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Can't set CREAD flag on serial port?
- From: mbarilli at midsouth dot rr dot com
- To: cygwin at cygwin dot com
- Date: 2004年2月24日 14:59:17 -0600
- Subject: Can't set CREAD flag on serial port?
I'm trying to write an application to access a serial port on a
Windows 2000 box, but the CREAD flag doesn't stay set when I do
`tcsetattr' and check the values with `tcgetattr'. Trying to read
from the port returns a ``Resource temporarily unavailable'' error (as
generated from perror). What would cause an app to fail to read from
the port, or is this a Win2K issue (permissions or something)?
One thing I should mention--this is a null modem cable attached to the
box. Would that have a bearing on the issue?
The following is the relevant code:
int
main ( void ) {
char buf[32];
int n;
struct termios newtio;
struct termios oldtio;
int tty_fd;
tty_fd = open("/dev/com2",O_RDWR|O_NDELAY|O_BINARY);
tcgetattr(tty_fd,&oldtio);
memcpy( &newtio, &oldtio, sizeof(newtio) );
newtio.c_cflag &= ~(CSIZE|CBAUD|CRTSCTS|PARENB|CSTOPB);
newtio.c_cflag |= (CLOCAL|CREAD|CS8);
cfsetispeed(&newtio,tty_speed);
cfsetospeed(&newtio,tty_speed);
newtio.c_lflag &= ~(ICANON|ECHO|ECHOE|ISIG);
newtio.c_lflag |= IEXTEN;
newtio.c_iflag &= ~(INPCK|ISTRIP|IXON|IXOFF|IXANY|BRKINT|ICRNL|INLCR|IGNCR|IUCLC);
newtio.c_oflag &= ~OPOST;
newtio.c_cc[VMIN] = 0;
newtio.c_cc[VTIME] = 0;
printf("+++ setting termios: cflag=%08X lflag=%08X iflag=%08X oflag=%08X ispeed=%d/%08X ospeed=%d/%08X\n",
newtio.c_cflag,
newtio.c_lflag,
newtio.c_iflag,
newtio.c_oflag,
newtio.c_ispeed,
newtio.c_ispeed,
newtio.c_ospeed,
newtio.c_ospeed);
tcsetattr(tty_fd,TCSANOW,&newtio);
/* *** At this point the CREAD flag is no longer set */
tcgetattr(tty_fd,&newtio);
printf("+++ updated termios: cflag=%08X lflag=%08X iflag=%08X oflag=%08X ispeed=%d/%08X ospeed=%d/%08X\n",
newtio.c_cflag,
newtio.c_lflag,
newtio.c_iflag,
newtio.c_oflag,
newtio.c_ispeed,
newtio.c_ispeed,
newtio.c_ospeed,
newtio.c_ospeed);
while ( 1 ) {
/* *** `read' fails at this point */
n = read( tty_fd, buf, sizeof(buf) );
if ( n < 0 ) {
perror("read");
exit(2);
}
if ( n == 0 )
break;
write(1,buf,n);
}
tcsetattr(tty_fd,TCSANOW,&oldtio);
close(tty_fd);
return 0;
}
--
Michael J. Barillier | ``Those who make peaceful
email: mbarilli(at)midsouth.rr.com | revolution impossible will make
web: <http://shadizar.dyndns.org/> | violent revolution inevitable.''
Public key available on request. | -- John F. Kennedy
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