It is possible that your real-time model needs longer than 1e-6 seconds to execute. Open the "RT Box Web Interface" by clicking on the blue monitor icon button in the “Target” tab of Coder Options dialog (it's next to the “Browse Available RT Boxes”binoculars button).
You can verify the execution time of your model here under "Processor load" > "current cycle time". Make sure that your "sample time" is larger than the "current cycle time" in the following image.
To see what the RT Box error is, click on the "Diagnostics" tab of the "RT Box Web Interface". The error info should be displayed under "Application Log".
Additionally, you can verify if your "sample step size" is good enough for your model or not by using“Codegen” mode, even before running your model on the RT Box. This means that instead of running the model on PLECS normally, you would run the model using the code generated by the PLECS coder within PLECS. For more details on "Code Generation" please go through pages 251-268 of the PLECS User Manual.
For example, consider the “Boost_codegen.plecs” example attached. To enable codegen mode, create a subsystem of the model you want to generate the code for, right click and go to Subsystem > Execution settings > check “enable code generation”. Then change the "simulation mode" to "CodeGen". Next, go to Coder > Coder Options and enter the desired sample step size value under "Discretization step size" of your subsystem. Then choose the "Target" as "Generic" and click "Build". This generates ANSI-C code of your model. Now run the simulation and verify if you are satisfied with the "sample step size”.
For more help, please send an email to firstname.lastname@example.org.