On Wed, Apr 02, 2008 at 03:27:55AM -0400, Mario Charest wrote:
> > We have an application which works under linux, but not qnx6.  It talks to a 
> > number of serial ports (max 16) and waits on a select for a port to receive 
> > data.  Each data packet is 12 bytes in length, and is binary data.  Data rate 
> > is 38k4 and running at full data rate.  We set vmin to 12 in order that the 
> > select doesn't get triggered before 12 bytes are available.
> > This works under linux, but under qnx6 the select always triggers on the first
> >  byte, not the 12th as it should do.  Consequently if O_NONBLOCK is set then 
> > EAGAIN is returned on the subsequent read or if O_NONBLOCK is clear then the 
> > read blocks until all the data is in or forever if the sending end aborts.  
> > Setting vtime overrides vmin so can't be used and the timeout is too long for 
> > us anyway.
> > Attached is a sample program we are using to test this compiled on linux with
> > ntox86-gcc -o testselect-q testselect.c
> > 
> > Any ideas?  It appears to us that the character/select interface is broken.
> 
> 
> Don't know about select and vmin stuff, can't help you there.   here is what I would.  Start a thread for each serial 
port and use readcond().  This is more efficient then using select which add extra context switch and message passing.
> 
> The parsing of the data can be handle by the thread.  If you have more then 1 core, you'll get better performance/
througput.

This should work though.  I've made PR 56779 on this.  Here's
another self contained test case.

-seanb


#include <err.h>
#include <termios.h>
#include <unix.h>
#include <errno.h>
#include <pthread.h>
#include <sys/poll.h>

#define OURVMIN 4

int
main(void)
{
	int		master, slave, vmin, ret;
	struct termios	tiold, tinew;
	char		buf[OURVMIN];
	struct pollfd	pollfd;

	vmin = 4;

	if (openpty(&master, &slave, NULL, NULL, NULL) == -1)
		err(1, "openpty");

	if (tcgetattr(slave, &tiold) == -1)
		err(1, "tcgetattr");

	memcpy(&tinew, &tiold, sizeof(tinew));
	cfmakeraw(&tinew);

	tinew.c_cc[VMIN] = OURVMIN;

	if (tcsetattr(slave, TCSANOW, &tinew) == -1)
		err(1, "tcsetattr");

	write(master, buf, 1);

	pollfd.fd = slave;
	pollfd.revents = 0;
	pollfd.events = POLLRDNORM;
	if ((ret = poll(&pollfd, 1, 1000)) != 0) {
		if (ret == -1)
			err(1, "poll");
		errx(1, "poll succeeded unexpectedly: ret = %d", ret);
	}

	write(master, buf, OURVMIN - 1);

	if ((ret = poll(&pollfd, 1, 1000)) != 1) {
		if (ret == -1)
			err(1, "poll");
		if (ret == 0)
			errx(1, "poll timed out");
		errx(1, "poll unexpected rval: %d", ret);
	}

	(void)tcsetattr(slave, TCSANOW, &tiold);

	printf("success\n");

	return 0;
}