# Usrp\_sink tx\_time tag

**URL:** <https://www.ruby-forum.com/t/usrp-sink-tx-time-tag/242922>\
**Category:** GNU Radio\
**Created:** [August 7, 2015, 4:09pm UTC](https://www.ruby-forum.com/t/usrp-sink-tx-time-tag/242922 "2015-08-07T16:09:43Z")\
**Posts on this page:** 3\
**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 7, 2015, 4:09pm UTC](https://www.ruby-forum.com/t/usrp-sink-tx-time-tag/242922/1 "2015-08-07T16:09:43Z")

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hi all

I’ve one more tag related question:

I want to sent packets in burst over a usrp\_sink. the time between two  
consecutive bursts should be 7ms. thus, I want to use a tx\_time\_tag  
along with every first item of a packet so that the usrp waits for 7ms  
before transmitting it. However, it seems that no matter what values I  
send along with the tx\_time tag, I always get a huge flood of “L”,  
which, as far as I know, means that the sample is too late. can anybody  
please enlighten me as to which values I have to transmit with the tag?  
As far as I know, the value should be a tuple, with one value being the  
integer part of a timestamp, the other the fractional part after the  
decimal point (right?) It seems obvious that I’m sending wrong values  
since I always get an “L”-flood no matter what number I transmit with  
the tag.

Note: I set the time of the USRP to 0 before I run the top\_block.start()  
command.

kind regards,  
Mat

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**Author:** ![okcomputer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/o/b38774/32.png) [@okcomputer](https://www.ruby-forum.com/u/okcomputer)\
**Post date:** [August 7, 2015, 6:43pm UTC](https://www.ruby-forum.com/t/usrp-sink-tx-time-tag/242922/2 "2015-08-07T18:43:46Z")

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Are you doing bursty transmission (i.e. using eob/sob tags, or using  
tagged streams)?

M

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**Author:** ![okcomputer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/o/b38774/32.png) [@okcomputer](https://www.ruby-forum.com/u/okcomputer)\
**Post date:** [August 7, 2015, 6:51pm UTC](https://www.ruby-forum.com/t/usrp-sink-tx-time-tag/242922/3 "2015-08-07T18:51:49Z")

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Martin B. wrote in post #1177442:

> Are you doing bursty transmission (i.e. using eob/sob tags, or using  
> tagged streams)?
> 
> M

yes, I’m using eob/sob tags. I’m assuming that the tx\_time tag should be  
on the same item as tx\_sob?