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FDC2214EVM: Time interval spike between two consecutive stream samplings

Guoxing Gu
Intellectual 590 points
Part Number: FDC2214EVM
Other Parts Discussed in Thread: FDC2214

Hi Application Engineers,

I have successfully done my Labview program to  fully control FDC2214 EVM. I found that time interval between two consecutive streaming data points has some spikes. The attached chart shows the result, which was obtained using only channels 0 and 1, stream reading lasted for 105 seconds after stream start and 9700 streaming data logs were recorded in a spreadsheet, average 92 streaming samples per second, which included about 5 repeating value numbers for each data with a new value. 

Majority of the time intervals was 10 ms, the highest was 95 ms, meaning 9 times longer than average.  Can someone tell me what is the cause for the time interval spikes?

 My Labview program followed the Python program sample  Q&A 41 provided on TI web.

Regards

  • 0
    TI__Genius 17440 points

    Hi Gu,

    I believe this is likely due to Labview. When your VI runs on the computer, it is sometimes placed at a lower priority than other tasks running on your computer, causing the additional delay. I don't think there is necessarily a problem with your code or with the EVM. You might ask for help on the NI forums. Typically they give quick responses.

    Best Regards,

  • 0 in reply to Kristin Jones93
    Intellectual 590 points

    Hi Kristin,

    I already contacted NI and was told that it is likely due to computer system's jitter, some background software may rise to occupy CPU. 

    The streaming data acquisition is a software timed operation, which can be influenced by many factors. A very important one is live data (XY graph) display updating, the more data collected the longer time is required to process the graph, making the time interval of 2 consecutive streaming data points an ascending trend.  

    Is there any way that the streaming data acquisition can be hardware timed operation using the onboard time clock? 

    Regards,

    Gu

  • 0 in reply to Guoxing Gu
    TI__Genius 17440 points

    Hello Gu,

    While you can certainly time the data collection from the FDC2214 using the MCU's clock and store that data on the MCU for future use, I do not think there is a way to stream the data using hardware timing. Any transactions over USB are going to be subject to the computer's software timing.

    Best Regards,