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

From: Eric Blossom
Subject: Re: [Discuss-gnuradio] UHD:SingleUSRP and buffer allocation policy
Date: Mon, 18 Oct 2010 19:04:17 -0700
User-agent: Mutt/1.5.21 (2010-09-15)

On Mon, Oct 18, 2010 at 08:37:33PM -0400, Marcus D. Leech wrote:
> 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).

Since you've got a usrp* source and an audio_sink, what you're seeing
could be related to the two different clocks in the flow graph.  Do
you see the problem if the audio_sink is NOT in the graph?


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