communication between two computers with 2 c++ programs

Question

Hello smart people,

I have one computer that is running a c++ program to control a robot and another computer that is running a computer vision system (also written in c++). I would like for these two programs to be able to talk to one another. The communication would not have to be complex, I would just need the robot computer to be able to tell the vision computer when a trial begins and ends (when to start and stop a data collection sequence). Do any of you have advice on how to approach this problem? Rs232 communication between the computers? Some kind of networking solution? smoke signals? Any suggestions would be welcome. thank you in advance

(edit) In case you think the statement above is vague:

I need to pass a binary (go/don't go) signal from one computer to another. Unfortunately I can't be more specific about what this will look like because (obviously) I don't know what is available. Both computers are on a network, and both computers are running windows. The goal is to syncronize data collected by the computer vision system with actions performed by the robot. The communication does need to be fast enough that it will not slow down either the robot or the computer-vision program. a "good" solution would be 1) easy to implement 2) fast. I do not know much about networking and I am looking for a place to start looking.

thank you again for your assistance

Answer 1

If they are network-connected you could just use sockets.

Answer 2

For Windows, you will need to open the COM n port as a file to communicate over a serial port[1]. I don't have access to my code now, I can look it up when I get home.

RS232 is easy and I like it. However, it it is slow. You need to consider that in your design.

[1] For C++.

Answer 3

You might use a simple UDP protocol - the advantage being that if you understand the concepts of simple packet protocols on RS232 you'll find it easy to transfer that knowledge to sending the packets via UDP.

If you want a reliable (as in, other parts of the system will worry about errors and retries) stream of bytes between the two PCs, then TCP/IP is not much more complicated to use than UDP.

Both UDP and TCP are accessed through 'sockets'. I'm afraid you'll find that from C++ there is rather a lot of tedious boilerplate to getting that working, but there are lots and lots of examples around.

Answer 4

That sounds like a fairly good use for the network socket. If both your machines are on Windows you can even use named pipes.

Answer 5

The best option will be to use network communication. The easiest way to approach this should be to look at the networking examples in Qt.

You basically will create a client and a server application. You decide what the client does when it sees a certain message from the server. That's all. Qt should take care of the rest of the stuff.

Other answers suggests TCP/IP, UDP, RS232, ... All those things are just options when you use QtNetwork module. I assume that since you ask your question, you don't know about the difference between those. So the safest bet will be to use the highest level (free) library, hence the suggestion to look into Qt.

Another option is to use Boost.Asio. I tend to prefer Qt solution since their API is nicer.

Answer 6

Most modern computers have Ethernet capability, so get yourself a cheap hub or switch and look at networking APIs. There's usually some fairly easy socket stuff. One advantage of this is that, if you want to increase communication ability later, such as having your vision software provide instructions and guidance to your robot, you've got the basics set up.

Alternately, set up your vision program so you can start and stop it by hitting random keys. When you're going to use it, put the keyboard in front of the robot computer's CD drive, and eject at the start and end of the robot run.

Answer 7

This may be overkill in your situation, but if I were in your shoes I would probably implement it using the HTTP protocol. The vision computer would run a HTTP server and the robot computer would communicate the state changes using POST requests. The Poco C++ Net library provides you with the facilities required to do this.

Answer 8

I would use a TCP/IP socket for communications. TCP guarantees that the data will make it. So, all you need to do is parse the data.

Answer 9

RS232 is an easy option to program for, however modern PCs don't tend to have RS232 ports. You may need to get USB-RS232 adapters or install a PCI card.

The other problem with RS232 is that you have an additional wire to worry about which can be a nusiance. Also RS232 cables can be limited in length (5-15m) unless you invest in some clunky RS232 repeaters or bluetooth connectors, etc.

On top of all that you're also adding one more item to your project that can go wrong and cost you time in deploying and debugging.

IMO, an elegant engineering solution would be to utilise the hardware that you have and use TCP/IP sockets to communicate.

The web is awash with examples on passing messages between servers and clients:

If you're using Linux: http://www.linuxhowtos.org/C_C++/socket.htm

Using Windows: http://www.adp-gmbh.ch/win/misc/sockets.html

Answer 10

I also might look at something like 0MQ to make the connection more robust. It will transmit and reassemble messages regardless of the transport, and handle buffering in the case of temporary loss of connectivity.

But the bottom line is that I would use TCP/IP, but depending on the nature of the robot you may want a slightly more robust connection system than TCP sockets. UDP is nice because it's connectionless-- if the robot temporarily travels out of range/sight/etc you wont have to rebuild the socket and context.