[Discuss-gnuradio] UHD:SingleUSRP and buffer allocation policy

[Marcus D. Leech]

I've noticed latency issues with one of the applications I'm working on.
Latencies of up to tens of seconds
  have been observed, which I tried to combat by specifying
recv_buff_size in the parameter list.

Right now, I'm running with 4096 bytes, which at 400Ksps, gives me a
roughly 1 second latency between
  input and output (where output is both an audio sink, and a couple of
different file sinks as well as a
  scopesink2, and an FFT sink).  But increasing it beyond 4096 bytes
causes the latency to go up very
  quickly, and if I drop it to 1024 bytes, I start seeing over-runs.  If
you do the math, however, 4096 bytes is
  nowhere near 1 second worth of buffer.  One second is 1.6Mbytes
(400Ksps x 4bytes per sample).

How is downstream buffer allocation policy affected by settings of
recv_buff_size in UHD::SingleUsrp?

This is probably the same can of worms I was talking about a few weeks
ago, with trying to understand
  latency issues, and where they'd "bite" you for various classes of
applications.  For purposes of data recording,
  my current application can't really tolerate several seconds of
latency--since events recorded will potentially need
  to be cross-correlated with other receivers (although not
phase-synchronous, just event correlation down to one or
  two seconds of accuracy).


-- 
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org