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Re: [Discuss-gnuradio] Question about stream tag

From: Tom Rondeau
Subject: Re: [Discuss-gnuradio] Question about stream tag
Date: Thu, 24 May 2012 10:34:26 -0400

On Thu, May 24, 2012 at 10:27 AM, Pan, Luyuan <address@hidden> wrote:
> 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
> 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
> 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.
> --
> 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

I'm not sure there's a good example of this, and we don't really have
a 'best practices' for this right now.


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