Serial port polling
 

I am building a shell script on a Dreambox (Sat receiver).

What I need to do is sending a command through the serial port to steer my dish. This was easy to do and it worked with no problems at first attempt.

I need to wait for the answer from the other device from the same port (when the dish is in the new desired position. It can take from few seconds to 30-40 seconds), and, after that and only after that, I can continue with the other commands of the script.
I therefore need to poll the serial port and read what the other device answers. Possibly with the least load on the CPU of the machine.
This is what I still cannot do and I would really be very thankful if you could give me a hint on how to do it...


The shell has a very limited number of commands. It is just a subset of the usual shells.
Therefore I need to use very basic commands (compiling a C program is an option, but I would need to delve in crosscompiling and other quite difficult things, for me at least).

I thank you in advance for your help!

Sneezie

Well you only need to print out the contents of the tty file and watch for it match a specific string. You should be able to do something like:

Where response is the line you are waiting for from the dish. That is of course assuming you have grep. If not, then that changes things. It might help to post a list of what commands you actually have available if the shell is really that minimal.

Can you help me there, then? I have a script for a Dreambox 7020 almost ready, what I need now is how to send a command on the serial port...

Sending a command should look something like:

Thanks, I guess the serial port on a 7020 is /dev/ttyS2 (but I'm not sure). I also assume that I may need to do a SETSERIAL command first.