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.\" Devin Reade, January 1997
.\" $Id: tty.4,v 1.2 1998/04/16 05:03:39 gdr-ftp Exp $
.TH TTY 4 "15 April 1998" GNO Devices
.BR tty
\- general terminal interface
#include <sgtty.h>
This file documents the special file
.BR .tty
and the terminal drivers used for user-oriented I/O.
Terminals are controlled through calls to the
.BR ioctl (2)
system call:
#include <sgtty.h>
ioctl(int \fIfiledes\fR, unsigned long \fIcode\fR, void *\fIarg\fR);
This is a very flexible interface where
.I filedes
specifies the terminal to modify,
.I code
indicates an action code, and
.I arg
is a pointer to a parameter block. The type of variable pointed to by
.I arg
and how it is interpreted depends on the value of
.IR code.
Due to the colorful history of UNIX systems, the data structures used to
manipulate terminal modes and settings are separated into five groups.
Future revisions of GNO will implement the POSIX termio interface, which
consolidates these structures into one place.
This manual page first explains the concepts of
.IR "controlling terminals" ,
.IR "process groups" ,
.IR "terminal modes" .
It then goes on to explain each
.I code
that can be used with
.BR ioctl (2)
to control a terminal. Since there are five data structures used in
.BR ioctl
calls to control terminals, the description of the possible
.IR code s
in this man page is ordered by the type of the data structure pointed to by
.IR arg .
.IP "\fBThe Controlling Terminal\fR"
Every process has associated with it a controlling terminal, which is
the terminal from which the process was invoked. In some versions of
UNIX, the controlling terminal association is responsible for job
control; this is not so under GNO. A process' controlling terminal is
inherited from its parent. By opening the special file
.BR .tty ,
a process can access its controlling terminal. This is useful where the
input and output of a process was redirected and the process wants to
be sure of getting input from or output to the user at the terminal.
.sp 1
A process can remove the association it has with its controlling terminal
by opening the file
.BR .tty
and issuing the system call:
ioctl (\fIfd\fR, TIOCNOTTY, NULL);
.IR fd
is the file descriptor associated with
.BR .tty .
This is often desirable in server processes.
.IP "\fBProcess Groups\fR"
Every terminal has an associated process group. Any time a
signal-generating special character is typed at the terminal, the
terminal's process group is sent that signal. UNIX systems set process
groups using
.BR ioctl (2)
calls, but under GNO a new interface method is used;
process group assignments are controlled with the
.IP \fBModes\fR
.\" NOTE:
.\" The GNO v2.0.1 manual page listed four modes. The GNO v2.0.4
.\" listed only three. I asked Jawaid about this, and he doesn't
.\" recall what if any changes were made. What really needs to be
.\" done is to have a kernel code review to see what the current
.\" implementation does. In the interim, I have left (commented out)
.\" the descriptions from the v2.0.1 manual page, below.
.\" -- Devin Reade
.\" cooked mode
.\" On Unix systems, this mode also allows for input editing. It
.\" is called cooked mode and is the normal state of the terminal driver.
.\" Due to the history of the Apple II and it's operating systems, this
.\" this precedent was not followed. Instead, to get input editing
.\" features, use the ReadLine Toolbox call. Cooked-mode input editing
.\" may be implemented for future releases of GNO.
.\" newline mode
.\" This mode is selected by using the GS/OS NewLine call. Input is
.\" collected until one of the newline characters specified in the
.\" NewLine call is encountered. At that point, the line of input is
.\" returned, even if less than the number of bytes requested in the
.\" Read call are read. I/O processing features are enabled and
.\" disabled independently of newline mode; see cooked, cbreak, and raw.
.\" cbreak mode
.\" With GNO, this mode is the default state of the terminal driver,
.\" and is synonymous with cooked mode. The requested number of
.\" characters are read without regard to any newline setting; input
.\" is not line buffered before being returned to the process.
.\" raw mode
.\" Like cbreak mode, except that no input or output processing whatsoever
.\" is performed. The driver does not check for any special characters.
There are three modes in which terminal drivers operate. These modes
control how the driver deals with I/O.
.IP \fIcooked\fR
This is the default mode of the terminal driver. If an incoming character
is one of the special characters defined in
.BR sgttyb ,
.BR tchars ,
.BR ltchars ,
the appropriate action is performed (see below).
This mode also allows for input editing, as input is internally buffered
line by line, and data is returned to a reading process only when CR is
.IP \fIcbreak\fR
Input is returned on a per-character basis, instead of line by line as in
.I cooked
mode. If no data is available, a read will block the calling process.
