Hi Marius,
I'm taking the GNU Radio discussion list into CC: here, as we're also
kind of talking more about general GNU Radio usage; feel free to follow
up on either list (you'll need to sign up for discuss-gnuradio, though,
if you want to directly post there, see [1]).
So, stream tags, PDUs and bursty transmission are three different things:
* Think of stream tags really as annotations tagged to your sample stream.
* Think of PDUs just as buffer full of data/samples with a simple
"that's how many samples there are" header. They usually are transported
as messages, not as streams.
* Think of tagged streams as the combination of specially formed stream
tags with the ability of blocks to understand that what it sees are
packets of items, marked by a "begin/length" tag. That constructs a
"packetized" or "burst" transmission mechanism atop of the "normal"
stream processing.
So, the UHD USRP sink are able to consume a stream of samples, usually.
That's the "normal" modus of operation. If you tell the sink to look for
a specific length tag, it will switch to a mode where it will expect the
stream to contain that tag, and send out the the bursts defined by those
tags, either at the point of reaching the USRP sink, or at the point in
time contained in another tag, the "tx_time" tag.
So two ressources to point you at
1. The official Guided Tutorials of the GNU Radio community. These are
sequential, so I strongly recommend starting at part 1 and finishing
with part 6 or 7, if you haven't already. [2]
2. The GNU Radio doxygen, which contains a description of the USRP sink
and what tags it takes [3] [4].
Best regards,
Marcus
[1] https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
[2] https://gnuradio.org/redmine/projects/gnuradio/wiki/Guided_Tutorials
[3] http://gnuradio.org/doc/doxygen/page_uhd.html
[4] http://gnuradio.org/doc/doxygen/classgr_1_1uhd_1_1usrp__sink.html
On 10/30/2015 06:18 PM, Marius via USRP-users wrote:
> Hi Martin,
> Yesterday I started reading about stream tag and I’m still trying to
> understand how it works. I definitely know that this is the right track for
> me,
> but I could’t find any explained python examples that could be similar to my
> project.
> I’m not looking to create PDUs, but to be able to transmit a signal from a
> file, for a predefined nr. of seconds and at certain periods in time.
>
> Please, If you have the time to send some links that you consider it will
> help me, knowing what I want to achieve with my program.
>
> I know this looks easy for you, but for a newcomer in GNU Radio, trust me,
> it looks quite difficult.
> I’ll take it easily and probably will manage to understand it.
>
> Thank you.
>
>
> _______________________________________________
> USRP-users mailing list
> usrp-us...@lists.ettus.com
> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
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