Re: [Discuss-gnuradio] Flow graph blocking when doing 2x1 transmission

[David Halls]

Hi Marcus,

Yes, your diagram represents what I am trying to achieve.

Using two sinks would be really nice! But I have had some problems with achieving sync using time stamps (where as using one UHD sink is very straightforward). For example, how do I obtain the current time from the transmit USRPs, but from another block in the flow graph - in order to create a tx_time with the right value? Where I have a UHD source its easy as these output an rx_time tag...

I thought that I could use

::uhd::time_spec_t
    usrp_sink_impl::get_time_now(size_t mboard)
    {
      return _dev->get_time_now(mboard);
    }

but how do I get a pointer to this in other blocks in the flow graph?

I like the idea of the block to creates zeros (with rate limiting), unless there is an input signal. Will this block get scheduled even if there are no items at its input, though? Isn't that similar to my simple idea of using a mux between a noise source (with 0 amplitude) with sample source b?

I will try to provide some more detail, although the setup is complicated indeed and might involve explaining a lot of the background...

Regards,

David
________________________________________
From: address@hidden address@hidden on behalf of Marcus Müller address@hidden
Sent: 02 June 2014 15:50
To: address@hidden
Subject: Re: [Discuss-gnuradio] Flow graph blocking when doing 2x1      transmission

Hi David,
Generally, this sounds like in principle, your application looks like
(nb: not an actual GR flowgraph)

+-----------------+             +------+
| sample source a |------------>| USRP |---> [USRP1]
+-----------------+             |      |
                                | sink |
+-----------------+             |      |
| sample source b |------------>|      |---> [USRP2]
+-----------------+             +------+

Let's assume a is continuous and b starts later, or bursts or the like.
Can't you just split the flow graph into two independent flowgraphs,
syncing the USRPs using time stamps?

Alternatively, what about having a block that (rate limitedly) produces
zero-samples, unless data comes in on a message port?

Generally, using start-of-burst tags, the newly added command time
message interface for the uhd blocks, and multiple ways to detangle your
sample streams, there are many ways to solve your issues.
I think it would be wise if you described your setup in a little more
detail.

Greetings,
Marcus

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