Devices asy(7D)
NAME
asy - asynchronous serial port driver
SYNOPSIS
#include
#include
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 con-
nected via the ISA-bus, in addition to basic asynchronous
communication support. The asy module supports those
termio(7I) device control functions specified by flags in
the ccflag word of the termios structure, and by the
IGNBRK, IGNPAR, PARMRK, INPCK, IXON, IXANY, or IXOF flags
in the ciflag word of the termios structure. All other
termio(7I) functions must be performed by STREAMS modules
pushed atop the driver. When a device is opened, the
ldterm(7M) and ttcompat(7M) STREAMS modules are automati-
cally pushed on top of the stream, providing the standard
termio(7I) 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 Car-
rier Detect signal being asserted, either through hardware
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Devices asy(7D)
or an equivalent software mechanism. These devices are com-
monly 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 simi-
larly for ttyb-, ttyc-, and ttyd- parameters). For infor-
mation on these parameters, see the eeprom(1M) 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.
APLICATION PROGRAMING 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
TIOCBRK 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
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Devices asy(7D)
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, SLIP and certain other binary protocols
should not be run over the serial console port when Alter-
nate Break sequence is in effect. Although P is a binary
protocol, it is able to avoid these sequences using the ACM
feature in RFC 1662. For Solaris P 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(1M) for details):
asyncmap 0x00002000
By default, the Alternate Break sequence is a three charac-
ter sequence: carriage return, tilde and control-B (CR ~
CTRL-B), but may be changed by the driver. For more informa-
tion on breaking (entering the debugger or monitor), see
kbd(1) and kb(7M).
ERORS
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 dev-
ice 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 sig-
nal.
FILES
/dev/term/[a-d] dial-in tty lines
/dev/term/[012...]
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Devices asy(7D)
/dev/cua/[a-d] dial-out tty lines
/dev/cua/[012...]
/kernel/drv/amd64/asy 64-bit kernel module for 64-bit x86
platform
/kernel/drv/asy.conf asy configuration file
ATRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
ATRIBUTE TYPE ATRIBUTE VALUE
Architecture x86
SEE ALSO
tip(1), kbd(1), uucp(1C), eeprom(1M), pppd(1M), 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 character
could be serviced.
asyn: ring buffer overflow.
The driver's character input ring buffer overflowed
before it could be serviced.
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