLY Select newline delays:
NL0
NL1
CRDLY Select carriage-return delays:
CR0
CR1
CR2
CR3
TABDLY Select horizontal tab delays or tab expansion:
TAB0
TAB1
TAB2
TAB3 Expand tabs to spaces
XTABS Expand tabs to spaces
BSDLY Select backspace delays:
BS0
BS1
VTDLY Select vertical tab delays:
VT0
VT1
FFDLY Select form feed delays:
FF0
FF1

If OPOST is set, output characters are post-processed as indicated by the
remaining flags; otherwise, characters are transmitted without change.

If OLCUC is set, a lower case alphabetic character is transmitted as the
corresponding upper case character. This function is often used in
conjunction with IUCLC.

If ONLCR is set, the NL character is transmitted as the CR-NL character
pair. If OCRNL is set, the CR character is transmitted as the NL
character. If ONOCR is set, no CR character is transmitted when at column
0 (first position). If ONRET is set, the NL character is assumed to do the
carriage-return function; the column pointer is set to 0 and the delays
specified for CR are used. Otherwise, the NL character is assumed to do
just the line-feed function; the column pointer remains unchanged. The
column pointer is also set to 0 if the CR character is actually
transmitted.

The delay bits specify how long transmission stops to allow for mechanical
or other movement when certain characters are sent to the terminal. In all
cases, a value of 0 indicates no delay. If OFILL is set, fill characters
are transmitted for delay instead of a timed delay. This is useful for
high baud rate terminals that need only a minimal delay. If OFDEL is set,
the fill character is DEL; otherwise it is NULL.

If a form-feed or vertical-tab delay is specified, it lasts for about 2
seconds.

Newline delay lasts about 0.10 seconds. If ONLRET is set, the carriage-
return delays are used instead of the newline delays. If OFILL is set, two
fill characters are transmitted.

Carriage-return delay type 1 is dependent on the current column position,
type 2 is about 0.10 seconds, and type 3 is about 0.15 seconds. If OFILL
is set, delay type 1 transmits two fill characters, and type 2 transmits
four fill characters.

Horizontal-tab delay type 1 is dependent on the current column position.
Type 2 is about 0.10 seconds. Type 3 specifies that tabs are to be
expanded into spaces. If OFILL is set, two fill characters are transmitted
for any delay.

Backspace delay lasts about 0.05 seconds. If OFILL is set, one fill
character is transmitted.

The actual delays depend on line speed and system load.

Control Modes


The c_cflag field describes the hardware control of the terminal:

CBAUD Baud rate:
B0 Hang up
B50 50 baud
B75 75 baud
B110 110 baud
B134 134 baud
B150 150 baud
B200 200 baud
B300 300 baud
B600 600 baud
B1200 1200 baud
B1800 1800 baud
B2400 2400 baud
B4800 4800 baud
B9600 9600 baud
B19200 19200 baud
EXTA External A
B38400 38400 baud
EXTB External B
B57600 57600 baud
B76800 76800 baud
B115200 115200 baud
B153600 153600 baud
B230400 230400 baud
B307200 307200 baud
B460800 460800 baud

CSIZE Character size:
CS5 5 bits
CS6 6 bits
CS7 7 bits
CS8 8 bits
CSTOPB Send two stop bits, else one
CREAD Enable receiver
PARENB Parity enable
PARODD Odd parity, else even
HUPCL Hang up on last close
CLOCAL Local line, else dial-up
CIBAUD Input baud rate, if different from output rate
PAREXT Extended parity for mark and space parity
CRTSXOFF Enable inbound hardware flow control
CRTSCTS Enable outbound hardware flow control
CBAUDEXT Bit to indicate output speed > B38400
CIBAUDEXT Bit to indicate input speed > B38400

The CBAUD bits together with the CBAUDEXT bit specify the output baud rate.
To retrieve the output speed from the termios structure pointed to by
termios_p see the following code segment.

speed_t ospeed;
if (termios_p->c_cflag & CBAUDEXT)
ospeed = (termios_p->c_cflag & CBAUD) + CBAUD + 1;
else
ospeed = termios_p->c_cflag & CBAUD;

To store the output speed in the termios structure pointed to by termios_p
see the following code segment.

speed_t ospeed;
if (ospeed > CBAUD) {
termios_p->c_cflag |= CBAUDEXT;
ospeed -= (CBAUD + 1);
} else {
termios_p->c_cflag &= ~CBAUDEXT;
}
termios_p->c_cflag =
(termios_p->c_cflag & ~CBAUD) | (ospeed & CBAUD);

The zero baud rate, B0, is used to hang up the connection. If B0 is
specified, the data-terminal-ready signal is not asserted. Normally, this
disconnects the line.

