Mail Archives: cygwin/1999/08/24/01:33:13
Chris,
The problem with fopen() is that it returns a FILE* where open() return
an int. fopen() is way to advanced for use with serial port I/O as
the concept of a FILE is meaningless on a serial channel i.e. there is
no name or path etc. associated with a raw serial stream. In
addition read() and write() uses an int file descriptor and not a FILE*.
The open(), read(), and write() functions are the most low level
I/O handling ANSI C can handle. The f*() functions are all built on
these functions. If I use fopen() I have no way of controlling the
channel characteristics such as baud rate, bits, parity etc. This
I can do with the int returned from the open() function.
If however you should have some running code (the code below _will_
run) using fopen() I'd sure like to see it for the educational value.
Thanks for your response.
/Kim
PS: Why are you posting everything twice ?
Chris Faylor wrote:
>
> On Mon, Aug 23, 1999 at 11:49:37AM +0200, Kim Poulsen wrote:
> >Corinna Vinschen wrote:
> >> Kim Poulsen wrote:
> >> > I've got the following problem:
> >> > I need to access the serial ports of my PC through an ANSI C program.
> >> > How do I do that ? I have already tried using fopen("/dev/com2", "r")
> >> > and fopen("com2", "r") but these only causes a core dump.
> >> > [...]
> >> AFAIK this is a known problem in b20.1. Try to use a newer snapshot.
> >
> >I have the problem solved. A a contribution to the mailing list I
> >submit the solution to the problem below.
>
> I'm not sure how this solves your problem. You aren't using fopen. That
> appears to be it.
>
> As is so often the case, with these kinds of problems, simply running the
> program using gdb would have probably provided worlds of information for
> debugging the problem.
>
> If the code sample below is getting you running, then fine. It is not
> a generic solution for people who want to use stdio for serial I/O,
> however. AFAIK, that does work.
>
> -chris
>
> >#include <fcntl.h>
> >#include <termios.h>
> >#include <stdio.h>
> >#include <unistd.h>
> >
> >#define BAUDRATE B9600
> >#define MODEMDEVICE "com2"
> >
> >main()
> >{
> > int fd,c, n;
> > char str[2];
> > struct termios options;
> >
> > fd = open(MODEMDEVICE, O_RDWR | O_NOCTTY );
> > if (fd <0) {perror(MODEMDEVICE); exit(-1); }
> >
> > options.c_cflag = BAUDRATE;
> > options.c_cflag &= ~CSIZE; /* Mask the character size bits */
> > options.c_cflag |= CS8; /* Select 8 data bits */
> >
> > /* Write something */
> > n = write(fd, "UART is functional\n\r", 19);
> > if (n < 0)
> > puts("write() of 19 bytes failed!");
> >
> > /* Make read() return immediately */
> > fcntl(fd, F_SETFL, FNDELAY);
> >
> > /* Read something until 'Q' recieved */
> > while(str[0] != 'Q') {
> > if(read(fd, str, 1) != -1) {
> > printf("%s\n", str);
> > }
> > }
> >}
>
> --
> Want to unsubscribe from this list?
> Send a message to cygwin-unsubscribe AT sourceware DOT cygnus DOT com
--
Kim Poulsen, B.Sc.E.E, System Developer HW
Ericsson Telebit A/S Tel: + 45 86 28 81 76
Fabriksvej 11 Fax: + 45 86 28 81 86
DK-8260 Viby J E-mail: info AT tbit DOT dk
Denmark URL: http://www.tbit.dk/
--
Want to unsubscribe from this list?
Send a message to cygwin-unsubscribe AT sourceware DOT cygnus DOT com
- Raw text -