Re: [Discuss-gnuradio] How to synchronize feedback between blocks?

[Michael Dickens]

Hi Martin -

On Apr 29, 2010, at 9:23 AM, Martin Braun wrote:
> y(n) = x(n) + x(n-2)
>
> My question is: can GNU Radio be modified to accept this? It's a
> perfectly valid flow graph (similar to ones you find in DSP  
> textbooks),
> and thanks to the history of the delays, one that should work. I'd be
> very interested to hear some comments on this.

Shortest Answer: Yes, this could be done -- GNU Radio is open  
source :).  Go for it!  I think you'll find that it's not trivial to  
implement.  Further: If you look at the radio of computation time  
versus overhead time (one version of "computational intensity") of any  
such loops -- when implemented in a data-flow block fashion such as  
what GNU Radio does (and, all SDRs that I know of) -- it will be very  
low compared with writing a specific block that internally handles the  
feedback.  So, low efficiency but allowing for feedback, or high  
efficiency but no feedback ... hmm ... seems obvious which to choose  
at least for the initial implementation.  Maybe some future  
implementation will deal with feedback loops in some special way.   
Hope this helps! - MLD