On Sun, 2 May 2010 12:01:59 -0700 "J.C. Roberts"
<[email protected]> wrote:
> The other problem is understanding what is happening. Unless you
> specifically configured the descriptor to return immediately, your
> read(2) call will sleep until it gets the requested number of bytes
> from the descriptor, until an interval timer expires, or until an
> error occurs. Since the instrument is not sending you any data, it
> sleeps until you lose your patience and hit CTL-C to end the program.
> --This should not be a surprise. ;)
I should have referenced your code so the above makes sense.
>> int open_port(void)
>> {
>> int fd;
>>
>> fd = open("/dev/ttyU0", O_RDWR | O_NOCTTY | O_NDELAY);
>> if (fd < 0)
>> {
>> errx(1,"open_port: Unable to open /dev/ttyS0.");
>> }
>> else
>> {
>> fcntl(fd, F_SETFL, 0);
>> }
>> return (fd);
>> }
Setting O_NDELAY (or better said O_NONBLOCK) on open gets wiped out
when you run "fcntl(fd, F_SETFL, 0)"
I have no idea why you're doing that (probably just mistyped example
code), but if you insist, then you'd actually want:
fcntl(fd, F_SETFL, FNDELAY);
or
fcntl(fd, F_SETFL, FNONBLOCK);
Hence the reason why you're actually blocking on read.
--
The OpenBSD Journal - http://www.undeadly.org
