Re: [Discuss-gnuradio] Tag Propagation Question

[Tom Rondeau]

On Mon, Jul 20, 2015 at 4:58 PM, Nowlan, Sean <address@hidden> wrote:

First, there may be multiple tags per sample. Use “get_tags_in_range” or “get_tags_in_window” to get all the tags you need. Using “get_tags_in_window(0, noutput_items, …)” will get you all the tags associated with samples passed as your inputs. (Perhaps you know this already and were just choosing a toy example, but I wanted to make it clear).

 

There is a pruning routine in the scheduler that will toss out “old” tags, i.e., tags that have been accounted for based on “nitems_read”, which is updated when you call consume_each. So I think you will end up getting the last 5 tags again on the next call to work. But you have already propagated them, so you will be adding duplicates. The solution is to only propagate tags in the range that you intend to tell the scheduler you’ve consumed.

 

(Caveat emptor: I haven’t tested this out, but I believe this is how it would work).

 

Sean

Sean is (should be...) correct here.

To help, you can take a look at the scheduler overview, which has info about the tag stream system:

http://www.trondeau.com/blog/2013/9/15/explaining-the-gnu-radio-scheduler.html

And my original presentation on them:

http://www.trondeau.com/grc2011-abstracts#thursday_1700_1730

Hope these help clear things up.

Tom

 

 

From: discuss-gnuradio-bounces+sean.nowlan=address@hidden [mailto:discuss-gnuradio-bounces+sean.nowlan=address@hidden] On Behalf Of Richard Bell
Sent: Monday, July 20, 2015 3:51 PM
To: address@hidden
Subject: [Discuss-gnuradio] Tag Propagation Question

 

If I set_tag_propagation policy(TPP_DONT) and then re-add all tags in range to the output, but only produce a portion of the input items to output, what effect does this have?

Here is a good corner case example of what I mean:

Suppose I'm given 10 items, and every item has a tag associated with it. I then make the following actions

set_tag_propagation policy(TPP_DONT)

for( ii = 0; ii < 9; ii++)
{
    add_item_tag(0, tags[ii].offset, tags[ii].key, tags[ii].value, tags[ii].srcid);
}

consume_each(5);

return 5;

I'm concerned this might cause tags to be added or lost.

Thanks,

Rich