[olug] OT? C programming question.

[Cooper Vertz]

I think the receiver is one of these thingies:
http://www.ftionline.com/products/DVR_Instructions.pdf

*Using the PERMCH Command to dynamically change channels on the WEGENER DVR
series IRD. NOTE: all four FREQ CMD dip switches must be in the up position.
*
...
*PERMCH (spacebar) 1 & Enter – dynamically selects SCOLA Channel Seven*

And I think the problem is, you need a literal ampersand in your string.

n = write(fd, "permch 1&\r", 9);

The number of arguments to the write function seems correct,

$ man 2 write

NAME
       write - write to a file descriptor

SYNOPSIS
       #include <unistd.h>

       ssize_t write(int fd, const void *buf, size_t count);

DESCRIPTION
       write() writes up to count bytes to the file referenced by the file
descriptor fd from the
       buffer starting at buf.  POSIX requires that a read() which can be
proved to occur after a
       write()  has returned returns the new data.  Note that not all file
systems are POSIX con-
       forming.

RETURN VALUE
       On success, the number of bytes written are returned (zero indicates
nothing was written).
       On  error,  -1 is returned, and errno is set appropriately.  If count
is zero and the file
       descriptor refers to a regular file, 0 may be returned, or an  error
could  be  detected.
       For a special file, the results are not portable.




On Wed, Sep 1, 2010 at 12:23 PM, Dan Anderson <dan-anderson at cox.net> wrote:

> The "receiver" appears to be something hung off the serial port.
>
> I don't understand the problem either though.
>
> If one of the parameters (?) has an extra char, I guess I'd filter it
> (which
> you should do anyway).
>
> I'd also check to make sure that I am sending the correct cr/lf that the
> "receiver" expects (i.e. \r versus \r\n).  "Enter" means different things.
>
> Dan
>
> On Wed, Sep 1, 2010 at 11:42 AM, Obi-Wan <obiwan at jedi.com> wrote:
>
> > I write C code for a living, but I'm not quite sure what you're asking
> > from us or what the current problem is.  Can you elaborate?
> >
> > Is the "receiver" just a socket connection to some other program that's
> > expecting ASCII commands?
> >
>
>
> > > Â Â Â Â Â  fd = open( "/dev/ttyS0", O_RDWR | O_NDELAY);
> > > Â Â Â Â Â  fd = open( "/dev/ttyS0", O_RDWR | O_NOCTTY | O_NDELAY);
> > > This is from the user guide of the receiver (using a terminal
> emulator):
> > >
> > > Using the PERMCH Command to dynamically change channels on the
> receiver.
> > NOTE: all four FREQ CMD dip switches must be in the up position.
> > > PERMCH (spacebar) 8 & Enter – dynamically selects Channel 1
> > > PERMCH (spacebar) 12 & Enter – dynamically selects Channel 2
> > > PERMCH (spacebar) 14 & Enter – dynamically selects Channel 3
> > > PERMCH (spacebar) 15 & Enter – dynamically selects Channel 4
> > > PERMCH (spacebar) 7 & Enter – dynamically selects Channel 5
> > > PERMCH (spacebar) 3 & Enter – dynamically selects Channel 6
> > > PERMCH (spacebar) 1 & Enter – dynamically selects Channel 7
> > > PERMCH (spacebar) 5 & Enter – dynamically selects Channel 8
> >
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