termios.4

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.B Control Modes
.PP
The c_cflag field describes the hardware control of the terminal:
.PP
.TS
tab(@);
lw(1i) lw(2i).
_
.sp 6p
.HB
Mask Name@Description
.R
.sp 6p
_
.sp 6p
CSIZE@Character size:
CS5@5 bits
CS6@6 bits
CS7@7 bits
CS8@8 bits

CSTOPB@T{
Send two stop bits, else one.
T}
CREAD@Enable receiver.
PARENB@Parity enable.
PARODD@T{
Odd parity, else even.
T}
HUPCL@T{
Hung up on last close.
T}
CLOCAL@T{
Ignore modem status lines.
T}
TAUTOFLOW@T{
Use hardware monitored flow control.
T}
.sp 6p
_
.TE
.PP
In addition, the input and output baud rates are also stored in the c_cflag 
field.  The following values are supported:
.PP
.TS
tab(@);
ll.
_
.sp 6p
.HB
Name@Description
.R
.sp 6p
_
.sp 6p
B0@Hang up
B50@50 baud
B75@75 baud
B110@110 baud
B134@134.5 baud
B150@150 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
B38400@38400 baud
.sp 6p
_
.TE
.PP
The following interfaces are provided for getting and setting the values
of the input and output baud rates in the 
.PN termios 
structure.  The effects on
the terminal device do not become effective until the 
.PN tcsetattr() 
function is successfully called.
.EX
speed_t cfgetospeed (termios_p)
struct termios *termios_p;
         
int cfsetospeed (termios_p, speed)
struct termios *termios_p;
speed_t speed;

speed_t cfgetispeed (termios_p)
struct termios *termios_p;

