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Re: [Discuss-gnuradio] Another good project

From: Eric Blossom
Subject: Re: [Discuss-gnuradio] Another good project
Date: Mon, 20 Jan 2003 12:44:42 -0800
User-agent: Mutt/1.4i

On Mon, Jan 20, 2003 at 11:09:13AM -0800, Chris Albertson wrote:
> Matt,
> Thanks,  I've been looking for something like this for use on
> another project.  
> You said "This widget library might be a good start".  I think the
> _last_ thing we want to do is to modify qwt.  Much better to 
> simply link to it.

Speaking for Matt, I think that's what he meant.  
You'll need to write the glue between qwt and GNU Radio.

> One thing that needs to be investigated is how fast the graphs can
> updated and how much of a load that places on the CPU.  A 'scope
> or spectrum analyzer needs to re re-drawn about 30 times a second
> if it is to look smooth to the eye.

Our current FFT widget redraws at 30 Hz.  It uses a trivial amount
of the CPU of a 1.5 GHz pentium or Athlon.

> That RTlab.org link seems to be an interface to the same
> "Real-Time Linux" that I wrote about a few minutes ago in another
> post.  In a nutshell, that way RTL works in you install a 
> real-time modual and then have it run at (say) 1Khz.  If will then
> run forever 1000 times persecond.  Normal user programs can
> comunicate with it via a normal UNIX FIFO pipe in both
> directions.  I would assume the graph widgets are written to
> support this model.

No need for the real time kernel.  Our existing mc4020 driver is
capable of keeping up with the full 20 MSPS stream and getting it into
GNU Radio land with *very* little overhead.

For the FFT or o'scope example, there's really no reason to update
more than, say 50 times / sec.  All you've got to do is skip samples
until you get to the window you're supposed to be looking at.  The
existing code does this.  It's a bit of a kludge, but is a working
starting point.

Take a look at gnuradio/src/gnu/example/simple_fft.cc for a simple top
level driver.

The existing FFT graph modules are:

    gnuradio/src/gnu/lib/grio/GrFFTSink.h       // real or complex output
    gnuradio/src/gnu/lib/grio/GrFFTSinkAvg.h    // average magnitude


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