Re: tcflush hang problem

[Brian Ford <ford at vss dot fsi dot com>]

Sorry, my fingers aren't working.  I keep accidentally replying to the
sender rather than/in addition to the list.

Cygwin's current tcflush implimentation is rather crude.  Although, it may
not be possible to do any better.  PTC.

  if (queue == TCIFLUSH || queue == TCIOFLUSH)
    /* Input flushing by polling until nothing turns up
       (we stop after 1000 chars anyway) */
    for (int max = 1000; max > 0; max--)
      {
        COMSTAT st;
        if (!PurgeComm (get_handle (), PURGE_RXABORT | PURGE_RXCLEAR))
          break;
        low_priority_sleep (100);
        if (!ClearCommError (get_handle (), &ev, &st) || !st.cbInQue)
          break;
      }

So, your not really hung.  Just stuck for a long time.

As a work around, tell the device to shut up first, then flush.

On Mon, 13 Oct 2003, Martin Farnik wrote:

> Hi.
> I use CYGWIN_98-4.10 mine 1.5.5(0.94/3/2) 2003-09-20 16:31 i686 uknown
> unknown Cygwin
>
> First i try to describe a situation:
> I have a device which is connected with computer thru serial line.
> Device is still sending data.These data isn't for my program.I have
> open com port and let them go into buffer . When a want to talk with
> device i flush input buffer, send it a command paket and device stop
> sending data and wait for my next command.
> Problem is when I want to flush INPUT buffer before I send a command. In
> this point it hangs, maybe for buffer full.
> Here is piece of code:
>
> -----I open port when i start program -----
>
>  fd = open(PORT0, O_RDWR | O_NOCTTY );
>  tcgetattr(fd,&oldtio); /* save current port settings */
>
>         bzero(&newtio, sizeof(newtio));
>         newtio.c_cflag = CS8 | CLOCAL | CREAD | CSTOPB;
>         newtio.c_iflag = 0;
>         newtio.c_oflag &= ~OPOST;
>         newtio.c_lflag = 0;
>
>         newtio.c_cc[VTIME]    = 1;
>         newtio.c_cc[VMIN]     = 0;
>
> 	cfsetispeed(&newtio,B19200);
> 	cfsetospeed(&newtio,B19200);
>         tcflush(fd, TCIFLUSH);
>         tcsetattr(fd,TCSANOW,&newtio);
> -------------------------------------------------
> --this code is execute when a want to talk with device----
>
>        tcflush(fd, TCIFLUSH);	    <--------- in this point where it hangs
> 	err = write (fd,iobuffer,10);
>

-- 
Brian Ford
Senior Realtime Software Engineer
VITAL - Visual Simulation Systems
FlightSafety International
Phone: 314-551-8460
Fax:   314-551-8444

--
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple
Problem reports:       http://cygwin.com/problems.html
Documentation:         http://cygwin.com/docs.html
FAQ:                   http://cygwin.com/faq/