Real-Time Workshop

External Mode Communications Overview

This section gives a high-level overview of how a Real-Time Workshop generated program communicates with Simulink in external mode. This description is based on the TCP/IP version of external mode that ships with Real-Time Workshop.

For communication to take place:

• The server (target) program must have been built with the conditional EXT_MODE defined. EXT_MODE is defined in the model.mk file if the External mode code generation option was selected at code generation time.
• Both the server program and Simulink must be executing. Note that this does not mean that the model code in the server system must be executing. The server may be waiting for Simulink to issue a command to start model execution.

The client and server communicate via two sockets. Each socket supports a distinct channel. The message channel is bidirectional; it carries commands, responses, and parameter downloads. The unidirectional upload channel is for uploading signal data to the client. The message channel is given higher priority.

If the target program was invoked with the -w command line option, the program enters a wait state until it receives a message from the host. Otherwise, the program begins execution of the model. While the target program is in a wait state, Simulink can download parameters to the target and configure data uploading.

When the user chooses the Connect to target option from the Simulation menu, the host initiates a handshake by sending an EXT_CONNECT message. The server responds with information about itself. This information includes:

• Checksums. The host uses model checksums to determine that the target code is an exact representation of the current Simulink model.
• Data format information. The host uses this information when formatting data to be downloaded, or interpreting data that has been uploaded.

At this point, host and server are connected. The server is either executing the model or in the wait state. (In the latter case, the user can begin model execution by selecting Start real-time code from the Simulation menu.)

During model execution, the message server runs as a background task. This task receives and processes messages such as parameter downloads.

Data uploading comprises both foreground execution and background servicing of the upload channel. As the target computes model outputs, it also copies signal values into data upload buffers. This occurs as part of the task associated with each task identifier (tid). Therefore, data collection occurs in the foreground. Transmission of the collected data, however, occurs as a background task. The background task sends the data in the collection buffers to Simulink via the upload channel.

The host initiates most exchanges on the message channel. The target usually sends a response confirming that it has received and processed the message. Examples of messages and commands are:

• Connection message / connection response
• Start target simulation / start response
• Parameter download / parameter download response
• Arm trigger for data uploading
• Terminate target simulation / target shutdown response

Model execution terminates when the model reaches its final time, when the host sends a terminate command, or when a Stop Simulation block terminates execution. On termination, the server informs the host that model execution has stopped, and shuts down both sockets. The host also shuts down its sockets, and exits external mode.

The Design of External Mode

External Mode Source Files