tty.4

来自「<B>Digital的Unix操作系统VAX 4.2源码</B>」· 4 代码 · 共 1,190 行 · 第 1/3 页

input to be erased from the
screen with a \*(lqbackspace-space-backspace\*(rq
sequence when character- or word-deleting sequences are used.
LCRTERA must be used with LCRTBS for this functionality.
A LCRTKIL bit can be set as well, causing the input to
be erased in this manner on line kill sequences as well.
.PP
.I "Echoing of control characters"
If the LCTLECH bit is set
in the local state word, then nonprinting (control)
characters are normally echoed as 
\f(CW^\fIx\fR
(where \fIx\fP is the character used in combination with the CTRL key),
rather than being echoed unmodified; delete is echoed as 
.PN ^? .
.PP
The normal modes for using the new terminal driver on CRT terminals
are speed-dependent.
At speeds less than 1200 baud, the LCRTERA and LCRTKILL processing
is slow, so 
.MS stty 1
normally just sets LCRTBS and LCTLECH; at
speeds of 1200 baud or greater, all of these bits are normally set.
The
.PN stty
command summarizes these option settings and the use of the new terminal
driver as ``newcrt''.
.PP
.B "Output Processing"
.NXR "terminal interface" "processing output"
.PP
When one or more
characters are written, they are actually transmitted
to the terminal as soon as previously written characters
have finished typing.
(As noted above, input characters are normally 
echoed by putting them in the output queue
as they arrive.)
When a process produces characters more rapidly than they can be typed,
it is suspended when its output queue exceeds some limit.
When the queue has drained down to some threshold, 
the program is resumed.
Even parity is normally generated on output.
The EOT character is not transmitted in cooked mode, to prevent terminals
that respond to it from hanging up; programs using RAW or CBREAK mode
should be careful.
.PP
The terminal drivers provide necessary
processing for cooked and CBREAK mode
output including delay generation 
for certain special characters and parity
generation.   Delays are available after backspaces (CTRL/H), form feeds 
(CTRL/L), carriage returns (CTRL/M), tabs (CTRL/I), and newlines (CTRL/J).
The driver also optionally
expands tabs into spaces, where the tab stops are assumed to be set every
eight columns.
These functions are controlled by bits in the tty flags word.
(See \fBSummary\fR.)
.PP
The terminal drivers provide for mapping between uppercase and lowercase
on terminals lacking lowercase, and for other special processing on
deficient terminals.
.PP
Finally, in the new terminal driver, there is an output flush character,
normally CTRL/O, which sets the LFLUSHO bit in the local mode word, causing
subsequent output to be flushed until it is cleared by a program or more
input is typed.
This character has effect in both cooked and CBREAK modes
and causes pending input to be retyped if there is any pending input.
An ioctl to flush the characters
in the input and output queues, TIOCFLUSH,
is also available.
.PP
.B "Uppercase Terminals and Hazeltines"
.NXR "terminal" "lowercase letters and"
.PP
If the LCASE bit is set in the tty flags, then
all uppercase letters are mapped into
the corresponding lowercase letter.
The uppercase letter may be generated by preceding
it by a backslash (\\).
If the new terminal driver is being used,
then uppercase letters
are preceded by a a backslash (\\) when output.
In addition, the following escape sequences can be generated
on output and accepted on input:
.PP
.nf
for	\`	|	~	{	}
use	\e\|\'	\e\|!	\e\|^	\e\|(	\e\|)
.fi
.PP
To deal with Hazeltine terminals, which do not recognize the tilde (~) as
an ASCII character,
the LTILDE bit may be set in the local
mode word when using the new terminal driver; in this case, the tilde (~)
will be replaced with the grave accent (\`) on output.
.PP
.B "Flow Control"
.NXR "terminal" "suspending output"
.PP
There are two characters (the stop character, normally CTRL/S, and the
start character, normally CTRL/Q), that cause output to be suspended and
resumed respectively.  Extra stop characters typed when output
is already stopped have no effect, unless the start and stop characters
are made the same, in which case output resumes.
.PP
A bit in the flags word may be set to put the terminal into TANDEM mode.
In this mode, the system produces a stop character (default CTRL/S) when
the input queue is in danger
of overflowing, and a start character (default
CTRL/Q) when the input has drained sufficiently.  This mode is useful
when the terminal is actually another machine that obeys the
conventions.
.PP
A bit in the local mode word may be set to put the terminal into AUTOFLOW mode.
In this mode, flow control characters are responded to at the hardware
level.  Upon receipt of a stop character, the hardware suspends output.  This
allows for quick response to the stop character, which prevents buffer 
overflow (in printers for example).  AUTOFLOW functionality is only 
provided if the start character is CTRL/Q and the stop character is
CTRL/S.
