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Re: [Discuss-gnuradio] synchronization between blocks

From: Michael Dickens
Subject: Re: [Discuss-gnuradio] synchronization between blocks
Date: Mon, 3 Feb 2014 14:30:48 -0500

On Feb 3, 2014, at 10:14 AM, Nemanja Savic <address@hidden> wrote:
> at the moment I thought that the problem was solved, but actually something 
> strange is going on. I would only like to ask whether delay between two paths 
> can roll out somehow (i don't know if this verb exists). The point is that at 
> the beginig of the execution, it looks like the script is doing fine, but 
> then I realize signs of unalligned signals which I can't in some other way.

IIRC: Because of the way GNU Radio internally handles data processing (it waits 
for data upstream to become available before -starting- processing for a given 
block), and since -your specific graph- contains only sync blocks (yes?), then 
the sample delay difference between the 2 branches of -your specific graph- 
should be constant.  Further, it should be the same constant for every graph 

If any blocks within a specific path are not sync blocks, e.g., a packet 
decoder, then the sample delay difference is not guaranteed (constant or 

The wall-clock delay difference will not be constant; it can be any 
non-negative (and, generally > 0) time.

All of the above said: If you're into compiling GNU Radio, you can go into 
gnuradio-runtime/lib/block_executor.cc and set "ENABLE_LOGGING" to 1.  
Recompile/reinstall GNU Radio, then when you execute your graph you'll get a 
printout dump of what each block is doing.  That printout might help you debug 
this issue; or, not.  You might also add LOG messages in that file which could 
help ... maybe; or, not.

Hope this helps! - MLD

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