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Re: [Discuss-gnuradio] UHD accessing metadata


From: Criss Swaim
Subject: Re: [Discuss-gnuradio] UHD accessing metadata
Date: Sun, 09 May 2010 15:46:47 -0600
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gnuradio does not offer any kind of sample decoration. So, the metadata is present in the simple uhd source block, and dropped on its way out of the block.

You would need to make some kind of c++ app in gnuradio or maybe standalone to deal with the metatdata. I dont know another way.

Also, the uhd comes with an example app called rx_timed_samples.cpp, you may want to take a look at this to see how the api deals with the metadata. I will expand this example to include clock configuration when i get the chance as well.

I hope that helps,
-Josh

On 05/06/2010 12:35 PM, Criss Swaim wrote:
I have been working with the uhd version of gnuradio and have attached a
gps unit to the usrp2 to set the pps.  So far, I have not figured out
how to extract the time (secs and nsecs) metadata for a signal sample.
This is mostly due to my limited C++ coding skills.  Has anyone
successfully extracted the time metadata and would you be willing to
share the C++ code to show me how to capture and extract the  time metadata.

  
Josh:

for discussion, consider a model:      uhd-source-block ---> custom filter block ----->custom sink (sample file)
 
For clarification, when you say the metadata is present in the uhd source block but dropped on the way out, this implies that if I want the time associated with a sample, I need to modify the uhd source block with the code to pull the secs/nsecs.  Is this correct?  Currently, I have a custom filter block attached to the USRP source block, but your comment indicates that the metadata is not present when the sample is passed to my custom filter block.  If that understanding is correct, then I must capture the time data in a new custom uhd block, push it to an array with some identifier and then in my existing custom block, re-attach the metadata with the sample based on the key or position in the array.  Am I understanding this correctly?

The example is quite helpful and I have spent much of the weekend working through it.  thanks
-- 
Criss Swaim
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