int cfsetispeed (termios_p, speed)
struct termios *termios_p;
speed_t speed;
.EE
The type speed_t is defined in 
.PN <termio.h> .
.PP
The 
.I termios_p 
argument is a pointer to a termios structure that allows
the c_cflag field to be manipulated.
The cfgetospeed() returns the output baud rate stored in cflag.
.PP
Additionally, the
cfsetospeed() sets the output baud rate stored in the cflag to speed.
The zero baud rate, B0, is used to terminate the
connection.  If B0 is specified, the modem control line can no longer be
asserted.  Normally, this disconnects the line.
Both cfsetispeed() and cfsetospeed() return a value of zero if successful
and \-1 to indicate error.
.PP
The cfgetispeed() returns the input baud rate stored in cflag.
.PP
The cfsetispeed() sets the input baud rate stored in cflag to speed.  If the
input baud rate is set to zero, the input baud rate is specified by the
value of the output baud rate.  For any particular hardware, unsupported baud
rates are ignored.  This refers to changes and baud rates not supported by
the hardware, and to changes setting the input and output baud rates to
different values if the hardware does not support this.
.PP
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.  For example, at 
110 baud, two stop bits are normally used.
.PP
If CREAD is set, the receiver is enabled.  Otherwise, no characters 
are received.
.PP
If PARENB is set, parity generation and detection is enabled and a parity bit is
added to each character.  If parity is enabled, PARODD specifies odd parity, if
set. Otherwise, even parity is used.
.PP
If TAUTOFLOW is set, hardware monitored flow control is performed, if the
hardware supports this functionality.  In this mode, the hardware terminal
multiplexer suspends output upon receipt of a STOP character (ASCII DC3).
The hardware resumes output after a START character (ASCII DC1) has been
received.  The advantage of this mode is that it provides quick response to
flow control characters which would be useful in preventing overflow
of the terminal device's input buffer.  TAUTOFLOW is a local extension to the
termios specification.
.PP
If HUPCL is set, the modem control lines for the port are lowered when the
last process with the port open closes the port or the process terminates.
The modem connection is broken.  If HUPCL is not set, the control lines
are not altered.
.PP
If CLOCAL is set, a connection does not depend on the state of the modem status
lines.
If CLOCAL is clear, the modem status lines are monitored.
CLOCAL is typically used by direct connect terminal lines.
.PP
Under normal circumstances, a call to the open(2) function waits for the
modem connection to complete.  However, if the O_NONBLOCK flag is set,
or, if CLOCAL has been set, the 
.MS open 2
function returns 
immediately without waiting for the connection.
For further information, see
.MS open 2 .
For those files on which the 
connection has not been established, or on which a modem disconnect has
occurred, and for which CLOCAL is not set, both 
.MS read 2
and 
.MS write 2
return a zero character count.  For 
.MS read 2 ,
this is equivalent to an end-of-file condition.
.PP
The initial hardware control value after open(2) is CS8, CREAD, HUPCL, B300.
.PP
.B Local Modes
.PP
The c_lflag field of the argument structure is used to control various 
functions.
.PP
.TS
tab(@);
lw(1i) lw(3i).
_
.sp 6p
.HB
Mask Name@Description
.R
.sp 6p
_
.sp 6p
ISIG@Enable signals
ICANON@T{
Canonical input (erase and kill processing).
T}
NOFLSH@T{
Disable flush after interrupt, quit, or suspend.
T}
TOSTOP@T{
Send SIGTTOU for background output.
T}
ECHO@Enable echo.
ECHOE@T{
Echo ERASE as an error-correcting backspace.
T}
ECHOK@Echo KILL.
ECHONL@Echo \\n.
IEXTEN@Enable extended (implementation defined) functions.
TCTLECH@T{
Echo input control chars as ^char, delete as ^?.
T}
TCRTKIL@T{
BS-space-BS erase entire line on kill.
T}
TPRTERA@T{
Hard-copy terminal erase mode using \char.
T}
.sp 6p
_
.TE
.PP
If ISIG is set, each input character is checked against the special control
characters INTR, QUIT, and SUSP.  If an input 
character matches one of these control characters, the function associated
with that character is performed.  If ISIG is not set, no checking is done.
Thus, these special input functions are possible only if ISIG is set.
.PP
If ICANON is set, canonical processing is enabled.  This enables the erase, 
word erase, reprint,
and kill edit functions, and the assembly of input characters into lines
delimited by NL, EOF, and EOL, as described in Canonical Mode Input Processing.
.PP
If ICANON is not set, 
.MS read 2
requests are satisfied directly from the input
queue.  A 
.MS read 2
is not satisfied until at least MIN characters have been
received or the timeout value TIME expired between characters.  The time value
represents tenths of seconds.  See the Noncanonical Mode Input Processing 
section for more details.
.PP
If NOFLSH is set, the normal flush of the input and output queues associated 
with the INTR, QUIT, and SUSP characters is not done.
.PP
If TOSTOP is set, the signal SIGTTOU is sent to the
process group of a process that tries to write to its controlling terminal, if
