TCP communication in real time simulink

I am trying to send TCP messages from a simulink model that is running realtime on a target computer. Matlab says that TCP is supported in realtime simulink but I only see a TCP block in Instrument control box. Also when I try to use those blocks and build the model on the target computer, it gives the following error:

Error evaluating registered method 'Start' of MATLAB S-Function 'stcpipsb' in 'testing_TCP/TCP//IP Send'.

Caused by:
The block TCP/IP Send could not connect to the specified port. Please specify a different port or wait for the current port to become available.

I have configured the IP address of the TCP block to be that of the target computer and used different port numbers like 22222 (which is what I have configured in the simulink realtime explorer), 30000, 30, 10 all to no avail. Where is it going wrong and what is causing the error?

Answer 1

[Prashant Arora]

HI Rajashree,

There is a TCP Send block in the Simulink Real-Time library, which you should use for sending data from a Target computer to another remote device.

https://www.mathworks.com/help/releases/R2020a/xpc/io_ref/tcpsend.html

You can check out the following example, which shows communication between two targets using TCP/IP.

https://www.mathworks.com/help/releases/R2020a/xpc/ug/target-to-target-communication-using-tcp.html

Check the TCP configuration blocks in the example to understand the IP address and port specification for communication.

[Rajashree Ravi]

I am not able to find TCP send block in the Simulink Real-Time library. I am only able to see the option TCP under Instrument toolbox library and the Simulink Realtime library options don't seem to have it as shown in the image. Is there an update for this library in 2016b version? Please explain how I can get this block. Thanks

[Prashant Arora]

Hi Rajashree,

I think support for TCP in Simulink Real-Time from Target to other devices was added in R2017a. This is why you are unable to see the library block. In R2016b, you can consider UDP transmission using UDP Send and Receive blocks.

https://www.mathworks.com/help/releases/R2016b/xpc/io_ref/udpsend.html

[Paul Stansell]

The links in this answer are dead

[Walter Roberson]

https://www.mathworks.com/help/slrealtime/referencelist.html?type=block for new links

[Stefanie Schwarz]

For more recent versions, see these pages:

https://www.mathworks.com/help/slrealtime/tcp.html

https://www.mathworks.com/help/slrealtime/io_ref/tcpsend.html

https://www.mathworks.com/help/slrealtime/ug/target-to-host-communication-using-tcp.html

Answer 2

[THOMAS JOHN]

Hello Prashant

I am a researcher currently doing a project related to signal transmission & reception using TCP & UDP. At the moment, I am able to achieve signal transmission and reception using TCP in normal non-real time MATLAB/Simulink but I am unable to achieve signal reception when I do real-time operation using TCP in MATLAB/Simulink.

Do I need to use real-time TCP/UDP models or is there any other option? The problem is that my remote receiver do not have a real-time simulink library & real-time TCP/UDP blocks. Please kindly suggest an alternative solution if possible. Many Thanks.

Best Regards

Dr Thomas John

[Andrea Assorati]

For real-time applications, in MATLAB command line i used 'flushinput' command to clean the input buffer and just delete the data in eccess. I am unable to make this operation in Simulink too.