Re: [Discuss-gnuradio] Question about stream tag

[Nowlan, Sean]

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).

-----Original Message-----
From: address@hidden [mailto:address@hidden On Behalf Of Pan, Luyuan
Sent: Thursday, May 24, 2012 11:03 AM
To: Tom Rondeau
Cc: address@hidden
Subject: Re: [Discuss-gnuradio] Question about stream tag

On 2012/5/24 22:34, Tom Rondeau wrote:
> 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.h
>> tml 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 
> 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

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