su - asynchronous serial port driver
The su module is a loadable STREAMS driver that provides
basic support for standard UARTS that use Intel-8250,
National Semiconductor-16450/16550 hardware and Southbridge
1535D (16550 compatable) Super I/O hardware. The module also
provides keyboard and mouse I/O support for Sun machines
using those same Intel, National Semiconductor and South-
bridge chipsets. The su driver provides basic asynchronous
communication support for serial ports. Both the serial dev-
ices and keyboard/mouse devices will have streams built with
appropriate modules pushed atop the su driver by means of
either the autopush(1M) or dacf.conf(4) facilities, depend-
ing on the OS revision and architecture in use.
The su module supports those termio(7I) device control func-
tions 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) 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
The character-special devices /dev/ttya and /dev/ttyb are
used to access the two standard serial ports. The su module
supports up to ten serial ports, including the standard
ports. The tty[a-z] devices have minor device numbers in the
range 00-03, and may be assigned names of the form
/dev/ttyd_n_, 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/cua_n, it is possible to open a port without the Car-
rier Detect signal being asserted, either through hardware
or an equivalent software mechanism. These devices are com-
monly known as _dial-out_ lines.
APPLICATION PROGRAMMING INTERFACE
Once a /dev/cua_n_ line is opened, the corresponding tty, or
ttyd 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/ttyd_n_ 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 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.
The standard set of termio ioctl() calls are supported by
Breaks can be generated by the TCSBRK, TIOCSBRK, and
TIOCCBRK ioctl() calls.
The input and output line speeds may be set to any of the
following baud rates: 0, 50, 75, 110, 134, 150, 200, 300,
600, 1200, 1800, 2400, 4800, 9600, 19200, 38400, 57600 or
115200. The speeds cannot be set independently; for example,
when the output speed is set, the input speed is automati-
cally set to the same speed.
When the su 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).
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.
dial-out tty lines
dial-in tty lines
binary compatibility package device names
See attributes(5) for descriptions of the following attri-
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
| Architecture | SPARC |
strconf(1), kbd(1), tip(1),uucp(1C), autopush(1M),
kstat(1M), ioctl(2), open(2), termios(3C), dacf.conf(4),
attributes(5), kb(7M), ldterm(7M), ttcompat(7M), termio(7I)
The su driver keeps track of various warning and error con-
ditions using kstat counters. The output of the kstat su
command provides kstat counters. The counters and their
The internal chip FIFO received more data than it
could handle. This indicates that the Solaris operat-
ing environment was not servicing data interrupts fast
enough possibly due to a system with too many inter-
rupts or a data line with a data rate that is too
ring buffer overflow
The su module was unable to store data it removed
from the chips internal FIFO into a software buffer.
The user process is not reading data fast enough, pos-
sibly due to an overloaded system. If possible, the
application should enable flow control (either CTSRTS
or XONXOFF) to allow the driver to backpressure the
remote system when the local buffers fill up.
Man(1) output converted with