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Re: [Discuss-gnuradio] UHD Underrun with Wav File Source and USRP Sink

From: Marcus D. Leech
Subject: Re: [Discuss-gnuradio] UHD Underrun with Wav File Source and USRP Sink
Date: Fri, 16 Nov 2012 19:26:30 -0500
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On 16/11/12 07:15 PM, Tom Hendrick wrote:
Does anyone have some ideas on what else I can try right now?  I'm out of ideas on what is causing the underruns at the start of running the script that reads the WAV file and outputs to the USRP LFTX.

Thank you, -Tom

Most systems like this have startup glitches.  The analog hardware is one source, and in your case, it's the
  kernels buffer management getting "ramped up".  Back in the 1980s, we had to deal with this a lot on
  low-speed packet-radio systems layered on top of ordinary analog FM radios.  There was no way to make
  the radios not glitch on startup, so we simply devised mechanisms to deal with it.

My suggestion is to setup up a *continuous* transmitter graph, and gate-in "real" samples when you need them.

Also, I'd gently suggest that a receiver chain that can't handle the odd glitch isn't much of a receiver chain, in
 the signal-processing sense.  Radio is analog. It's subject to distortions, glitches, pops, wheezes, snorts and
 shudders that are utterly outside of your control.  Your receiver has to be able to deal with them, regardless
 of whether the source is "natural", or a quirk of the buffer-startup behaviour.

Principal Investigator
Shirleys Bay Radio Astronomy Consortium

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