HP-UX Reference (11i v1 00/12) - 5 Miscellaneous Topics, 7 Device (Special) Files, 9 General Information, Index (vol 9)

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modem(7) modem(7)

NAME

modem - asynchronous serial modem line control

SYNOPSIS

#include <sys/modem.h>

DESCRIPTION

This section describes the two modes of modem line control and the three types of terminal port access. It

also discusses the effect of the bits of the termio structure that affect modem line control. The modem

related ioctl(2) system calls are discussed at the end of the document.

Deﬁnitions

There are several terms that are used within the following discussion which will be deﬁned here for refer-

ence. ‘‘Modem control lines’’ (CONTROL) are generally deﬁned as those outgoing modem lines that are

automatically controlled by the driver. ‘‘Modem status lines’’ (STATUS) are generally deﬁned as those

incoming modem lines that are automatically monitored by the driver. CONTROL and STATUS for a termi-

nal ﬁle vary according to the modem line control mode of the ﬁle (see Modem line control modes below). An

open(2) to a port will be considered to be

BLOCKED if it is waiting for another ﬁle on the same port to be

closed. An open to a port is considered to be

PENDING if it is waiting for the STATUS to be raised. An open

to a port is considered to be

SUCCESSFUL

if the open system call has returned to the calling process without

error.

Open ﬂag bits

Currently, the only open ﬂag bits recognized by the driver is the

O_NDELAY

and O_NONBLOCK bits. When

either of these bits is set, an open call to the driver will never become blocked. If possible, the open will be

returned immediately as

SUCCESSFUL, and the driver will continue the process of opening the tty ﬁle. If it

is not possible, then the open will be returned immediately with the appropriate error code as described in

the appropriate section.

Termio bits

When set, the CLOCAL bit in the termios or termio structure (see termio(7)) is used to remove the driver’s

automatic monitoring of the modem lines. However, the user’s ability to control the modem lines is deter-

mined only by the mode in effect and does not depend on the state of

CLOCAL.

Normally, the driver will

monitor and require the

STATUS to be raised. An open system call will raise the

CONTROL and wait for the

STATUS before completing unless the CLOCAL bit is set. (If the O_NDELAY

or O_NONBLOCK bit is set, the

open will be returned immediately, but the driver will otherwise continue to monitor the modem lines as

normal based on the state of the

CLOCAL bit.) Normally, loss of the STATUS

will cause the driver to break

the modem connection and lower the

CONTROL. However, if CLOCAL is set, any changes in the STATUS

will

be ignored. A connection is required before any data may be read or written, unless

CLOCAL is set. Any

timers that would normally be in effect (see Modem line control modes and Modem timers below) will be

stopped while

CLOCAL is set.

When the CLOCAL bit is changed from clear to set, the driver will assume the existence of an active device

(such as a modem) on the port regardless of the STATUS. If any of the CONTROL are raised at that point in

time, they will continue in that state. The STATUS will no longer be actively monitored. When the CLOCAL

bit is changed from set to clear, the driver will resume actively monitoring the STATUS. If all of the CON-

TROL

andSTATUS are raised at that point in time, the driver will continue the modem connection. If any of

the STATUS are not raised, the driver will act as though those signals were lost (as described in Modem line

control modes below) and, if the device is a controlling terminal, a hangup signal will be sent to the control-

ling process. If any of the

CONTROL are not raised, the driver will break the modem connection by lowering

all the CONTROL.

The HUPCL bit in the termios or termio structure determines the action of the driver regarding the CON-

TROL

when the last close system call is issued to a terminal ﬁle. If the HUPCL bit is set, the driver will

lower the CONTROL at close time and the modem connection will be broken. If HUPCL is not set and a

modem connection exists, it will continue to exist, even after the close is issued. The driver will not change

the CONTROL.

Terminal port access types

There are three types of modem access: call-in connections, call-out connections, and direct (no modem con-

trol) connections. A given port may be accessed through all three types of connection by accessing different

ﬁles. The modem access type of a terminal ﬁle is determined by the ﬁle’s major and/or minor device

numbers.

Section 7−−66 − 1 − HP-UX Release 11i: December 2000

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