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Simple question: What's meaning of "increasing the Fetch rate" ? Thank you.

Hi friends, 

 

My program got an error: 

Possible reason(s):
Overflow: an internal receive buffer has filled before the data could be returned. Consider reducing the I/Q rate, increasing the Fetch rate, or increasing the number of samples per Fetch. The recommended number of samples per Fetch is a multiple of 364

 

I do know how to increase or decrease I/Q rate, because there is an option (I/Q sampling rate) for me to do that. 

But my question is that where to do the "increasing the Fetch rate, or increasing the number of samples per Fetch" ? Where is the fetch rate?   Fetch rate is acquisition duration (frame size)? Please let me know where to modify the fetch rate or number of samples per Fetch in the pictures below (my program is very similar, from in built examples: niUSRP EX PSK Rx and niUSRP EX PSK Tx).  Thank you for your help and time.  

 

1.png

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Hi sunson,

 

the "fetch rate" is the rate at which you request new samples from your device. The timing of the data request loop should only be determined by your device with no additional wait functions…

 

Example:

You could use a DAQmx task set to sample rate of 1k samples/s. You could read 100 samples per DAQmxRead resulting in a "fetch rate" of 10 Hz. You could also read just 10 samples to yield a fetch rate of 100 Hz. Or you could read 1000 samples per request giving you a fetch rate of 1 Hz. (Keep in mind the overhead of those read operations: it doesn't make sense to try to read each sample one by one, you will not reach a fetch rate of 1kHz this way…)

Best regards,
GerdW


using LV2016/2019/2021 on Win10/11+cRIO, TestStand2016/2019
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hmm, thanks for your help. But I still dont get it.  Could you please show me where to modify the fetch rate?  Maybe I should use a special function to do that?  Like in the in built example, niUSRP EX PSK Rx and niUSRP EX PSK Tx. Where to do this in those 2 example? (I am not sure what "DAQmx task " is ) Thank you.  

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I'm sorry, I don't have USRP installed…

Best regards,
GerdW


using LV2016/2019/2021 on Win10/11+cRIO, TestStand2016/2019
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sunson29, check out this information on DAQmx tasks and how to create one:

Tasks in NI-DAQms

 

Francine P.
Applications Engineering
National Instruments
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