Latency Management in GnuRadio with Hardware Buffers

[Nieland, Michael]

Hi all,

I have more of a general question regarding latency management in GnuRadio that is also regarding to Matt Ettus talk on this topic at GRCon19 (https://www.youtube.com/watch?v=jq0RewceCwc).
In our application we are using essentially a very similar approach as outlined by Matt to minimize the TX latency. This is generally working quite well reducing the Flowgraph Latency down to around 13 ms instead of a couple of 100 ms without latency management.

However, the hardware buffers are not included right now which leads to an increased latency if the FG is run with Hardware (B210 USRP). An overview of the setup is attached.
We experimented with using the USRP sink underrun messages to control the packet insertion rate which led to a significant improvement in overall latency but also regular underruns and packet loss.

Matt spoke about the possibility of adding functionality to UHD such that it reports the actual time a certain tagged sample has been processed and sent to the DAC. From what I have seen by looking through the documentation this feature is not available but maybe I missed something there and you can point me in the right direction.

Are you aware of any other ways of including the hardware buffers of a USRP in such a control loop?

I would also appreciate any further insights regarding this topic and how other GnuRadio users are approaching latency minimization in GnuRadio with USRPs in the Flowgraph.

Best regards

 

Michael

Latency.pdf
Description: Latency.pdf