Tribblix: manual page: asy.4d

ASY(4D) Devices ASY(4D)

NAME

asy - asynchronous serial port driver

SYNOPSIS

#include <fcntl.h>

#include <sys/termios.h>

open("/dev/term/n", mode);

open("/dev/tty/n", mode);

open("/dev/cua/n", mode);

DESCRIPTION

The asy module is a loadable STREAMS driver that provides basic
support for Intel-8250, National Semiconductor-16450, 16550, and some
16650 and 16750 and equivalent UARTs connected via the ISA-bus, in
addition to basic asynchronous communication support. The asy module
supports those termio(4I) device control functions specified by flags
in the c_cflag word of the termios structure, and by the IGNBRK,
IGNPAR, PARMRK, INPCK, IXON, IXANY, or IXOFF flags in the c_iflag
word of the termios structure. All other termio(4I) functions must be
performed by STREAMS modules pushed atop the driver. When a device is
opened, the ldterm(4M) and ttcompat(4M) STREAMS modules are
automatically pushed on top of the stream, providing the standard
termio(4I) interface.

The character-special devices /dev/term/a, /dev/term/b, /dev/term/c
and /dev/term/d are used to access the four standard serial ports
(COM1, COM2, COM3 and COM4 at I/O addresses 3f8, 2f8, 3e8 and 2e8
respectively). Serial ports on non-standard ISA-bus I/O addresses are
accessed via the character-special devices /dev/term/0, /dev/term/1,
etc. 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/cua/n, 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.

Note -

This module is affected by the setting of certain eeprom variables,
ttya-ignore-cd and ttya-rts-dtr-off (and similarly for ttyb-,
ttyc-, and ttyd- parameters). For information on these parameters,
see the eeprom(8) man page.

Note -

For serial ports on the standard COM1 to COM4 I/O addresses above,
the default setting for ttya-ignore-cd and ttya-rts-dtr-off is
true. If any of these ports are connected to a modem, these
settings should be changed to false. For serial ports on non-
standard I/O addresses, the default setting for ttya-ignore-cd and
ttya-rts-dtr-off is false.

APPLICATION PROGRAMMING INTERFACE

Once a /dev/cua/n line is opened, the corresponding tty line cannot
be opened until the /dev/cua/n line is closed. A blocking open will
wait until the /dev/cua/n line is closed (which will drop Data
Terminal Ready, after which 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/cua/n line cannot be opened. This allows a modem to be attached
to /dev/term/[n] (renamed from /dev/tty[n]) 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/cua/n 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 signals
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, SLIP and certain other
binary protocols should not be run over the serial console port when
Alternate Break sequence is in effect. Although PPP is a binary
protocol, it is able to avoid these sequences using the ACCM feature
in RFC 1662. For Solaris PPP 4.0, you do this by adding the following
line to the /etc/ppp/options file (or other configuration files used
for the connection; see pppd(8) for details):

asyncmap 0x00002000

By default, the Alternate Break sequence is a three character
sequence: carriage 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(4M).

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.

EINTR
The open was interrupted by the delivery of a signal.

FILES

/dev/term/[a-d]
/dev/term/[012...]
dial-in tty lines

/dev/cua/[a-d]
/dev/cua/[012...]
dial-out tty lines

/kernel/drv/amd64/asy
64-bit kernel module for 64-bit x86 platform

/kernel/drv/asy.conf
asy configuration file

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:

+---------------+-----------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+-----------------+
|Architecture | x86 |
+---------------+-----------------+

DIAGNOSTICS

asyn: silo overflow.

The hardware overrun occurred before the input character could be
serviced.

asyn: ring buffer overflow.

The driver's character input ring buffer overflowed before it
could be serviced.

October 9, 2004 ASY(4D)