[USRP-users] Issues with dual full duplex on x310

Jonathon Pendlum jonathon.pendlum at ettus.com
Wed Jul 26 15:24:02 EDT 2017

Hi Mike,

Make sure your MTU is set to 9000. Are you using 1GigE or 10GigE? Do you
see underruns improve when running with only 1 TX radio?


On Tue, Jul 25, 2017 at 2:18 PM, Michael Carosino via USRP-users <
usrp-users at lists.ettus.com> wrote:

> Hi,
> I'm using gnuradio 3.7.12 and rfnoc-devel commit 1908672.
> I'm trying to use both daughter boards on the x310 each at full duplex
> (that is, I will have 2 independent tx paths and 2 independent rx paths).
> So far I have accomplished this by using the UHD: USRP Sink/Source blocks
> and setting them to 2 channels, selecting the appropriate antennas, and
> specifying a subdev spec of A:0 B:0. The flowgraph works perfectly sending
> and receiving 2 sets of data simultaneously.
> However, I need to have the same capability when using the RFNoC blocks.
> I've attempted to use 2 RFNoC radio blocks, one set to Tx, 2 channels, and
> the other set to Rx, 2 channels, however the block's parameters have only a
> radio select of A or B unlike the usrp source's subdev spec, so this setup
> does not appear to work no matter what configurations I try. Am I mistaken
> about what the 2 channels refers to here?
> I did finally get an RFNoC setup that works by using 4 RFNoC radio blocks
> (2 for transmit with radio select A, B respectively, and 2 for receive with
> radio select A, B respectively). However, with this setup I get tons of
> underflow "U" in the console. Curiously this happens even when using the
> DMAFIFO as ettus recommends so I'm not sure what's going on. My flowgraph
> is attached showing this setup.
> (A quick note on why I want to use the rfnoc blocks, apparently the uhd
> usrp sink block now automatically includes a DMAFIFO in the tx chain to
> deal with the underflow issue caused by tcp flow control, however for my
> application the depth/size of this fifo is much too large and causing
> massive delays, I've found that by reducing the depth I can minimize my
> delay and I'll only get underflows on flowgraph startup which I assume is
> due to the tcp slow start phase before backoff occurs. All this to say, if
> there is a way to adjust the dma fifo depth from the usrp sink blocks I'd
> gladly use that instead).
> Thanks,
> Mike
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