Editing Stream Tags

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When the tag propagation policy is set to TPP_ALL_TO_ALL or TPP_ONE_TO_ONE, the GNU Radio scheduler uses any information available to figure out which output item corresponds to which input item. The block may read them and add new tags, but existing tags are automatically moved downstream in a manner deemed appropriate.
When the tag propagation policy is set to TPP_ALL_TO_ALL or TPP_ONE_TO_ONE, the GNU Radio scheduler uses any information available to figure out which output item corresponds to which input item. The block may read them and add new tags, but existing tags are automatically moved downstream in a manner deemed appropriate.
When a tag is propagated through a block that has a rate change, the
item's offset in the data stream will change. The scheduler uses the
block's gr::block::relative_rate concept to perform the update on the
tag's offset value. The relative rate of a block determines the
relationship between the input rate and output rate. Decimators that
decimate by a factor of D have a relative rate of 1/D.
Synchronous blocks (gr::sync_block), decimators (gr::sync_decimator),
and interpolators (gr::sync_interpolator) all have pre-defined and
well-understood relative rates. A standard gr::block has a default
relative rate of 1.0, but this must be set if it does not work this
way. Often, we use a gr::block because we have no pre-conceived notion
of the number of input to output items. If it is important to pass
tags through these blocks that respect the change in item value, we
would have to use the TPP_DONT tag propagation policy and handle the
propagation internally.
In no case is the value of the tag modified when propagating through a
block. This becomes relevant when using [[Tagged Stream Blocks]].


As an example, consider an interpolating block. See the following flow graph:
As an example, consider an interpolating block. See the following flow graph:

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