For the "rtwsfcn" target, we currently do not support the absence of paddings in the generated code. This limitation arises from how buses (structs in code) are interpreted in Simulink. Simulink requires padding to ensure safety when copying elements, which helps prevent crashes or incorrect results.
In this case, you might benefit from using model references or a protected model for the low-level model. You can then generate code for the top model with the referenced model. In that case, there is no need to work with S-Functions or TLC, which will eliminate the "sl_padding" fields. For more information, please refer to the MATLAB Answers post on using reference models instead of S-Functions for target code generation.
Another alternative is to utilize a Functional Mockup Unit (FMU) for the low-level model and import that into Simulink to generate code. Please note that this workflow is supported starting from MATLAB R2024a. You can learn more about FMU on the FMU importing documentation page.
