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Re: [Discuss-gnuradio] Python function processing block

From: Eric Blossom
Subject: Re: [Discuss-gnuradio] Python function processing block
Date: Mon, 16 Oct 2006 22:28:37 -0700
User-agent: Mutt/1.5.9i

On Tue, Oct 17, 2006 at 02:31:28PM +1000, Murray Lang wrote:
> How did you go Marcus?
> I hunted high and low for a class that I could subclass to implement
> a gr.block in Python. My initial reason is that I want to implement
> a source that reads I/Q data from WAV files so that I can compare my
> GNU Radio results with PowerSDR using exactly the same data. Wav
> files are much easier to work with in Python than C++.

The easiest thing may be to convert the WAV files with sox.

I think something like this will work:

  $ sox -V foo.wav -f foo.raw

and foo.raw will end up with floating point values.
If the input has two channels, then I think you'll get interleaved
floats as output, which is equivalant to gr_complex (== std::complex<float>)

> I would also like to implement network data sources and sinks for
> remote SDR operation. Network programming is much easier in Python
> than in C++.

Agreed.  Just open the sockets in python then pass the corresponding
file descriptors (s.fileno()) to gr.file_descriptor_{sink,source}.

> In short it seems to me perfectly natural to have a gr.block class
> implemented in Python, particularly (but not only) sources and
> sinks. It would be really nice if there was a Python class that we
> could simply subclass to achieve that.

It's natural, but will be dog slow ;)

If that doesn't scare you off, then the next question is 
what i/o signature do you want to use?  Will the block
accept a single input and produce a single output, or will it accept a
varying number of inputs and produce a varying number of outputs?

I can imagine several common cases:

  float -> float
  complex -> complex
  float -> complex
  complex -> float

Would you expect your python code to accept input and produce
output a single sample at a time, or to deal with arrays of input and
output samples?

If you haven't already, please take a look at 
Though it's C++ centric, the same issues will exist in a python
implementation.  After reading that, please ask the question again,
and I can provide further assistance.

> Murray


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