opening port (blocking mode)

novice_din · 02-15-2005, 09:10 PM

Hi Gurus,

I am writing a serial communications program and wanted to support blocking and non blocking mode. non blocking mode works fine but the blocking mode sometimes just hang-up when opening a port. Anybody encounter this? Thanks in advance...

here's the code snippet

non blocking version

main()
{ int d
d=open("/dev/tty1", O_RDWR|O_NONBLOCK); /** works fine **/
write(d, "TEST", 4);
close(d);
}

blocking mode

main()
{ int d
d=open("/dev/tty1", O_RDWR); /** sometimes just hang-up here **/
write(d, "TEST", 4);
close(d);
}

thanks again!!!

PasiZ · 02-16-2005, 08:39 PM

Code:

/* blocking mode */

main()
{ int d
d=open("/dev/tty1", O_RDWR); /** sometimes just hang-up here **/
write(d, "TEST", 4);
close(d);
}

I suggest follow:

Code:

int d;
d = open("/dev/ttyS0", O_RDWR | O_NOCTTY | O_NDELAY);
write(d, "TEST", 4);
close(d);

Becouse with O_NDELAY, routine would'n care DCD signal state... I think that's the problem...
O_NOCTTY tells that this isn't controlling terminal, so abort signals etc wouldn't mess up the process.

You can change mode on the fly to blocking with:

Code:

fcntl(d, F_SETFL, 0);

and non blocking:

Code:

fcntl(d, F_SETFL, FNDELAY);

I'm sorry of this messy post, hope you understand me

no sleep whole night

novice_din · 02-17-2005, 08:36 PM

Pasiz,

Thanks for your reply. You solved my problem... I thought O_NDELAY and O_NONBLOCK are synonym.
Thanks again!