TLM-level Connecting Interfaces

This page only provided a brief description of the TLM methodology within the UNISIM environment. For a more detailed description of this methodology, you can refer to this article.

TLM-level modules mostly correspond to functional models. Those models usually do not involve timing, so they are usually not used for performance evaluation. The figure below presents the principles of TLM-level modeling:

In the figure above represents a little simulator composed of two tlm-level modules: An initiator module which is driving the simulation, and a target module which is serving the initiator module.

The scenario is the following:

• The initiator is first running the simulation, then it spawns a request to the target, waiting for an answer.
• The target module, which was waiting for such a request from an initiator is resolving it, and then sends back the result to the inititor module.
• The initator module receive the answer, and can continue the simulation.

Untimed TLM models are designed using the TLM Interface. In an Untimed TLM (UTLM) model, the delays for serving requests is not considered: The simulated time is stuck to zero and only delta cycles occur during simulation, as shown on the figure below:

The initiator calls target method Send to make the target serve the request. If the initiator waits for a response, i.e. waits for the response event.

Timed TLM models are also designed using the TLM Interface. In an Timed TLM (TTLM) model, some timing information is added to the messages during communication. The idea is to take advantage of the wait method as shown on the figure below:

The timing information is added when notifying the response. By setting this value, the target module inform the initator module the time needed to answer the response. Thanks to the wait method, the initator module will use the response after reaching this timepoint.