[USRP-users] Retune stream tag arriving before retune Is complete

Jacob Gilbert mrjacobagilbert at gmail.com
Tue Sep 9 20:01:03 EDT 2014


Hello,

I am having some trouble with a USRP B210 and quickly retuning it for a
wideband survey application. I have an OOT GR block which retunes (DSP
only, since the LO retune takes quite a while) the USRP via a call to the
usrp_source block's retune method, waits for the stream tag, passes some
data forward, then repeats.

The issue I am currently having is on occasion the stream tag indicating
the retune will arrive well before the data is actually valid for the
frequency the tag is indicating it just tuned to. I had originally thought
the uhd source block would insert a stream tag when the USRP indicated the
retune had been completed, however in looking into usrp_source_impl.cc:145,
it looks like the tag is appended (or indicated it should be appended)
immediately after the tune call is made regardless of whether or not the
tune in the FPGA has actually completed.

Is this correct? And if so, is there a better way to know when a DSP-only
tune has completed and the data stream is valid for the new frequency?


Thanks,

Jacob
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