Re: [Discuss-gnuradio] stream tag samples

[Nowlan, Sean]

 

From: discuss-gnuradio-bounces+address@hidden [mailto:discuss-gnuradio-bounces+address@hidden On Behalf Of Jenny Galasso
Sent: Friday, October 25, 2013 3:06 PM
To: address@hidden
Subject: [Discuss-gnuradio] stream tag samples

 

Today at 1:02 PM

Hi,
I'm using stream tags to time tag my data. In particular, I'm reading in one-second files and tagging the first sample read in with the time. I'm concerned with how the tag will be handled during decimation, filtering etc. I have read the documentation and understand that the tag is reassigned based on the relative_rate. For this particular data set though, it is important that the tags stay with the specific samples to which they were assigned, even if some of the tags are lost during decimation, filtering, etc.

Is this even possible? Are there any recommendations or tricks to get it to behave this way?

Thanks!

Jenny

 

 

Hi Jenny,

 

If you decimate by N, you’re getting rid of N-1 out of every N samples. So naturally you would want the tag to stick with the sample that doesn’t get thrown out. Similarly, if you interpolate by M, you introduce M-1 samples into the stream for every input sample; you’d naturally want the tag associated with input sample /i/ to be placed on the first sample of the corresponding batch of M output samples. The propagate_tags method in gnuradio/gnuradio-runtime/lib/block_executor.cc handles this by default. You can override this behavior in your own blocks by calling “set_tag_propagation_policy(TPP_DONT)” in your block’s constructor and then handling tags yourself in your work method.

 

Sean