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coherent
termio Device Driver termio
General terminal interface
Under the COHERENT system, all asynchronous ports use the same
interface, no matter what hardware is involved. The remainder of
this section discusses the common features of this interface.
When a terminal file is opened, it normally causes the process to
wait until a connection is established. In practice, users'
programs seldom open these files; they are opened by the program
getty and become a user's standard input, output, and error
files. The very first terminal file opened by the process group
leader of a terminal file not already associated with a process
group becomes the control terminal for that process group. The
control terminal plays a special role in handling quit and inter-
rupt signals, as discussed below. The control terminal is in-
herited by a child process during a call to fork. A process can
break this association by changing its process group using
setpgrp.
A terminal associated with one of these files ordinarily operates
in full-duplex mode. Characters can be typed at any time, even
while output is occurring, and are only lost when the system's
input buffers become completely full, which is rare, or when the
user has accumulated the maximum allowed number of input charac-
ters that have not yet been read by some program. Currently,
this limit is 256 characters. When the input limit is reached,
the sytems throws away all the saved characters without notice.
Normally, terminal input is processed in units of lines. A line
is delimited by a newline character (ASCII LF), an end-of-file
character (ASCII EOT), or an end-of-line character. This means
that a program attempting to read will be suspended until an en-
tire 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, however, necessary to read a whole line at
once; any number of characters may be requested in a read, even
one, without losing information.
During input, the system normally processes erase and kill
characters. By default, the backspace character erases the last
character typed, except that it will not erase beyond the begin-
ning of the line. By default, the <ccttrrll-UU> calls (deletes) the
entire input line, and optionally outputs a newline character.
Both these characters operate on a keystroke-by-keystroke basis,
independently of any backspacing or tabbing which may have been
done. Both the erase and kill characters may be entered liter-
ally by preceding them with the escape character (\). In this
case, the escape character is not read. You may change the erase
and kill characters.
Certain characters have special functions on input. These
functions and their default character values are summarized as
follows:
COHERENT Lexicon Page 1
termio Device Driver termio
IINNTTRR (<ccttrrll-CC> or ASCII ETX) generates an interrupt signal
that is sent to all processes with the associated con-
trol 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 the Lexicon entry for signal.
QQUUIITT (Control-\ or ASCII ES) generates a quit signal. Its
treatment is identical to that of 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 ccoorree) will be created in the current
working directory.
EERRAASSEE (<bbaacckkssppaaccee> or ASCII BS) erases the preceding charac-
ter. It will not erase beyond the start of a line, as
delimited by a newline, EOF, or EOL character.
KKIILLLL (<ccttrrll-UU> or ASCII NAK) deletes the entire line, as
delimited by a newline, EOF, or EOL character.
EEOOFF (<ccttrrll-DD> or ASCII EOT) generates an end-of-file
character 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,
which is to say the EOF occurred at the beginning of a
line. zero characters will be passed back, which is
the standard end-of-file indication.
NNLL (ASCII LF) is the normal line delimiter. It cannot be
changed or escaped.
EEOOLL (ASCII LF) is an additional line delimiter, line NL.
It is not normally used.
SSTTOOPP (<ccttrrll-SS> or ASCII DC3) can be used to suspend output.
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.
SSTTAARRTT (<ccttrrll-QQ> or ASCII DC1) resumes output that has been
suspended by a STOP character. While output is not
suspended, START characters are ignored and not read.
The start/stop characters can not be changed or es-
caped.
The character values for INTR, QUIT, ERASE, KILL, EOF, and EOL
may be changed. to suit individual tastes. The ERASE, KILL, and
EOF character may be escaped by a preceding \ character, in which
case the system ignores its special meaning.
When the carrier signal from the data-set drops, a hangup signal
is sent to all processes that have this terminal as the control
COHERENT Lexicon Page 2
termio Device Driver termio
terminal. Unless other arrangements have been made, this signal
causes the process to terminate. If the hangup signal is ig-
nored, any subsequent read returns with an end-of-file indica-
tion. Thus programs that read a terminal and test for end-of-
file can terminate appropriately when hung up on.
When one or more characters are written, they are transmitted to
the terminal as soon as previously written characters have
finished typing. Input characters are echoed by putting them
into the output queue as they arrive. If a process produces
characters more rapidly than they can be printed, it will be
suspended when its output queue exceeds some limit. When the
queue has drained down to some threshold, the program resumes.
Several calls to ioctl apply to terminal files. The primary
calls use the following structure, defined in <tteerrmmiioo.hh>:
#define NCC 8
struct termio {
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 relative positions and initial values for each function are
as follows:
0 INTR ^C
1 QUIT ^\
2 ERASE \b
3 KILL ^U
4 EOF ^D
5 EOL \n
6 reserved
7 reserved
The field c_iflag describes the basic terminal input control:
IGNBRK 0000001 Ignore break condition.
