HP-UX Reference (11i v2 04/09) - 3 Library Functions A-M (vol 6)

b
blmode(3C) blmode(3C)
(OBSOLETED in Itanium(R)-based Systems)
Read Requests
Read requests that receive data from block-mode transmissions do not return until the transmission is
complete (the terminal has transmitted all characters). If the read is satisfied by byte count or if a data
transmission error occurs, all subsequent data is discarded until the transmission is complete. The read
waits until a terminator character is seen, or until a time interval specified by the system has passed that
is longer than necessary for the number of characters specified.
The data-block-terminator character is included in the data returned to the user, and is included in the
byte count. If the number of bytes transferred by the terminal in a block-mode transfer exceeds the
number of bytes requested by the user, the read returns the requested number of bytes and the remaining
bytes are discarded. The user can determine if data was discarded by checking the last character of the
returned data. If the last character is not the terminator character, then more data was received than
was requested and data was discarded.
The [EIO] error can be caused by several events, including errors in transmission, framing, parity, break,
and overrun, or if the internal timer expires. The internal timer starts when the second trigger character
is sent by the computer, and ends when the terminating character is received by the computer. The
length of this timer is determined by the number of bytes requested in the read and the current baud
rate, plus an additional ten seconds.
User Control of Handshaking
If desired, the application program can provide its own handshake mechanism in response to the alert
character by selecting the
OWNTERM mode (see CB_OWNTERM below). With this mode selected, the
driver completes a read request when the alert character is received. No data is discarded before the
alert, and the alert is returned in the data read. The alert character may be escaped with a backslash (
\)
character. The second trigger is sent when the application issues the next read.
blmode Control Calls
First, the standard
open() call to a tty device must be made to obtain a file descriptor for the subse-
quent block-mode control calls (an open() is done automatically by the system for
stdin on the termi-
nal).
int bfdes;
bfdes = blopen (int fildes)
A call to blopen() must be made before any block-mode access is allowed on the specified
file descriptor. blopen() initializes the block-mode parameters as described below. The
return value from blopen() is a block-mode file descriptor that must be passed to all subse-
quent block-mode control calls.
int blclose (int bfdes)
A call to blclose() must be issued before the standard close() to ensure proper closure
of the device (see close(2)). Otherwise unpredictable results can occur. The argument bfdes is
the file descriptor returned from a previous
blopen() system call.
int blread (int bfdes, char *buf, size_t nbyte)
The blread() routine has the same parameters as the read() sytem call (see read(2)). At
the beginning of a read, the cb_trig1c character (if defined) is sent to the device. If
CB_BMTRANS is not set, and no cb_alertc character is received, the read data is processed
according to termio(7). If CB_BMTRANS is set, or if a non-escaped cb_alertc character is
received, echo is turned off for the duration of the transfer, and no further special character
processing is done other than that required for the termination character. The argument bfdes
is the file descriptor returned from a previous blopen() system call.
int blget (int bfdes, struct blmodeio *arg)
A call to blget() returns the current values of the blmodeio structure (see below). The
argument bfdes is the file descriptor returned from a previous blopen() system call.
int blset (int bfdes, const struct blmodeio *arg)
A call to blset() sets the block-mode values from the structure whose address is arg. The
argument bfdes is the file descriptor returned from a previous blopen() system call.
blmode Structure
The two block-mode control calls,
blget() and blset(), use the following structure, defined in
<sys/blmodeio.h>:
Section 3−−60 Hewlett-Packard Company − 2 − HP-UX 11i Version 2: September 2004