If data is available, a number of characters up to but not exceeding the
requested number will be returned. Special characters such as t_intrc are
not handled, but are passed on to the caller as data.
.IP \fIraw\fR
.I cbreak
mode, except that no input or output processing whatsoever is performed.
.IP "\fBstruct sgttyb\fR"
The basic ioctls use the sgttyb structure:
struct sgttyb {
char sg_ispeed;
char sg_ospeed;
char sg_erase;
char sg_kill;
short sg_flags;
sg_ispeed and sg_ospeed indicate the baud rates for input and output
according to the following table. Speed changes that do not apply to a
particular piece of hardware are ignored (for instance, the console driver
does not access a serial port so all baud rate settings are, in effect,
impossible). Also, not all the baud rates supported by a particular
device are allowed to be set from this interface.
These symbolic names for the baud rate settings are defined in <sgtty.h>.
B0 0 (hang up dataphone)
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
B19200 14 19200 baud
EXTA 14 19200 baud
B38400 15 38400 baud
EXTB 15 38400 baud
The sg_erase and sg_kill fields specify the line-editing erase and kill
characters. sg_erase is 0x7F (delete) by default, and sg_kill is not
currently used.
sg_flags is a bitmapped value that indicates various state settings for
the terminal driver (values are in hex).
EVENP 0x80 Use Even parity (serial devices only)
ODDP 0x40 Use Odd parity (serial devices only)
RAW 0x20 Raw mode: wake up on all characters,
8-bit interface
CRMOD 0x10 Map CR into LF; output LF as CR-LF
ECHO 0x08 Echo (full duplex)
CBREAK 0x02 Return each character as soon as typed
TANDEM 0x01 Automatic flow control
modes were described above, in Modes.
If the
bit is set, a line feed character is appended to any emitted carriage return.
bit controls input echoing; if enabled, any characters read from the terminal
are echoed. This behavior differs slightly from UNIX, where input characters
are echoed as soon as typed.
mode enables automatic software flow control utilizing the special characters
.B t_startc
.B t_stopc
in tchars (below). Whenever the input queue is in danger of overflowing,
the system sends t_stopc; when the queue has drained sufficiently, t_startc
is sent. This mode has no effect on the console driver.
.IR Note :
t_startc and t_stopc are used for both directions of flow control; when
t_stopc is received from a remote system (or user), the terminal stops
output, and when t_startc is received output resumes. Certain drivers
may also require t_stopc and t_startc to be the same character, in which
case one or the other setting will be ignored.
See the driver's documentation for details.
The ioctl
.IR code s
that apply to sgtty are:
Fetch the basic parameters associated with the terminal, and store in
the sgttyb structure pointed to by
.IR arg .
Set the terminal's basic parameters according to the sgttyb structure
pointed to by
.IR arg .
The input queue is flushed, and the call waits for the output queue to
drain before the parameters are changed.
This is like TIOCSETP, except there is no delay and the input queue is not
Set "exclusive-use" mode. The terminal may not be opened again by any
process until all existing references are closed.
.IR arg
is ignored and should be the NULL pointer.
Turns off "exclusive-use" mode.
.IR arg
is ignored and should be the NULL pointer.
When the last reference to the terminal is closed, the terminal line is
forced to hang up. This applies only to modem drivers.
.IR arg
is ignored and should be the NULL pointer.
The current line discipline number is stored in the int variable pointed to by
.IR arg .
This value is currently ignored.
The line discipline is set to the value of the int pointed to by
.IR arg .
The specified queue is flushed. If the value pointed to by
.I arg
is zero, both the input and output queues are flushed. If the value is
FREAD (defined in <sys/fcntl.h>), the input queue is flushed. If the value
is FWRITE, the output queue is flushed.
The character pointed to by
.IR arg
is placed in the input queue as if it had been typed on the terminal.
Begins a break sequence on the terminal.
.IR arg
is ignored and should be the NULL pointer.
Ends a break sequence.
.IR arg
is ignored and should be the NULL pointer.
The DTR line is turned on.
.IR arg
is ignored and should be the NULL pointer.
The DTR line is turned off.
.IR arg
is ignored and should be the NULL pointer.
Output is stopped as if t_stopc had been typed on the terminal.
.IR arg
is ignored and should be the NULL pointer.
If output is stopped, it is resumed as if t_startc had been typed on
the terminal.
.IR arg
is ignored and should be the NULL pointer.
The number of characters in the output queue is returned in the int
pointed to by
.IR arg .
The number of characters immediately available for input from the terminal
is returned in the int pointed to by
.IR arg .
