# Question about stream tag **URL:** \ **Category:** GNU Radio\ **Created:** [May 24, 2012, 4:28pm UTC](https://www.ruby-forum.com/t/question-about-stream-tag/220006 "2012-05-24T16:28:45Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Gurdipe\_D](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/b77776/32.png) [@Gurdipe\_D](https://www.ruby-forum.com/u/Gurdipe_D)\ **Post date:** [May 24, 2012, 4:28pm UTC](https://www.ruby-forum.com/t/question-about-stream-tag/220006/1 "2012-05-24T16:28:45Z")
Hello, I want to use my USRP2 to implement a TDMA system, and I want to send 5 seconds, receive 5 seconds, and do the recycle. I used the stream tag demo in gr-uhd/taguhd. The question is: 1. As sean have said in [Re: [Discuss-gnuradio] How to implement a TDMA system](http://lists.gnu.org/archive/html/discuss-gnuradio/2012-04/msg00506.html) we should use “tx\_time”, “tx\_sob” (start-of-burst), and “tx\_eob” (end-of-burst) to tag the data flow, but yend B in [How to align Tx/Rx timestamps - GNU Radio - Ruby-Forum](http://www.ruby-forum.com/topic/3832986) said the data not enclosed by sob-eob tag pair was dropped. Is this problem really exist? And any solution? 2. Is there any way to switch the Tx/Rx? And how to tell the USRP to receive for a desired time slot such as 5 seconds then stop? The only parameter I can see in gr\_uhd\_usrp\_source is ‘rx\_time’(tells when to start receive), I do not know how to stop the streaming after 5 seconds. Thank you for your help. Any suggestion is appreciated. ---
**Author:** ![PanS\_Luyuan](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/46a35a/32.png) [@PanS\_Luyuan](https://www.ruby-forum.com/u/PanS_Luyuan)\ **Post date:** [May 24, 2012, 4:36pm UTC](https://www.ruby-forum.com/t/question-about-stream-tag/220006/2 "2012-05-24T16:36:11Z")
On Thu, May 24, 2012 at 10:27 AM, Pan, Luyuan [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > ## solution? 2. Is there any way to switch the Tx/Rx? And how to tell the USRP to receive for a desired time slot such as 5 seconds then stop? The only parameter I can see in gr\_uhd\_usrp\_source is ‘rx\_time’(tells when to start receive), I do not know how to stop the streaming after 5 seconds. Thank you for your help. Any suggestion is appreciated. > > Best regards, > Pan, Luyuan It sounds like you need to add a rate control to your MAC layer. Obviously, when you aren’t transmitting, you don’t want to be generating any samples. You’ll need to buffer them. This is going to take some work outside of GNU Radio to create an app that has a thread to control the samples and pass them to a message source block in GNU Radio. I’m not sure there’s a good example of this, and we don’t really have a ‘best practices’ for this right now. Tom ---
**Author:** ![PanS\_Luyuan](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/46a35a/32.png) [@PanS\_Luyuan](https://www.ruby-forum.com/u/PanS_Luyuan)\ **Post date:** [May 24, 2012, 5:04pm UTC](https://www.ruby-forum.com/t/question-about-stream-tag/220006/3 "2012-05-24T17:04:47Z")
On 2012/5/24 22:34, Tom R. wrote: > > sob-eob tag pair was dropped. Is this problem really exist? And any > > Obviously, when you aren’t transmitting, you don’t want to be > > generating any samples. You’ll need to buffer them. This is going to > > take some work outside of GNU Radio to create an app that has a thread > > to control the samples and pass them to a message source block in GNU > > Radio. > > I’m not sure there’s a good example of this, and we don’t really have > a ‘best practices’ for this right now. > > Tom > In Tx side, This may be the ‘best’ solution at present. But in Rx side, > I just want the USRP to sample for 5 seconds, then stop. Is there any > way to reach this goal? Should I use the “stream\_cmd” in uhd to set the > receive mode in USRP or any better alternative? Can the modes (“Start > continuous”, “Stop continuous”,“Num samps and done”…) achieve my goal? > Any suggestion is appreciated. Thank you. > – > Best regards, > Pan, Luyuan ---
**Author:** ![PanS\_Luyuan](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/46a35a/32.png) [@PanS\_Luyuan](https://www.ruby-forum.com/u/PanS_Luyuan)\ **Post date:** [May 24, 2012, 6:56pm UTC](https://www.ruby-forum.com/t/question-about-stream-tag/220006/4 "2012-05-24T18:56:47Z")
If you know your sample rate, you can calculate how many samples will occur over 5 seconds and pass that as “num samps and done” to a stream command. (I’ve never used stream command interface myself, but I think this will work). ---
**Author:** ![PanS\_Luyuan](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/46a35a/32.png) [@PanS\_Luyuan](https://www.ruby-forum.com/u/PanS_Luyuan)\ **Post date:** [May 24, 2012, 8:36pm UTC](https://www.ruby-forum.com/t/question-about-stream-tag/220006/5 "2012-05-24T20:36:36Z")
> In Tx side, This may be the ‘best’ solution at present. But in Rx side, > I just want the USRP to sample for 5 seconds, then stop. Is there any > way to reach this goal? Should I use the “stream\_cmd” in uhd to set the > receive mode in USRP or any better alternative? Can the modes (“Start > continuous”, “Stop continuous”,“Num samps and done”…) achieve my goal? > Any suggestion is appreciated. Thank you. So, you have access to start(), stop() and set\_start\_time() on the source object; The issue is that you cant really stop the block while the flow graph is running or the source block will timeout, return 0, and quit. So, here is a potential fix to make the work function block when the streaming is stopped: [http://gnuradio.org/cgit/jblum.git/commit/?h=wip\_uhd\_stopper&id=c78d307ecd5dac4e28190e5aa9b8377538f65ffa](http://gnuradio.org/cgit/jblum.git/commit/?h=wip_uhd_stopper&id=c78d307ecd5dac4e28190e5aa9b8377538f65ffa) heres my git repo: git://gnuradio.org/jblum.git -josh