ブログ について NI USB6356 and Simulink Enable Highspeed Realtime Data Acquisition

Many engineers have experienced the frustration of working with National Instruments' X-series USB-6356 data acquisition card in MATLAB's DAQ toolbox, only to encounter compatibility issues when attempting to integrate it with Simulink Real-Time for code generation. When system requirements demand high responsiveness with update rates of at least 10 kHz, and the DAQ toolbox cannot directly generate code, this limitation becomes a significant roadblock in development processes. This article examines this common challenge and explores potential solutions.

The Critical Need for Simulink Real-Time in High-Speed Systems

Advanced engineering applications such as robotic control, precision instrumentation, and autonomous vehicle simulation often require high-speed closed-loop feedback systems. These systems must not only accurately collect data but also process it in real-time and respond quickly to maintain stability and performance.

While MATLAB's DAQ toolbox offers robust data acquisition capabilities and seamless integration with NI hardware for offline analysis and preliminary verification, its limitations become apparent when deploying to embedded systems or implementing high-frequency real-time control. The toolbox's inability to generate code prevents direct compilation of models into standalone executable programs.

Simulink Real-Time (formerly Real-Time Workshop) addresses this need by enabling compilation of Simulink models into efficient C code for real-time execution on target hardware. For systems requiring update rates of 10 kHz or higher, Simulink Real-Time becomes essential for achieving optimal performance, maximizing hardware resources while minimizing software overhead to ensure timely data acquisition, processing, and control signal generation.

The Official Compatibility Barrier with NI USB-6356

A significant challenge emerges with the NI X-series USB-6356: it lacks official support in Simulink Real-Time's compatibility list. This limitation stems from multiple factors:

• Driver Integration: Simulink Real-Time requires deep integration with hardware drivers for efficient data transfer and interrupt handling. While NI's DAQmx drivers are feature-rich, their architecture and API may present compatibility issues with Simulink Real-Time's kernel or require specialized adaptation.
• Hardware Constraints: USB interfaces weren't designed for hard real-time applications, potentially introducing transmission latency and jitter that could compromise performance in time-critical systems. Simulink Real-Time typically favors hardware with DMA capability, low-latency interfaces like PCIe, or devices specifically designed for real-time operation.
• Development Costs: Maintaining compatibility between specific hardware and real-time operating systems requires significant engineering resources that manufacturers may prioritize differently based on market demand.

Potential Workarounds for System Integration

Despite the lack of official support, engineers have explored several approaches to integrate the USB-6356 with Simulink Real-Time:

1. Leveraging NI-DAQmx C API for Low-Level Integration: Simulink Real-Time permits calling external C code through S-Function or MATLAB Function blocks. Engineers can develop C-based S-Functions that directly interface with NI-DAQmx's API to control the USB-6356. This approach requires substantial expertise in both DAQmx configuration and C programming, along with careful handling of data types and timing within the real-time environment.

2. Investigating Community-Supported Solutions: Technical forums occasionally contain unofficial implementations or custom drivers developed by other engineers facing similar challenges. While these resources may reduce integration effort, their stability and maintenance status require thorough evaluation before implementation.

3. Evaluating Alternative Hardware: When project timelines and performance requirements preclude workarounds, switching to Simulink Real-Time-certified hardware from manufacturers like Advantech or Speedgoat may prove most efficient, despite potential cost implications and platform adaptation requirements.

4. Optimizing Model Architecture: Regardless of hardware selection, proper model design remains fundamental to real-time performance. Techniques include using fixed-point arithmetic instead of floating-point, simplifying complex modules, and configuring appropriate sample times.

Conclusion

The NI X-series USB-6356 represents capable data acquisition hardware whose integration challenges with Simulink Real-Time present engineers with meaningful technical obstacles. While official support remains unavailable, understanding NI-DAQmx's underlying architecture, exploring community resources, or considering alternative hardware configurations can provide viable pathways to achieving system requirements. For engineering professionals, the ability to navigate such technical constraints while understanding the capabilities and limitations of available tools remains an essential competency in developing sophisticated real-time systems.