[USRP-users] A few questions about RFNoC streaming

Rob Kossler rkossler at nd.edu
Fri Mar 22 10:08:18 EDT 2019

Any suggestions?

On Wed, Mar 20, 2019 at 9:49 PM Rob Kossler <rkossler at nd.edu> wrote:

> Yes, the example was for illustration only.  You can throw a couple of
> DDCs in between the radio and add/sub block to slow the rate down.  But,
> the questions are still the same.
> On Wed, Mar 20, 2019 at 7:49 PM Nick Foster <bistromath at gmail.com> wrote:
>> First things first. The flow graph you're describing don't work because
>> the two radio blocks will saturate the bus going into the addsub block. You
>> will need to decimate the streams going into the addsub block.
>> I don't have a ready answer to your question about the streamers, but I'd
>> suggest using timed commands to align the two radio streams, if UHD isn't
>> smart enough to recognize the two radios and propagate the stream command
>> accordingly.
>> Nick
>> On Thu, Mar 21, 2019, 6:46 AM Rob Kossler via USRP-users <
>> usrp-users at lists.ettus.com> wrote:
>>> Hi,
>>> I am starting to develop more complicated RFNoC graphs and several
>>> questions occurred to me. I am using my own C++ application with the UHD
>>> RFNoC-enabled library.
>>> Consider a receive-only RFNoC graph with 2 radio blocks feeding a
>>> 2-input, 2-output Add/Sub block.  Also, assume there are two rx_streamers
>>> connected to the 2 output ports of the Add/Sub block.  Note that these
>>> streams are no longer independent or one-to-one matched with the radio
>>> channels.
>>> 1) How does an "issue_stream_cmd()" to one of the Add/Sub block ports
>>> propagate back to the radio block?  Actually, it would need to propagate
>>> back to both Radio blocks no matter which rx_streamer I used since they are
>>> no longer independent streams.  Does this make sense?
>>> 2) What happens if I only call "issue_stream_cmd()" for one of the
>>> rx_streamers instead of both? Perhaps since the other streamer isn't
>>> running, it backpressures the streaming such that it eventually quits and
>>> thus quits for the other port as well?
>>> 3) Do I have to do anything in the Add/Sub block to sync up the streams
>>> or can I rely on the first sample from Radio 0 being time-aligned with the
>>> first sample from Radio 1 (assuming I issued timed start commands)?
>>> Rob
>>> _______________________________________________
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>>> USRP-users at lists.ettus.com
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