it is not in the foreground process group for that terminal.  This signal,
by default, stops the members of the process group.  Otherwise, the output 
generated by that process is output to the current output stream.  Processes
that are holding or ignoring SIGTTOU signals are accepted and allowed to 
produce output and the SIGTTOU signal is not sent.
.PP
If ECHO is set, input characters are echoed back to the terminal.  If ECHO is 
not set, input characters are not echoed.
.PP
The echo functions (ECHOE, ECHOK, ECHONL, TCTLECH, TCRTKIL, and TPRTERA) are
performed if ICANON is set.
.PP
If ECHOE and ICANON are set, 
the ERASE character causes the terminal to erase the last
character in the current line from the display, if possible.
.PP
If ECHOK and ICANON are set, the KILL character, either the terminal erases the
line from the display or echoes the \\n character after the KILL character.
.PP
If ECHONL and ICANON are set, 
the \\n character is echoed even if ECHO is not set.
.PP
If IEXTEN is set, implementation defined functions are recognized from the 
input data.  In this manner the DSUSP, RPRNT, FLUSH, WERASE, LNEXT, and QUOTE
special characters in the c_cc array are only recognized if the IEXTEN
flag is set. 
.PP
If TCTLECH is set, all control characters are echoed as ^X, where X is the
character obtained by adding the octal value of the character A (100) to
the octal code for the control character.  In this context, a control character
is defined to be a character whose octal value is less than 37.
The following control characters
are excluded from TCTLECH operations: ASCII NL, ASCII TAB, as well as control
characters that are defined in the c_cc array but are not returned to 
user programs (such as START and STOP).  
TCTLECH is a local extension to the local modes.
.PP
If TCRTKIL is set, the response to a kill character is to erase the
present input line through a sequence of backspace-space-backspace.
TCRTKIL is a local extension to the local modes.
.PP
If TCRTERA is set, characters that are logically erased are printed out
backwards preceded by a backslash (\\) and followed by a slash (/).  
This mode is useful when a hard-copy terminal is in use.
TCRTERA is a local extension to the local modes.
.PP
The initial local control value after 
open (2) is 0 (all bits clear).
.PP
.B Special Control Characters
.PP
The special control characters values are defined by the array c_cc.  The
subscript name and description for each element in both canonical and
noncanonical modes are as follows.
.PP
.TS
tab(@);
ll.
_
.sp 6p
.HB
Subscript@Description
.R
.sp 6p
_
.sp 6p
VINTR (INTR)@Interrupt character
VQUIT (QUIT)@Quit character
VERASE (ERASE)@Erase character
VKILL (KILL)@Kill character
VEOF (EOF)@T{
End-of-file character
T}
VEOL (EOL)@T{
End-of-line character
T}
VMIN (MIN)@T{
Value for noncanonical reads
T}
VTIME (TIME)@T{
Value for noncanonical reads
T}
VSTART (START)@Start character
VSTOP (STOP)@Stop character
VSUSP (SUSP)@Suspend character
VDSUSP (DSUSP)@T{
Delayed suspend character
T}
VRPRNT (RPRNT)@Reprint character
VFLUSH (FLUSH)@Flush character
VWERASE (WERASE)@Word erase character
VLNEXT (LNEXT)@T{
Literal next character
T}
VQUOTE (QUOTE)@T{
Erase and kill quoting character
T}
.sp 6p
_
.TE
.PP
The following subscripts are local extensions to the c_cc array:
VDSUSP, VRPRNT, VFLUSH, VWERASE, VLNEXT, and VQUOTE.
The constant NCCS defines the total number of elements in the c_cc array.
.PP
Setting the value of a special character to POSIX_V_DISABLE causes that
function to be disabled; that is, no input data will be recognized as the
disabled special character.  If ICANON is not set, the value of POSIX_V_DISABLE
has no special meaning for the VMIN and VTIME entries of the c_cc array.
.PP
.B Line Discipline
.PP
The c_line field of the termios data structure is used to
specify the line discipline.  
Support is provided for the
basic termios line discipline only.  For this reason, the
value of this field should be set to 
the value TERMIODISC (the default value) by convention.  The value of c_line
is reset to TERMIODISC by the system, if attempts are
made to set c_line to other values.  This field is a local
extension. 
.PP
.SH Control Functions
.PP 
The functions that are used to control the general terminal function are 
described in this section.  
Unless otherwise noted for a specific command, these functions are restricted
from use by background processes.  Attempts to perform these operations  
cause the process group to be sent a SIGTTOU signal.  If the calling process is
blocking or ignoring SIGTTOU signals, the process is allowed to perform the
operation and the SIGTTOU signal is not sent.
.PP
In all the functions, 
.I fildes 
is an 
open 
file descriptor.
However, the functions affect the underlying terminal file, not just the
open instance associated with the file descriptor.
.PP
.B Get and Set State
.PP
Functions: 
.PN tcgetattr() ,
.PN tcsetattr()
.PP
.B Syntax
.EX
#include <termios.h>

int tcgetattr (fildes, termios_p)
int fildes;
struct termios *termios_p;

int tcsetattr (fildes, optional_actions, termios_p)
int fildes;
int optional_actions;
struct termios *termios_p;
.EE
.B Description