HP-UX Reference (11i v1 05/09) - 7 Device (Special) Files, 9 General Information, Index (vol 10)

m
modem(7) modem(7)
Terminal port access interlock
An interlock mechanism is provided between the three access types of terminal files. It prevents more than
one file from being successfully opened at a time, but allows certain opens to succeed while others are
PENDING so that a port can be opened through a call-out connection while getty has a pending open at a
call-in connection. The three access types are given a priority that determines which open will succeed if
more than one file has an open issued against it. The three access types are ordered from lowest priority to
highest as follows: call-in, call-out, and direct.
If an open is issued to a port which already has a
SUCCESSFUL open on it of a lower priority type, the new
open will be returned with an EBUSY error. (EBUSY will also be returned by an attempted open on a
CCITT call-out file if an incoming call indication is currently being received. In this case, if there is a
PENDING open on the corresponding CCITT call-in file, this
PENDING open will complete.) If the lower
priority open is
PENDING, the new open will succeed if possible, or will be left
PENDING if waiting for the
STATUS and the lower priority open will become
BLOCKED. If a higher priority open has succeeded or is
PENDING, the new open will be BLOCKED, unless the new open has the
O_NDELAY flag bit set, in which case
the open will be returned with an EBUSY error. Once an open on one type of file is
SUCCESSFUL, any
PENDING opens on lower priority files will become
BLOCKED.
When a file of one priority is closed, a BLOCKED open on the next lower priority type file will become active.
If all of the STATUS are raised, the open will be
SUCCESSFUL, otherwise the open will become PENDING
waiting for the STATUS. If the lower priority open is
SUCCESSFUL (because the connection was maintained
when the higher priority file was closed), the port characteristics (speed, parity, etc.) that were set by the
higher priority file will be inherited by the lower priority file. If the connection is not maintained through
the close, the port characteristics will be set to default values.
Modem timers
There are four timers currently defined for use with modem connections. The first three of the timers are
applicable only to CCITT mode connections. In general, the effect of changing a timer value while the
timer is running is system dependent. However, setting the timer value to zero is guaranteed to disable
the timer even if it is running.
The connect timer is used to limit the amount of time to wait for a connection to be established once it has
been begun. This timer is started when an incoming call has been received on a call-in file, or when an
open has been issued on a call-out file for which no opens are already pending. If the connection is com-
pleted in time, the timer is aborted. If the time period expires, the connection is aborted. For a call-in file,
the driver will again wait for an incoming call and the open will remain pending. For a call-out file, the
open will be returned with an EIO error.
The carrier detect timer is used to limit the amount of time to wait before causing a disconnect if
DCD
drops. If carrier is not re-established in this time, a disconnect will occur. If carrier is re-established before
the timeout, the timer will be aborted and the connection maintained. During the period when carrier is
not raised, no data will be transferred across the line.
The no activity timer is used to limit the amount of time a connection will remain open with no data
transfer across the line. When the data line becomes quiescent with no data transfer, this timer will be
started. If data is again transferred over the line in either direction before the time limit, the timer will be
aborted. If no activity occurs before the timeout has occurred, the driver will disconnect the line. This can
be used to avoid long and costly telephone connections when data transfer has been stopped either normally
or abnormally.
The last timer defined, the hangup timer, is used for both CCITT and simple modes. This timer controls
the amount of time to wait after disconnecting a modem line before allowing another open. This time
period should be made long enough to guarantee that the connection has been terminated by the telephone
switching equipment. If this period is not long enough, the telephone connection may not be broken and a
succeeding open may complete with the old connection.
HP-UX Modem ioctls
Several ioctl system calls apply to manipulation of modem lines. They use the following information
defined in <sys/modem.h>:
#define NMTIMER 6
typedef unsigned long mflag;
struct mtimer {
unsigned short m_timers[NMTIMER];
};
Section 7−−72 Hewlett-Packard Company − 3 − HP-UX 11i Version 1: September 2005