Hi,
I am trying to write user interface software to communicate with a robot via TCP/IP. It is a prototype, so the documentation for it is extremely limited. The robot appears to receive and respond to everything I send it, but I am having trouble processing its replies. This is important because it tends to overheat, so I need to be able to send frequent requests for motor temperature readings and process the responses, in order to cut the power if it is getting too hot.

I'm using:
C/C++
socket type: streaming

Here's my problem. When I send it a string, for example:
"12HI\r"
it sends back
"=>"
(not sure about the delineator stuff in the response).

I know what the robot is sending back because I've been using a Windows terminal program to test it. Using the Windows terminal program I received from the manufacturer, everything seems to be fine - it prints out only the responses that I am expecting to get from it.

After sending the same command from my Linux code, I do a read(), and I get:
"12HI
=>".
Or I might get "12H", then "I =>" or something. I pretty much always read() or recv() what I sent to it, along with its response.

Say I send several commands, for instance:
"12HI\r"
"34HI\r"
"123 SET TIE 0\r"
"1234567 GET MV\r"
"1234567 SET MODE 0\r"
and do a read() after each one.

Here's what I printf()ed from my last read():
"1234567 SET MODE 0
=> 00 1000 500 1000 1000 1000
=>"

(FYI, the response it sent back for the SET MODE command was "=>", and as for the GET MV, it sent me "1000 1000 1000 500 1000 1000 1000".)

I also checked the length of the stuff in the last read(), and I got a length of 55. I'm not sure exactly where the 55 chars are coming from. The length of the last thing it sent me, "=>", should have been no more than 3-4.

Sometimes it's more jumbled junk than that. I'd be totally fine with that if it would put my expected response at the front end of the string. But it doesn't. I get the response I'm looking for somewhere in that garbled junk. The problem is that I don't know where to find it, and I cannot process it if I can't find it in the string.

When I send it a command, why would that command be sent to the robot and reflected back into my system buffer - i.e. why am I reading what I sent it?

Also, is there any way to clear out the system buffer after each read and write? How are the system buffers for reading and writing connected?

Also, a real newbie question: I am saving what I read into an array; how do I clear the contents of an array? Should I use free()? Or set it equal to {0}? I tried both, and it doesn't seem to help. Based on what I've seen, it appears that it's the system buffer that needs to be cleared somehow.

Thanks,

TheBrain

Cheers!