labview cannot send IQ signal to usrp continuously，error says "Underflow: the Tx buffer was emptied before new data was provided."

[phil_col]

when I set IQ rate above a specific value, the signal trasmission to the usrp will stop.
the error shows:
Underflow: the Tx buffer was emptied before new data was provided. Consider reducing the I/Q rate, increasing the Write rate, or increasing the number of samples per Write. The recommended number of samples per Write is a multiple of 1020
If you know how to solve this problem, I'm very gratefull to have your advice!

[GerdW]

Hi phil,

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@phil_col wrote:

when I set IQ rate above a specific value, the signal trasmission to the usrp will stop.

If you know how to solve this problem, I'm very gratefull to have your advice!

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Have you considered the items from the error message:

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@phil_col wrote:

Consider reducing the I/Q rate, increasing the Write rate, or increasing the number of samples per Write.

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So what have you tried and where are you stuck?

Mind to attach your VI?

[phil_col]

Hello Gerdw:

  I'm very gratiful to have your reply.

  I have seen the error message, but our purpose is to raise IQ rate, at the same time we receive the signal continuously.

  If the IQ rate is 50M, we can transmit the signal for 1 minutes until the tx buffer error shows up and terminate the transmission.

  If the IQ rate is 80M, we can  transmit the signal for only 1 second.

  If the IQ rate is 100M, we can not even detect the signal while the program shut down immediately.

  The utmost IQ rate of USRP-2974 is 160M, we want to send signal at this IQ rate and can get the signal continuously for us to save and deal with it.

  We think it is our lack of information about tx buffer or datasteam that leads to this problem.

  Here are pictures of this vi.

  I don't know if I have myself clear, thank you again for your help!

  Best Regards,

  Phil

[wiebe@CARYA]

You'd network bandwidth might be limiting the data to the USRP...

Even though the USRP supports 160MHz data, the entire system needs to support this.

For example, I used a 100MB network card years back, which wasn't accepted by the USRP. I fix this with a 1 GB hub, the USRP did accept that. However, the bandwidth was obviously limited by the 100MB network card.

You can tweak your network, making sure it's a dedicated connection, there are plenty of TCP\IP settings (jumbo frames, time outs, buffer sizes, etc.) that could have effect.

There might be some buffer size properties for the USRP too...

This was decades ago, but I do recall sending I16's (not doubles or singles) make a difference. And that makes sense as a I16 is half the size of a single, 1/4 of a double.