[USRP-users] A few questions about RFNoC streaming

Nick Foster bistromath at gmail.com
Mon Mar 25 12:37:47 EDT 2019


I can tell you the answer to #3 off the top of my head: the two streams
will be sample-aligned, and if you use timed start commands, they will be
time-aligned.

The other two are probably best answered by trying it out. Maybe someone
from Ettus can chime in.

Nick

On Fri, Mar 22, 2019 at 7:09 AM Rob Kossler via USRP-users <
usrp-users at lists.ettus.com> wrote:

> 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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>>>>
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