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Re: [Discuss-gnuradio] consuming all inputs, small outputs

From: Sylvain Munaut
Subject: Re: [Discuss-gnuradio] consuming all inputs, small outputs
Date: Mon, 19 Jan 2015 21:39:19 +0100

> I am trying to create a block that outputs one number from each chucnk of
> data it takes in, I would like to output this number and be able to use it
> in visualizations, what would the best block be for this? Would a decimation
> block work? what if I would like to out put three numbers from one chunk of
> input and visualize those (lets say I'm doing an autocorellation and would
> like to know  sample number I found the highest correlation and the size of
> the correlation peak) and I want to plot them. Thanks, I'm finding this all
> REALLY confusing and every time I try something I am just running in to
> problems

If the output is not a "flow", then you probably want to use a message
port and not a normal port.

Normal ports are really meant for streaming sample data and they're
optimized for this with among other things buffering and so if you
only produce a very few output, those might end up being buffered for
a very long time before being given to the next block.

Another option is sometime not to 'output' anything, but just have the
sample stream pass through your block and just 'tag' some samples. The
corr_and_sync block does that. It searches for a training sequence in
an input stream and tags where it find one. So the next block in the
chain can take this input stream and know that at this particular
sample, there was a correlation peak and it had this value and
estimated frequency error. (note that this is correlation with a
training sequence, not autocorrelation so might not be applicable to
your case).



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