The AUTOFLOW bit is cleared if the start or stop characters are
not standard values, or if the RAW bit is not set.
.PP
.B "Line Control and Breaks"
.NXR "terminal" "controlling line"
.PP
There are several
.PN ioctl
calls available to control the state of the terminal line.
The TIOCSBRK ioctl sets the break bit in the hardware interface,
causing a break condition to exist. This can be cleared by TIOCCBRK, 
usually after a delay with
.MS sleep 3 .
Break conditions in the input
are reflected as a null character in RAW mode
or as the interrupt character in cooked or CBREAK mode.
The TIOCCDTR ioctl clears the data terminal ready condition.
It can be set again by TIOCSDTR.
.PP
When the carrier signal from the dataset drops (usually
because the user has hung up his terminal), a
SIGHUP hangup signal is sent to the processes in the distinguished
process group of the terminal.
This usually causes them to terminate
(the SIGHUP can be suppressed by setting the LNOHANG bit in the local
state word of the driver.)
Access to the terminal by other processes is then normally revoked,
so any further reads fail,
and programs that read a terminal and test for
end-of-file on their input terminate appropriately.
.PP
When using an ACU,
it is possible to ask that the phone line be hung up on the last close
with the TIOCHPCL ioctl.  This is normally done on the outgoing line.
.PP
.B "Interrupt Characters"
.NXR "terminal" "interrupt characters"
.PP
There are several characters that generate
interrupts in cooked and CBREAK
mode.  All are sent the processes in the control group of the terminal,
as if a TIOCGPGRP ioctl were done to get the process group and then a
.MS killpg 2
system call were done,
except that these characters also flush pending input and output when
typed at a terminal
(for example, TIOCFLUSH).
The characters shown here are the defaults.
The field names in the structures 
are also shown.
The characters may be changed,
although this is not often done.
.IP ^?
\fBt_intrc\fR (Delete) generates a SIGINT signal.
This is the normal way to stop a process that is no longer interesting 
or to regain control in an interactive program.
.IP ^\e
\fBt_quitc\fR (FS) generates a SIGQUIT signal.
This is used to cause a program to terminate and produce a core image,
if possible, in the file
.B core
in the current directory.
.IP ^Z
\fBt_suspc\fR (EM) generates a SIGTSTP signal that is used to suspend
the current process group.
.IP ^Y
\fBt_dsuspc\fR (SUB) generates a SIGTSTP signal as CTRL/Z does, but the
signal is sent when a program attempts to read the CTRL/Y, rather than when
it is typed.
.PP
.B "Job Access Control"
.NXR "terminal" "controlling job access"
.PP
When using the new terminal driver,
if a process that is not in the distinguished process group of its
control terminal attempts to read
from that terminal, its process group is
sent a SIGTTIN signal.  This signal normally causes the members of
that process group to stop. 
If, however, the process is ignoring SIGTTIN, has SIGTTIN blocked,
is an
.IR "orphan process" ,
or is in the middle of process creation using
.MS vfork 2 ,
it is returned an end-of-file instead.  (An
.I "orphan process"
is a process whose
parent has exited and that has been inherited by the
.MS init 8
process.)
.NXR "orphan process" "defined"
Under older UNIX systems
these processes would typically have had their input files reset to
.PN /dev/null ,
so this is a compatible change.
.PP
When using the new terminal driver with the LTOSTOP bit set in the local
modes, a process is prohibited from
writing on its control terminal, if it is
not in the distinguished process group for that terminal.
Processes that are holding or ignoring SIGTTOU signals, that are 
orphans, or that are in the middle of a 
.PN vfork 2 ,
are excepted and allowed to produce output.
.PP
.B "Modem Control"
.NXR "modem" "controlling"
.PP
Ioctls have been added to provide more flexible modem control on
tty lines. The new commands are summarized below. 
.NXR "terminal interface" "modem ioctl list"
.IP TIOCMODEM 15
Indicate to the system that this tty line has a modem attached to it
and should not ignore modem signals. 
The argument to this ioctl is the address of a word that contains
either zero or a nonzero value.
Zero indicates that the effect of the ioctl is temporary,
and the line is reset to its condition prior to the ioctl, when
the tty line is closed.
Nonzero indicates that the effect of the ioctl should be permanent.
Root privilege is required to effect a permanent change.
.IP TIOCNMODEM
Indicate to the system that modem transmissions should be ignored on 
this line. This is useful for connections that do not implement the
full RS-232 standard (most direct connections to terminals).
.NXR "RS-232 standard" "modems and"
The argument to this ioctl is the address of a word that contains
either zero or a nonzero value.
Zero indicates that the effect of ioctl is temporary,
and the line is reset to its condition prior to the ioctl, when
the tty line is closed.
Nonzero indicates that the effect of the ioctl should be permanent.
Root privilege is required to effect a permanent change.
