USRP 2954R Tx Underflow at IQ-Rates >50MHz

[TobiSt90]

Hey,

I'am new to the USRP topic and I started playing around with the hardware which i mentioned in the subject field.

In a first attempt I just try to generate a Chirp signal which i wann to send over the TX front end to a beam antenna. (At the end of my project i wann a realize a radar application with the USRP...)

Unfortunatelly I got an error message which says that iam running into an TX underflow... I allready tried different solutions which where recommended at this forum like changing the registry entry "FastSendDatagramThreshold" to 1500, add a Time Trigger, higher the array size of the input samples and so on...

I could improve the possible IQ sampling rate from 10MSps at the beginning to 50MSps with changing the thinks mentioned above. But actually I like to use the full bandwidth of the device and obtain a sampling rate of 200MSps. At the moment thats not possible.

I'am using following hardware:

Host PC: NI PXIe-1071

USRP: NI USRP-2954R

Connection Host-USRP: NI PXIe8374 x4

I also attach my code.

Perhaps you can help me and give me some hints. Thank you in advance!

Greetings,

Tobias

[muffin.vi]

Hi TobiSt90,

Which driver API are you using? the niUSRP API, or the USRP-RIO API? It's a bit confusing, but one is host-only, while the other uses the FPGA on the device. If you based your code off of the sample streaming project, for instance, you are using the USRP-RIO API. 

[TobiSt90]

Hey Muffin,

at the moment i use the niUSRP API. Does it mean that when I use this API the FPGA on the USRP isnt in use? I thought that the FPGA is the "interface" between the frontend and the host pc and runs in the background with a standard bitfile similiar to the simple streaming one. Is there any hardware limitation (sampling rate, etc...) when I only use the niUSRP API?

Thank you!

[muffin.vi]

In my experience, the niUSRP API does not get full streaming rates over PCIe. If you switch to using the USRP RIO API, you should be able to stream at full rate. Alternatively, you could also use 10 GbE using the niUSRP API and get full rate that way as well.