SIL Kit 4.0.52 – Sequence of API Calls in Co-Simulation with Time Synchronization

[saanjh-sengupta]

I'm working with SIL Kit version 4.0.52 and would like to understand the typical sequence of API calls during co-simulation, particularly in the context of Coordinated Mode.

I understand that StartLifecycle initiates the simulation, and from the demo, it appears that frame transmission is handled within the SetSimulationStepHandler.

Could someone clarify the typical order in which the following APIs are expected to be invoked during simulation execution?

• AddFrameHandler
• AddFrameTransmitHandler
• SetSimulationStepHandler

[VDanielEdwards]

Hello @saanjh-sengupta,

thank you for your question! Usually an application using SIL Kit will have the following structure:

1. Load the participant configuration (SilKit::Config::ParticipantConfigurationFrom...(...)).
2. Create the participant object (SilKit::CreateParticipant(...)) which uses the configuration object.
3. Create the controllers and services from the participant object.
4. Set or add any handlers on the controllers and services.
5. Start the lifecycle.

Sending frames, publishing messages, or other interactions with controllers should generally only be done from the simulation step handler (if time-synchronization is used). Otherwise it isn't guaranteed from which simulation-step the message will originate. Any of these should also not be called from other handlers (e.g., a frame handler), for the same reason.

[VDanielEdwards]

This is demonstrated in the Simple CAN Demo.

Thank you @KonradBreitsprecherBkd for the suggestion!

[saanjh-sengupta]

Hi @VDanielEdwards,

Thank you for your response! My question originally relates to Coordinated Mode, specifically when Time Synchronization is being used.
For each simulation step, I’m trying to understand the chronological sequence of events :

• When does TX occur?
• When does RX occur?
• At what point is the acknowledgement sent to confirm that every participant has completed the simulation step?

Could you clarify how these actions are ordered in Coordinated Mode?

[VDanielEdwards]

You can find an explanation of the time-synchronization algorithm, as well as its interaction with sending and receiving in the SIL Kit documentation.

RX

Any handlers for messages (e.g., registered via ICanController::AddFrameHandler) are invoked immediately when the corresponding message arrives on the participant.

If the participant uses the ITimeSyncService::SetSimulationStepHandlerAsync, message handlers may be invoked between the return from the simulation step handler and the call to ITimeSyncService::CompleteSimulationStep.

This does not imply that these messages originate from this simulation step, you must check the timestamp field of the delivered ...Event structure.

TX

For sending messages (e.g., via ICanController::SendFrame), there are two major cases.

1. If sending is triggered (read: SendFrame is called) from within a handler (e.g. the simulation step handler), the message will be sent after the handler is returned from.

   The 'blocking' simulation step handler (ITimeSyncService::SetSimulationStepHandler) takes care to complete the simulation step only after any messages sent from within the handler are actually dispatched.

   If sending is triggered after the 'async' simulation step handler (ITimeSyncService::SetSimulationStepHandlerAsync) is returned from, but before ITimeSyncService::CompleteSimulationStep is called, the message is sent as-if it was sent from within the simulation step handler itself with regards to time-synchronization.

2. If sending is triggered otherwise (e.g., from the main thread), the message will be sent as-soon-as-possible.

   There is no guarantee that such a message is sent from a particular time-step.