Logic Analyzer Streaming

NCI logic analzyers store each trace capture to high-speed RAM inside the device. Our approach supports more channels, the fastest sampling rates, and the most accurate trace data captures. After the logic analyzer fills its memory and stops running, the captured data is downloaded to the PC memory for display and analysis.

Why Stream?

USB 3.1 offers enough bandwidth to directly stream captured data to PC memory provided…

• 16 or fewer channels are required.
• Slower sampling rates are adequate.

In theory, streaming the trace data to the PC offers several benefits. First, omitting high-speed memory inside the logic analyzer reduces the analyzer’s cost. Second, trace captures should be limited only by the size and speed of installed PC memory. Third, the trace data could be displayed on screen while it’s being captured.

Why Not Stream?

Advanced logic analyzers which capture modern digital signals require…

• More than 16 channels are required.
• GHz sampling rates are required.

The largest problem with streaming logic analyzers is that Windows offers no guarantees it won’t pause a USB data transfer at random moments. Any OS interruption manifests as a “gap” in the trace data. When an OS preemption occurs, an entire trace capture may be wasted. Worse, any “gaps” in the trace data are often undetectable.

Certainly, features can be integrated into a streaming logic analyser to minimize streaming errors. For example, the logic analyzer might use a very large First-In-First-Out (FIFO) queue to act as a buffer. The logic analyzer can also support error flags to detect buffer “over-runs” or USB stalls. Eventually, the “cheap and simple” stream-to-disk logic analyzer becomes complex as an unlimited design using local high-speed memory. Worse, USB streaming errors can still occur, even with these safeguards. Closing other programs, disabling virus scanning, and disabling Windows Automatic Updates may reduce the chances of buffer over-runs and USB stalls, but the OS can still wreck streamed trace captures even with these workarounds.

NCI logic analzyers offer gigabytes of installed memory. That’s a lot of data to display, manage, and analyze. You actually need a capable workstation PC to just display and analyze that much trace data.

The features offered by NCI logic analyzers eliminate any need for direct streaming methods. A single trace capture using Transitional Timing can span days, months, or even years yet still provide nanosecond sampling resolution. Even while using GHz oversampling, slow input signals or very long periods of inactivity do not waste logic analzyer memory.