# Padding burtsy blocks

**URL:** <https://www.ruby-forum.com/t/padding-burtsy-blocks/243136>\
**Category:** GNU Radio\
**Created:** [August 25, 2015, 4:01am UTC](https://www.ruby-forum.com/t/padding-burtsy-blocks/243136 "2015-08-25T04:01:28Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Sadaf\_N](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/858c86/32.png) [@Sadaf\_N](https://www.ruby-forum.com/u/Sadaf_N)\
**Post date:** [August 25, 2015, 4:01am UTC](https://www.ruby-forum.com/t/padding-burtsy-blocks/243136/1 "2015-08-25T04:01:28Z")

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I have a flowgraph that I’m trying to develop in simulation first before  
deploying to some sort of hardware like a USRP. The flowgraph begins  
with  
a ZMQ Pull Source and then I have all my signal processing blocks  
afterwards (eventually there would be a UHD Sink). The ZMQ block only  
produces samples when it receives a message so when it doesn’t receive  
samples the flowgraph doesn’t run.

If the work function for any block is only called when there are samples  
in  
the input buffer I don’t see how adding any blocks after my ZMQ Pull  
Source  
could help. So that leaves making my own ZMQ Pull Source that emits  
zeros  
when it has no other message. Do I have any other options? If I add a  
this feature would be useful to merge back into GR or is this not really  
an  
intended use case for GR?

Thanks,  
Devin

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**Author:** ![devin\_kelly](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/13edae/32.png) [@devin\_kelly](https://www.ruby-forum.com/u/devin_kelly)\
**Post date:** [August 25, 2015, 8:25am UTC](https://www.ruby-forum.com/t/padding-burtsy-blocks/243136/2 "2015-08-25T08:25:31Z")

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Hi Devin,

the “padding with zeros unless samples occur within a specific time” job  
can be done with gr-eventstream [1] [2] , but:

If you’re going to use USRP sink anyway, what about using tagged stream  
blocks[3]?  
You could replace your “Pull Source” with a “Pull Message Source” →   
“PDU to tagged stream”-\>signal processing-\>“USRP Sink” (with “packet  
length tag name” set accordingly)

Best regards,  
Marcus

[1] [https://github.com/osh/gr-eventstream](https://github.com/osh/gr-eventstream)  
[2] [http://oshearesearch.com/tag/gr-eventstream/](http://oshearesearch.com/tag/gr-eventstream/)  
[3] [https://gnuradio.org/doc/doxygen/page\_tagged\_stream\_blocks.html](https://gnuradio.org/doc/doxygen/page_tagged_stream_blocks.html)