BRKINT 0000002 Signal interrupt on break.
IGNPAR 0000004 Ignore characters with parity errors.
PARMRK 0000010 Mark parity errors.
INPCK 0000020 Enable input parity check.
ISTRIP 0000040 Strip character.
INLCR 0000100 Map NL to CR on input.
IGNCR 0000200 Ignore CR.
COHERENT Lexicon Page 3
termio Device Driver termio
ICRNL 0000400 Map CR to NL on input.
IUCLC 0001000 Map upper-case to lower-case on input.
IXON 0002000 Enable start/stop output control.
IXANY 0004000 Enable any character to restart output.
IXOFF 0010000 Enable start/stop input control.
If IGNBRK is set, the break condition (a character-framing error
with data all zeros) is ignored, that is, not put on the input
queue and therefore not read by any process. Otherwise, if
BRKINT is set, the break condition generates an interrupt signal
and flushes both the input and output queues. If IGNPAR is set,
characters with other framing and parity errors are ignored.
If PARMRK is set, a character with a framing or parity error
which is not ignored is read as the three character sequence
0377, 0, X, where X is the data of the character received in er-
ror. To avoid ambiguity in this case, if ISTRIP is not set, a
valid character of 0377 is read as 0377, 0377. If PARMRK is not
set, a framing or parity error which is not ignored is read as
the character NUL.
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.
If ISTRIP is set, valid input characters are stripped to 7-bits
before being processed; 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 will suspend output and a received START character
will restart output. All start/stop characters are ignored and
not read. If IXANY is set, any input character will restart out-
put which has been suspended.
IF IXOFF is set, the system will transmit START/STOP characters
when the input queue is nearly empty/full.
The initial input control value is all bits clear.
The field c_oflag field specifies the system treatment of output:
OPOST 0000001 Postprocess output.
OLCUC 0000002 Map lower case to upper on output.
ONLCR 0000004 Map NL to CR-NL on output.
OCRNL 0000010 Map CR to NL on output.
ONOCR 0000020 No CR output at column 0.
COHERENT Lexicon Page 4
termio Device Driver termio
ONLRET 0000040 NL performs CR function.
OFILL 0000100 Use fill characters for delay.
OFDEL 0000200 Fill is DEL, else NUL.
NLDLY 0000400 Select new-line delays:
NL0 0
NL1 0000400
CRDLY 0003000 Select carriage-return delays:
CR0 0
CR1 0001000
CR2 0002000
CR3 0003000
TABDLY 0014000 Select horizontal-tab delays:
TAB0 0
TAB1 0004000
TAB2 0010000
TAB3 0014000 Expand tabs to spaces.
BSDLY 0020000 Select backspace delays:
BS0 0
BS1 0020000
VTDLY 0040000 Select vertical-tab delays:
VT0 0
VT1 0040000
FFDLY 0100000 Select form-feed delays:
FF0 0
FF1 0100000
If OPOST is set, output characters are post-processed as in-
dicated by the remaining flags; otherwise, characters are trans-
mitted without change.
If OLCUC is set, a lower-case alphabetic character is transmitted
as the corresponding upper-case character. This function is of-
ten used 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 trans-
mitted when at column 0 (first position). If ONLRET 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 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 trans-
mitted.
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 NUL.
If a form-feed or vertical-tab delay is specified, it lasts for
about two seconds.
COHERENT Lexicon Page 5
termio Device Driver termio
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 four fill characters.
Horizontal-tab delay type 1 depends on the current column posi-
tion. 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.
The initial output control value is all bits clear.
The field c_cflag describes the hardware control of the terminal,
as follows:
CBAUD 0000017 Baud rate:
B0 0 Hang up
B50 0000001 50 baud
B75 0000002 75 baud
B110 0000003 110 baud
B134 0000004 134.5 baud
B150 0000005 150 baud
B200 0000006 200 baud
B300 0000007 300 baud
B600 0000010 600 baud
B1200 0000011 1200 baud
B1800 0000012 1800 baud
B2400 0000013 2400 baud
B4800 0000014 4800 baud
B9600 0000015 9600 baud
B19200 0000016 19200 baud
B38400 0000017 38400 baud
CSIZE 0000060 Character size:
CS5 0 5 bits
CS6 0000020 6 bits
CS7 0000040 7 bits
CS8 0000060 8 bits
CSTOPB 0000100 Send two stop bits, else one
CREAD 0000200 Enable receiver
PARENB 0000400 Parity enable
PARODD 0001000 Odd parity, else even
HUPCL 0002000 Hang up on last close
CLOCAL 0004000 Local line, else dial-up
COHERENT Lexicon Page 6
termio Device Driver termio
The CBAUD bits specify the baud rate. 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 discon-
nects the line. For any particular hardware, the system ignores
impossible changes to the speed.
