Exchanging UDP Data Between Simulink® Model and SimWB Test Session

This example shows how to send data back and forth between a running Simulink model and a SimWB test session running on the real-time host. This can be useful to update variables in Simulink based on the value of variables calculated via the scripts and models running in SimWB and vice versa. For example, you can drive animation in Simulink® based on the state of the system being simulated in the test session running on the real-time host.

Overview
Determinism Limitations
Example Setup
Example Resources

Overview

Real-Time Host UDP Communication

Use the NET-IO I/O device in SimWB to send/receive UDP (or TCP) data from the real-time host. Map the relevant RTDB variables to field in Input/Output messages.

Use NET-IO I/O device for UDP communication to/from the SimWB Test Session
Figure 1: I/O Mapping for NET-IO device depicting a message being received from Simulink® into SimWB.

Simulink UDP Communication

Use the From_SimWB_Host and To_SimWB_Host blocks from the simwbUDPBlocklib library to send/receive UDP data from the Simulink model. UDP communication is supported by both fixed-step and variable-step models.

Use the From_SimWB_Host and To_SimWB_Host blocks in the simwbUDPBlocklib library for UDP communication to/from a Simulink model
Figure 2: From_SimWB_Host and To_SimWB_Host in the simwbUDPBlocklib library.

Determinism Considerations

UDP communication can introduce nondeterministic behavior in a real-time test. Therefore, for tests where real-time considerations are important, ideally, UDP communication should be reserved for slow-changing and non-real-time-critical variables. You must analyze the reliability of your UDP channel and determine the merits of the tradeoff and accordingly specify transmission/receive rates.

The following factors contribute to the lack of determinism in UDP communication between the real-time host and a Simulink instance:

Simulink is running outside the SimWB framework, and there is no synchronizing process between the two programs. Also, generally, the Simulink execution frame runs as fast as possible, which may lead to non-deterministic execution.
Quality of connection between the two machines.

Example Setup

This example comprises the ccur_udp Simulink model and the udp_example RTDB and Test. The following diagrams depict the flow of data between the Simulink model and the SimWB test.

Data originating in Simulink travels to SimWB and is routed back to Simulink model
Figure 3: Details of how data is sent from the Simulink model to SimWB and routed back to the Simulink model.

Data originating in SimWB travels to the Simulink model and is routed back to SimWB
Figure 4: Details of how data is sent from SimWB to the Simulink model and routed back to SimWB.

To run this example, perform the following steps on the real-time host machine:

The example is configured to send UDP messages to the 127.0.0.1 IP address, which is the loopback IP address. Therefore, the example assumes that the Simulink model is run on the SimWB real-time host machine. If you want to run the Simulink model on a different machine, refer to Modify Example to Run Between Two Different Machines for additional steps.
Verify the ports used for this example are free (ports 25001 through 25004). If they are being used, then you must either make the ports available or follow the steps in Modify Example to Run Between Two Different Machines to change the port numbers that are used by the example. To check whether the ports are free, execute the following command at the terminal. If no output is returned, then the ports are free.
```
                lsof -i :25001-25004
```
Open the ccur_udp Simulink® model in a MATLAB® installation on the real-time host that is running SimWB. The SimWB UDP communication blocks are supported in MATLAB R2011a and subsequent releases.

Figure 5: Simulink model: ccur_udp.

The following blocks are instances of the SimWB UDP communication blocks. Double-click the blocks for configuration information.
Run the model.
Open the SimWB Control Center.
Set the project to Simulink®.
Open the Test Sessions tab.
Start a session of the udp_example Test.
Use the Real-Time Viewer table and chart to verify that data is flowing between SimWB and Simulink® as expected.

Figure 6: Sine and triangular wave travelling between Simulink and SimWB, seen in an RT-Viewer Chart.

Figure 7: Constant values travelling between Simulink and SimWB, seen in an RT-Viewer Table.
In the Simulink model, open the Scope to monitor the signals.

Figure 8: Sine and triangular wave travelling between Simulink and SimWB, seen in a Simulink Scope

The sine wave emitted by Simulink® travels to SimWB and then returns to Simulink, leading to a 1-frame delay at a minimum, in addition to any network propagation issues and other delays. This lag is reflected in the non-zero difference between the sine signal (original Simulink source signal) and the from_simwb_sine signal.
Change the values and characteristics of the various sources to test the update rate.

Modify Example to Run Between Two Different Machines

Suppose you want to run the Simulink® model from a different machine. Assume the Simulink model machine IP address is IP_Simulink and the SimWB real-time host machine IP address is IP_SimWB. The port numbers for the four UDP messages are indicated by PORT_message_name.

Change the following values to ensure proper data propagation:

In ccur_udp:
- Double-click the originating_in_simulink_to_host block. Change the:
  - Remote IP address parameter to IP_SimWB
  - Remote IP port parameter to PORT_originating_in_simulink_in
  Similarly, double-click the originating_in_simwb_to_host block and change the:
  - Remote IP address parameter to IP_SimWB
  - Remote IP port parameter to PORT_originating_in_simwb_in
- Double-click the originating_in_simulink_from_host block. Change the:
  - Local IP address parameter to IP_Simulink
  - Local IP port parameter to PORT_originating_in_simulink_out
  - Remote IP address parameter to IP_SimWB
  Similarly, double-click the originating_in_simwb_from_host block and change the:
  - Local IP address parameter to IP_Simulink
  - Local IP port parameter to PORT_originating_in_simwb_out
  - Remote IP address parameter to IP_SimWB
In the NET-IO I/O Mappings pane, with the udp_example RTDB loaded:
- Under Input:
  - For the originating_in_simulink_in message, set the Port parameter to PORT_originating_in_simulink_in
  - For the originating_in_simwb_in message, set the Port parameter to PORT_originating_in_simwb_in
- Under Output:
  - For the originating_in_simulink_out message, set the:
    - Port parameter to PORT_originating_in_simulink_out.
    - Dest IP parameter to IP_Simulink
  - For the originating_in_simwb_out message, set the:
    - Port parameter to PORT_originating_in_simwb_out.
    - Dest IP parameter to IP_Simulink

Example Resources

Simulink model - ccur_udp.
SimWB resources in the Simulink project on the SimWB real-time host machine:
- RTDB - udp_example
- Test - udp_example
- Script - udp_example_script