UNIX for Dummies Questions & Answers

Hi again! Sorry for the delay...
Well, the comm driver is setup prior to use. I thought that serial communication would be the same with UNIX as it is with QNX. My mistake... I do:
---------------
fd=open("/dev/ser1", O_RDONLY);
read(fd, buffer, len);
close(fd);
---------------
So I'm not aware of the tty interface.

But that's not the heart of the problem anyway.
Here's what I need help on:
I tried using a fifo as suggested and it does what I need. That's the bridge I was thinking of ;-)
Here is a portion of the code to "test from user input":

Code:

// test_app
char key;
while(1)
{
   cin >> key;
   switch(key)
   {
       // issue various commands to the device
       // and read back answer from it
   }
}

So I can start the program and feed it from the keyboard to test all the cases. That simple.
Now I start it with "fifo_file" redirected as input, and I
start a shell script "feeder" with output redirected to "fifo_file".
This script loops forever: "echo" 1 sequence of character (a "word") and then sleeps a bit. This way I can automate testing.
This works very good and fills my need.

Just curious what I should do to avoid this: if I stop feeding the fifo_file, the test_app that uses it as input keeps on getting the last character it got (and very fast)!

Thanks everybody for taking the time to share your knowledge!

added code tags for readability --oombera

starless, you really need to mention that you're using QNX. I guess that I shouldn't have remembered that you use QNX, but I didn't.

Your /dev/ser may indeed behave in ways that I don't understand. Or it may be very close to the unix tty. I'm not sure.

I'm not a c++ programmer nor do I know QNX. But I think that I understand this last character repeating business...maybe. But I'll have to explain unix system calls invoked from c.

I guessing that you're doing the equivalent of
read(fd, buffer, len)
and fd is now one side of a fifo. You need to change that to:
iret=read(fd, buffer, len)
if(iret == 0) { /* arrange to stop reading */ }
if (iret == -1) { /* error routine */ }

The read is failing, but you're not noticing this. Your buffer is not being touched. You're just assuming that it got a character. On unix, this situation would cause read to simply return a zero. In your case, you may being getting an error of some kind.

You can prove that you're not simply getting the last character... put some other character in the buffer just prior to the read. That will become the character that you seem to be reading in a loop.