Timeout on serial port read
"Gary S. Moss", VLD/VMB
moss at BRL.MIL
Thu May 3 23:29:59 AEST 1990
< I am trying to set the ioctl call so that a raw read from a
< serial port will time out after a few seconds. No matter what I
< set the TIME value for in the control structure, the machine
< still hangs waiting for characters. What am I doing wrong, if anything.
< new_settings.c_iflag = IGNBRK | IGNPAR;
< new_settings.c_oflag = NULL;
< new_settings.c_cflag = B9600 | CS8 | CREAD | CLOCAL;
< new_settings.c_lflag = ICANON;
< new_settings.c_line = NULL;
< new_settings.c_cc[0] = NULL;
< new_settings.c_cc[1] = NULL;
< new_settings.c_cc[2] = NULL;
< new_settings.c_cc[3] = NULL;
< new_settings.c_cc[4] = NULL;
< new_settings.c_cc[5] = TIMEOUT;
For one thing, if you set ICANON, you will not get RAW input; do the
following instead. Also, if you want to get 1 character at a time
without blocking, set the VMIN (element 4) of c_cc to 1, and set
TIMEOUT to 0.
new_settings.c_lflag &= ~ICANON; /* Canonical input OFF. */
new_settings.c_cc[VMIN] = 1;
new_settings.c_cc[VTIME] = 0;
Other indices for c_cc should be written using their mnemonics as defined
in /usr/include/sys/termio.h for portability if nothing else.
CAVIAT: the VMIN/VTIME mechanism is intended for reading DMA bursts, and
does not really work for general timeouts. What you probably need to
use poll(2) or select(2) rather than ioctl(2) (if I understand your
question).
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