Questions about tagging

GNU Radio
1

Hi,

I have looked at the python examples tagging where a trigger signal is
used
to insert “burst” tags at various stream sample locations. However, what
I
would like to do is add a tag at the first sample of a packet. The tag
will
be called “send_at_time” and will have a value of time at which to
send. Following questions arise (I am assuming the use of send_pkt()
used in
examples in digital):

  1. Is it possible to tag the first bit? For e.g. can I modify
    “message_from_string” called in pkt.py (if I can find the source for it)
    msg = gr.message_from_string(pkt,time_to_send)

  2. If tagging bits is not easy to do, is there some property of stream
    samples that indicates “first sample of a packet”?

Thanks,
Ragh

2

On Tue, Jun 14, 2011 at 1:22 PM, [email protected] wrote:

“message_from_string” called in pkt.py (if I can find the source for it)
msg = gr.message_from_string(pkt,time_to_send)

  1. If tagging bits is not easy to do, is there some property of stream
    samples that indicates “first sample of a packet”?

Thanks,
Ragh

Ragh,
Yes, the stream tagging system was designed pretty much exactly for this
purpose. What you’ll need to do is create a new GNU Radio block that
looks
for the start of packet, and when it finds it, adds a tag to the stream.

Have a look at gnuradio-core/src/lib/runtime/qa_block_tags.cc for an
idea
of how the stream tags work (that is, how to add them to the stream and
how
to get them).

Tom