Unclear handling of CAN message size in virtual CAN networks

[JannisRln]

Title
Unclear handling of CAN message size in virtual CAN networks

Description
While integrating virtual CAN networks using SIL Kit, it is unclear how CAN message size constraints are handled by the framework. The current API documentation does not clearly specify whether message size validation, truncation, or error handling is performed internally, or whether this responsibility is delegated entirely to the user.

This ambiguity makes it difficult to design robust applications that rely on virtual CAN communication and to ensure consistency with real CAN/CAN FD behavior.

Questions / Points needing clarification

1. What is the maximum supported payload size for CAN and CAN FD messages in virtual CAN networks?
2. Does SIL Kit validate message size against CAN/CAN FD limits when transmitting?
3. If an oversized message is sent: - Is it rejected with an error? - Silently truncated? - Passed through unchanged?
4. Where in the API or documentation is this behavior formally defined?

Expected outcome

• Clear documentation describing how message size is handled for virtual CAN networks.
• Explicit guarantees about validation, error handling, and consistency with CAN/CAN FD specifications.
• (Optional) Example code or API references demonstrating correct usage of large messages.

Environment

SIL Kit version: 5.0.3
OS: Windows 64bit
Language bindings: C API and C++ API used in python with pybind11 (https://github.com/JannisRln/SilKit_py)

[KonradBreitsprecherBkd]

Hi @JannisRln,

thanks for bringing this up and your awesome work on SIL Kit python bindings!
In general, SIL Kit tries to avoid bus protocol restrictions. This allows for user applications to define their own level of detail for the vehicle network. E.g. a testing participant may want to inject faulty CAN Frames and SIL Kit itself should not prevent this.

If a more detailed vehicle network is needed that includes validation, precise timings, protocol detail etc, SIL Kit has a NetworkSimulator API that allows to create a centralized simulator. This is described in https://vectorgrp.github.io/sil-kit-docs/api/netsim.html. Vector Informatik provides a licensed NetworkSimulator that does exactly that (see https://www.vector.com/int/en/products/products-a-z/software/sil-kit/#c399452).

To address your questions:

1. Maximum supported payload size of the CAN variants:

• Classic CAN: Maximum payload is 8 bytes.
• CAN FD: Maximum payload is 64 bytes.
• CAN XL: Up to 2048 bytes.

2. Does SIL Kit validate message size?

• No automatic validation or enforcement of CAN/CAN FD payload size limits.
• The CanFrame struct allows any payload size via its dataField member.
• Responsibility for validation is delegated to the user/application.

3. What happens if an oversized message is sent?

• Oversized messages are passed through unchanged.
• SIL Kit does not reject, truncate, or raise an error for messages exceeding CAN/CAN FD limits.

4. Where in the API or documentation is this behavior formally defined?
   Agreed, this should be stated clearly somewhere in the docs. We will extend this, possibly in
   https://vectorgrp.github.io/sil-kit-docs/index.html#guiding-principles and
   https://vectorgrp.github.io/sil-kit-docs/index.html#vehicle-networks.

Regards,
Konrad Breitsprecher

[JannisRln]

Thank you for your detailed reply.

I believe this is the correct behavior. The user or application should handle payload size limits. Therefore, in simple applications, messages that are normally chunked can be sent as a single message.