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Re: [Discuss-gnuradio] Cannot Achieve 50MSPS Sampling Rate

From: labarowski
Subject: Re: [Discuss-gnuradio] Cannot Achieve 50MSPS Sampling Rate
Date: Mon, 5 Mar 2012 13:58:39 -0800 (PST)

Josh Blum-3 wrote:
>>- dont use a throttle, the usrp sink *is* back-pressuring the stream
>>- use this new signal source on my new_blocks or next branch, its much
>>much faster:
> Didn't realize that a throttle was unnecessary with the usrp. Thanks for
> pointing that out. I see that you have a lot of other blocks in your
> repository as well. Do these have any advantage to the ones included with
> gnuradio?
>>50 Msps is serious amount of data to push through your computer. More
>>than a feeling, even the most serious computers can easily have a
>>bottleneck. I suspect that the gnuradio core signal source cannot
>>sustain 50Msps in 1 thread/1 work function.
> Makes sense. I would assume that, as long as I'm using grc at least, I'm
> limited to one thread?
>>Why do you think you cant change the wire format? It sounds like you
>>changed it to sc8 format (above).
> Should have worded that more carefully. I can choose 8 or 16 bits over the
> wire. My thinking was that I might be able to increase the rate of
> decimation (on second thought, decimation has more to do with sampling
> frequency than a data bottleneck) and also decrease the precision and use
> an integer less than 8bits. Basically, I thought ethernet may have been
> the bottleneck. Decreasing precision shouldn't be necessary, I'm just
> trying to build an understanding here.
>>I prototyping whatever it is you are trying to do at a lower rate, then
>>optimizing it in SIMD routines to get up to 50 Msps on the host.
> I was totally unaware of SIMD before you mentioned it. That's an
> interesting subject. It is my understand that SIMD is integrated into
> gnuradio through VOLK as of Dec. 2010. Doesn't look like I can use VOLK
> directely from grc, or even from Python. Looks like it needs to be
> implemented at the block level in C++. Is this the case?
>>Also, try examples/tx_waveforms with --otw=sc8 --rate=50e6 and
>>experiment with that so you can see if your PC can sustain the rate with
>>minimal load.
> I actually couldn't find that in my /usr/local/share/gnuradio/examples
> folder. Do I need to download it elsewhere?
Thanks for the informative post Josh! 50MSPS will probably prove unnecessary
for the project that I'm working on. I was worried that perhaps I was doing
something fundamentally wrong and that's why  I wasn't getting the full
sampling rate out of this device.
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