Asynchronous Serial Communications Programmer's Reference Manual (32022-90052)

Chapter 8 167
Intrinsics Reference
FCONTROL(4)
FCONTROL(4)
Parameters
controlcode 4 — Sets a read timeout value for the next read.
param 16-bit unsigned integer by reference
(required)
Passes a timeout value (in seconds) to the device that
owns the file whose file number is specified in filenum.
Notes A call to FCONTROL with a controlcode value of 4
allows you to set a time limit on the next read from a
terminal. The timeout value is specified in seconds,
with a maximum value of 65535.
Any read that does not complete before the time limit
expires is transferred to the user buffer and the read
length is returned. A condition code of CCL is returned
to the calling program. A call to FCHECK after the
timeout returns Error code 22, Software
Timeout.
If you are setting a timeout value for a read posted
against a device connected through a PAD, DTC Telnet,
or Telnet/iX, you should take care to add enough time to
compensate for any time delays that might be caused
by the network.
A timeout value should be used any time your program
is reading from an unattended device, to prevent
“hangs” that might occur if the device is not ready or a
problem exists with the device or its connection to the
system. You can also use a timeout value to terminate
binary reads. Refer to the discussion of
FCONTROL(26,27) for more information on
terminating reads in binary mode.
The timeout value is in effect only for the next read
from the terminal, and must therefore be reissued for
each read. A timeout value of 0 cancels the timeout.
During block mode reads the timer halts when the DC2
character is received. At this point, the block mode read
timer is activated by the system. The block mode read
timer is set by the system software, and its values are
not user changeable.