If the CIBAUDEXT or CIBAUD bits are not zero, they specify the input baud
rate, with the CBAUDEXT and CBAUD bits specifying the output baud rate;
otherwise, the output and input baud rates are both specified by the
CBAUDEXT and CBAUD bits. The values for the CIBAUD bits are the same as
the values for the CBAUD bits, shifted left IBSHIFT bits. For any
particular hardware, impossible speed changes are ignored. To retrieve the
input speed in the termios structure pointed to by termios_p see the
following code segment.

speed_t ispeed;
if (termios_p->c_cflag & CIBAUDEXT) {
ispeed = ((termios_p->c_cflag & CIBAUD) >> IBSHIFT)
+ (CIBAUD >> IBSHIFT) + 1;
} else {
ispeed = (termios_p->c_cflag & CIBAUD) >> IBSHIFT;
}

To store the input speed in the termios structure pointed to by termios_p
see the following code segment.

speed_t ispeed;
if (ispeed == 0) {
ispeed = termios_p->c_cflag & CBAUD;
if (termios_p->c_cflag & CBAUDEXT)
ispeed += (CBAUD + 1);
}
if ((ispeed << IBSHIFT) > CIBAUD) {
termios_p->c_cflag |= CIBAUDEXT;
ispeed -= ((CIBAUD >> IBSHIFT) + 1);
} else {
termios_p->c_cflag &= ~CIBAUDEXT;
}
termios_p->c_cflag =
(termios_p->c_cflag & ~CIBAUD) | ((ispeed << IBSHIFT) & CIBAUD);

The CSIZE bits specify the character size in bits for both transmission and
reception. This size does not include the parity bit, if any. If CSTOPB
is set, two stop bits are used; otherwise, one stop bit is used. For
example, at 110 baud, two stops bits are required.

If PARENB is set, parity generation and detection is enabled, and a parity
bit is added to each character. If parity is enabled, the PARODD flag
specifies odd parity if set; otherwise, even parity is used.

If CREAD is set, the receiver is enabled. Otherwise, no characters are
received.

If HUPCL is set, the line is disconnected when the last process with the
line open closes it or terminates. That is, the data-terminal-ready signal
is not asserted.

If CLOCAL is set, the line is assumed to be a local, direct connection with
no modem control; otherwise, modem control is assumed.

If CRTSXOFF is set, inbound hardware flow control is enabled.

If CRTSCTS is set, outbound hardware flow control is enabled.

The four possible combinations for the state of CRTSCTS and CRTSXOFF bits
and their interactions are described below.

Case A: CRTSCTS off, CRTSXOFF off. In this case the hardware flow control
is disabled.

Case B: CRTSCTS on, CRTSXOFF off. In this case only outbound hardware
flow control is enabled. The state of CTS signal is used to do
outbound flow control. It is expected that output will be
suspended if CTS is low and resumed when CTS is high.

Case C: CRTSCTS off, CRTSXOFF on. In this case only inbound hardware flow
control is enabled. The state of RTS signal is used to do inbound
flow control. It is expected that input will be suspended if RTS
is low and resumed when RTS is high.

Case D: CRTSCTS on, CRTSXOFF on. In this case both inbound and outbound
hardware flow control are enabled. Uses the state of CTS signal
to do outbound flow control and RTS signal to do inbound flow
control.

Local Modes


The c_lflag field of the argument structure is used by the line discipline
to control terminal functions. The basic line discipline provides the
following:

ISIG Enable signals.
ICANON Canonical input (erase and kill processing).
XCASE Canonical upper/lower presentation.
ECHO Enable echo.
ECHOE Echo erase character as BS-SP-BS &.
ECHOK Echo NL after kill character.
ECHONL Echo NL.
NOFLSH Disable flush after interrupt or quit.
TOSTOP Send
SIGTTOU for background output.
ECHOCTL Echo control characters as char, delete as ^?.
ECHOPRT Echo erase character as character erased.
ECHOKE BS-SP-BS erase entire line on line kill.
FLUSHO Output is being flushed.
PENDIN Retype pending input at next read or input character.
IEXTEN Enable extended (implementation-defined) functions.