This is the preferred method of non-blocking I/O (checking for the presence
of characters without waiting for them).
.IP "\fBstruct tchars\fR"
The second structure associated with a terminal defines special
characters. The structure is defined in <sys/ioctl.h> which is
automatically included by <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 ^C, ^\, ^Q, ^S, ^D and -1
respectively. A value of -1 for any of the characters means that the
effect of that character is ignored. The stop and start characters may
be the same to produce a 'toggle' effect. It is not recommended to set
any of the other characters to the same values; the order in which the
special characters are checked is not defined, and the results you get
may not be what was expected.
The ioctl calls that apply to tchars are:
Returns the special characters settings in the tchars structure pointed to by
.IR arg .
The special characters are set according to tchars structure pointed to by
.IR arg .
.IP "\fBLocal Mode\fR"
The third "structure" in the terminal interface is a local mode word;
.IR arg
points to an int variable, which is broken up into bitfields.
.\" From the GNO v2.0.1 man page:
.\" None of the options are currently implemented for the console driver.
.\" Other drivers may implement them; see the appropriate manpages for
.\" details.
The various bitfields in this word are as follows:
LCRTBS 0x0001 Backspace on erase rather than echoing erase
LPRTERA 0x0002 Printing terminal erase mode
LCRTERA 0x0004 Erase character echoes as backspace-space-backspace
LTILDE 0x0008 Convert ~ to ` on output (for Hazeltine terminals)
LMDMBUF 0x0010 Stop/start output when carrier drops
LLITOUT 0x0020 Suppress output translations
LTOSTOP 0x0040 Send SIGTTOU for background output (not implemented)
LFLUSHO 0x0080 Output is being flushed
LNOHANG 0x0100 Don't send hangup when carrier drops
LPASSOUT 0x0200 Cooked mode with 8-bit output
LCRTKIL 0x0400 BS-space-BS erase entire line on line kill
LPASS8 0x0800 Pass all 8 bits through on input, in any mode
LCTLECH 0x1000 Echo input control chars as ^?
LPENDIN 0x2000 Retype pending input at next read or input character
LDECCTQ 0x4000 Only ^Q restarts output after ^S
LNOFLSH 0x8000 Inhibit flushing of pending I/O when intr char is typed
The ioctl's used to access the local mode follow. In all cases
.IR arg
is a pointer to an int.
The bits of the local mode word specified by `1' bits in the argument are set;
this operation is a bit-wise OR.
The bits of the local mode word specified by `1' bits in the argument are
cleared; this operation ANDs the local mode with the bitwise negation of
the argument.
Sets the local mode word to the value of the argument.
Returns the local mode word in the int pointed to by arg.
.IP "\fBstruct ltchars\fR"
The fourth terminal structure is another set of special
characters. The structure is named ltchars (for Local Special Characters)
and is again defined in <ioctl.h>.
struct ltchars {
char t_suspc; /* stop process signal */
char t_dsuspc; /* delayed stop process signal */
char t_rprntc; /* reprint line */
char t_flushc; /* flush output (toggles) */
char t_werasc; /* word erase */
char t_lnextc; /* literal next character */
Defaults for these characters are ^Z, ^Y, ^R, ^O, ^W, and ^V.
As with tchars, a value of -1 disables the effect of that character.
Only t_suspc is currently implemented for the console driver.
The applicable ioctl functions are:
sets the local characters according to the ltchars structure pointed to by
.IR arg .
retreives the local characters, storing them in the ltchars structure
pointed to by
.IR arg .
.IP "\fBstruct winsize\fR"
The fifth structure associated with terminals is the winsize struct.
Provision is made in the kernel for storage of the current window or terminal
size along with the other terminal information. This info is
recorded in a winsize structure, and is defined in <ioctl.h>:
struct winsize {
unsigned short ws_row; /* rows, in characters */
unsigned short ws_col; /* columns, in characters */
unsigned short ws_xpixel; /* horizontal size, pixels */
unsigned short ws_ypixel; /* vertical size, pixels */
A '0' in a field indicates that the field value is undefined. '0' is
the default when a terminal is first opened. These values are not used
by the terminal driver itself; rather, they are for the benefit of
applications. The ioctl calls for winsize are:
Returns the window size parameters in the provided winsize structure.
Sets the window size parameters. If any of the values differ from the
old ones, a SIGWINCH signal is sent to the terminal's process group.
.BR ".tty"
.BR ".ttyco" " (console driver)"
.BR ".tty*" " (user-installed drivers)"
.IR "GNO Shell Reference Manual" ,
.BR stty (1),
.BR ioctl(2),
.BR signal(2)