Mail Archives: cygwin/1999/08/24/12:19:53
On Tue, Aug 24, 1999 at 07:29:23AM +0200, Kim Poulsen wrote:
>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.
fileno(), q.v.
>Thanks for your response.
>
>PS: Why are you posting everything twice ?
You are on the mailing list and in the Cc line. It's common to receive
two copies in this case.
cgf
>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);
>> > }
>> > }
>> >}
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