Re: [Discuss-gnuradio] Questions on stream tags

[Martin Braun]

On 05.05.2014 09:56, Hoang Ngo Khac wrote:
> Dear List,
>
> I'm new to stream tags. Could someone help me to understand about stream
> tags and know how to use it?

Remember that we have a lot tag debugging tools available, such as the 
QT GUI Time Sink and tag debug.

> 1. In GNU Radio Manual: "A stream tags is generated by a block's work
> function and from there on flows the downstream...*until it reaches a
> sink*...".
> If we use tags to tell the USRP Sink to start/stop the TX chain, do we
> need to modify the USRP Sink block?

Probably not... are you talking about tx_sob and tx_eob?

> I found that gr_uhd_usrp_sink.cc file contains the get_tags_in_range()
> function. However, this file is not, at first, in the GNU Radio 3.7.0
> source folder. How to add this to project and make it work with USRP Sink?

Look in gr-uhd/, there it is.

> 2. I am implementing a model of ofdm-based two-way relaying network
> apply network coding. Up to now, each single transmission in one time
> slot are done, but the model runs without any timing synchronization.
> For this, I need to use TDMA, and stream tags is the solution. I list
> here the steps to make TDMA with stream tags. Could you leave some
> comments if I miss some thing?
> + Add tags to stream; using provided block such as PDU to Tagged Stream,
> or custom block.
> + Write a block for error checking, repeat request...

Seems right. You shouldn't need other blocks to control UHD.

M