Re: read() blocking and TIOCINQ

[Igor Peshansky <pechtcha at cs dot nyu dot edu>]

Ugh, top-posting...  Reformatted.

On Tue, 5 Sep 2006, Ernesto Paiser wrote:

> Igor Peshansky wrote:
> > On Tue, 22 Aug 2006, Ernesto Paiser wrote:
> >
> > > Hello Corinna,
> >
> > FYI, this is a mailing list, and unless you're replying to a specific
> > message, you're actually talking to many people.
> >
> > > I have problems with read() function blocking and
> > > waiting for characters on serial line with cygwin:
> > >
> > > Here are some code fragments:
> > > ========================================================
> > > fd = open(sl, O_RDWR | O_NOCTTY | O_NONBLOCK | O_NDELAY)
> > >
> > > newpio.c_cflag = brate | CS8 | CLOCAL | CREAD;
> > > newpio.c_iflag = IGNPAR | ICRNL;
> > > newpio.c_oflag = 0;
> > > newpio.c_lflag = 0;
> > > newpio.c_cc[VTIME]    = 1;
> > > newpio.c_cc[VMIN]     = 0;
> > > ...
> > >
> > > n = ioctl(fd, TIOCINQ, &n); //It gives me an error (return -1) why??!!!
> > >
> > > and
> > >
> > > n = read(fd, buffer, 1);  <<< HERE IS BLOCKING!!!
> > > ========================================================
> > >
> > > TIOCINQ is working on CYGWIN,
> > >
> > > Is there another way to solve this problem???
> >
> > Please post a complete compilable test case that reproduces the
> > problem. For example, in the above code, it's unclear what the
> > variable sl contains (and I suspect it contains "COM1", which is a
> > no-no -- you should be using "/dev/ttyS0").
> > 	Igor
>
> Hello Igor,
> Sorry for my incomplete question.
> I attach to you the following file that could be compiled with gcc in
> CYGWIN.
> Accepted commands start by '?' character, and when the device is not
> connected on the serial line the function read(...) blocks:
>
>
>    DEVICE test program
>    -------------------
>
> Type your commands ('.' to quit):
> >> Enter command: ?ver
>
>
> Then, blocked....:-((
>
>
> Note that in our computers the serial line name is COMn not /dev/ttySn.

And therein lies your problem.  When you use COMn, you get access to the
raw Windows device, without Cygwin's POSIX emulation, so it's not
surprising that ioctl() doesn't work.

> I tried before with /dev/ttySn and I receive file not found as answer.

That's probably because COMn = /dev/ttyS{n-1} (e.g., COM1 -> /dev/ttyS0).
HTH,
	Igor
--
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