Re: [Discuss-gnuradio] High-Level Stream Questions

[Josh Blum]

On 07/16/2012 10:17 AM, Alexander Olihovik wrote:
> Hello all,
> I have general questions on streams:
> 
> 1. When precisely does a stream start? When a source is connected to its
> sink? When you call .run() on a top-block?
> 

The UHD Source block has a set_stream_time() which you can call before
starting the flow graph. This will precisely control when samples start
flowing.

> 2. When adding stream tags to a stream, does the stream itself get altered?

No. The tags are basically in an external queue and and tied to the
absolute sample count of the stream.

> If I were to output the stream to a binary file, would the file look the
> same with and without stream tags?
> 

Yes. There isnt a facility to write the tags yet. But I have heard of a
such a utility in the works.

> 3. If I have multiple USRPs receiving data at the same frequency and
> sampling rate, all outputting their streams to separate binary files, will
> sample n on binary file 0 be taken at the same time as sample n on binary
> files 1, 2 ... up to the number of USRPs, assuming all USRPs have been
> synchronized with the same clock and PPS signal?
> 
> 

Yes, 1) If you have multiple source blocks and set the stream time to be
the same. Or, 2) you have a multi channel source block, this will just
work as all channels are automatically aligned


-josh