Thanks for the info. Would writing the same program using c++ gnuradio apis give better performance? is there anything else we can to to significantly improve performance aside from not using gnuradio? Thanks again.
-Scott On Mon, Mar 6, 2017 at 10:08 Marcus D. Leech <[email protected]> wrote: > On 03/06/2017 08:27 AM, Thomas Wright wrote: > > Hi all, > > I have a simple flowgraph: > > usrp n210 -> low pass filter -> stream to vector decimator -> msg queue > sink > > with important parameters: > sample rate = .195312 MSps > vector length = 128 > decimation rate = 16 > msg queue length = 1 > > and my application is trying to capture samples of a given signal as fast > as possible. I'm using a GRC generated python script that I'm editing, and > looking at time stamps I'm creating with python's datetime.now(). My > general code is: > > TIMESTAMP1 > flowgraph.usrp.set_center_freq(center freq) > TIMESTAMP2 > > flowgraph.set_sample_rate(samplerate) #does usrp, filter, etc. > TIMESTAMP3 > > flowgraph.start() > TIMESTAMP4 > > flowgraph.msg_queue.delete_head() #waits for there to be data in the queue > TIMESTAMP5 > > flowgraph.stop() > > average difference between timestamps: > 1 -> 2 = .5ms > 2 -> 3 = 1ms > 3 -> 4 = 4ms > 4 -> 5 = 80ms > > My issue is that I think the time between timestamps 4 and 5 should take > about 10ms: > > 128 samp/vector * 16 vector * (1second / 195312 samp) =~ 10ms. > > My questions that arise from this: > How much overhead SWIG/python introduce, could that be significantly > hampering performance? Would a c++ version perform significantly better? > Would a higher end usrp perform significantly better? > How close I can expect to get to the theoretical minimum? > > I appreciate any information anyone could provide. Thanks very much. > > -Scott > > This has nothing to do with your USRP. You're likely looking at Gnu > Radio's buffering mechanism, which at low sample rates can often > produce considerable latency. > > > _______________________________________________ > Discuss-gnuradio mailing list > [email protected] > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > -- -- Thomas "Scott" Wright B.E. Electrical Engineering Co-op '17 M.E. Systems Engineering '17 Sigma Phi Epsilon Fraternity Email: [email protected] Phone: 619-867-2993
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