In Simulink MATLAB, Hardware-in-the-Loop (HIL) testing can throw errors when the sample time is set to less than 0.01 seconds due to several possible reasons. Here are the key factors that may be causing this issue:

1. Many real-time targets and hardware interfaces (e.g., DAQs, communication buses) have specific limitations on how fast they can handle data exchange. If the sample time is set too low (e.g., less than 0.01 seconds), the hardware might not be able to process the input and output data within that time, leading to buffer overflows or missed deadlines.

2. Check the specifications of the real-time hardware you're using to ensure that it supports the desired sample rate.

3. Real-time systems are designed to meet hard timing requirements. If the model or hardware interface requires more computation than the available processor can handle in the specified sample time, it can cause overruns. To address this, try optimizing the model to reduce computational load, or increase the sample time to accommodate the processing requirements.

4. Simulink models often use a fixed-step solver for real-time simulation. Ensure that the solver settings are properly configured for the hardware's real-time execution.

- For example, ensure you are using a fixed-step discrete solver like `ode1 (Euler)` when simulating in real time, as variable-step solvers are not suitable for HIL testing.

- Set the fixed-step size in the solver settings to match the sample time you are using, and avoid setting a step size that is too small for real-time execution.

5. The real-time kernel or scheduler on your system may have limits on task execution timing. If the requested sample time is too short, it may not be able to schedule the task effectively, causing overruns.

- Review the settings of the real-time kernel (such as Simulink Real-Time or Simulink Desktop Real-Time) and adjust the sample time based on the kernel’s ability to handle high-frequency tasks.

6. Complex models with many states, subsystems, or intensive computations may not run efficiently with very small sample times in real time. Try simplifying the model to ensure real-time execution is achievable with a smaller sample time.

>>> Troubleshooting Tips:

1. Use the Simulink Profiler to understand the computation times and identify any bottlenecks in the model.

2. Start with a larger sample time (e.g., 0.01 seconds) and gradually reduce it to see where the performance issue arises.

3. Break your model into smaller subsystems and test their real-time behavior individually before integrating them.

By reviewing and adjusting these areas, you can help mitigate errors and achieve real-time performance with smaller sample times in your HIL testing.