[Discuss-gnuradio] C++ interface to USRP

[Sebastiaan Heunis]

---------- Forwarded message ----------
From: Sebastiaan Heunis <address@hidden>
Date: Sat, 21 Jun 2008 19:31:30 +0200
Subject: Re: [Discuss-gnuradio] C++ interface to USRP
To: address@hidden

Chuck

I know about the interp = 128, meaning that the data gets decimated to
decrease the number of samples.  I have captured some samples in
GnuRadio using the Python code.  I just need to figure out how to
reblock it from 500096 to 500000 samples and still maintain all the
info or if there is a way to get 500000 samples.  For what I need to
do, C++ will be better.  Something else for anyone that might be able
to know?  In the C++ code the data transfer from the USRP to the
application is started by urx->start(); and stopped by urx->stop();.
The calculations that I am doing in C++ takes about half a minute to
complete.  What I would like to do is capture 500000 samples, do the
calculations, display the result, capture another 500000 samples,
calculate, update the display and so forth.  So I would like to only
read in samples when one set of calculations are complete.  Otherwise
I might have to use 2 threads to handle the data reads and calculation
processes.  Has anyone done something similar?

Thank you.

Sebastiaan

On 6/21/08, Charles Swiger <address@hidden> wrote:
> Hi - Someone else should know this better, but a stab at it: The USRP
> samples at a fixed 64e6 rate, and you can control the amount of data
> sent over the usb by using interp.  You get a usrp rate of 500000 by
> using interp = 128, which is very doable.   I think you can process
> units of 500000 by reading in multiples of 128 and reblocking to 500000
> somehow.  Just a guess. Read in enough to get over 500000, tie a ribbon
> on that package and send it off to your app, use the residual and keep
> appending data until you get over 500000 again, repeat. You don't *have*
> to read exactly 500000 samples, just make sure your app can process,
> or buffer it somewhere, faster than the usrp can send it.
>
> --Chuck
>
>
> On Sat, 2008-06-21 at 11:48 -0400, Sebastiaan Heunis wrote:
>> Hi
>>
>> Can anyone please help me?  I want to use the C++ interface in order
>> to use the Qwt C++ library to create contour plots, etc.
>> UsrpFAQ/CppInterface has some code illustrating how to do this.  I
>> just have a few questions concerning this.  I'm sorry, but my
>> understanding of sampling is not what it is supposed to be.  In the
>> code samples per read needs to be a multiple of 128.  So if I'm
>> sampling at 500 000 samples per second in the USRP, I can only read in
>> 499968 samples into the C++ program?  Is the rest just discarded and
>> if I read again, do I read in 499968 samples of the next time sampling
>> time?  I would ideally like to sample at 500000.  Can I set the USRP
>> to this, read in more than 500000 samples and just discard the rest?
>>
>> Thank you very much.
>>
>> Sebastiaan
>>
>>
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