If ISIG is set, each input character is checked against the special control
characters INTR, QUIT, SWTCH, SUSP, STATUS, and DSUSP. If an input
character matches one of these control characters, the function associated
with that character is performed. (Note: If SWTCH is set and the character
matches, the character is simply discarded. No other action is taken.) If
ISIG is not set, no checking is done. Thus, these special input functions
are possible only if ISIG is set.

If ICANON is set, canonical processing is enabled. This enables the erase
and kill edit functions, and the assembly of input characters into lines
delimited by NL-c, EOF, EOL, and EOL. If ICANON is not set, read requests
are satisfied directly from the input queue. A read is not satisfied until
at least MIN characters have been received or the timeout value TIME has
expired between characters. This allows fast bursts of input to be read
efficiently while still allowing single character input. The time value
represents tenths of seconds.

If XCASE is set and ICANON is set, an upper case letter is accepted on
input if preceded by a backslash `\' character, and is output preceded by a
backslash `\' character. In this mode, the following escape sequences are
generated on output and accepted on input:

FOR: USE:
` \'
| \!
~ \^
{ \(
} \)
\ \\

For example, input A as \a, \n as \\n, and \N as \\\n.

If ECHO is set, characters are echoed as received.

When ICANON is set, the following echo functions are possible.

+o If ECHO and ECHOE are set, and ECHOPRT is not set, the ERASE,
ERASE2, and WERASE characters are echoed as one or more ASCII BS
SP BS, which clears the last character(s) from a CRT screen.

+o If ECHO, ECHOPRT, and IEXTEN are set, the first ERASE, ERASE2,
and WERASE character in a sequence echoes as a backslash `\',
followed by the characters being erased. Subsequent ERASE and
WERASE characters echo the characters being erased, in reverse
order. The next non-erase character causes a `/' (slash) to be
typed before it is echoed. ECHOPRT should be used for hard copy
terminals.

+o If ECHOKE and IEXTEN are set, the kill character is echoed by
erasing each character on the line from the screen (using the
mechanism selected by ECHOE and ECHOPR).

+o If ECHOK is set, and ECHOKE is not set, the NL character is
echoed after the kill character to emphasize that the line is
deleted. Note that a `\' (escape) character or an LNEXT
character preceding the erase or kill character removes any
special function.

+o If ECHONL is set, the NL character is echoed even if ECHO is not
set. This is useful for terminals set to local echo (so called
half-duplex).

If ECHOCTL and IEXTEN are set, all control characters (characters with
codes between 0 and 37 octal) other than ASCII TAB, ASCII NL, the START
character, and the STOP character, ASCII CR, and ASCII BS are echoed as ^X,
where X is the character given by adding `100' octal to the code of the
control character (so that the character with octal code `1' is echoed as
^A), and the ASCII DEL character, with code `177' octal, is echoed as ^?.

If NOFLSH is set, the normal flush of the input and output queues
associated with the INTR, QUIT, STATUS, and SUSP characters is not done.
This bit should be set when restarting system calls that read from or write
to a terminal (see sigaction(2)).

If TOSTOP and IEXTEN are set, the signal SIGTTOU is sent to a process that
tries to write to its controlling terminal if it is not in the foreground
process group for that terminal. This signal normally stops the process.
Otherwise, the output generated by that process is output to the current
output stream. Processes that are blocking or ignoring SIGTTOU signals are
excepted and allowed to produce output, if any.

If FLUSHO and IEXTEN are set, data written to the terminal is discarded.
This bit is set when the FLUSH character is typed. A program can cancel
the effect of typing the FLUSH character by clearing FLUSHO.

If PENDIN and IEXTEN are set, any input that has not yet been read is
reprinted when the next character arrives as input. PENDIN is then
automatically cleared.

If IEXTEN is set, the following implementation-defined functions are
enabled: special characters ( WERASE, REPRINT, DISCARD, and LNEXT) and
local flags ( TOSTOP, ECHOCTL, ECHOPRT, ECHOKE, FLUSHO, and PENDIN).

Minimum and Timeout


The MIN and TIME values were described previously, in the subsection,
Non-canonical Mode Input Processing. The initial value of MIN is 1, and
the initial value of TIME is 0.