.IP TIOCNCAR
Ignore soft carrier when doing reads or writes.  If carrier is not
present on a modem line, then reads or writes normally fail.
This ioctl allows reads and writes to succeed, regardless of the
state of this line.
This is useful for dealing with automatic call units that send status
messages before carrier is present on the line.
The alternative would be to use
the TIOCNMODEM ioctl and ignore all modem
signals and force soft carrier to be present. 
The latter alternative is not desirable, if full modem control is 
required.
.IP TIOCCAR
The opposite effect of TIOCNCAR.
If carrier is not present on modem lines, then reads and writes fail.
.IP TIOCWONLINE
This ioctl blocks the process until carrier is detected.
.PP
The following example demonstrates how one might deal with a modem:
.NXR(e) "modem" "setting up"
.EX 0
 /* open the line and don't wait for carrier */
 fd = open(dcname, O_RDWR|O_NDELAY); 
 /* we are attached to a modem so don't ignore modem signals */
 ioctl(fd, TIOCMODEM, &temp);
 ioctl(fd, TIOCNCAR); 	/* ignore soft carr while dialing number */
 /* 
  * dial phone number and negotiate with auto call unit.
  */
 ioctl(fd, TIOCCAR);  	/* don't ignore carrier anymore */
 alarm(40);  		
 ioctl(fd, TIOCWONLINE); /* wait for carrier */
 alarm(0);
.EE
.PP
.B "Shared tty Lines"
.NXR "terminal" "implementing shared lines"
.PP
The following ioctls are used by 
.MS getty 8 ,
.MS tip 1 ,
and
.MS uucp 1
to implement shared terminal lines:  TIOCSINUSE/FIOSINUSE, 
TIOCCINUSE/FIOCINUSE.
Shared terminal lines can be used for both incoming and outgoing
connections.  For further information, see the 
.I Guide to System Environment Setup. 
These ioctls can be used by any user process on any file type, but
they do not work on a socket. 
.IP TIOCSINUSE 15
TIOCSINUSE is defined to FIOSINUSE.  This command 
checks to see if the file is marked ``in use''.
If the file is not ``in use'', it is marked 
``in use'' by the current process and the ioctl succeeds.
If the file is already ``in use'' by some other
process, the ioctl fails and errno is set to EALREADY. 
For further information, see 
.MS open 2 .
.IP TIOCCINUSE 
TIOCCINUSE is defined to FIOCINUSE.  This command 
clears the ``in use'' flag on a file, if the current process was
the one that set the ``in use'' flag.
Any process that is blocked and waiting for the ``in use''
flag to clear will be resumed. 
For further information, see 
.MS open 2 .
.PP
.B "Summary of Modes"
.PP
Unfortunately, due to the evolution of the terminal driver,
there are four different structures that contain various portions of the
driver data.  The first of these (\fBsgttyb\fR)
contains that part of the information
largely common between Version 6 and Version 7 UNIX systems.
The second contains additional control characters added in Version 7.
The third is a word of local state peculiar to the new terminal driver,
and the fourth is another structure of special characters added for the
new driver.  
.PP
.B Basic modes: sgtty \- 
There are two versions of the sgttyb structure: one for BSD (default)
and one for SYSTEM_FIVE. The basic
.IR ioctl s
use the structure
defined in
.PN <sgtty.h> :
.NXR "sgttyb file"
.PP
You get this version of sgttyb if you include 
.PN <sgtty.h> , 
into your .c source, 
and then compile
with `cc \-YBSD ....' or `setenv PROG_ENV BSD' or by default to BSD if
PROG_ENV is not defined, or `\-Y' is not specified.
.EX 5
struct sgttyb {
       char     sg_ispeed;
       char     sg_ospeed;
       char     sg_erase;
       char     sg_kill;
       short    sg_flags;
};
.EE
.PP
You get this version of sgttyb if you include 
.PN <sgtty.h> 
in your .c source, 
and then compile using the `\-Y' or `\-YSYSTEM_FIVE' option of 
.PN cc ,
or set PROG_ENV environment to `SYSTEM_FIVE'.
.EX 5
struct sgttyb {
       char     sg_ispeed;
       char     sg_ospeed;
       char     sg_erase;
       char     sg_kill;
       int      sg_flags;
};
.EE

.PP
The
.I sg_ispeed 
and 
.I sg_ospeed
fields describe the input and output speeds of the
device according to the following table,
which corresponds to the
speeds offered on most Digital terminal multiplexers.
If other hardware is used,
impossible speed changes are ignored.
Symbolic values in the table are as defined in
.PN <sgtty.h> .
.PP
.nf
.ta \w'B9600   'u +5n
B0	0	(hang up dataphone)
B50	1	50 baud
B75	2	75 baud
B110	3	110 baud
B134	4	134.5 baud