Re: [Discuss-gnuradio] MIMO source - bursts

[Josh Blum]

On 08/03/2010 08:35 AM, Zohair wrote:
> Dear All,
>
> Have anybody tried that using USRP2 to received bursts of data rather than
> countinous?
>
> I have tried doing this as the the sampling rate is very high and I have a
> several blocks (that are calculation intensive) in my flow graphs. I am not
> really interested in receiveing all the samples. reading a 1000 samples each
> 1 second is fine.  I tried doing this y modifying the MIMO sourse already
> implemented. by doing this:
>
>    void set_streaming(bool enb){
>
>         if (enb){
>             uhd::stream_cmd_t
> stream_cmd(uhd::stream_cmd_t::STREAM_MODE_NUM_SAMPS_AND_MORE);
>             stream_cmd.stream_now = false;
>             stream_cmd.num_samps=1000;
>             stream_cmd.time_spec = get_time_now() +
> uhd::time_spec_t((kk++)+0.05); // kk is 0 initially
>           _dev->issue_stream_cmd(stream_cmd);
>        }
>    else
>       _dev->issue_stream_cmd(uhd::stream_cmd_t::STREAM_MODE_STOP_CONTINUOUS);
>       _is_streaming = enb;
>
>   }
>
> What happens is that it reads the first 1000 samples and this stops,
> displaying a message that the block doen't produce any output.

The return values from the work function are important here. First, you 
get the 1000 samples. After that, a call to recv returns 0 samples and a 
timeout. A return value of zero to gnuradio means: stop the flowgraph 
and complain. However, if you return -1, the flowgraph will properly 
shutdown. So, you may want to maintain a count of received samples and 
return -1 after that amount has been accumulated.

Also, if you want to receive multiple 1000 sample bursts, you will have 
to issue multiple commands. If those busts are non-contiguous, you 
should use STREAM_MODE_NUM_SAMPS_AND_DONE

-Josh