Re: [Discuss-gnuradio] X310 with 2 WBX in full duplex

[Michael Carosino]

Hi,

I've successfully gotten the two tx-rx setup on an x310 you've
described but I did it somewhat differently. Instead of using the usrp
source/sink blocks I ended up using the RFNoC blocks - the main reason
for this is because a USRP Sink block is made up of the following
RFNoC blocks: RFNoC DMAFIFO -> RFNoC DUC -> RFNoC Radio. It turns out
that the DMAFIFO included by the USRP Sink block has a default depth
size of 32MB and this results in multiple seconds of delays for the
sample rates I was using (Ettus includes this fifo due to some flow
control latencies in their protocol that they use for transport
between the USRP and host over ethernet).

Anyways, by manually creating the radio chain in RFNoC as described
above, you can adjust the default depth size of the DMAFIFO. By
playing around I found that a depth of 2^20 = 1.04MB worked well.  It
is also of note that if you do this method you need four total radio
blocks - 2 for transmit and 2 for receive (for some reason the
multi-channel selection in the rfnoc radio block did not work, this
method does however).

I would also run 'ethtool -G eth0 rx 4096' to ensure packets aren't
dropped in your NIC. Also you may get underflows depending on your
sample rate, in my case these were solved by moving the bpsk transmit
chain to fabric (RFNoC) as the host was not fast enough to generate
samples otherwise.

Finally, you will probably experience occasional errors on flow graph
startup about synchronization errors (timeout waiting for PLL to lock,
backend sync failed, unexpected fifo depth), retrying to run the
flowgraph (sometimes it takes a few tries) will usually get it
running. I've spoken to Ettus about this and they are tracking this
issue so hopefully its solved soon.

Attached a picture of transmit/receive configuration in RFNoC.

regards,
Michael



On Thu, Nov 2, 2017 at 7:12 PM, Bakshi, Arjun
<address@hidden> wrote:
> Few mistakes I caught after sending it. Center frequencies I had chosen were
> out of range for WBX. Fixed now. Also, image file now has proper extension.
>
>
> Thank you,
>
>
> AB
>
> ________________________________
> From: Bakshi, Arjun
> Sent: Thursday, November 2, 2017 9:38:48 PM
> To: address@hidden
> Subject: X310 with 2 WBX in full duplex
>
>
> Hi,
>
>
> I'm trying to get two Tx-Rx links running with an X310 with two WBX
> daughterboards in it. I've used multi-channel USRP source/sink blocks, but
> I'm experiencing latency (L) errors with the connection, and then the
> application (GRC) hangs. I've attached an image of my USRP source/sink
> blocks. I'm connected to the X310 with a 1GB ethernet connection.
>
>
> Can anyone point out the reason/mistake? Also, is the sub-device spec
> correct? Followed instructions for WBX from here:
> https://www.ettus.com/content/files/kb/application_note_frontends_subdevices_antenna_ports.pdf
>
> My goal:
>
> I want to have a Tx-Rx link in freq F1 and another in freq F2 at the same
> time. One daughterboard TXes in F1 and RXes in F2, while other TXes in F2
> and RXes in F1. Is this possible with the equipment I have?
>
>
> Thank you,
>
>
> AB
>
>
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> Discuss-gnuradio mailing list
> address@hidden
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>

Transmit.png
Description: PNG image

Receive.png
Description: PNG image