SunOS man pages : asy (7)
Devices asy(7D)
NAME
asy - asynchronous serial port driver
SYNOPSIS
#include <fcntl.h>
#include <sys/termios.h>
open("/dev/ttynn", mode);
open("/dev/ttydn", mode);
open("/dev/cuan", mode);
DESCRIPTION
The asy module is a loadable STREAMS driver that provides
basic support for the standard UARTS that use Intel-8250,
National Semiconductor-16450 and 16550 hardware, in addition
to basic asynchronous communication support. The asy module
supports those termio(7I) device control functions specified
by flags in the c_cflag word of the termios structure, and
by the IGNBRK, IGNPAR, PARMRK, or INPCK flags in the c_iflag
word of the termios structure. All other termio(7I) func-
tions must be performed by STREAMS modules pushed atop the
driver. When a device is opened, the ldterm(7M) and
ttcompat(7M) STREAMS modules are automatically pushed on top
of the stream, providing the standard termio(7I) interface.
The character-special devices /dev/tty00 and /dev/tty01 are
used to access the two standard serial ports ( COM1 and COM2
) on an x86-based system. The asy module supports up to four
serial ports, including the standard ports. The ttynn dev-
ices have minor device numbers in the range 00-03, and may
be assigned names of the form /dev/ttydn, where n denotes
the line to be accessed. These device names are typically
used to provide a logical access point for a dial-in line
that is used with a modem.
To allow a single tty line to be connected to a modem and
used for incoming and outgoing calls, a special feature is
available that is controlled by the minor device number. By
accessing character-special devices with names of the form
/dev/cuan, it is possible to open a port without the Carrier
Detect signal being asserted, either through hardware or an
equivalent software mechanism. These devices are commonly
known as dial-out lines.
APPLICATION PROGRAMMING INTERFACE
Once a /dev/cuan line is opened, the corresponding tty, or
ttyd line cannot be opened until the /dev/cuan line is
closed. A blocking open will wait until the /dev/cuan line
is closed (which will drop Data Terminal Ready, after which
SunOS 5.8 Last change: 14 May 1999 1
Devices asy(7D)
Carrier Detect will usually drop as well) and carrier is
detected again. A non-blocking open will return an error. If
the /dev/ttydn line has been opened successfully (usually
only when carrier is recognized on the modem), the
corresponding /dev/cuan line cannot be opened. This allows a
modem to be attached to a device, (for example, /dev/ttyd0,
which is renamed from /dev/tty00) and used for dial-in (by
enabling the line for login in /etc/inittab) or dial-out (by
tip(1) or uucp(1C)) as /dev/cua0 when no one is logged in on
the line.
IOCTLS
The standard set of termio ioctl() calls are supported by
asy.
Breaks can be generated by the TCSBRK, TIOCSBRK, and
TIOCCBRK ioctl() calls.
The input and output line speeds may be set to any speed
that is supported by termio. The speeds cannot be set
independently; for example, when the output speed is set,
the input speed is automatically set to the same speed.
When the asy module is used to service the serial console
port, it supports a BREAK condition that allows the system
to enter the debugger or the monitor. The BREAK condition is
generated by hardware and it is usually enabled by default.
A BREAK condition originating from erroneous electrical sig-
nals cannot be distinguished from one deliberately sent by
remote DCE. The Alternate Break sequence can be used as a
remedy against this. Due to a risk of incorrect sequence
interpretation, binary protocols such as PPP, SLIP, and oth-
ers should not be run over the serial console port when
Alternate Break sequence is in effect. By default, the
Alternate Break sequence is a three character sequence: car-
riage return, tilde and control-B (CR ~ CTRL-B), but may be
changed by the driver. For more information on breaking
(entering the debugger or monitor) , see kbd(1) and kb(7M)
ERRORS
An open() will fail under the following conditions:
ENXIO The unit being opened does not exist.
EBUSY The dial-out device is being opened while the
dial-in device is already open, or the dial-in
device is being opened with a no-delay open and
the dial-out device is already open.
EBUSY The unit has been marked as exclusive-use by
another process with a TIOCEXCL ioctl() call.
SunOS 5.8 Last change: 14 May 1999 2
Devices asy(7D)
EINTR The open was interrupted by the delivery of a
signal.
FILES
/dev/tty[00-03]
hardwired tty lines
/dev/ttyd[0-3]
dial-in tty lines
/dev/cua[0-3]
dial-out tty lines
/platform/i86pc/kernel/drv/asy.conf
asy configuration file
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Architecture | IA |
|_____________________________|_____________________________|
SEE ALSO
tip(1), kbd(1), uucp(1C), ioctl(2), open(2),
termios(3C), attributes(5), ldterm(7M), ttcompat(7M),
kb(7M) termio(7I)
DIAGNOSTICS
asyn: silo overflow.
The hardware overrun occurred before the input charac-
ter could be serviced.
asyn: ring buffer overflow.
The driver's character input ring buffer overflowed
before it could be serviced.
SunOS 5.8 Last change: 14 May 1999 3
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