Terminal Size


The number of lines and columns on the terminal's display is specified in
the winsize structure defined by <sys/termios.h> and includes the following
members:

unsigned short ws_row; /* rows, in characters */
unsigned short ws_col; /* columns, in characters */
unsigned short ws_xpixel; /* horizontal size, in pixels */
unsigned short ws_ypixel; /* vertical size, in pixels */

Termio Structure


The SunOS/SVR4 termio structure is used by some ioctl()s; it is defined by
<sys/termio.h> and includes the following members:

unsigned short c_iflag; /* input modes */
unsigned short c_oflag; /* output modes */
unsigned short c_cflag; /* control modes */
unsigned short c_lflag; /* local modes */
char c_line; /* line discipline */
unsigned char c_cc[NCC]; /* control chars */

The special control characters are defined by the array c_cc. The symbolic
name NCC is the size of the Control-character array and is also defined by
<termio.h>. The relative positions, subscript names, and typical default
values for each function are as follows:

Relative Positions Subscript Names Typical Default Values
0 VINTR EXT
1 VQUIT FS
2 VERASE DEL
3 VKILL NAK
4 VEOF EOT
5 VEOL NUL
6 VEOL2 NUL
7 Reserved

The MIN values is stored in the VMIN element of the c_cc array; the TIME
value is stored in the VTIME element of the c_cc array. The VMIN element
is the same element as the VEOF element; the VTIME element is the same
element as the VEOL element.

The calls that use the termio structure only affect the flags and control
characters that can be stored in the termio structure; all other flags and
control characters are unaffected.

Modem Lines


On special files representing serial ports, modem control lines can be
read. Control lines (if the underlying hardware supports it) may also be
changed. Status lines are read-only. The following modem control and
status lines may be supported by a device; they are defined by
<sys/termios.h>:

TIOCM_LE line enable
TIOCM_DTR data terminal ready
TIOCM_RTS request to send
TIOCM_ST secondary transmit
TIOCM_SR secondary receive
TIOCM_CTS clear to send
TIOCM_CAR carrier detect
TIOCM_RNG ring
TIOCM_DSR data set ready

TIOCM_CD is a synonym for TIOCM_CAR, and TIOCM_RI is a synonym for
TIOCM_RNG. Not all of these are necessarily supported by any particular
device; check the manual page for the device in question.

The software carrier mode can be enabled or disabled using the TIOCSSOFTCAR
ioctl(). If the software carrier flag for a line is off, the line pays
attention to the hardware carrier detect (DCD) signal. The tty device
associated with the line cannot be opened until DCD is asserted. If the
software carrier flag is on, the line behaves as if DCD is always asserted.

The software carrier flag is usually turned on for locally connected
terminals or other devices, and is off for lines with modems.

To be able to issue the TIOCGSOFTCAR and TIOCSSOFTCAR ioctl() calls, the
tty line should be opened with O_NDELAY so that the open(2) will not wait
for the carrier.

Default Values


The initial termios values upon driver open is configurable. This is
accomplished by setting the "ttymodes" property in the file
/kernel/drv/options.conf. Since this property is assigned during system
initialization, any change to the "ttymodes" property will not take effect
until the next reboot. The string value assigned to this property should
be in the same format as the output of the stty(1) command with the -g
option.

If this property is undefined, the following termios modes are in effect.
The initial input control value is BRKINT, ICRNL, IXON, IMAXBEL. The
initial output control value is OPOST, ONLCR, TAB3. The initial hardware
control value is B9600, CS8, CREAD. The initial line-discipline control
value is ISIG, ICANON, IEXTEN, ECHO, ECHOK, ECHOE, ECHOKE, ECHOCTL.

IOCTLS


The ioctl()s supported by devices and STREAMS modules providing the
termios(3C) interface are listed below. Some calls may not be supported by
all devices or modules. The functionality provided by these calls is also
available through the preferred function call interface specified on
termios.

TCGETS The argument is a pointer to a termios structure. The
current terminal parameters are fetched and stored into that
structure.

TCSETS The argument is a pointer to a termios structure. The
current terminal parameters are set from the values stored in
that structure. The change is immediate.

TCSETSW The argument is a pointer to a termios structure. The
current terminal parameters are set from the values stored in
that structure. The change occurs after all characters
queued for output have been transmitted. This form should be
used when changing parameters that affect output.

TCSETSF The argument is a pointer to a termios structure. The
current terminal parameters are set from the values stored in
that structure. The change occurs after all characters
queued for output have been transmitted; all characters
queued for input are discarded and then the change occurs.

TCGETA The argument is a pointer to a termio structure. The current
terminal parameters are fetched, and those parameters that
can be stored in a termio structure are stored into that
structure.

