Re: [Discuss-gnuradio] synchronization between blocks

[Nemanja Savic]

Thank you Michael.

Well, I think the problem comes from the block which is not of sync type. INputs to this block are demodulated signal and the very input signal, and the output are sybol values and signal value at the point of sampling.

However I will try with logging and see what can I find. But just for clarification, can the problem come from forecast function where I ask for the same amount of input samples as the number of output samples (which is like with sync block), but I produce like 20 times less?

Best regards

On Mon, Feb 3, 2014 at 8:30 PM, Michael Dickens <address@hidden> wrote:

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 execution.

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 otherwise).

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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Nemanja Savić