Re: [Discuss-gnuradio] Thoughts on stream tag propagation

[Martin Braun]

On Thu, Sep 08, 2011 at 09:41:03AM -0700, Eugene Grayver wrote:
> Hello,
> I am starting to actively use stream tags and am finding them quite useful.  I
> have one suggestion:
> 
> Tags propagated through a block with a known delay (set_history) should be
> adjusted by that delay.  For example, an input to an FIR filter gets reflected
> in the output after a delay.  Since the GR executor has access to the delay
> info, there's no reason it should not use it.
> 
> Comments?

An FIR filter is a good example why this is not always a good idea: The
group delay (which would be a sensible delay for a tag, I guess) is half
the delay GNU Radio knows about. Can stream tags be delayed w/ respect
to the sample position? That would be more useful, I guess.

MB


> 
> On a separate note, I have observed a _rare_ case where tags get lost.  The
> scenario involves an output attached to two inputs.  The two inputs consume
> data in different (random) chunk blocks.  It appears that if one of the inputs
> consumes items with the tag well before the second input gets to the tagged
> item, the second input sometimes does not see the tag.  I have not debugged
> this enough to confirm that there's no bug in my code.
> 
> Eugene
> ________________________
> Eugene Grayver, Ph.D.
> Aerospace Corp., Sr. Eng. Spec.
> Tel: 310.336.1274
> ________________________

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