TCSETA The argument is a pointer to a termio structure. Those
terminal parameters that can be stored in a termio structure
are set from the values stored in that structure. The change
is immediate.

TCSETAW The argument is a pointer to a termio structure. Those
terminal parameters that can be stored in a termio structure
are set from the values stored in that structure. The change
occurs after all characters queued for output have been
transmitted. This form should be used when changing
parameters that affect output.

TCSETAF The argument is a pointer to a termio structure. Those
terminal parameters that can be stored in a termio structure
are set from the values stored in that structure. The change
occurs after all characters queued for output have been
transmitted; all characters queued for input are discarded
and then the change occurs.

TCSBRK The argument is an int value. Wait for the output to drain.
If the argument is 0, then send a break (zero valued bits for
0.25 seconds).

TCXONC Start/stop control. The argument is an int value. If the
argument is 0, suspend output; if 1, restart suspended
output; if 2, suspend input; if 3, restart suspended input.

TCFLSH The argument is an int value. If the argument is 0, flush
the input queue; if 1, flush the output queue; if 2, flush
both the input and output queues.

TIOCGPGRP The argument is a pointer to a pid_t. Set the value of that
pid_t to the process group ID of the foreground process group
associated with the terminal. See termios(3C) for a
description of TCGETPGRP.

TIOCSPGRP The argument is a pointer to a pid_t. Associate the process
group whose process group ID is specified by the value of
that pid_t with the terminal. The new process group value
must be in the range of valid process group ID values.
Otherwise, the error EPERM is returned.

TIOCGSID The argument is a pointer to a pid_t. The session ID of the
terminal is fetched and stored in the pid_t.

TIOCGWINSZ The argument is a pointer to a winsize structure. The
terminal driver's notion of the terminal size is stored into
that structure.

TIOCSWINSZ The argument is a pointer to a winsize structure. The
terminal driver's notion of the terminal size is set from the
values specified in that structure. If the new sizes are
different from the old sizes, a SIGWINCH signal is set to the
process group of the terminal.

TIOCMBIS The argument is a pointer to an int whose value is a mask
containing modem control lines to be turned on. The control
lines whose bits are set in the argument are turned on; no
other control lines are affected.

TIOCMBIC The argument is a pointer to an int whose value is a mask
containing modem control lines to be turned off. The control
lines whose bits are set in the argument are turned off; no
other control lines are affected.

TIOCMGET The argument is a pointer to an int. The current state of
the modem status lines is fetched and stored in the int
pointed to by the argument.

TIOCMSET The argument is a pointer to an int containing a new set of
modem control lines. The modem control lines are turned on
or off, depending on whether the bit for that mode is set or
clear.

TIOCSPPS The argument is a pointer to an int that determines whether
pulse-per-second event handling is to be enabled (non-zero)
or disabled (zero). If a one-pulse-per-second reference
clock is attached to the serial line's data carrier detect
input, the local system clock will be calibrated to it. A
clock with a high error, that is, a deviation of more than 25
microseconds per tick, is ignored.

TIOCGPPS The argument is a pointer to an int, in which the state of
the even handling is returned. The int is set to a non-zero
value if pulse-per-second (PPS) handling has been enabled.
Otherwise, it is set to zero.

TIOCGSOFTCAR The argument is a pointer to an int whose value is 1 or 0,
depending on whether the software carrier detect is turned on
or off.

TIOCSSOFTCAR The argument is a pointer to an int whose value is 1 or 0.
The value of the integer should be 0 to turn off software
carrier, or 1 to turn it on.

TIOCGPPSEV The argument is a pointer to a struct ppsclockev. This
structure contains the following members:

struct timeval tv;
uint32_t serial;

tv is the system clock timestamp when the event (pulse on the
DCD pin) occurred. serial is the ordinal of the event, which
each consecutive event being assigned the next ordinal. The
first event registered gets a serial value of 1. The
TIOCGPPSEV returns the last event registered; multiple calls
will persistently return the same event until a new one is
registered. In addition to time stamping and saving the
event, if it is of one-second period and of consistently high
accuracy, the local system clock will automatically calibrate
to it.

FILES


Files in or under /dev

SEE ALSO


stty(1), fork(2), getpgid(2), getsid(2), ioctl(2), setsid(2), sigaction(2),
signal(3C), tcsetpgrp(3C), termios(3C), signal.h(3HEAD), streamio(7I)

illumos March 17, 2019 illumos