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 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 charac-
ters will be received.
If HUPCL is set, COHERENT disconnects the line when the last
process with the line open closes the line or terminates; that
is, the data-terminal-ready signal is not asserted.
If CLOCAL is set, the system assumes that the line to be a local,
direct connection with no modem control. Otherwise, it assumes
modem control.
The initial hardware control value after open is B300, CS8,
CREAD, HUPCL.
The line discipline uses the field c_lflag to control terminal
functions. The basic line discipline (0) provides the following:
ISIG 0000001 Enable signals.
ICANON 0000002 Canonical input (erase and kill processing).
XCASE 0000004 Canonical upper/lower presentation.
ECHO 0000010 Enable echo.
ECHOE 0000020 Echo erase character as BS-SP-BS.
ECHOK 0000040 Echo NL after kill character.
ECHONL 0000100 Echo NL.
NOFLSH 0000200 Disable flush after interrupt or quit.
If ISIG is set, the system checks each input character against
the special control characters INTR and QUIT. If an input
character matches one of these control characters, the system ex-
ecutes the function associated with that character. If ISIG is
not set, the system performs no checking; thus, these special in-
put functions are possible only if ISIG is set. You can disable
these functions individually by changing the value of the control
character to an unlikely or impossible value (e.g. 0377).
COHERENT Lexicon Page 7
termio Device Driver termio
If ICANON is set, the system enables canonical processing. This
enables the erase and kill edit functions, and limits the as-
sembly of input characters into lines delimited by NL, EOF, and
EOL. If ICANON is not set, read requests are satisfied directly
from the input queue. A read will not be satisfied until at
least MIN characters have been received or the timeout value TIME
has expired. This allows the system to read efficiently fast
bursts of input while still allowing single-character input. The
MIN and TIME values are stored in the position for the EOF and
EOL characters, respectively. The time value represents tenths
of seconds.
If XCASE is set, and if ICANON is set, an upper-case letter is
accepted on input by preceding it with a \ character, and is out-
put preceded by a \ character. In this mode, the following es-
cape sequences are generated on output and accepted on input:
_F_o_r: _U_s_e:
` \'
| \!
~ \^
{ \(
} \)
\ \\
For example, AA is input as \aa, \nn as \\nn, and \NN as \\\nn.
If ECHO is set, characters are echoed as received.
When ICANON is set, the following echo functions are possible: If
ECHO and ECHOE are set, the erase character is echoed as ASCII BS
SP BS, which clears the last character from the screen. If ECHOE
is set and EHO is not set, the erase character is echoed as ASCII
SP BS. If ECHOK is set, the NL character is echoed after the
kill character to emphasize that the line will be deleted. Note
that an escape character preceding the erase or kill character
removes any special function. If ECHONL is set, the NL character
is echoed even if ECHO is not set. This is useful for terminals
set to local echo (``half duplex''). Unless escaped, the EOF
character is not echoed. Because EOT is the default EOF charac-
ter, this prevents terminals that respond to EOT from hanging up.
If NOFLSH is set, the normal flush of the input and output queues
associated with the quit and interrupt characters is not done.
The initial line-discipline control value is all bits clear.
The primary calls to ioctl have the following form:
COHERENT Lexicon Page 8
termio Device Driver termio
ioctl( fildes, command, arg )
struct termio *arg;
The following commands use this form:
TTCCGGEETTAA Get the parameters associated with the terminal and
store in the termio structure referenced by arg.
TTCCSSEETTAA Set the parameters associated with the terminal from
the structure referenced by arg. The change is im-
mediate.
TTCCSSEETTAAWW Wait for the output to drain before setting the new
parameters. This form should be used when changing
parameters that affect output.
TTCCSSEETTAAFF Wait for the output to drain, then flush the input
queue and set the new parameters.
Additional calls to ioctl have the following form:
ioctl( fildes, command, arg )
int arg;
The following commands use this form:
TTCCSSBBRRKK Wait for the output to drain. If arg is zero, then
send a break (zero bits for 0.25 seconds).
TTCCXXOONNCC Start/stop control. If arg is zero, suspend output; if
one, restart suspended output.
TTCCFFLLSSHH If arg is zero, flush the input queue; if one, flush
the output queue; if two, flush both the input and out-
put queues.
***** Files *****
/dev/tty*
***** See Also *****
device drivers, ioctl(), stty, termio.h
COHERENT Lexicon Page 9
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